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Chapter 4
The Biology of Behaviour
Chapter 4 - The Biology of Behaviour
Slide 1
Sections
• The Brain and its Components
• Studying the Brain
• Control of Behaviour
• Control of Internal Functions and automatic behaviour
• Drugs and behaviour
Chapter 4 - The Biology of Behaviour
Slide 2
The Brain and its Components
• The Structure of the Nervous System
• Cells of the Nervous System
• The Action Potential
• Synapses
• A Simple Neural Circuit
• Neuromodulators
Chapter 4 - The Biology of Behaviour
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Structure of the Nervous System
Nervous System
Central Nervous System
Brain Stem
Peripheral Nervous System
Brain
Spinal Cord
cerebellum
Cerebral Hemispheres
Steve, show BIO15 overhead here depicted the brain with the
above structures indicated
Chapter 4 - The Biology of Behaviour
Slide 4
Protecting the CNS
For protection purpose, both the brain and the spinal cord
are incased in bone (the skull and spine respectively)
In addition, both the brain and spinal cord are separated from
their bony armor by a 3-layered set of membranes called
the meninges.
Between the two layers of meninges is a clear liquid called
the cerebral spinal fluid. This fluid in combination with the
meninges provides a “waterbed” of sorts that protects the
sensitive CNS from becoming damaged by the bone that
surrounds them
Chapter 4 - The Biology of Behaviour
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The Cerebral Cortex
Our most complex psychological processes occur within
the thin layer of grey matter on the outside of our brain called
the cerebral cortex
The cortex is connected to the other parts of the brain through
a set of nerve fibers called white matter (see figure 4.3 in the
book for a look at this distinction)
In order to maximize the size of the cortex, the human brain
has become wrinkled, containing fissures and gyri
Chapter 4 - The Biology of Behaviour
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Structure of the Nervous System
Nervous System
Central Nervous System
Peripheral Nervous System
Somatic System
(Voluntary)
Autonomic System
(Involuntary)
Sympathetic
(4 Fs)
Parasympethetic
(relaxation)
Steve, show BIO2 overhead here depicted the brain with the
above structures indicated
Chapter 4 - The Biology of Behaviour
Slide 7
Cells of the Nervous System
The basic unit of the human nervous system is the cell.
The nerve cell is made up of four parts, (1) the dendrites,
(2) the soma, (3) the axon, and (4) the axon terminals.
> BIO7 overhead … note myelin
Neurons transmit information through electrical currents
termed action potentials that flow from the soma, through
the axon, to the axon terminals … where it is then passed
to the dendrites of other neurons
> wave demo & overhead BIO8
Chapter 4 - The Biology of Behaviour
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Transmission of Information Between
Cells
Information is passed from one cell to another via a process
termed synaptic transmission
This process involves the release of neurotransmitter molecules
from one neuron which then “fit into” receptor sites on the
dendrites on other neurons - BIO9 overhead.
Some neurotransmitters send excitatory signals, some inhibitory.
These signals are summed by the soma of the receiving neuron
which “decides” whether to send an action potential - BIO10
After the signal is sent, the neurotransmitters return to the sending
neuron in a process termed re-uptake.
Chapter 4 - The Biology of Behaviour
Slide 9
A Simple Neural Circuit
To illustrate this system in action, consider the following
two situations:
1. Touching a hot iron … sensory neurons detect the heat and
send an excitatory message to inter-neurons in the spinal cord
or brain. These inter-neurons then send excitatory signals to
the motor neurons to retract the hand immediately
2. Carrying a hot casserole dish … again, the heat may make
you want to drop the dish via the same process described above,
BUT this message is temporarily countered by the brain by
it sending inhibitory signals either to the inter-neurons or to the
motor neurons
Chapter 4 - The Biology of Behaviour
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Neuromodulators
As described, neurons send messages to other neurons via
chemicals called neurotransmitters or neuromodulators.
These chemicals can effect many sites in the brain simultaneously
leading to many different behavioural effects
Humans have also used synthetic versions of these chemicals
sometimes for recreational (or abusive) purposes and sometimes for
therapeutic purposes.
> e.g., Marijuana question
Chapter 4 - The Biology of Behaviour
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Study of the Brain
Much of our understanding of nerve cells has come from studies
conducted on animals
Animal research has also lead to the discovery of a number of
drugs that have helped patients suffering from such diseases as
Parkinson’s syndrome, schizophrenia, depression and others
The use of animals is considered justified in two ways:
1) in some cases in leads to obviously beneficial results
for humans as in the case of drug studies
2) in other cases, it advances our knowledge of the
human system which is considered worthwhile in and of itself
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RM - Lesion Studies
One of the oldest research methods used by physiological
psychologists involves examining the behavioural effects of
damage to certain parts of the brain.
