slide 1 chapter 4 the biology of behaviour chapter 4 - the biology of behaviour

Chapter 4

The Biology of Behaviour

Chapter 4 - The Biology of Behaviour

Sections

• The Brain and its Components

• Studying the Brain

• Control of Behaviour

• Control of Internal Functions and automatic behaviour

• Drugs and behaviour


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


Structure of the Nervous System

B ra in S tem cereb e llu m C ereb ra l H em isp h eres

B ra in S p in a l C ord

C en tra l N ervou s S ys tem P erip h era l N ervou s S ys tem

N ervou s S ys tem

Steve, show BIO15 overhead here depicted the brain with theabove structures indicated


Protecting the CNS

For protection purpose, both the brain and the spinal cordare incased in bone (the skull and spine respectively)

In addition, both the brain and spinal cord are separated fromtheir bony armor by a 3-layered set of membranes calledthe meninges.

Between the two layers of meninges is a clear liquid calledthe cerebral spinal fluid. This fluid in combination with themeninges provides a “waterbed” of sorts that protects thesensitive CNS from becoming damaged by the bone that surrounds them


The Cerebral Cortex

Our most complex psychological processes occur withinthe thin layer of grey matter on the outside of our brain calledthe cerebral cortex

The cortex is connected to the other parts of the brain througha 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


C en tra l N ervou s S ys tem

S om atic S ys tem(V o lu n ta ry)

S ym p ath e tic(4 F s )

P arasym p eth e tic(re laxa tion )

A u ton om ic S ys tem(In vo lu n ta ry)

P erip h era l N ervou s S ys tem

N ervou s S ys tem

Steve, show BIO2 overhead here depicted the brain with theabove structures indicated

Structure of the Nervous System


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 currentstermed action potentials that flow from the soma, throughthe axon, to the axon terminals … where it is then passed to the dendrites of other neurons

> wave demo & overhead BIO8


Information is passed from one cell to another via a processtermed synaptic transmission

This process involves the release of neurotransmitter moleculesfrom 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 sendingneuron in a process termed re-uptake.

Transmission of Information Between Cells


To illustrate this system in action, consider the followingtwo situations:

1. Touching a hot iron … sensory neurons detect the heat andsend an excitatory message to inter-neurons in the spinal cordor brain. These inter-neurons then send excitatory signals tothe motor neurons to retract the hand immediately

2. Carrying a hot casserole dish … again, the heat may makeyou want to drop the dish via the same process described above,BUT this message is temporarily countered by the brain byit sending inhibitory signals either to the inter-neurons or to themotor neurons

A Simple Neural Circuit


Neuromodulators

As described, neurons send messages to other neurons viachemicals 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 chemicalssometimes for recreational (or abusive) purposes and sometimes for therapeutic purposes.

> e.g., Marijuana question


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 ofdrugs that have helped patients suffering from such diseases asParkinson’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 studies2) in other cases, it advances our knowledge of the

human system which is considered worthwhile in and of itself


RM - Lesion StudiesOne of the oldest research methods used by physiological psychologists involves examining the behavioural effects ofdamage to certain parts of the brain.

Typically, this involves having the researcher creating a lesionthrough a surgical procedure in order to wipe out the specific part of the brain they are interested in - see BIO1 overhead fora depiction of the stereotopic apparatus used to do this

The “destruction” of brain tissue is usually done by touching asmall 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


RM - Measurement & Stimulation

Electrodes inserted via surgical procedures can also be usedto measure the activity in nerve cells in response to stimulation

The electrode is then connected to a recording device andmeasures of electrical activity can be taken while the animal performs various tasks

Electrodes can also be used to stimulate brain areas withoutdestroying 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


Enter the Reaper

Irrespective of the study, after it is done the researcher has toverify that the electrode was in the location (s)he thought itwas in. The typical procedure for doing this involves

> 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 morecomplicated procedure must be used call profusion … Stevewill explain

I’ll be leavingnow, thanks!


