The claim that humans only use about 10 percent of the brain has not been proven. Even
when Flourens and Lashley took out large parts (90%) of the brain still had its basic
Psychology: the study of behaviour and attempting to describe, explain, change, and
Neuropsychology: the study of behaviour too but a specialty, including the relation between
behaviour and the activity of the brain, assuming that the activity of the brain is partially
responsible for one’s behaviour. There are 2 types of neuropsychology:
Clinical neuropsychology: the branch of neuropsychology dealing with psychological
assessment, management, and rehabilitation of neurological disease and injury.
Experimental Neuropsychology: also known as cognitive neuroscience/
neuropsychology, thebranch of neuropsychology focusing on how human behaviour
arises from brainactivity, including how behavioural changes can be explained in
terms of damaged neuralcomponents.
It is important to learn the history of neuropsychology because there were many instances
in time where scientist created theories about brain and behaviour relationships that are
now proven to be false. Today we know that the brain affects behaviour but in the past that
was not the case.
Empedocles (known for theory about matter being composed of water, air, fire and
earth): a philosopher who proposed the idea of “the cardiac” or “cardiocentric
hypothesis”, where the heart was the source of behaviour. This hypothesis still has an
effect on pop culture today, like how humans associate love with the heart and not the
Aristotle: also came to the conclusion that the heart was the centre involved with
thought and sensation but only because it is warm and active and that since heat rises,
the brain was the blood cooling centre because it is covered with a network of
vasculature so according to him it must have been the radiator. He was wrong the blood
actually helps cool the brain.
Hippocrates and Galen: argues that the brain is not the source of human behaviour,
they proposed the “brain hypothesis” or “cephalocentric hypothesis” where the brain is
responsible for thought and sensation. Both of them were still wrong about some of the
details. Galen thought that the brain’s ventricles and cerebrospinal fluid (supports,
nourishes, cleans brain) played a role in cognition, which was later corrected by Magnus
Despite the ancient claims that the heart controls emotions and intellect, there is evidence
others experimented with brain function. Observations of a fossilized skull fracture suggests
that there was recognition that damaging the brain would cause death or disabling of an
individual. Another skull that was found from 7000 years ago was cut open twice for
surgical purposes and the individual survived this surgery as shown in bone regrowth. This
was done to cure something. Ancient Egyptian writing from 5000 years ago also documents
symptoms of brain damage but they didn’t consider the brain important enough to
mummify . They appreciate the brain in behaviour and perhaps some diseased states. Early theories did not recognize the importance of the brain in higher cognitive functions. It was
looked at as an interpreter of signals while the mind was characterized as a separate entity
from the brain.
Trephination: producing a hole in the skull to produce therapeutic effects in ancient
times. It was thought that the brain interpreted signals and that the mind was a separate
Mind-Body Problem: The brain – behaviour idea made a lot of phiolosphical questions become
a problem. René Descartes proposed a reflexive theory of controlling behaviour describes as
flowing animal spirits through valvules in nervous tissue. It described how external stimuli
would move the skin then the filaments, releasing spirits and innervating the muscles. It could
account for involuntary behaviour but could not account for voluntary behaviour or the
variability in behaviour. Descartes believed the voluntary behaviours depended on a
mechanical body with a decision-making soul, located in the pineal gland since it doesn’t have a
left and right component it is a midline structure and was surrounded by cerebrospinal fluid
that cleanses and supports the brain (contained animal spirits which produce movement during
voluntary action). Therefore voluntary movement caused movement of the pineal gland,
resulting in the release of animal spirits throughout the body causing the body to move.
Hydraulic machines were in at the time in Paris and this affected his theory. Theories of the
human brain over time really relied on explanations from technologies that were present at the
time. One explanation didn’t even look at the brain as just a computers, it looked at the brain as
a network of computers like todays supercomputers. However with all of this mechanical
associations with behaviour, it still couldn’t solve the variability in behaviour in the same
situations. According to the Harvard Law of Animal Behaviour animals in the same situations
will react as it pleases. However the variability in behaviour isn’t the only problem, Descartes
proposed that the body and mind are separate but interacting entities. This is referred to as
dualism. But what has been left unexplained is how they both interact or what affects what.
Dualism: an idea proposed by Descartes that the mind and body are separate but interact.
Monism: the idea that the mind and body are one, accepted today.
1990s was the age of the brain where a lot was discovered but still rooted back to the
research of the pioneers, it still reached out to many other disciplines too.
Lesioning: destroying tissue in the medulla was discovered by Legallois to stop breathing. This
respiratory centre was the first widely accepted function to be localized in the brain.
Magendie and Bell: they studied the nerves that exited the spinal cord. They discovered that
the dorsal roots that leave the spinal cord on the back have sensory functions and the ventral
roots the nerves that leave the spinal cord from the front had motor functions, which suggested
that the brain could also be divided into sensory and motor areas for functional as well as
anatomical segragational reasons.
Franz Joseph Gall: suggested that the cortex was functionally localized. He stated that the brain
was divided into 27 different areas called faculties (cognitive abilities), which could be found on
the cortex of the human brain (nonhuman animals had 19 of these faculties). However these
faculties were not distinguished well in terms of cognitive abilities but some of the cognitive
localizations he made have been proven today. He also believed the cortex acted as a muscle,
where a larger area was associated with a larger function, for example the wiser a person the
bigger there brain. This increase in size of the cortical area would cause a bump (deformation of the skull), which could be empirically measured by cranioscopy. This measurement in relation
to personality became known as phrenology.
