Transcript Event-related Potentials (ERPs)

Ways of Studying the Brain
Recap
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What does fMRI stand for?
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What does it measure?
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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
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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
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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)
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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
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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;