Psych 1XX3 – Notes on Neuroscience II – Jan 27th, 2010
In humans, the nervous system axis, or "neuraxis", curves as you can see in this
Dorsal always refers to the back of the axis, and ventral means to the front of the
axis or "to or the belly".
Because of the curve in the neuraxis, at the level of the head dorsal is up, but at
the level of the spinal cord dorsal is to the back. The term rostral means towards
the top of the axis, and caudal means towards the bottom of the axis.
Finally, locations in the brain that are more central or towards the midline of the
brain are medial, and regions towards the outside of the brain are lateral. These
terms can be combined to locate a very specific brain region.
Studying the Brain:
Neuroscientists have long been interested in case studies of accidental brain injury
which can link anatomy with associated cognitive and behavioural deficits that
Consider the famous case study of Phineas Gage. In 1848, Gage was the victim of
a tragic accident, resulting in the blasting of a 3 foot iron rod completely through
his left cheekbone and through the top of his skull. Remarkably; Gage survived,
and he recovered completely. However, once an upbeat, polite and caring person,
Gage became prone to selfish behaviour and bursts of profanity. He became
erratic and unreliable, and had trouble forming and following through on plans.
Gage's case provided support for the view that the brain has specialized structures
for complex behaviours. Case studies such as Phineas Gage have given neuroscientists tantalizing hints to
the relationship between structure and function in the brain.
A limitation of most case studies of human brain lesions is that they are rarely
isolated to specific brain structures. This certainly makes a more difficult task of
assigning impaired function to specific brain areas.
This problem can be overcome by studying specific brain lesions induced in
animal models. In such ablation studies, a researcher destroys, removes or
inactivates a defined brain region and observes the result on behaviour.
The accuracy of this emerging understanding of structure and function can depend
on the precision of the lesion. Even so, because the brain is so highly
interconnected, often a variety of behaviours are affected by a single lesion.
Stimulation and Signal Cell Recording:
An alternative approach to lesioning is to electrically stimulate an area of the
brain and observe the result on behaviour to build an anatomical map related to
This technique was used extensively by the Canadian neurologist Penfield as he
performed brain surgery to treat patients with severe epileptic seizures.
Single Cell Recording:
Penfield revolutionized techniques in brain surgery as he perfected his "Montreal
Procedure" to treat patients experiencing severe seizures.
In doing so, he had to be sure that critical areas of the brain were left intact.
Because the brain itself does not have pain receptors, a patient undergoing surgery
could be under local anaesthetic and fully conscious, working with Penfield to
probe the exposed brain to locate and remove the scarred tissue that caused the
Penfield used a thin, wire carrying a small electric charge to stimulate the cortex.
This stimulation leads individual neurons to fire, and thus Penfield could very
accurately map perceptual processes and behaviours to specific brain regions.
For example, if an area of the visual cortex was stimulated, a patient reported
seeing flashes of light and if an area of the motor cortex was stimulated, a patient
would experience a muscle twitch.
Penfield’s pioneering work revealed specific function to previously unmapped
regions of the brain.
Electrodes can also be used to record ongoing electrical activity in the brain
through single cell recording techniques.
A small electrode is inserted into the nervous tissue of a live animal model with
its tip held just outside the cell body of an individual neuron.
From this electrode, neural activity is recorded while the animal performs a task
or a stimulus is presented. The pattern of firing reveals a particular neuron’s
For example, in your study of Vision, you will encounter the seminal work of
Hubel and Wiesel. In a typical experiment, cats were presented with specific
visual stimuli while recording from single cells in the visual cortex.
In this wary, individual cell types were identified that responded to specific
categories of visual stimuli.
Limitation: it only provides information about a limited area in the brain. Structural Neuroimaging:
To study large-scale structure and function of brain regions, neuroscientists
use structural and functional neuroimaging techniques.
The first structural neuroimaging technique developed was computed
tomography (or CT).
During a CT scan, a series of X ray slices of the brain are taken and pieced
together to produce a relatively quick and inexpensive picture of the brain.
These scans are often helpful to diagnose brain injuries.
Limitation: its relatively low resolution.
For a more detailed structural image of the brain, neuroscientists use MRI, or
magnetic resonance imaging. In an MRI machine, powerful magnetic fields
are generated which align the hydrogen atoms found throughout the brain.
While these atoms are aligned, an MRI can be used to localize tissue very
precisely throughout the brain.
Cognitive neuroscientists can use a functional imaging technique such as
positron emission tomography (or PET scan), to learn how brain function
relates to cognitive tasks such as language and memory.
In a PET scan, a radioactive tracer of glucose or oxygen, is injected into the
bloodstream. The radioactive molecules make their way to the brain and are
used in metabolic processes, which are detected by the PET scan.
The logic is that more active brain areas will use more metabolic resources,
and so an image of the brain's relative pattern of activity can be constructed.
Disadvantage: requires a radioactive tracer to be injected, a relatively invasive
Functional magnetic resonance image (fMRI) is often preferred because it can
produce a relatively clear image of the brain's activity without the need for a
fMRI works by measuring the blood oxygen dependent signal, and uses many
of the same principles as the MRI.