Flourens: was a strong believer in phrenology and did experiments with it, he believed it was
subjective and that all the analysis were performed post hoc. For example if one who was good
at music had a bump in the music centre of the head, and another good at music didn’t, it was
assumed that the second person was better at a different aspect of music and therefore had
the bump elsewhere. He was a strong believer in empirical methods and he performed
numerous studies with nonhuman animals under lesioning techniques to study corresponding
effects of behaviour. He concluded that the cerebellum was important to movement and the
medulla was important to vital processes. Also, he found that regions with injury or lesions
might restore functions, not to the one area but to all areas and functions, he used this to
support the idea that the brain was cortically equipotent and functioned as a whole. Flourens
was against the idea that cognitive abilities were localized to specific areas of the brain. He
thought the cortex functioned as a whole. It was later determined by Friedrich Goltz that the
size of the lesion, not the location affected behaviour of nonhuman animals as he removed
cortex from the brains of cats and dogs. Based on this he concluded that cognitive abilities
cannot be localized. Although cortical equipotentiality was strongly believed at the time, it was
not universal. David Ferrier suggesested that the behavioural observations of the decoricate
dogs and monkeys were inconsistent with the stance that cortical equipotentiality had.
Ferrier and Hitzig: found that lesioning was consistent with localizing sensory and
motor functions with discrete portions of cortex, for example hitzig and fritsch that lesion to
the frontal cortex caused abnormal motor behaviour and intact sensation. This overturned the
theory of cortical equipotentiality. Overall, Gall was right for the wrong reasons and Goltz and
Flourens used the right technique with wrong conclusions. They also studied the relationship
between the brain, movement and electricity by observing electrical. Even though Gall had this
amazing discovery of the localization of language, he is widely more known for phrenology.
stimulations in a dog’s brain as a result of movement.
Paul Broca: was the first to accept that the frontal cortex playa s role in speech and he based this on a
patient with damage to this frontal areexamined a patient with a problem in speech’s brain and
discovered a lesion or soft tissue on the anterior left hemisphere/lobe now called broca’s area.
People that have this damage lose the capacity for speech but retained the ability for
Aphemia/ Aphasia: Broca’s term for being unable to speak but able to understand language,
and became known as Broca’s aphasia. He did not localize this area to speech and right
handedness right away though, he waited some time before he suggested specific roles. Some
words are known, sentences are slow and spaced out but prepositions, pronouns, conjunctions,
if, and, or are left out similar to telegraphs called agrammatism. They have trouble finding
words (anomia), phenomic paraphasia, and sense sentences with same words/diff order as
equal in meaning. Others suggested that the left frontal lobe plays a role in speech before
Broca but Broca was the first to publish it and he focused specifically on how it was only the
articulate speech that was affected. Two major components of speech that Broca did not study
was the emotional tone of speech and the loss of comprehension of language associated with
the preservation of speech.
Prosody: emotional tone of speech, which Broca did not study directly, and loss of comprehension of language. Important to distinguishing meaning of words (ex.
sarcasm), detected by the right hemisphere, while the left is for emotion. Jackson
proposed that content and tone were separable
Jackson: first articulated that the content and tone in language were separable. He observed
that speech involves linguistic abilities as well as complex motor skills. He suggested there are
possible dissociations between the semantic content of language (meaning) and tone when he
saw patients that were unable to name objects but swear aloud when they were upset.
Carl Wernike: suggested there was an auditory centre (wernike’s area) in the temporal
lobes. When damaged, the individual could produce speech but not hear, comprehend,
or put meaning on words together when spoken by others. This is known as Wernike’s aphasia,
involving non-random meaningless word salad, neologisms (made up words), unawareness of
condition, occurring without motor deficit, and more paraphasia than in Broca’s aphasia. Global
aphasia includes not being able to hear/understand or produce sound, a result of lesions in
Wernike’s and Broca’s areas.
Three main hurdles that were hard to overcome when studying the brain was the size of
cells, the texture of the brain and the lack of pigmentation. Neurons are about 0.02 mm in
diameter and for the naked eye to see a neuron it must be atleast 0.1 mm in diameter. So it
had to be magnified and in the 1800’s the compound microscope was invented.
Theodore Schwann: a zoologist that proposed that all living tissue was composed of
microscopic units called cells (now called the cell doctrine). To see the neurons, very thin slices
of the brain must be made, early histologists used the microtome to make the slices. The brain
has a consistency of that of toothpaste so it has to be hardened before it can be sliced. So the
brain is fixed/hardened by formaldehyde for an extended period of time. Thinly fixed cells have
no color and so must be stained to be visible.
Histology: the study of thinly sliced, fixed, stained tissues. This was required to study
neurons since they are very thin. Histology is powerful in studying the brain as new techniques
develop we see new developments in neuroscience. Many stains developed by the pioneers are
still used today. Some stains included the Nissl stain which distinguishes neuron cells from
other cells in the brain and the Golgi stain which contained silver and turned neurons dark over
time, which helped distinguish the axon and dendrites and trace connections to the brain.
Santiago Cajal: used Golgi stain to trace connections to the brain, examine dendrites.
He proposed neurons are not continuous and must communicate (neuron doctrine). He
noted that neurons come in all shapes and sizes that correspond to certain parts of the
brain known as cytoarchitecture. He also saw that neurons also had dendrites that were
covered in spines. Golgi and Cajal were rivals, Golgi thought that neurons fuse together to form
a circuit while Cajal thought that neurons are not continuous and that they must communicate
by contact. Cajal was correct. They both shared a nobel prize for understanding the neuron
The electrical impulses that travel down the axon are different from the ones that travel
down the dendrite. Luigi Galvani first studied electrical impulses on the body, he discovered
what today is called a crude battery and discovered that muscle and nerve cells produce
electricity. The galvanometer was used by Reymond to measure the movement of the current
in the muscles and tied the internal production of current to movement.
Galvani and Bois-Reymond: Galvani discovered that muscle and nerve cells produce electricity and Reymond used the galvanometer measure the current in muscles to link
it to movement. Together they dismissed the idea of fluid-based neural communication.
Sherrington: Along with Fritsch and hitzig and ferrier he studied the relationship between the
brain, movements and electricity. Fritsch and HItzig discovered that the stimulation to a dogs
cortex could cause movement in the dog. Ferrier extended this to many other animals.
