EEG and MEG
Imaging techniques that detect electrical activity
Electro-encephalography (EEG) and magneto-encephalography (MEG) are functional imaging methods used to measure brain activity directly and non-invasively (from outside the head). EEG detects synchronised electrical activity of large groups of neurons, whereas MEG detects the tiny changes in magnetic fields that this electrical activity is associated with. The images produced by EEG and MEG are not very localised, but they can monitor how electrical activity changes with time very precisely.
EEG requires electrodes to be attached to the scalp. It can be used to detect general patterns of electrical activity, such as the brain waves that occur during sleep. Researchers used EEG to compare the visual cortex activity of people who are born blind with those who are not blind, and they found that the visual cortex of blind people was active. EEG can also be used to detect electrical signals associated with specific sensory stimuli, thought processes or movements. Detecting and measuring these ‘event-related potentials’ can be done at a single electrode, but in practice, many are used. They are spread across the scalp, to help researchers pinpoint where in the brain the neurons responsible for the potentials are.Lead image:
Mel Yeneralski, Cambridge University Hospitals NHS Foundation Trust/Wellcome Collection CC BY NC