(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).

 

Computed Tomography (CT)

A CT scanner uses lower energy X-rays and computer technology 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.

Note that CT scans can also show detailed images of any part of the body, including the bones, muscles, fat, organs and blood vessels.
 

Positron emission tomography (PET)

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

 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

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Key points - Summary of ideas

Based on the syllabus-specifications for students taking the AQA, Edexcel and OCR GCSE level biology examinations (~US grades 9-10).

Revision notes on how we can study the brain for medical diagnosis, covering techniques such as Transcranial Magnetic Stimulation (TMS), Positron Emission Tomography (PET), Computed Tomography (CT), and Magnetic Resonance Imaging (MRI).

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How We Study the Brain to Help with Medical Diagnosis

1. Transcranial Magnetic Stimulation (TMS)

Overview of TMS:

• A non-invasive technique that uses magnetic fields to stimulate nerve cells in the brain.

• Helps researchers understand brain function and is used to treat depression and other neurological disorders.

How TMS Works:

• A coil is placed near the scalp, generating a magnetic field.

• The magnetic pulses stimulate neurons, temporarily altering brain activity.

• Effects can be observed through changes in behaviour or brain function.

Uses of TMS in Medical Diagnosis:

• Helps in diagnosing motor neuron disorders by analyzing motor responses.

• Used in research on brain plasticity and recovery after a stroke.

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2. Positron Emission Tomography (PET)

Overview of PET:

• PET scans use radioactive tracers to study brain activity and detect diseases.

How PET Works:

• A radioactive tracer is injected into the bloodstream.

• The tracer emits positrons, which collide with electrons in the brain, producing gamma rays.

• A scanner detects these gamma rays to create detailed images of brain activity.

Uses of PET in Medical Diagnosis:

• Used to detect Alzheimer’s disease by identifying reduced glucose metabolism in affected brain areas.

• Helps in identifying tumours and areas with abnormal activity, aiding in cancer diagnosis.

• Assists in mapping brain function, including conditions like epilepsy.

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3. Computed Tomography (CT) Scans

Overview of CT:

• A CT scan combines X-ray images to create a detailed cross-sectional view of the brain.

How CT Works:

• A series of X-ray beams are passed through the head.

• A computer compiles these images into a 3D representation of the brain’s structure.

Uses of CT scans in Medical Diagnosis:

• Helps diagnose brain injuries such as bleeding, fractures, and swelling.

• Detects brain tumours and abnormal structures.

• Used to examine the brain after stroke or trauma.

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4. Magnetic Resonance Imaging (MRI)

Overview of MRI:

• MRI scans use strong magnetic fields and radio waves to produce detailed brain images.

How MRI Works:

• The patient lies inside an MRI scanner, which generates a magnetic field.

• Radio waves cause hydrogen atoms in brain tissues to emit signals.

• A computer processes these signals into detailed images.

Uses of MRI in Medical Diagnosis:

• Used to diagnose brain tumors, stroke, and multiple sclerosis.

• Helps detect structural abnormalities in the brain.

• Provides high-resolution images of soft tissues for detailed analysis.

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Comparison of Brain Imaging Techniques

Technique	Type	Used for	Key Advantage
TMS	Magnetic stimulation	Brain function research, depression treatment	Non-invasive, used for treatment
PET	Radioactive tracer	Cancer, Alzheimer's, epilepsy	Shows brain metabolism & activity
CT	X-ray imaging	Brain injuries, tumors	Quick and widely available
MRI	Magnetic field & radio waves	Tumors, stroke, brain structure	High-resolution images of soft tissues

These techniques allow scientists and doctors to study brain structure and function, improving diagnosis and treatment of neurological conditions.

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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.

Know that these are non-invasive medical investigation techniques.

Know that CT and other scans can show detailed images of any part of the body, including the brain, bones, muscles, fat, organs and blood vessels.

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

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