Sherringtion studied reflex movements in mammals, also named the gap between neurons the
synapse as proposed by Cajal. He also observed agonistic/antagonistic movement of muscles
(reciprocal innervation), and the neural control of reflexes for which got a nobel prize.
Although they knew it was electricity that passed through these circuits they didn’t
know what produced this electricity.
Julius Bernstein: a German physiologist who was the first to measure the speed of an
electrical signal in an axon (action potential) and to discover that the membrane covering the
axon had a charge on it when at rest (resting membrane potential). He also proposed that the
neuron could conduct electricity by changing its concentration of ions. Hodgkin and
Huxley expanded on this idea by first studying the electrical propogation of neural impulses in a
sciatic nerve of a frog.
John Young: Used the axon of a squid as it was better to understand because it is 1000 times
larger than that of a mammal and can be studied for 6 hours after dissection.
Hodgkins and Huxley: soon found that the axon of squids and finding that ions movement
in/out of the This discovery of how the electrical charge works got them the nobel prize.
Neurons communicate with each other by releasing chemical – neurotransmitters.
Neurotransmitter: a chemical substance used in neuronal communication at synapses.
It is released from the active zone of the terminal button and diffuses across the
synapse, to the dendrite where it binds to its specific receptor protein. Otto Loewi
believed there had to be a chemical involved in the transfer of the impulse, and his
experiments with stimulating frog hearts allows studies to be done to discover these. It was
known that if a heart was dissected and placed in a solution it would keep beating. He also
discovered that when stimulating the vagus nerve (nerve to the heart) the heart rate would
slow and a fluid was released which was shown to slow heart rate. When another heart was
placed in this fluid even when the vagus nerve wasn’t stimulated it still slowed down the heart.
This fluid was later named acetylcholine by Dale and the study of how it is stored, released, and
deactivated was discovered by Axelrod. Dale discovered that Ach was the same in amphibians
and mammals. All three of these scientists received a nobel prize for their work.
Golgi and Cajal noted that different areas of the brain had varying cytoarchitectures.
Brodmann: created maps that numerically label each brain region with different
cytoarchitecture, as he believed different regions with different cytoarchitecture had
different functions, but had little evidence to prove it. This was his cytoarchitectural map. Each
area with a different cytoarchitecture was denoted by a number. The numbers are in no specific
order. Table 1.3 has the numbers for the most famous areas of the brain. Today a lot research
supports this and even regiosn next to one another can control completely different actions.
This numbering system is still used to today especially in functional neuroimaging.
Lashley and Franz: investigated memory of rats as they taught rats sensory discriminations and
how to get through a maze, and showed rats could perform the task even after lesions
occurred. The experiments were done to find the location of the engram, the hypothetical change in the brain responsible for storing memories in case of lesion. When impairments were
found it was related to the size of the lesion rather than the location of the lesion, this
contradicted the whole idea of an engram. This led Lashley to formulate two interdependent
laws. Although he was against the idea of cortical specialization, he realized that sensory and
motor functions had to some degree cortical specializations but not in the same way as
memory and intelligence. This is still agreed upon today.
Law of Equipotentiality: the cortex functions as a whole with no function
specialization. Lashley believed this was the case except for primary sensory and motor
functions (but not for memory, intelligence etc.)
Law of Mass Action: the degree of deficit is proportional to the part of the brain that is
Wilder Penfield: trained in many places and became montreals first neurosurgeon and created
a neurological institute there. He attempted to treat epilepsy (uncontrollable seizures) by
removing suspicious brain tissue while still trying to spare healthy brain tissue and brain
function if possible. It wasn’t about stopping the seizures rather it was about removing the least
tissue and he was pretty successful. To minimize the amount of tissue that was removed he
stimulated areas of the brain that would cause an aura, a smell or something that onsets the
seizures. He discovered that the patient’s auras were connected to low electrical stimulation in
around that area of the brain and these areas would initiate the seizures. He used a local
anesthetic so he could communicate and understand what they perceived during surgery. Since
the brain has no somatosensory receptors, Penfield was able to painlessly stimulate the brain
and receive feedback from the patient about auras. This allowed him to localize the source of
the seizure and remove them. When areas in the centre of the auditory cortex in the temporal
lobe was stimulated people reported a bell ringing or a buzzing noise. When the primary
auditory cortex was stimulated people reported with greater specificity such as crickets
churping. His suspicion that he could localize areas of epilepsies using auras was correct. Auras
were provoked by stimulating cortex in the temporal lobe and when this area was removed,
seizures were reduced. He is also famous for mapping the somatosensory and motor complex
called somatosensory homunculus (by stimulating postcentral gyrus of the parietal lobe and
having patients reporting where they felt sensation and which sensations were stronger, the
brain was labeled with body parts where size depended n the intensity of sensation.) This is a
map of the surface of the body (somatropic). Learn figure 1.3.
Functional neurosurgery developed overtime. Goltz observation that dogs with
temporal lobe damage were more tame then unlesioned dogs led Burkhardiet to
operate on 6 schizophrenic patients in an insane asylum. 2 died but the others seemed
to be more calm and so neurosurgeries were limited for a good amount of time.
Jacobson found that lesions in the front cortical areas reduced aggressive behaviours.
These reductions appear without other losses or changes such as such as object
recognition or memory. This proved that the frontal lobes were involved in neurosis,
Fulton was able to induce neurosis in chimps with intact frontal lobes but wasn’t able to
in chimps with large frontal lesions.
The first physician to implement these finding on people was Antoni Egaz Moniz, he
developed a method called leucotomy.
Leucotomy: started by Moniz in attempt to reduce aggression, was a procedure involving severing the tracts between the frontal lobe and the thalamus by a special knife called
the leukotome. First two holes are created in the skull by trepanning. Then the leukotome was
inserted and moved side to side to severe the white matter connections to the frontal lobes.
