Brain cells communicate with each other by producing tiny electrical impulses. In an EEG, this faint electrical activity is measured by putting electrodes on the scalp. In 1875 Richard Caton, a physician, used EEG for the first time in animals and in 1929, Hans Berger, developed and applied the first EEG techniques on human beings. EEG, illustrates the brain activity, which is affected by various biological factors, but also by the subject's cognitive state.
A normal human EEG, is divided in categories of bands: Delta(0.5 - 4 Hz), Theta(4 - 8 Hz), Alpha(8 - 12 Hz) and Beta(+12 Hz). Each band is assossiated with specific states of behaviour and perception. For instance Theta waves, are assossiated with creativity, inner focus and deep relaxiation.
The signal comes from the electrically charged (polarized) neurons. Those neurons keep their charge by their membrane transport proteins that pump ions. Neurons are constantly exchanging ions with the extracellular milieu, for example to maintain resting potential and to propagate action potentials. Ions of like charge repel each other, and when many ions are pushed out of many neurons at the same time, they can push their neighbours, who push their neighbours, and so on, in a wave. This process is known as volume conduction. When the wave of ions reaches the electrodes on the scalp, the electrodes of the EEG sees the potential difference with a voltmeter over time (much like the ECG functions to record cardiac activity).
Because of the nature of EEG, healthy signals are difficult to be separated from unhealthy ones. Therefore the procedure needs to take place over a large period of time and it's clinical uses are primarily in the domain of epilepsy, to distinguish and characterize epileptic seizures or localize the region of brain from which a seizure originates. Also it serves as an adjunct test of brain death, to prognosticate (in certain instances) in patients with coma and to monitor the depth of anesthesia.
If you are further intrested in the physiological function of neurons i.e. where does the voltage comes from, take a look at the following video series
No comments:
Post a Comment