Typically, this involves having the researcher creating a lesion
through a surgical procedure in order to wipe out the specific part of
the brain they are interested in - see BIO1 overhead for
a depiction of the stereotopic apparatus used to do this
The “destruction” of brain tissue is usually done by touching a
small wire to the brain site of interest, then passing an electrical
current through the wire in order to heat and destroy the area
A similar procedure is also sometimes used on humans to alleviate
symptoms of some diseases
Chapter 4 - The Biology of Behaviour
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RM - Measurement & Stimulation
Electrodes inserted via surgical procedures can also be used
to measure the activity in nerve cells in response to stimulation
The electrode is then connected to a recording device and
measures of electrical activity can be taken while the animal
performs various tasks
Electrodes can also be used to stimulate brain areas without
destroying them … and effects of stimulation can be studied
> famous rat self-stimulation experiment
Sometimes the stimulation and measurement are combined to
examine things like learning … long-term potentiation example
Chapter 4 - The Biology of Behaviour
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Enter the Reaper
Irrespective of the study, after it is done the researcher has to
verify that the electrode was in the location (s)he thought it
was in. The typical procedure for doing this involves
I’ll be leaving
now, thanks!
> sacrificing the animal via drug overdose
> removal of brain
> slicing up of brain
> dying of the brain slices
> examination of the sliced and dyed brain to verify
location
Sometimes, in order to stain the brain appropriately a more
complicated procedure must be used call profusion … Steve
will explain
Chapter 4 - The Biology of Behaviour
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Human Subjects
Clearly, many of the procedures we perform on animals would
not be considered ethical if performed on humans
However, there are now means of doing things that parallel the
animal work … thanks largely to brain scanning technology
CT (computerized tomography) scans send a narrow beam of
X-rays through the head and the computer calculates the amount of
radiation that passes through, then is able to generate a “slice” of the
brain, showing brain density at specific regions - BIO13
MRI (magnetic resonance imaging) do the same thing as CTs, but
with more detail (uses magnetic fields and radio waves instead of
X)
PET (positron emission tomography) scans measure processing
rather than structure by examining blood flow
Chapter 4 - The Biology of Behaviour
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Methods that Parallel Animal Work
Given these scanners, we can now describe at least two methods
that parallel those done with animals
First, due either to natural (e.g. stroke) or unnatural (e.g., accident)
situations, human brains become damaged -- or lesioned. Scanners
can now be used to localize the damage, and behavioural methods
can be used to assess the relation between certain brain areas and
certain behaviours
Second, we can also measure processing in the brain (via a PET)
while the subject engages in some activity … much like using
electrodes to measure processing in the rat brain
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So, what have we learned about the
brain from all this?
The cerebral cortex vs. lower level brain structures
The cerebral cortex is the place where high level perception of
the world occurs, and is also the place where controlled motor
activities originate. In this sense, it is the place where all our
controlled interactions with the external world occur.
This contrasts with a number of more basic brain regions
which are more devoted to monitoring and controlling internal
behaviours and automatic responses to external stimuli.
Each will now be discussed in turn
Chapter 4 - The Biology of Behaviour
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The Cerebral Cortex
Primary Motor and Sensory Cortex:
> There most definitely are certain parts of the brain that
are responsible for very specific tasks, especially when
it comes to sensation and motor responses - BIO18, and
FIG 4.23
> These areas are organized in a contralateral manner,
such that the left side of the brain represents the right
side of the body, and vice-versa
> The amount of brain dedicated to various regions is not
determined by the size of the region but, instead, by the
sensitivity of it - sensory homunculus
Chapter 4 - The Biology of Behaviour
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The Cerebral Cortex
Association Cortex
The remainder of the cerebral cortex is termed “association
cortex” and is thought to be where sensations are drawn
together to support higher level cognitive functions such as
perception, learning, and memory - Penfield’s surgery
Perception, then, is not the same as sensation but, instead,
is the interpretation of that sensation as performed by the
association cortex - CAT IN THE HAT example
The association cortex is often discussed in terms of lobes of
the brain; frontal, occipital, parietal & temporal - FIG 4.24
Distinction between somatosensory vs motor association cortex
Chapter 4 - The Biology of Behaviour
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Sensation is not Perception
Chapter 4 - The Biology of Behaviour
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The Cerebral Cortex
Lateralization of Function
The two hemispheres of the brain do not perform identical
functions … rather, each hemisphere seems to specialize in
certain things - BIO23
We are not aware that the hemispheres perceive the world
differently because they completely communicate with one
another via a brain structure called the corpus collosum
In certain extreme cases of epilepsy, the corpus collosum of a
patient is severed, in order to prevent the siezures. This leads
to an interesting splitting of experience from awareness BIO24 … more to come in Chapter 9
Lateralization is less clean than implied
Chapter 4 - The Biology of Behaviour
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The Occipital & Temporal Lobes
The occipital (and lower part of the temporal) lobes are devoted
to vision.
