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School Biology revision notes: Brain 2. Studying brain functions

The Brain 2. How can we study the brain? How does this help diagnose brain damage and disease?

Doc Brown's GCSE level Biology exam study revision notes

There are various sections to work through, after 1 they can be read and studied in any order.

Sub-index for biology notes on the brain's structure and function


(2) How do we study the brain?  How can this help in medical diagnosis?

and the development of diagnostic techniques to help treat patients with brain disorders

We understand quite a lot of how the brain works, but there is still an awful lot we don't know about brain functions.

Because of its complexity and delicate nature, investigation brain function is tricky and difficult to do without great caution (its like a thick jelly).

To investigate brain function we need to 'get inside' the brain and observe in some direct, but safe way, and preferably not by surgical methods - cutting the skull open to examine brain tissue carries a high risk of permanent brain damage!

 

(i) Patients with brain injuries

Much has been learned historically from people who have suffered in some small way with brain damage - in other words damage to one small part of the brain.

The effect of this brain damage on the patient can tell a clinician what the function of the damaged part of the brain was responsible for.

e.g. if an area at the back of the brain was damaged by a stroke and the patient went blind, you would know that part of the brain was involved with vision.

A stroke in the brain stem or cerebellum of a patient can affect breathing and heartbeat. It can also cause speech impairment, hearing and cause vertigo (difficulty in balancing).

People who have suffered massive brain injury, but survive, would give us some insight, but, would it be ethical to study someone who might not be in a position to grant (informal consent) the brain investigation?

You can study the brains of people who have died - in your will or donor card system, you can leave parts or all of your body for medical research.

 

(ii) Connecting electrodes to the brain

You can push tiny electrodes into brain tissue and give it a tiny electrical stimulus.

You can then observe what happens on stimulating various parts of the brain.

You can then relate that part of the brain with what happens.

e.g. If you stimulate the part of he brain called the motor area, it causes muscle contraction and movement.

An electroencephalogram (EEG) is a test that detects electrical activity in your brain using small, metal discs (electrodes) attached to your scalp - the electrodes pick up patterns of electrical activity in the brain.

Your brain cells communicate via electrical impulses and are active all the time, even when you're asleep. With electroencephalography you can monitor this activity, which shows up as wavy lines on an EEG recording.
 

(iii) Modern technology - brain imaging techniques

Non-invasive scanning-mapping techniques external to the body

The advancement in new technology is helping academics research the brain with plenty of spin-offs to help patients with brain conditions. We can now examine the brain without intrusive surgery using various 'high-tech' scanning machines.

A magnetic resonance imaging scanner (MRI machine) is a complex and costly way of producing a very detailed picture of the brain's structure.

MRI uses strong magnetic fields and radio waves to produce a highly detailed image of the nervous system of the brain (and any other part of the body too).

You can monitor the brain's activity while a person is doing particular things e.g. solving a problem, doing a skilled or unskilled physical task or doing a memory test and while they are enclosed in the MRI scanner.

An fMRI scanner (functioning magnetic resonance imaging) is a more advanced MRI scanner which is able to detect increased blood flow in the activated areas of the brain, an MRI scanner cannot.

MRI is a very safe non-invasive technique that doesn't use ionising radiation, so safer than CF scanning and PET scans (both briefly described next).

A CT scanner uses X-rays to produce an image of the main structures of the brain.

However, a CT scanner cannot show the functioning of the imaged parts of the brain.

BUT, the CT scan can show a damaged or diseased part of the brain which can be related to some loss of function by the patient.

e.g. loss of mobility or loss of vision can be related to damaged areas of the brain in the CT scanner image.

PET scanners are much more sophisticated and involve the use of radioactive tracer

Positron emission tomography (PET) scans are used in medicine to produce highly detailed three-dimensional images of the inside of the human body.

PET images can clearly show the part of the body being investigated e.g. brain function, including any abnormal behaviour.

The patient is injected with a radioisotope, whose emitted radiation is monitored by detection screens. The radioisotope (radioactive tracer) atom is incorporated in a molecule that moves around the body e.g. a derivative of glucose. This molecule accumulates in more active cells.

You can actually monitor the patient's brain activity while they are in the PET scanner.

The PET scan can show which parts of the brain are active and behaving normally or abnormally - unusual reduced activity or not functioning at all.

PET scans are so detailed you can investigate brain structure in real time and see how the patient's brain is functioning while they are in the PET scanner.

This means PET scans can be used to study disorders that change the brain's activity like Alzheimer's disease.

Here, certain parts of the brain become less active e.g. the memory region, and the PET scan can be compared with that of a normal brain.

For more details on pet scans see Uses of radioactive isotopes in medicine

PET scans are often combined with computerised tomography (CT) scans to produce even more detailed 3D images, known as PET-CT scans.

PET scans may also occasionally be combined with a magnetic resonance imaging (MRI) scan, known as a PET-MRI scan.

Techniques are getting increasingly sophisticated and costly, but all for the patient's benefit.

Transcranial magnetic stimulation (TMS) uses a magnetic field to change brain activity in targeted areas of the brain.

TMS uses magnetic fields to stimulate selected nerve cell activity and has been used to treat depression.

 

Footnotes on scanners: Despite the wonderful technology, interpreting these scans for diagnostic purposes is not always clear cut i.e. it can inform to help in a prognosis and affect a treatment decision, but its not always that 'simple'.

One problem is that the brain function observed in the scanner, might not be what you would 'theoretically' observe in real life outside the scanner. The mere fact that you are lying down and enclosed inside the scanner means you are not in an everyday state!

Another problem is that our knowledge is still inadequate in knowing how treat certain brain conditions and we cannot adequately access some areas of the brain - so test results can be hard to fully interpret for the benefit of the patient.

For more see the uses of radioactive materials in medicine notes


Summary of learning objectives and key words or phrases for how we can study brain function

Be able to describe some techniques for investigating the brain functions.

Be able to describe in simple terms brain imaging techniques to obtain an MRI scan, a CT scan, a PET scan, TMS scan.

Appreciate that electrodes can be used give the brain an electrical stimulus to monitor brain function.


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