This was the best they had until antipsychotic drugs were created. He won a nobel prize for
showing leucotomy can work for psychoses. He was pretty conservative as he thought
psychosurgery should be a last resort and only done to people that could harm themselves. He
was shot my his own patient in the spine. This practice was continued by Freeman and Watts
and was known as a prefrontal lobotomy perforating the skull through the tear duct with a
hammer and cutting the connections to the prefrontal cortex. This was done with a local
anesthetic and he didn’t even have a liscence but he conducted many surgeries. In the 1950s
drugs were developed for psychoses, anxiety and depression. The chances of one getting better
from a lobotomy were about 30 percent!
Functional neuroimaging shows the metabolism of the brain ( the oxygen and glucose use). This
shows which parts of the brain are active and has revolutionized the mapping of the brain. But
there are limitations. One is individual variation and there is no average brain. Before functional
neuroimaging, structural imaging (MRI, CT and others) already revolutionized neuropsychology.
Chapter 12: Evolution of Humans
Evolutionary Psychology: attempts to apply the principles of evolution to human
behaviour to figure out what it means to be human. As a species it is difficult to apply the
principle of evolution to ourselves. It is difficult to examine behaviour through a fossil however,
a male skeleton would show more fracture and dents, especially on the left side, compared to
females indicating the males did the fighting and were injured by a right-handed opponent.
Evolutionary theory was created by Darwin and Wallace. Wallace explored the amazon
river and Indonesia while Darwin explored on the HMS Beagle. There thoughts were
based upon 3 things: 1. Classification of organisms by Linneas, he observed
commonalities that supported the theory 2. Geologist Charles lyell and William Smith
supported the idea that the earth was much older then previously thought. They found
fossils of extinct animals and when things changes it did in the strata of the earth. The
also thought there were processes that shaped the earth. 3. Thomas Malthus thought
on poverty and population during the industrial revolution. Basically food supplies affect
population. Exponental growth until we surpass the food limits (survival of the fittest).
Charles Darwin: assisted by Wallace, published the Origin of Species, which presents
the theory of evolution.
Historical theory of evolution can be summarized by 3 terms: inheritance, variation and
differential reproduction. The mechanism underlying this is natural selection.
Variation: the differences in morphology that are characteristic of each individual that is passed
on through generations. Genetic variation involves differences in traits or alleles (form of a
gene), caused by meiosis, mutation, transposable elements, crossing over, etc. An individuals
phenotype is an expression of the genotype and environment interacting, however the
phenotype can change with the environment and genotype only with mutation.
Inheritance: passing differences in morphology from one generation to the next.
Differential Reproduction: organisms that are best suited for an environment will be able to better survive and have a greater fitness than those that don’t.
Natural Selection: proposed by Darwin, the mechanism causing change over time.
This idea involves all individuals being unique and that any trait causing reproductive
advantage will be passed on and therefore magnified in the population. It is the
competition for survival and reproduction. If such a trait exists and is selected for it is an
adaptation and helps solve a problem with the physical/chemical/social/developmental
environment. For a trait to be an adaptation it must be inherited from one generation to the
next. Every environment has its own adaptation and variation will always be present. Natural
selection continually occurs. Somethings like male peacock feathers cant be explained by
natural selection (competetiton among individual to contribute to the gene pool) but can be by
sexual selection (competition among individuals for reproduction).
Sexual Selection: another mechanism of evolution there are two types, intersexual which
involves anorganism selecting a mate based on specific traits (colour, size, call, age etc), and
intrasexual which involves members of the same gender competing for mates.
Modern Theory of Evolution: also known as the modern synthesis involves many areas such as
molecular biology and paleontology, explains new ideas that were not present in Darwin’s
original theory of evolution. This includes knowledge that traits are passed on by genes made of
DNA and that change occurs after a mutation causing variation. Genes cause change at a
molecular level but evolution occurs on a level of populations and gene frequency, natural
selection, genetic drift, and gene flow (movement of genes in a population).
Modern synthesis is based on genes, DNA chromosomes, and population biology. Genes
assort in pairs and are locaed on chromosomes. Human have between 26 to 40 K of
genes on there 26 pairs of chromosomes. Each parent contributes half resulting in
variation. More of our genetic make up is the same as other then there are differences,
resulting in the bipedal gait and our eyes among our members of species. The
differences allow for unique features. Your genotype is your genetic makeup and is
invariant during ones lifetime except for radiation and chemicals. Your phenotype is an
interaction with the environment as you develop (nutrition and height example).
Natural selection acts on phenotypes but it’s the genetypes that are passed down
through genereations. Genes do not make traits or diseases they make proteins. There
is often more then one form of a gene, these are called alleles. When a allele codes for
color in the eyes it is really making the protei melanin in the eyes in various colors.
Mendel explained the inheritance of genes but his view was pretty simplistic because
very few raits are expressed by just one gene. When multiple genes affect one trait this
is called polygenic.
Polygenic Traits: when multiple genes, which may be on different chromosomes, affect
a trait, for example eye colour is affected by 3 genes on 2 different chromosomes. These traits
do not follow a simple dominant recessive. Polygenic traits associate with one another people
with brown eyes often have brown hair too, people with blonde hair tend to blue eyes. So the
dominant recessive situations is not followed. It is thought that inherited behaviours such as
bipedal gait are polygenic traits.
In any population there is genetic variation, these variation come about as random
mutations and a recombination of DNA. Mutation cause a change in a genotype as
there is an error in replication. Rate of mutations is slow but they are ususally harmful resulting in reduced ability to survive. Variation causes a varying abilities of survival of
organisms. Evolution passes on the genes of those better suited for survival.
Summary of modern synthesis:
1. Certain environments select certain phenotypes and phenotypes are the expression
of genotypes interacting wih the environment. Natural selection can only see
phenotypes not genotypes. The environment cannot change the genotype except
for chemicals resulting in mutations.
