The first technique is to look at case studies of brain damaged patients, by doing this they can understand the impaired and intact abilities of the individual which will lead to a better understanding of cognitive functioning and hopefully allow for rehabilitation. It also helps us to understand the link between the damaged area of the brain and the resulting change in behaviour, thus allowing for localised function.
One particularly famous case study was on a patient called Henry Molaison (nicknamed HM) who was a young man who suffered from severe epileptic fits attributed to a sever bicycle accident at the age of 7. In order to remedy his epileptic fits HM was offered surgery which he accepted. Parts of HM's medial temporal lobe were removed from both sides of his brain including two thirds of his hippocampus, after the surgery his hippocampus appeared to be non functional and he suffered from severe antrograde amnesia, meaning he could not commit new events to his long term memory. Case studies such as this have helped neuropsychologists considerably in localising function, they are useful because we are not allowed to lesion parts of someone's brain in the name of science, therefore natural cases of brain damage are quite rare and therefore valuable to our understanding.
Another interesting fact is that we have touch receptors all over our bodies, and there are more receptors in some areas of our bodies compared to others. This means that there is more cerebral cortex used to process the feeling of touch in some areas of our body compared to others.
The image to the right of this page shows an image of a body in direct proportion to how much cerebral cortex is used to process touch for each body part.
Neuropsychologists also use behavioural studies to help there research. These studies can take many different forms but one example would be to put some one in front of a blank computer screen and ask them to press the space bar when they see a black dot appear, from this you can measure a persons accuracy and latency in response, which will test there cognitive functioning.
More recently Neuroimaging techniques are used to study the living brain. Neuroimaging falls into two broad categories, structural imaging scans which look at the structure of the brain and are used to diagnose large intracranial diseases/injury's (such as tumours) and functional imaging, used to identify metabolic diseases such as Alzheimer's. The main ones used by neuropsychologists are the
Electroencephalogram (EEG) : measures and records the electrical activity of your brain by attaching electrodes to the patients scalp, these electrodes are hooked up to a computer and record the electrical impulses (event-related potentials) from the brain. The positives are that it is a non invasive technique which gives high temporal resolution, and is relatively easy and cheap to run however it is weak at localising function and not very effective at dealing with mass neural activity.
Positron Emission Tomography (PET): Measures emissions from a radioactive isotope that is injected into the blood stream. The isotope gives off positrons that collide with electrons and create gamma rays which are detected by the PET scanner and can build up a detailed image of the brains functioning. The benefits are that it gives high spatial resolution, a 3D representation of activity, and that by injecting different compounds you can measure different things such as blood flow, oxygen consumption and glucose metabolism. However it is invasive and has poor temporal resolution, as well as being very expensive.
Magnetic Resonance Imaging (MRI): A technique that uses magnetic fields and radio waves to produce high quality two- or three-dimensional images of brain structures. Advantages of this technique is that it gives good spatial resolution and is non invasive and non toxic, as well as providing both 2D and 3D images. However the machine used is quite claustrophobic and noisy and radio frequencies must be shielded.
Functional Magnetic Resonance Imaging (fMRI): Measures Blood Oxygen Level Dependent (BOLD) responses. Activity of neural funtion is measured by an increase in blood flow. The advantages are that it is non invasive and non toxic, with high temporal resolution and excellent spatial resolution. However analysis of the scans is complex and expensive to run, also not good for people who are claustrophobic and very noisy.
Transcranial Magnetic Stimulation (TMS): Causes depolarisation or hyperpolarisation in the neurons of the brain by using electromagnetic induction to induce weak electrical currents using a magnetic field. Thus can induce activity in specific or general parts of the brain with, minimal discomfort, allowing us to study the functions or interconnections of the brain in detail.
It has been found that there is a cross over in the visual pathway. The diagram below shows what happens when we see something in our visual field.
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