Ways of Studying the Brain

Recap 1) What does fMRI stand for? 2) What does it measure? https://www.youtube.com/watch?v=nvB9hAarzw4

fMRI works on the principle that the neurons in the brain most active on a task will be using more energy. This requires glucose and oxygen. Oxygen is carried in the bloodstream attached to protein molecules called haemoglobin Oxygenated haemoglobin has different magnetic qualities than deoxygenated blood, due to the amount of energy released by the hemoglobin Therefore, the magnetic signal indirectly measures the amount of blood flow in different areas of the brain This produces an activation map – showing which area is active, and is a moving picture (Blood flow sent to the needed area is called the haemodynamic response)

Electroencephalogram EEG http://www.bbc.co.uk/schools/gcsebitesize/science/aqa_pre_2011/radiation/anintroductiont owavesrev2.shtml Activity in the brain is electrical – action potentials/nerve impulses transmitted along neurons Some methods involve inserting electrodes into the brain to access a small group or single neuron, however this isn’t performed on humans. The EEG provides an overall view of brain electrical activity Developed by Hans Berger A large number of small electrodes are distributed over the surface of the skull using a skull cap. They measure the electrical activity in the neurons beneath the electrode, so the more electrodes, the fuller the picture. These pick up the electrical activity of many millions of neurons

EEGs have basic properties, showing amplitude (the size or intensity of the electrical activity) and frequency (the speed of the electrical activity). Different brain states have different EEGs There can be synchronized patterns – ie a recognizable waveform – a repeated pattern with a particular amplitude and frequency There are also desynchronized patterns, with no recognizable waveform (although frequency can be determined) Synchronized patterns are most typical in sleep (see later), with different waveforms in each stage of sleep, whereas a desynchronized EEG is typical of the waking alert state. Therefore, EEGs are useful in the study of sleep. It can also be used to identify abnormalities of brain function, e.g. where people don’t have the expected regular rhythm, due to epilepsy, sleep disorders or a brain tumour.

Event-related Potentials (ERPs)   ERPs use the same apparatus as EEGs, but record when there is activity in response to a stimulus introduced by the researcher. For example, a sound or a picture is presented to the pt, and the psychologist looks for specific electrical response to that stimulus (which can also be a motor event or cognitive event). This is difficult as the specific response may not stand out from the background electrical activity of the brain. The way around this is to present the stimulus several hundred times and the recordings for several seconds after presentation are then averaged together, allowing a computer to ‘filter out’ the background EEG activity.

Post-mortem examinations This is when the brain (and body) are examined after death (post-mortem). This is used to see where damage has occurred in the brain and how that might explain unusual behaviour or mental processing exhibited by the individual before death. Examples we have already studied……… Tan – Broca’s area;