2. Altough genes occur at the level of the individual, evolutionary change occurs at the
level of the population. Population evolve by changes in gene frequency that are
brought about by natural selection, random genetic drift and gene flow. Natural
selection can produce an evolutionary change if a gene or genes show slight fitness
advantage meaning an increase in the number of offsprings that survive to
reproduce. Small changes in genes can result in huge changes in the genetic makeup
of a population in a short period of time if they provide survival or reproductive
advantage for those who possess the gene. Genetic Drift when an isolated
population depart from the original genetic composition of the population, also can
produce evolutionary changes. This drift is probably due to the extensive inbreeding
and adaptation to the isolated environment. Gene Flow is the movement of genes
through a population that results from mating. This can be profound when there is
extensive inbreeding. Genes that are adaptive at one point can die down because
they become maladaptive as the environment changes.
3. Species represent gene pools rather then fundamentally unique groups. Species are
judged by there genotype not there phenotypes. When we judge speciation based
on phenotypes we are often misled. Gradual change in species genotypes over time
results in new species rather then a new species developing from nothing. However
fossil records point out that there were rapid morphological changes and long
periods of stasis.
There are 3 difference between the modern and historic evolutionary theory: 1. Modern
theory recognizes that traits are the result of genes that are inherited from ones parents
and interacts with the environment. 2. Modern synthesis recognizes that there are
mechanisms other then natural selection that affect evolutionary change 3. Modern
synthesis recognizes that what we call a species is only a difference in gene pools of a
population, not totally distinct or formed out of nowhere.
Researchers cant look at fossilized brains but they can look at fossilized skulls to obtain
cluses about our ancestors brains. Humans don’t have the largest brain in the animal
kingdom but we have one of the largest in comparison to our body but even then we
don’t have the largest. Our brain in 2.33 percent of our body weight but out brain has
3.2 times the amount of cortex than does any other species. Another way to examine
the skull is to make an endocast.
Endocast: a mold of the inside of the skull it looks much like the brain when it is covered with
the meninges, to allow for inspection of sulci and gyri over time from early humans to modern
humans. This has shown significant changes in the organization of the brain overtime. For
example modern human brain are assymetrical but this is not as apparent in the brains of
Australopithecines suggesting the asymmetry has evolved over time. Different placement of sulci and the frontal lobe size similarities in homo erectus and homo sapiens suggests some
form of speech or language. It is hard to tell when this change in the frontal lobe occurs
because brains of australopithecines did not preserve the frontal lobes so well. This suggests
that the H erectus used some rudimentary form of speech. This frontal area is also seen in
neadertals meaning they also had some form of speech. Some limitation are that we do not
know for sure if these changes are just individual variations or if it belonged to that groups of
hominids but this is still the best way to study the evolution of the brain. There was a switch
front the olfactory areas of the brain to the frontal regions suggesting a change in behaviour
from smelling to more complex reasoning. Largest changes to the human brain were seen in the
once flattened parietal lobe of ancient primates and australopithecines, the increase in size in
this area was beneficial when it came to tool making and hunting. Australopithecines had
enhances frontal areas wheras later other hominids had an increase in paretial lobes suggesting
an independent evolution of these structures. Others believe that studying the DNA of our
brains and those of other primates says a lot because it can tell us when we shared an
ancestor. Other comparisons among species tend to compare the brain stem and the cortex
and this focuses on three major points of differences among species:
1. Newere species have larger brains
2. The increase in size observed in newer species is primarily in cortical areas.
3. Newer species have increasingly complex cortex as defined by the number of layers of the
cells and the number of cortical convolutions.
Large brains may not always be so adaptive because they are more difficult to cool than small
brains and large brains require more energy to function both of which require metabolic
resources. Large brain require big heads making it harder to deliver babies and it take a long
time to develop requiring a longer period of parental care.
Animals and humans have many adaptive behaviours. Some behavious are no
dependent on learning but they are dependent on out evolutionary past. The origin of
fear is not always the result of personal experience. The moth example of the eyes
instead of flying away when it is antagonized. Was this a past experience or just a neural
Proximate Cause: answers “how” a behaviour is performed, it is the internal mechanisms that
underlie behaviour, or an immediate cause of behaviour. Ex. A human will swat away a bug if
they are scared of it.
Ultimate Cause: answer “why” a behaviour is performed, its describes the evolutionary basis
behind behaviour and why the behaviour is adaptive. Ex. A human will swat away a bug
because it will prevent a bite, especially if poisonous, which will increase reproductive fitness.
If we are talking about the moth the proximate cause is the genetic coding behind the
eyes on the wings, the sensation of threat and the physiology of wing movement. The
ultimate cause would have to explain how it increased its chance of survival and firther
reproduction. It mmay have freightened off some of its predators because it looks like
Also something like fear can be explained with the amygdala but it still fails to explain
why. Fear may have been developed as a facilitation of survival and reproduction by our
ancestors. In addition to aversions, human preference can also be a result of evolutionary
influences. Human preferences vary considerably but there are similarities such as
sweet, salty and fatty foods. Our ancestors may have wanted sweet foods for the
vitamins. This was adaptive then but present day, it is not as adaptive.
Adaptations: when a trait that allows for reproductive advantage is selected for, it is
adaptive. There are some adaptations such as likes and dislikes that are different for
each person and some that are generally the same for all humans. For example, one
person may like the colour blue and someone else may dislike it. However, a preference
for sweet foods is something all humans display, which in the past was good because
sweet foods were fruits and were healthy, today they are junk food and therefore are not
adaptive. The problem with evolution is that it take a really long time for adaptive behaviour to
be initiated through mutations. For example our lungs have no adapted to the exhaust of cars
but this has only been present for a couple generations. An example of an adaptation that we
no longer use is our appendix. When people migrate to areas that have a higher prevalence of a
disease their bodies are have a higher chance of getting the disease too. Our physiological
adaptions to acute stress found in our ancestors environment are not adaptive to the chronic
stresses that our modern life delivers.
Fossil records do inform us of behaviour, for example the neandertal that was a
homicide victim. Fossils reveal some themes that are relavent to behaviour. Male
skeletons have many more fractures and dents then women meaning males were
involved in more combat. These dents were mostly on the left side meaning that they
struck each other with the right hand. Evolutionary behaviour can also be studied
experimentally by using various different species to understand the evolutionary
aspects of something.