Primary visual cortex is directly related to sight, and damage to
it produces a hole in a persons visual field … a scitoma
Association cortex in this area
performs the function of providing
an interface between visual input
and memory … allowing one to
categorize visual images. Damage
can lead to agnosia, the inability to
name common objects
Chapter 4 - The Biology of Behaviour
A Pencil?
Slide 23
The Temporal Lobe
Most of the temporal lobe is devoted to audition
Primary auditory cortex is mostly hidden from view, lying on
the inside to the upper temporal lobe. Damage to this leads to
hearing problems
Auditory association cortex is located on the lateral surface
of the upper temporal lobe
> Damage to left leads to severe language deficits … patients
losing the ability to comprehend or produce meaningful speech
> Damage to the right affects the patients ability to properly
perceive non-speech sounds, like the rhythm in music
Chapter 4 - The Biology of Behaviour
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The Parietal Lobe
Primary sensory function involves perception of the body
The association cortex here seems to be involved in complex
spatial functions, that differ across the hemispheres
The left parietal appears to keep track of the spatial location
of our body parts - proprioception
> Damage often associated with poor motor movements
The right parietal appears to keep track of the spatial location
of things in our external world
> Damage can lead to problems of neglect and spatial
integration of parts
Chapter 4 - The Biology of Behaviour
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The Frontal Lobes
Thought to be responsible for many very high level cognitive
functions such as planning, strategy shifting, self-awareness,
and the initiation of motor activity.
Damage to the motor area of frontal cortex causes paralysis of
the associated motor functions in the opposite side of the body
Damage to the pre-frontal cortex ( e.g. frontal labotomies)
causes very complex and interesting effects including:
1. The slowing of thoughts and loss of spontaneity
2. Perseveration errors - Card sorting example
3. Loss of self-awareness and flat affect, especially empathy
4. Deficiencies in foresight and planning
5. Tendency to confabulate
Chapter 4 - The Biology of Behaviour
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Wisconsin Card Sorting Task
Sort by number
Sort by shape
Sort by colour
Chapter 4 - The Biology of Behaviour
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Sub-cortical Brain Regions
The brain stem is involved in many of our
most basic behaviours including the control of
heart rate, blood pressure, and respiration (medulla),
sleep (pons), fighting and sexual behaviour (midbrain)
The cerebellum, in co-ordination with the frontal lobes,
carries out the detailed computations necessary for precise motor
movements … in addition it also controls adjustments for posture,
and corrects for things like head movement when controlling eyes
In addition, there are also a number of regions within the cerebral
hemispheres that also play a role including the thalamus, the
hypothalamus, and the limbic system
Chapter 4 - The Biology of Behaviour
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The Thalamus and Hypothalamus
The thalamus, located in the very center of the brain, performs
two basic functions; (1) the reception and integration of perceptual
information, and (2) the passing on of this information to the
relevant cortical regions … attention??
The hypothalamus is located below the thalamus and is very small.
It monitors a number of characteristics of the blood that flows thru
the brain (e.g., temperature, composition) and controls the
pituitary gland, an endocrine gland attached to the base of the skull
Endocrine glands release hormones which act like neurotransmitters
except over longer distances … they stimulate receptor sites causing
physiological reactions
The pituitary is the master endocrine, as it can command target
receptors on other endocrine glands
Chapter 4 - The Biology of Behaviour
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The Limbic System
Includes two structures, the amygdala, and the hippocampus.
The amygdala appears to control emotional reactions, especially
negative ones. In addition it provides energy for fighting and
fleeing
> damage to the amygdala causes a loss of “stress” and “anger”
reactions … which is actually bad news for survival
The hippocampus plays an important role in memory. It is
especially critical for learning new information … many of those
most striking cases of amnesia are caused by damage to the
hypocampus
Chapter 4 - The Biology of Behaviour
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Drugs and Behaviour
This section I leave to you … I will not discuss it beyond
that which we have done already … you are responsible
for it though, so read up!
Chapter 4 - The Biology of Behaviour
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