Methods of cortical specialisation
Methods of studying cortical specialisation are divided into two groups: the invasive, and the non-invasive. The invasive methods are those, in which something is injected into the brain, to find out what the problem is. The non-invasive methods are more ethical, as there are no changes in the brain area, therefore no damage can be done to it.
One of the invasive methods of cortical specialisation is neurosurgery. It involves manipulating with the structures within the brain. There are two main ways of performing neurosurgery: ablation, which is a surgical procedure used to remove certain areas of the brain, and lesioning, which is cutting neural connections within the brain.
An advantage of using neurosurgery, is that it allows for a lot of control and detail in the location of faults within the brain. On the other hand, cutting neural connections, or removing certain parts of the brain, may damage other ones, which may lead to a more severe consequence.
Another invasive method is electrical and chemical stimulation. It is a very important technique, which involves electrical stimulation of certain parts of the brain.
There is also the Wada test, which is a chemical test used to establish which functions correspond to which hemisphere of the brain, which is done by injecting an anaesthetic into one hemisphere at a time in order to stop any language or memory functions in that hemisphere. A strength of this method, is that stimulating the brain is less harmful than surgery, therefore making it more ethical, however, the research conducted on animals, cannot be applied onto humans, which may cause unreliable results.
Post-mortems, are another method. They are used to compare brains to look for faults. A patient, who has a rare affliction, is examined after his death. The part of the brain that is damaged is then associated with the affliction.
Before the introduction of scans and X-rays, this was one of the only ways to study cortical specialisation. It provides a great understanding on rare cases in individual patients, but getting a person’s brain for experimental purposes, can be very difficult.
One of the main non-invasive methods of studying cortical specialisation, is the electroencephalogram, or the EEG, which is a measurement of electrical activity via a recording from electrodes placed on the patient’s head. The signal is then shown on a computer screen which the doctors can analyse.
An advantage of this, is that the doctor is not interacting with the brain, therefore natural measurements are taken, which in turn increases the reliability, but electrodes may not be sensitive enough to pick up the slight actions which may be the cause for a fault.
Scans are also a very good way of studying the brain. There are 3 main types of scans: the CAT scan, the PET scan, and the MRI scan. Computerised axial tomography (CAT) is a scan, where a narrow X-ray beam is sent through a patient’s head to measure the amount of radiation absorbed.
This is done on hundreds of axes throughout the head. These are then fed onto a computer. They are useful for evaluating the amount of swelling due to tissue damage. Position emission tomography (PET) is a procedure where different levels of neural activity are assessed when the brain is active. A small amount of radioactive glucose is injected into the patient’s veins, which then is used by the brain like normal glucose, and scientists can measure the amount of radiation.
This scan may seem invasive, but no unusual substance is directly injected into the brain, therefore no harm is done. Magnetic resonance imaging, is a very sophisticated technique where scanners use magnetic fields and radio waves to produce a high quality image of a person’s brain. This is done by placing a patient in a tunnel surrounded by a magnet, and then, the body is exposed to a pulse, to which the tissues react, and the reaction is measured by the scientist.
This is done repeatedly to produce precise images. Scans provide high amounts of detailed knowledge of areas of the brain while they are active, therefore they give the most reliable results, but on the other hand, they do not record spontaneous behaviour, and also they can be very time consuming.