Tabula Rasa: proposed by John Locke, the idea that at birth, the human brain was a
blank slate, and that all knowledge must be gained from experience. There are no
innate abilities, and knowledge cannot go past one’s experiences. The brain absorbs info
through the five senses and the process of reflection. This went against socarates view of innate
knowledge. The Standard Social Science Model describes a person as a computer that is
programmed from birth. However having innate features is something we all have across all
ethnicities and cultures, are passed down to future generations (influenced by genetics), and
enhance survival such as reflexes or certain motor skills, creating social groups, using gestures,
using tools, sex drive, psychological defense mechanisms etc. Some of these are just instincts
we are just born with and they seems to be adaptations. To be an adaption a feature must
recur through generations, appear reliably through the developmental life of an organism, the
appearance is influenced by genetic specifications, they interact with feature of the
environment that are normally present, they help to solve an adaptive problem that there
ancestors would have faced, and they were propagated during the period of selection because
they enhanced survival.
Chapter 13: Neural Development
Early Development – Early in embryonic life (3 weeks into conception) the neural plate
forms from the ectoderm of the embryo. The Neural Plate is a patch of cells on the
dorsal surface of the embryo that becomes the nervous system. The cells of the dorsal ectoderm in the neural plate are stem cells that are pluripotent, meaning that they have
the potential to develop into various types of nervous system cells (because it is in the
nervous system they cant turn into any other kind of cell like skin cells). As development
progresses the neural plate starts to form groove which by embryonic day 24 fuses to
form a neural tube. The different section of the neural tube become different parts of
the nervous system as its interior surface becomes the ventricles and the central canal
of the spinal cord. Between the third and fifth month of gestation rapid cell
proliferation and neural migration are dominant events. So the cells of the neural tube
and ventricular zone are rapidly dividing and this is called proliferation and by
embryonic day 40 there are 3 bumps on the anterior portion of the neural tube, these
bumps eventually form the forebrain, midbrain and the hindbrain of the CNS. Cells also
migrate from the interior ventricular zone to their final location by following certain
types of glia, there are waves of proliferation and migration in the developing CNS.
Starting at the second month of gestation the telencephalon undergoes tremendous
growth, developing from the cortical plate. As migration occurs from the inside out it is
the the deepest layer of neurons that develops first, further layers of neurons must
migrate through the already established neurons to reach their destination.
Once neurons migrate they grow axons and dendrites (occurs before and after birth)
and differentiate to there final form (complete at birth). The axons and dendrites follow
chemical to position themselves in there initial place on the cortical plate. Problems
with any step along the way can cause abnormalities in the CNS. The brain is most
vulnerable I the last 4 to 5 months of gestation. Problems can start with the neurons
themselves so chromosomal abnormalities or problem can be caused by external
factors. External factors include intrauterine trauma or exposure to toxins such as lead
The extent of the effects depends on the nature, duration and extent of disruption, but
the type of CNS malformation can give of clues as to what happened. Fro example a
congenital malformation occurs in the CNS when the neural tube fails to close.
Complete failure of the tube to close is fatal resulting in a condition called
craniorachischisis. This is characterized but the CNS appearing as a groove in the top of
the head and body. Defective closure of the neural tube is rarely complete and
syndromes starting from spina bifida and anencephaly result from partial closure of the
neural tube. Anencephaly is when the rostral part of the neural plate does not fuse and
is characterized by the absence of the cerebral hemisphere, this usually fatal but not all
neural tube defects are fatal. For example spina bifida is caused when the tube doesn’t
completely close. There are many subtypes and the symptoms depend on the part of
the tube that doesn’t close. This syndrome affects the spinal cord and there affect
locomotion rather than cognitive abilities. Milder disruption in the tube occur later in
development and result in behavioural effects such as learning disabilities.
By the 7 month of development the neurons have migrated and are in there final form
but this is only the start of brain growth and change. Neurons undergo a long period of
synaptogenesis and dendritic branching producing more synapse and dendrites then
are needed in the adult brain, they even occur after birth and sometimes into
adulthood. Dendritic branching occurs very slowly and with time they become more complex adding branches and spines. It is on the dendritic spine that most synapse
occur. During early embryonic life synaptogenesis is very sparse but starting from right
before birth to 2 years of age it enters a rapid period of growth. Then a period synapse
reduction occurs and reaches it maximal rate at puberty. 50 percent more neurons are
produced in the developing brain then are needed in the adult brain so apoptosis is
normal. Much of neural death is apoptotic, but it is unclear what triggers this but it is
controlled by genes. Synapse that form the wrong connections die and new ones sprout.
Apoptosis usually occurs after birth and may have something to do with environement
and experiences of the individual.
Postnatal development – The emergence of a babys behaviour of sitting and walking is
due to extensive growth in the cortical areas of the brain which increases it size by 4
times between birth and adulthood. One way to study this is to examine a part of the
brain and figure out whether or not the behaviour becomes active one this part is fully
mature. Or you can figure out whether or not the emergence of a behaviour like walking
is associated with the development of a specific part of the motor cortex.
Just as much as the environment plays a role on the CNS in prenatal
development, it does in postnatal development too. Plastic Change is the ability
of the CNS to change to alter itself in response to environmental stimuli. There
are critical periods in plastic change in which there the environment has its
maximal effects on the CNS. The duration of these critical periods vary between
species but longer lived species have prolonged crtical periods that usually occur
later in life. Shaping of the CNS during these periods does not depend on random
events in the environment but plasticity during critical periods occurs in
response to one`s experience. There are two types of these experiences:
1. Experience – expectant plastic changes – those CNS changes that are
dependent on experiences during the crical period for specific synapse to
develop as they should. Most of the sensory cortex has experience –
expectant critical periods. Studies have shown that if a person does not
experience sensory stimulation during the critical period, there will be
impairments in the sensory modality. Experience is also important during the
critical period because sensory impairments that occur after the critical
period often have limited effects on the cortex.
