Chapter 2: Cognitive Neuroscience
Cognitive neuroscience: the study of the physiological basis of cognition
Neurons: the building blocks and transmission lines of the nervous system
Neurons: The Building Blocks of the Nervous System
The Microstructure of the Brain: Neurons
The nature of electrical signals in the brain & pathways had just begun being discovered in the
Nerve net: a network believed to be continuous
Camillo Golgi, in the 1870s developed a staining technique which involved immersing a thin
slice of brain tissue in a solution of silver nitrate.
Ramon y Cajal, a Spanish physiologist discovered neurons (the basic building blocks of the
brain) which became the centerpiece of the neuron doctrine. Concepts introduced by Cajal
include: neurons, synapses, and neural circuits (basic principles used today to explain how the
brain creates cognitions).
Neuron doctrine: the idea that individual cells transmit signals in the nervous system, and
that these cells are not continuous with other cells as proposed by nerve net theory.
The cell body contains mechanisms to keep the cell alive.
Dendrites branch out from the cell body to receive signals from other neurons.
Axon/Nerve fiber transmits signals to other neurons.
Receptors: neurons similar to brain neurons cause they have a cell body and axon, but
have specialized receptors that pick up information from the environment (Cajal).
Synapse: the small gap between the end of the neuron’s axon and the dendrites or cell body
of another neuron.
Neural circuits: a circuit which consists of the connection of many neurons.
The Signals That Travel in Neurons
Determining the actual nature of signals transmitted from neurons awaited the development of
electronic amplifiers, powerful enough to make the extremely small electrical signals generated
by the neuron visible.
In the 1920s, Edgar Adrian recorded electrical signals from single sensory neurons, getting the
Nobel Prize in 1932 as a result.
Method: Recording From a Neuron
Microelectrodes used by Adrian recorded electrical signals from single neurons using small shafts of hallow glass filled w/ a conductive salt solution that can pick up electrical signals
at the electrode tip and conduct these signals back to a recording device.
The recording electrode is connected to a recording device and to another electrode
called the reference electrode.
The reference electrode: is located outside of the tissue (figure 2.5a)
Nerve impulse/action potential: an electrical signal transmitted down the axon.
Neurotransmitter: a chemical that makes it possible for action potentials to be transmitted
across the synaptic gap which separates the end of the axon from the dendrite or cell body of
Adrian studied the relation between nerve firing and sensory experience by measuring how the
firing of a neuron from a receptor in the skin changed as he applied more pressure to the skin.
Therefore increased stimulus intensity causes an increase in the rate of nerve firing.
Localization of function: a principle stating that neurons serving different cognitive
functions transmit signals to different areas of the brain.
Localization of Function
Localization of function: one of the basic principles of brain organization.
Cerebral cortex: serves most cognitive function, it is a layer of tissue about 3 mm thick
covering the brain.
Localization for Perception
Primary receiving areas (for the senses): (see figure 2.7) vision = occipital lobe; skin
senses = parietal lobe (dotted area); hearing = temporal lobe (located within temporal lobe).
The frontal lobe responds to all senses and is involved in higher cognitive functioning.
Temporal lobe: neurons in this lobe respond to sound, and neurons in another area in the
temporal lobe to faces.
Occipital lobe: occupied by the primary receiving area, neurons in the occipital lobe
respond to stimulation of the eye with light.
Parietal lobe: the area for the skin senses touch, temperature, and pain.
Areas of taste and smell are located on the underside of the temporal lobe (smell) and in a
small area within the frontal lobe (taste).
Frontal lobe: receives signals from all of the senses and plays an important role in
perceptions involving the coordination of information received through two or more senses.
Prosopagnosia: inability to recognize faces resulting from damage to a certain area of the
temporal lobe on the lower right side of the brain (not the auditory area, which is higher up in
the temporal lobe).
Method: Brain Imaging Brain imaging: used for measuring brain activity in humans allowing researchers to create
images showing which areas of the brain are activated as awake humans carry out various
Positron emission tomography (PET): a brain imaging technique that takes advantage
of the fact that blood flow increases in areas of the brain that are activated by a cognitive task. To
measure blood flow, a low dose of a radioactive tracer is injected into a person’s bloodstream. The
brain is then scanned by the PET apparatus, measuring the signal from the tracer at each location
in the brain (figure 2.8).
Subtraction technique (figure 2.9): Brain activity is measured first in a “control state,” before
stimulation is presented, and again while the stimulus is presented.
Functional magnetic resonance imaging (fMRI): fMRI is based on the measurement
of blood flow. An advantage of fMRI is that blood flow can be measured without radioactive tracers.
fMRI takes advantage of the fact that haemoglobin, which carries oxygen in the blood, contains a
ferrous (iron) molecule and therefore has magnetic properties. If a magnetic field is presented to
the brain, the hemoglobin molecules line up, like tiny magnets. fMRI indicates the presence of brain
activity because the hemoglobin molecules in areas of high brain activity lose some of the oxygen
they are transporting. This makes the hemoglobin more magnetic, so these molecules respond
more strongly to the magnetic field. The fMRI apparatus determines the relative activity of various
areas of the brain by detecting changes in the magnetic response of the hemoglobin. The
subtraction technique is also used for fMRI. FMRI is the main method for determining which areas
of the brain are activated by different cognitive functions because it doesn‘t require radioactive
Fusiform face area (FFA): the fusiform gyrus on the underside of the temporal lobe,
corresponds to the area usually damaged in patients with prosopagnosia.
Parahippocampal place area (PPA): activated by pictures representing indoor and
outdoor scenes. The important part of this area is information about aptial layout, because
increased activation occurs when viewing pictures both of empty room and of rooms that are
Extrastriate body area (EBA): activated by pictures of bodies and parts of bodies (but not
Modularity is often used to refer to localization.
Module: an area specialized for a specific function.
The fusiform face area, extra striate body area, and parahippocampal place area are modules for
perceiving faces, bodies, and palces, respectively. Localization for Language
Broca’s area: area in the frontal lobe that is specialized in producing language.
Broca’s aphasia: having difficulty in speech after suffering a stroke but can still
understand the speech of others. Those w/ Broca’s aphasia have difficulty processing
connecting words such as “was” and “by”.
Wernicke’s area: area of the temporal lobe that specializes in speech.
Wernicke’s aphasia: producing meaningless speech and unable to understand speech
The results of many behavioural and physiological experiments have caused some researchers
to distinguish not between problems of production and understanding, but between
problems of form and meaning.
Method: EventRelated Potential
Eventrelated potential (ERP): recorded with small disc electrodes placed on a person’s
scalp. Each electrode picks up signals from groups of neurons that fire together. A disadvantage of
the ERP is that it is difficult to pinpoint where the response is originating in the brain. ERP is suited
for studying dynamic processes like language. The ERP is useful in distinguishing between form
and meaning because the ERP consists of a number of waves that occur at different delays after a
stimulus is presented and that can be linked to different functions. Two components responding to
different aspects of language are the N400 component and the P600 component, where N stands
for “negative” (note the negative is up in ERP record) and P for “positive.” (see figure 2.14) The
N400 wave of the ERP is affected by the meaning of the word and the P600 wave of the ERP is
affected by grammar.
1. Specific language functions are localized in specific brain areas, so that localization of function
is an important part of language processing; and
2. Language processing is distributed over a large area of the brain.
Distributed Processing in the Brain
Distributed processing: specific functions being processed by many different areas in the
brain (figure 2.15 & 2.16).
Memory, language, making decisions, and solving problems, all involve distributed activity in the
Multiple areas in