THE STUDY OF WHAT STRUCTURES HAVE WHAT FUNCTIONS

IB LEARNING OUTCOME:E X P L A I N O N E S T U D Y R E L AT E D TO

L O C A L I Z AT I O N O F F U N C T I O N O F T H E B R A I N

I N I B - S P E A K T H I S M E A N S “ G I V E A D E TA I L E D A C C O U N T I N C L U D I N G R E A S O N S A N D C A U S E S ”

Localization of Function

Why is brain function special?

The human brain is capable of carrying out different functions such as vision movement, comprehension, speech, hearing and overall body control.

Unlike other organs such as lungs or kidneys that perform the same function, different parts of the brain execute different functions.

Therefore, localization of function is relevant in the human brain.

But how do we find out? Methods involving alteration/change

Accidental damage – Phineas Gage (frontal cortex)

Deliberate damage/lesion (ablation)

Stimulation of the brain – electrodes inside the brain

Strokes/tumors Jill Bolte Taylor, the doctor who had a stroke in her

left hemisphere. ‘Tan’ – Broca’s patient who could only say ‘tan’

because of brain damage. Broca’s area was revealed in (postmortem) autopsy

Head trauma Phineas Gage – had a rod go through his frontal cortex

Viral attacks Clive Wearing – ‘flu’ on his temporal lobe and

hippocampus causing anterograde amnesia

Accidental damage – and cases we know of

Ablation affects…

Motivation lesions on the hypothalamus of rats disturbed eating behavior.

Aggression removing the amygdala in animals reduces aggression.

Memory case of HM who had his hippocampus removed.

Consciousness Sperry cut Corpus Callosum in epileptic patient, who then

experienced ‘split brain’Psychopathology

mental inmates were given lobotomy to control their behavior.

I knew you would ask about split brain!

Sperry cut the patient’s corpus callosum to alleviate their epilepsy symptoms. This structure enables the two hemispheres to communicate.

Split brain – right and left are ‘divorced’

The patients hemispheres were disconnected, and they experiences ‘split brain’

A patient with a split brain, when shown an image in his or her left visual field, will be unable to vocally name what he or she has seen.

This is because the speech-control center is in the left side, and the image from the left visual field is sent only to the right side of the.

http://ibpsychology.wetpaint.com/page/Gazzaniga+Key+Study - watch this clip

Electrical stimulation

Animal studies Delgado stimulated areas of the limbic system to

inhibit aggression in a charging bull with a remote control - while standing right in front of it!

Human studies Penfield stimulated areas of the cortex in patient

during surgery to locate areas controlling movement, hearing, sense etc.

Evaluation – can you evaluate the methods?

Accidental damage

Ablation

Electrical Stimulation

Evaluation

Accidental damage

Lack of precision – we cannot control the damage Hard to compare before and after damage (no

concrete records of ‘before’) Confounding variables – could Gage’s behavior be

caused by social relations? Ethically good, as the damage occurs naturally in

these natural experiments

Evaluation

Ablation

Ethical problems – not just in humans! Animal studies – we cannot necessarily generalize Neuroplasticity – the brain can compensate, so the

missing part may not be showing Good because there is greater control – precision of

damage and therefore easier to compare

Evaluation

Stimulation Less harmful than ablation More valid – a better way of investigation ‘living’

function of the brain However, it is invasive – surgery is risky The brain’s interconnectedness makes it hard to know

if the stimulated areas affect other areas.

Discussion – can we localize function?

”The brain is a highly complex, heavily

interconnected system that displays non-linear properties and this is clearly a short fall of localization of function. 

(This means that we can argue that is is hard to localize a function to a specific structure of the brain, since the structures are interconnected)

Methods of localization that do not involve alteration

Direct reading of neuron activity Very precise, but too focused. Is furthermore invasive and

time-consuming. External recording (EEG)

Non-invasive, and helpful in studying sleep, epilepsy etc. Crude and imprecise

Scanning techniques (Still pictures – CAT, Dynamic pictures – fMRI, PET) Detailed knowledge of structure and function in

conscious patients – even while they are performing tasks Expensive, hard to interpret, sensitive to disruption (e.g.

movement), uncomfortable for patients

Structures and their function

We know of Broca’s area (language production, pt. Tan) Wernicke’s area (language understanding) Frontal lobes (judgment, inhibition, pt. Phineas Gage)

Here is a more detailed description http://ibpsychology.wetpaint.com/page/Evaluation+of

+Localisation+of+Function

What do we know about the hemispheres?

Cerebral Cortex is asymmetrical

LeftSerial processorLinear processorLanguageControls right side of

the body

RightParallel processorHolistic processorIntuitionControls left side of

the body

WHAT SIDE ARE YOU ON?

DON’T SAY THE WORD!

We will focus on the limbic system – specifically the hippocampus

WE WILL USE THE CASE OF HM

Born in Connecticut in 1926

Suffered from severe epilepsy

Had neurosurgery in 1953

Doctors removed parts of his temporal lobe to alleviate his symptoms

Bilateral Medial Temporal Lobe resection

Doctor’s removed large portions of the temporal lobe from both hemispheres of the brain.