2. Experience – Dependent plastic changes – the idiosyncratic experiences that
occur during the critical periods that also affect brain development. One
example is that musical training as a kid can have long lasting changes on the
size of the auditory cortex in adulthood. This was more profound in kids who
learned before 9 years old. Also the size of the motor cortex is affected in
kids who play string instruments, there was more cortical representation for
the left hand as the string as pulled with that hand. However all of this
depends on the age of which the child begins to play meaning that there is a
critical period in which maximal effects take place. These are individual
experiences but they are not random, that is musical learning affected a part
of the brain associated with musical abilities and no other part of the CNS
was affected. cortical grey matter volumes increase until 4 years of age with much of the
postnatal and plastic changes that occur in the brain resulting from
synaptogenesis, myelination of axons and dendritic branching. Synaptogenesis
and dendritic branching occur pre and post natally and presumably maximally
during the critical periods. The brains abililty to engage in plastic change reduces
as we age but there are exceptions. Significant environmental events can cause
the less plastic areas to change. Factors underlying plastic change are not
completely unswrstood but something to do with neurotrophins such as nerve
growth factors that are secreted by the brain to enhance the survival of neurons
and neurottansmitters play a large role. Also synaptogenesis and dendritic
branching are more sensitive to experience expectant and experience dependent
Cortical white matter volumes increase steadily until about 20 years of age.
Myelination barely occurs before and most after birth. It does not occur
uniformly throughout the cortex. The primary motor and sensory areas have
complete myelination by the age of 4, while the frontal cortex exhibits competle
myelination sometime during the late teens. Flechsig thought myelination
ockcured n accordance to behaviour. Sensory and motor areas conduct
behaviour first while complex behaviour controlled by parts the brain and are
not myelinated till later. This a correlation not causation, there may be other
factors causing it too. Much of this is studied using neuroimaging techniques.
Paretial lobe – Compared to the other lobes very little is know about this lobe. It has
inconsistent levels of development at birth, some parts of this lobe are more mature
then others. Paretial lobe is associated with spatial abilities and visual perception but
this doesn’t develop until later after birth. Somatosensory functions develop rapidly as
seen in the reflexes of a baby, this is consistent with the fact that myelination occurs in
the spinal cords and thalamic centres prenatally and is complete by one year. From 3
months to 3 years babies utilize large amounts of glucose in the paretial lobe and this
may be what causes the improvements in visuospatial and visuosensorimotor skills.
Basic tactile perception develops early but complex tactile discriminations take longer to
develop (distinguishing which finger was touched by touch perception only. The parietal
lobe is a ccomponent of the dorsal visual system, the component that is involved with
the processing of spatial information and directing behaviour towards certains points in
space. An important part of the dorsal visual system is processing of motion. The adult
level of global motion processing in a child occurs are 4 years old. Braddick thought that
this involved the coordination of motion and form processing. Accurate global motion
processing involves the participation of numerous cortical areas including the slow to
develop frontal lobes.
Williams Syndrome – a genetic condition in which some of chromosome 7
has been deleted. This has given more info about the development of the
paretial lobe and the connection between this lobe and others to mediate
spatial behaviour. These people have moderate cognitive impairments that
cause sparing of the verbal ability and significant visuospatial disabilities.
These people have a reduction in size of the brain but it is not uniform throughout the CNS. They have relative sparing of the frontal and temporal
lobe but have disproportionate reduction in the paretial and occipital lobe.
There is also a reduction white matter and there is also impoverished
connectivity among the lobes. These reductions, congenital defects and
losses may have been coded on the lost part of chromosome 7.
Occipital Lobe – Just like the paretial lobe the occipital lobe is incomplete at birth. This
doesn’t mean newborns have bad visual systems, they can tell apart 2D and 3D structures. They
have a rudimentary form of perception, as they become more competent with more complex
stimuli such as faces really quickly. Competence with visual stimuli depends on the myelination
of the optic tract and depends on whther the optic raditions are functionally connected with
sensory organs or with other areas of the brain. At birth myelination is moderate and optic
radiation myelinations are minimal. At 3 months of age there is heavy myelination. At 6 weeks
they they experience binocular vision and at 6 months this is stable.
The visual cortex is dependent on the environmental experience of an individual. For
example uncorrected congenital cataracts that deprive a child of patterned visuall
experience results in irreversiable changes in the visual cortex. If the cataract is removed
after the critical period the person has poor visual acuity, exhibiting amblyopia and
limited to no binocular vision. Similar result appear when the eyes are misaligned, as in
strabismus. These people who receive corrective measures after the crtitcal period have
impaired depth of perception probably because of the loss of binocular cells in the visual
cortex. For human the crtical period for binocular vision is withing the first few months
of life and peaks between 1 and 3 years of age. When Strabismus develops after the age
of 4 there are no long lasting effects on binocular vison once strabismus is corrected
suggesting that the critical periods end some time between the third and fourth years of
life. More complex visual tasks take longer to develop as they use numerous areas of
the cortex. Simple face regonition can be done at 6 but matching emotional cues to
faces develops at 14. These complex action require the development of the brain and so
they don’t occur till the teens.
Temporal lobe – The temporal has divided function such as linguistic abilities and
hippocampally dependent memory function. The development of speech production and
comprehension is due to the cooperation of the frontal and temporal lobes. Language
development requires the ability to perceive and comprehend sounds along with the ability to
coordinate the mouth and tongue to produce language sounds. So language development
requires both lobes and myelination and connections among the lobe. It is assumed that the
auditory cortex is functional at birth but this cortex may not make connections with other
important language areas. Both Wernickes and Brocas areas have significant extensive dendritic
branching and synaptic remodelling during the second year of life. Between 1 and 2 years of
age the commissural systems like the corpus callosum, anterior commissure and the fornix. All
of these are involved in connecting the left front and temporal lobesamd omcreases functional
connectivity both ipsilaterally and bilaterally. The CNS changes are due to the explosion in
language abilities during this period. This is a critical period for language, if one doesn’t learn at
this point there will be life long deficit of language.
