EEG:
EEG stands for electroencephalogram. EEG portrays the electrical potential difference between different points on the surface of the scalp. EEG is a useful tool in identifying the different states of consciousness.
Electrodes are attached to head by a salty paste that conducts electricity, pick up electrical signals generated in brain and transmit them to a machine that records them as EEG. Action potentials in individual neurons are also far too small to be picked up on EEG. Rather, EEG patterns are largely due to synchronous graded potentials i.e., summed post synaptic potentials in brain neurons that underlie the recording electrodes. The majority of electrical signal recorded in EEG originate in pyramidal cells of cortex. The processes of these cells lie close to and perpendicular to the surface of brain, and the EEG records post synaptic potentials- in their dendrites.
EEG patterns are complex waveforms with large variations in both amplitude and frequency. A large amplitude indicates that many neurons are being activated simultaneously and vice versa. Amplitude may range from 0.5 to 100 mV (about 100 times smaller than an action potential). The frequency of wave indicates how often it cycles from maximal to minimal amplitudes and back. It may vary from 0.5 to 40 Hz or higher. Low EEG frequencies indicate less responsive states, such as sleep whereas high frequency indicate increased alertness.
Wave patterns may vary not only as a function of state of consciousness but also according to where on scalp they are recorded. Clusters of thalamus neurons provide a fluctuating action potential frequency output through neurons leading from thalamus to cortex. The cortical synaptic activity comprises most of recorded EEG signal. This synchronicity reflects degree of synchronous firing of thalamic neuronal clusters that are generating EEG.
EEG is used in diagnosis of and treatment of epilepsy and in diagnosis of coma and brain death, It was also used in detection of brain areas damaged by tumor, blood clots or hemorrhage.
Electrodes are attached to head by a salty paste that conducts electricity, pick up electrical signals generated in brain and transmit them to a machine that records them as EEG. Action potentials in individual neurons are also far too small to be picked up on EEG. Rather, EEG patterns are largely due to synchronous graded potentials i.e., summed post synaptic potentials in brain neurons that underlie the recording electrodes. The majority of electrical signal recorded in EEG originate in pyramidal cells of cortex. The processes of these cells lie close to and perpendicular to the surface of brain, and the EEG records post synaptic potentials- in their dendrites.
EEG patterns are complex waveforms with large variations in both amplitude and frequency. A large amplitude indicates that many neurons are being activated simultaneously and vice versa. Amplitude may range from 0.5 to 100 mV (about 100 times smaller than an action potential). The frequency of wave indicates how often it cycles from maximal to minimal amplitudes and back. It may vary from 0.5 to 40 Hz or higher. Low EEG frequencies indicate less responsive states, such as sleep whereas high frequency indicate increased alertness.
Wave patterns may vary not only as a function of state of consciousness but also according to where on scalp they are recorded. Clusters of thalamus neurons provide a fluctuating action potential frequency output through neurons leading from thalamus to cortex. The cortical synaptic activity comprises most of recorded EEG signal. This synchronicity reflects degree of synchronous firing of thalamic neuronal clusters that are generating EEG.
EEG is used in diagnosis of and treatment of epilepsy and in diagnosis of coma and brain death, It was also used in detection of brain areas damaged by tumor, blood clots or hemorrhage.
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