It is able to measure the relative use of oxygen throughout the brain and
operates under the same basic assumption as the PET scan - more active areas
of the brain require more metabolic resources.
Popular, but has limitations: Provides a very rough image of brain activation.
Oxygen use by the brain often spikes a few seconds later than the spikes of
activity in the brain - and a few seconds can be a very long time in terms of
As such, fMRI is not the best method to use if a researcher is interested in the
precise timing of brain activation and function.
A final neuroimaging method to consider is the electroencephalogram (EEG).
The electrical activity of the brain can recorded through the scalp by wearing
a cap of very sensitive electrodes.
The EEG provides only a very rough image of the brain's overall activity,
from populations of neurons. However, with a few clever modifications, the
EEG can become more informative.
In an event related potential (or ERP) experiment, a specific stimulus is
presented to the subject repeatedly while the EEG is recording. Although the EEG will generally produce very noisy waves, the specific stimulus presented
can have a small and consistent effect on the readout.
By averaging the EEG signal across many trials, the noise can be balanced
out, and what remains is a characteristic signal.
These ERP signals can still be difficult to interpret, but there are a number of
reliable signals reported throughout the literature that serve as markers for
different types of neural processes.
Example: one such marker is called the N170 wave, which is thought to
correspond to face processing when combined with a behavioural measure,
EEG and ERP signals can be highly informative markers, with very precise
temporal resolution, on the order of milliseconds.
The Brain Regions (See image below.)
Your look at the brain will progress through three broad regions: the
hindbrain, midbrain, and forebrain.
The Hindbrain: (See image below.)
Def’n: Region at base of brain that connects the brain to the spinal cord.
All information into and out of the brain travels through cranial nerves or
through the spinal cord, which connects to the hindbrain at the very base of
The hindbrain consists of the medulla, pons, reticular formation, and the
These structures are evolutionarily the oldest parts of the brain and found in
some form in nearly every vertebrate species. And so it's not surprising that
they are primarily involved in the regulation of vital bodily functions. The Hindbrain: The Medulla
The medulla is the most caudal part of the hindbrain and lies directly above
the spinal cord. Structurally, it looks like an extension of the spinal cord and
plays an important role in vital functions such as breathing, digestion and
regulation of heart rate.
The Hindbrain: The Pons
The pons is a small structure that is rostral to the medulla. The pons relays
information about movement from the cerebral hemispheres to the cerebellum.
The pons also contains a number of nuclei that are generally part of the
Additionally the pons processes some auditory information and is thought to
be involved in some aspects of emotional processing.
The Hindbrain: The Reticular Formation
The reticular formation is a set of interconnected nuclei found throughout the
hindbrain (excluding the cerebellum).
The reticular formation has two main components: (1) The ascending reticular
formation (also called reticular activating system or RAS) is primarily
involved in arousal and motivation, and may be a part of a large network
responsible for your conscious experience.
Beyond that, the RAS plays an important role in circadian rhythms. Damage
to the RAS leads to devastating losses in brain function, and in the extreme
case a permanent coma.
(2) The descending reticular formation is involved in posture and equilibrium,
and plays a role in motor movement.
The Hindbrain: The Cerebellum
The cerebellum translates to "little brain" and resembles a miniature version of
the entire brain.
The cerebellum is the maestro of the orchestra that coordinates all movement.
Motor commands pass through the cerebellum as they signal muscles to
contract, and during the production of movement, sensory signals return to the
cerebellum for immediate error correction.
The importance of this structure is apparent in patients with damage to the
cerebellum who display exaggerated, jerky movements overshooting or
missing targets completely.
The midbrain is a relatively small region that lies between the hindbrain and
Generally, the midbrain contains two major subdivisions: the tectum and the
The Tectum: (Image shown on next page.)
Within these regions are a number of structures involved in a variety of
functions, including perception, arousal, and motor control.
The tectum is located in the dorsal portion of the midbrain and contains two
primary structures: the superior and inferior colliculi.
These two structures are involved in functions related to perception and
The superior colliculus is thought to be involved in eye movements and visual
reflexes, while the inferior colliculus is thought to be involved in auditory
integration. The Tegmentum:
The tegmentum contains important structures, including nuclei of the reticular
formation, the red nucleus, and the substantia nigra.
The Red Nucleus:
The red nucleus is an important structure involved in the production of
movement. In vertebrates with less complex brains, it is one of the most important
structures for the regulation and production of movement, as it projects directly to
the cerebellum and spinal cord.
In humans, with their relatively advanced fore brain structures, the red nucleus
plays a lesser role in the production of movement, and instead serves primarily as
a relay station for information from higher motor areas to and from the
cerebellum and spinal cord.
However, in the still developing brain of young infants, many motor behaviours
may still be controlled by the red nucleus. (See image below) The Substantia Nigra (See Image on Prev. Page):
The substantia nigra is another important and highly interconnected region of the
midbrain, with projections into a variety of forebrain regions.
The substantia nigra is involved in such tasks as motor planning and lear