Human SubjectsClearly, many of the procedures we perform on animals wouldnot 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 ofX-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


Methods that Parallel Animal Work

Given these scanners, we can now describe at least two methodsthat 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 usingelectrodes to measure processing in the rat brain


The cerebral cortex vs. lower level brain structures

The cerebral cortex is the place where high level perception ofthe world occurs, and is also the place where controlled motoractivities originate. In this sense, it is the place where all ourcontrolled interactions with the external world occur.

This contrasts with a number of more basic brain regionswhich are more devoted to monitoring and controlling internalbehaviours and automatic responses to external stimuli.

Each will now be discussed in turn

So, what have we learned about the brain from all this?


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

The Cerebral Cortex


Association Cortex

The remainder of the cerebral cortex is termed “associationcortex” and is thought to be where sensations are drawn together to support higher level cognitive functions such asperception, 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 theassociation cortex - CAT IN THE HAT example

The association cortex is often discussed in terms of lobes ofthe brain; frontal, occipital, parietal & temporal - FIG 4.24

Distinction between somatosensory vs motor association cortex

The Cerebral Cortex


Sensation is not Perception


Lateralization of Function

The two hemispheres of the brain do not perform identicalfunctions … rather, each hemisphere seems to specialize incertain things - BIO23

We are not aware that the hemispheres perceive the worlddifferently because they completely communicate with oneanother via a brain structure called the corpus collosum

In certain extreme cases of epilepsy, the corpus collosum of apatient is severed, in order to prevent the siezures. This leadsto an interesting splitting of experience from awareness - BIO24 … more to come in Chapter 9

Lateralization is less clean than implied

The Cerebral Cortex


The Occipital & Temporal Lobes

The occipital (and lower part of the temporal) lobes are devotedto vision.

Primary visual cortex is directly related to sight, and damage toit produces a hole in a persons visual field … a scitoma

Association cortex in this area performs the function of providingan interface between visual inputand memory … allowing one tocategorize visual images. Damagecan lead to agnosia, the inability toname common objects

A Pencil?


The Temporal Lobe

Most of the temporal lobe is devoted to audition

Primary auditory cortex is mostly hidden from view, lying onthe inside to the upper temporal lobe. Damage to this leads tohearing problems

Auditory association cortex is located on the lateral surfaceof 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


The Parietal Lobe

Primary sensory function involves perception of the body

The association cortex here seems to be involved in complexspatial functions, that differ across the hemispheres

The left parietal appears to keep track of the spatial locationof our body parts - proprioception

> Damage often associated with poor motor movements

The right parietal appears to keep track of the spatial locationof things in our external world

> Damage can lead to problems of neglect and spatial integration of parts


The Frontal Lobes

Thought to be responsible for many very high level cognitivefunctions such as planning, strategy shifting, self-awareness,and the initiation of motor activity.

Damage to the motor area of frontal cortex causes paralysis ofthe 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 spontaneity2. Perseveration errors - Card sorting example3. Loss of self-awareness and flat affect, especially empathy4. Deficiencies in foresight and planning5. Tendency to confabulate


Wisconsin Card Sorting Task

Sort by numberSort by shapeSort by colour


Sub-cortical Brain Regions

The brain stem is involved in many of ourmost basic behaviours including the control ofheart 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 motormovements … 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 cerebralhemispheres that also play a role including the thalamus, the hypothalamus, and the limbic system


The Thalamus and Hypothalamus

The thalamus, located in the very center of the brain, performstwo basic functions; (1) the reception and integration of perceptualinformation, 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 thruthe 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 neurotransmittersexcept over longer distances … they stimulate receptor sites causingphysiological reactions

The pituitary is the master endocrine, as it can command targetreceptors on other endocrine glands


The Limbic System

Includes two structures, the amygdala, and the hippocampus.

The amygdala appears to control emotional reactions, especiallynegative ones. In addition it provides energy for fighting andfleeing

> 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 thosemost striking cases of amnesia are caused by damage to the hypocampus


Drugs and Behaviour

This section I leave to you … I will not discuss it beyondthat which we have done already … you are responsiblefor it though, so read up!


slide 1 chapter 4 the biology of behaviour chapter 4 - the biology of behaviour

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