H. M.’s condition justified drastic measures, and the surgery he underwent was extensive and radical.

Tissue was removed from the anterior (front) tips of the temporal lobes on the medial (inner) surface of the brain, extending 8cm backwards.

The resection therefore completely removed the amygdala, the entorhinal and perirhinal cortices, and about two-thirds of the hippocampus

Bilateral Medial Temporal Lobe resection

The surgery was a success!

It reduced his seizures to two a year!BUT: HM was left with profound anterograde

amnesia and partial retrograde amnesia. To this day, he has no memory of anything that

has happened since he underwent surgery, and cannot acquire new factual knowledge about the world around him.

He is unable to retain any kind of new information for more than several minutes.

And he cannot remember much of what happened in the decade prior to his surgery.

HM upon losing his hippocampi

"Right now, I'm wondering, have I done or said anything amiss? You see, at this moment everything looks clear to me, but what happened just before? That's what worries me. It's like waking from a dream. I just don't remember."

What Henry can and can’t remember

Read the document, and answer these questions

What does HM’s case teach us about the role of the hippocampus?

Which type of memory was damaged?Which part remained intact?What can we conclude from this natural

experiment in terms of localization of function?

Implications/Conclusions – see point 2.4

The hippocampus is important in memory processing and particularly in the storage of new memories.

H.M. could learn a few new procedural memories so this indicates that such memories are not stored via the hippocampus.

The fact that H.M. had deficits in one part of the memory system but not in others is evidence that the brain has several memory systems and that these are supported by distinct brain regions.

Implications/Conclusions

Memory processes are much more complex – the hippocampus is very important in the storage of new memories it is not the only structure involved in the process.

Cortical areas are important for long-term memory, for facts and events (semantic and episodic memories), and the use of that information in daily life.

Ethical considerations in this case study. Lack of consent due to memory loss. However, the findings of the study are very important and this justifies it.

It is not usually possible to use the findings from a single case study to generalize about a larger population, but since the findings from other case studies of people with brain damage like H.M. tend to support those from this case study, it may be possible to generalize to some extent.

References to studies

Brenda Milner (1957) was the first to report the case of H.M. and the profound effects on memory functioning, following an operation which removed the hippocampus and adjacent areas in H.M.’s brain.

Corkin et al. (1997) did a MRI scan of H.M’s brain. Brain imaging was used because it allowed the researchers to get a precise picture of the brain damage. They discovered that parts of the temporal lobe, including the hippocampus and the amygdala, were missing, but also that the damage was not as extensive as previously believed.

8 Tips for writing a good SAQ

Make sure you understand the command term and know the difference between explain or discuss or whatever you might be asked to demonstrate your understanding of the Learning Outcome

Define the key words in the SAQ and integrate the definitions into a “In other words…” sentence.

Make sure you use the words from the question in your answer at least two or three times. If the SAQ is about physiology use this word rather than brain or body.

8 Tips for writing a good SAQ

Use studies to support your explanations. Give a brief summary of the study and then explain why this is relevant.

Take every opportunity to evaluate the study but do not just outline every strength and limitation, only the relevant ones.

For example there is no need to discuss ethical considerations with the Davidson meditation study from the BLOA, but the small sample size is relevant as it makes generalizing his finding that cognition can change brain physiology more limited.

8 Tips for writing a good SAQ

Aim for a short introduction and conclusion. These can be just one sentence in length.

If you are asked about two hormones or two studies or two neurotransmitters make sure you have two body paragraphs.

Example of an SAQ localization of function

Explain One Study Related to Localization of Function of the Brain One study which focused on localization of function in the brain was conducted by French

physician Paul Broca in the 19th Century. Broca set out to test his theory that damage to a specific part of the brain (the frontal lobe) was responsible for problems with speech.

Initially, Broca tested his theory through the use of case studies, one of which was on a patient named ‘Tan’ (the only word Tan was able to say). During these case studies, Broca gathered a substantial amount of evidence including the problems each individual faced and details of any medical issues. Broca found that his patients all had two main factors in common – they understood language but had distinct problems with speech, and each patient had suffered some element of damage to the left side of their brains in earlier life. This led Broca to hypothesize that there must be a link between specific head trauma and the development of speech-based problems.

  After Tan’s death, Broca carried out a postmortem study, and found that Tan had lesions on

the frontal lobe of his left hemisphere where damage had occurred earlier on in his life. Subsequent post-mortem research of several of his other patients identified that they too had specific damage to the left frontal lobe – an area now known as Broca’s area. The research that Broca carried out during his lifetime led him to the conclusion that different parts of the brain must be responsible for specific functions. In this case, speech can be said to be localized to the frontal cortex of the left hemisphere, a finding which has been supported by recent empirical research.

Mark Band/Level descriptor

Zero: The answer does not reach a standard described by the descriptors below.

Low (1-3): There is an attempt to answer the question, but knowledge and understanding is limited, often inaccurate, or of marginal relevance to the question.

Mid (4-6): The question is partially answered. Knowledge and understanding is accurate but limited. Either the command term is not effectively addressed or the response is not sufficiently explicit in answering the question.

High (7-8 ): The question is answered in a focused and effective manner and meets the demands of the command term. The response is supported by appropriate and accurate knowledge and understanding of research.

Where would you rate this SAQ and why? Remember the answer must observe the command term!