The Biology of Behaviour

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Chapter 4

• The Biology of Behaviour

Chapter 4 - The Biology of Behaviour
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Sections

• The Brain and its Components
• Studying the Brain
• Control of Behaviour
• Control of Internal Functions and automatic
  behaviour
• Drugs and behaviour

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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

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Structure of the Nervous System
Steve, show BIO15 overhead here depicted the
brain with the above structures indicated
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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
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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
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Structure of the Nervous System
Steve, show BIO2 overhead here depicted the brain
with the above structures indicated
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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. gt 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 gt wave demo
overhead BIO8
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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.
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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
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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. gt e.g., Marijuana question
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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 Parkinsons
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
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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 gt famous rat
self-stimulation experiment Sometimes the
stimulation and measurement are combined to
examine things like learning long-term
potentiation example
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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 gt
sacrificing the animal via drug overdose gt
removal of brain gt slicing up of brain gt dying
of the brain slices gt 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
Ill be leaving now, thanks!
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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
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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
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The Cerebral Cortex
Primary Motor and Sensory Cortex gt 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 gt
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 gt 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
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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 - Penfields 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
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Sensation is not Perception
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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
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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
A Pencil?
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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 gt Damage to left leads to severe
language deficits patients losing the
ability to comprehend or produce meaningful
speech gt Damage to the right affects the
patients ability to properly perceive
non-speech sounds, like the rhythm in music
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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 gt Damage often
associated with poor motor movements The right
parietal appears to keep track of the spatial
location of things in our external world gt
Damage can lead to problems of neglect and
spatial integration of parts
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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
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Wisconsin Card Sorting Task
Sort by number Sort by shape Sort by colour
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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
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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 informatio
n, 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 physiologica
l reactions The pituitary is the master
endocrine, as it can command target receptors on
other endocrine glands
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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 gt 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
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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