From 2 to 12 years of age marked changes in dendritic arborisation occur in speech
areas of the brain. In other areas of the brain the dendritic arborisation is sensitive to environmental stimuli. This means environment plays a role in the development of
The hippocampus attains the adult volume around 7 to 10 months and it shows high
level of glucose use from birth unlike the other structure that use lower level of glucose
until they are 4 years of age. In monkeys extensive synaptic remodelling and
myelination occur during the first 24 months. Other structures in the limbic system
exhibit major growth spurts between 1 and 2 years of age. So basically the size of the
hippocampus is big but the hippocampally dependent memorie processes aren’t mature
at birth. He hippocampus is one of the sites that in adulthood show signs of
neurogenesis. The memory function of the brain depend on the functional connections
with the paretial and frontal lobes and many hipocampally dependent memory
functions develop over the course of the first 5 to 7 years in humans. For example we
know visual memory is present at birth but doesn’t reach adult levels until 5 years of
age. The abaility to recall episodic or autobiographical information does not occur till 4
eyrs of age before this age the recollections are incomplete and cue dependent. Infact
people have amnesia about there lives before 4 years old meaning the coding and
storing sytems of the CNS were not well developed at the timeAutobiographical
memories involve many areas such as the cingulate, pareitial, temporal, and prefrontal
areas. Frontal lobes were the alst to mature. Areas of the preofrontal cortex involved
with memory increase until about 4 years of age which is consistent with the time frame
of the emergence of this type of memory. So the developmental features of memory are
associated with the development of the temporal lobes and connectivity of among
Frontal Lobe – involved in language and memory with the temporal lobe. However its
functions focus primarily on motor and executive function. At birth atleast the prefrontal cortex
is developed reaching the adult levels of myelination, glucose use, and cell differentiation
sometime in the late teens. Motor areas of the frontal lobe are finished mature quick, the
primary and supplementary motor cortex exhibit rapid development often with significant
maturation at 3 months. Basic functions use areas that develop faster than areas that conduct
complex functions. Motor development follows cephalocaudal and proximodistal patterns if
development. That is that the head is controlled before the arms and trunks are, while the arms
and trunks are controlled before the legs are. The term proximodistal refers to the observatiosn
that motor skills develop in the head, trunks and arms before they develop in the hands and
fingers. As such many gross motor skills develop before fine motor skills. Gross motor skills are
those involving the large muscles involved in walking and balancing where as the fine motor
skills involve the small muscles that are typically involved in the coordination of the hands and
fingers. At birth motor roots are highly myelinated and by 6 months many of the subcortical
motor areas have at least moderate myelination. By 3 months many of the secondary and
teritiary motor areas of the frontal lobes exhibit differentiated neurons and adult – type
inhibition. Myelination of these tract begin early but it extends well into childhood. Myelination
of the pyramidal tract occurs at the end of the frst year and is often associated with walking but
myelination is not the only change occurring in these areas. These other factor that affect
motor development can be closely studied in individuals with Rett Syndrome that occurs in
female births. These people develop normally until 4 months after birth, one a gene mutation begins to arrest brain development. This is more pronounced at the end of the first year and is
most obvious in the frontal and motor cortices. Symptoms are progressive and appear 6 and 18
months of age and include hypotonia (loss of muscle tone), loss of the use of hand and apraxia.
When there brains are examined there in no loss of myelin but it appears that dendritic
arborisation in motor cortices are heavily reduced. The mutation also affects neurotransmission
and there are alteration to neurotransmitters in the affected areas. Usually motor development
relies on postnatal differentiation of neurons, synaptogenesis, dendritic arborisation,
neurotransmission and myelination.
When solving a problem with strategies or ordering a sequence of events the frontal
lobe is heavily used. These diverse activities are called executive functions where the executive
is the prefrontal cortex and the other employees that carry them out is the motor cortex. The
prefrontal areas of the brain are the last areas of the brain to develop and this explains why
children cant do many tasks that are controlled by this area. People with damage in this areas
make poor decisions but they don’t have a significant change in IQ. They are only impaired that
they cannot produce multiple solution per problem and they are different in social setting
compared to other adults. Major deficits are seen when they undergoWisconsin`s card sorting
task. They have a bunch of rules for card sorting, they have trouble switching back and forth
between rules. This deficit is due to 2 problems: they have problems in shifting strategies and
they have difficulty in inhibiting incorrect resonses (preservation). Children get better t this as
they age. Some elements of executive function matures in bright children over those with lower
People with frontal lobe damage also have a loss of behavioural spontaneitiy. The take
longer to relate word s to doodles. They are usually easily distracted in everyday life so its hard
for them to begin activities. People with damage here have trouble identifying emotions from
ambiguous situations whne they are children.
Frontal Lobe Development: the prefrontal cortex is the least developed at birth and
doesn’t develop until late teens. However, motor areas of the frontal lobe develop
rapidly and are highly myelinated. The head and trunk develop before the arms and
fingers, which develop before the legs. Gross motor skills are also acquired first
(walking, balance, holding head up) before fine motor skills (hand/feet coordination).
Deficiencies in this lobe can cause issues with problem solving, judging and portraying
Cephalocaudal: development of motor functions in which the head and trunk are
controlled before the legs.
Proximodistal: development of motor skills that occur in the head, trunk and arms
before the hands and fingers.
Structural Abnormalities: these can be caused from toxins, lack of oxygen, infections,
malnutrition, or genetic disorders. Some abnormalities can be fatal and some are not
noticeable at all:
• Anencephaly: lack of brain development
• Microcephaly: drastic reduction in brain development
• Agenesis: when a specific structure of the brain fails to develop completely or at
• Dysgenesis: a specific structure of the brain develops abnormally.
Teratogen: an agent that can cause malforma