When patients are put into medically-induced comas, the EEG pattern may be used as measure of depth of coma, and the medication may be titrated to an EEG end-point.
Eeg definition psychology portable#
The EEG appearance of the onset of the seizure can provide significantly more definitive information about the patient's epilepsy than inter-ictal recordings can in many cases.Ĭontinuous EEG monitoring typically involves the use of a portable EEG machine connected to an ICU patient to look for seizure activity that is not apparent clinically (i.e., in the patient's mental status or by observing his/her movements). During these admissions, a patient's anti-epilpetic medications are often titrated off so that seizures can be recorded. Video-EEG monitoring may involve inpatient admissions for days to weeks. This is simultaneous recording of EEG and time-locked video/audio. In certain cases, video-EEG monitoring may be required. When a routine EEG is done in a patient with suspected or known epilepsy, often it is to look for inter-ictal discharges (i.e., abnormal activity resulting from "brain irritability" that shows a possible predisposition to epileptic seizures. These activation procedures include sleep, intermittent photic stimulation with a strobe light, hyperventilation and eye closure. During this time, it is common to perform different "activation procedures" which may evoke different activity than is seen during the resting awake state. The neuronal network underlying some of these oscillations are understood (such as the thalomocortical resonance underlying sleep spindles), while many others are not (e.g., the system that generates the posterior basic rhythm still defies understanding).Ī routine clinical EEG recording typically lasts 20-40 minutes. These oscillations represent synchronized activity over a network of neurons.
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These have a different characteristic frequencies, spatial distributions and associations with different states of brain functioning (such as awake vs. Scalp EEG activity is comprised of multiple oscillations. Because voltage fields fall off with the fourth power of the radius, activity from deep sources is more difficult to detect than currents near the skull. The EEG therefore benefits from the parallel, radial arrangement of apical dendrites in the cortex.
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Currents that are tangential to the scalp are not picked up by the EEG. Rather, surface EEG is the summation of the synchronous activity of thousands of neurons that have similar spatial orientation, radial to the scalp. While it is post-synaptic potentials which generate the EEG signal, it is not possible to determine the activity within a single dendrite or neuron from the scalp EEG. The EEG is not sensitive to axonal action potentials.
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It is these extracellular currents which are responsible for the generation of EEG voltages. This results in compensatory currents in the extracellular space. The activity of many types of receptors results in a flow of ions into or out of the dendrite. The neurotransmitter diffuses across the synaptic cleft and binds to receptors in a post-synaptic dendrite. An action potential in a pre-synaptic axon causes the release of neurotransmitter into the synapse. Scalp EEG measures summated activity of post-synaptic currents. Because of the filtering characteristics of the skull and scalp, icEEG activity has a much higher spatial resolution than surface EEG. These terms refer to the recording of activity from the surface of the brain (rather than the scalp). A technique similar to the EEG is intracranial EEG (icEEG), also referred to as subdural EEG (sdEEG) and electrocorticography (ECoG). The data measured by the scalp EEG are used for clinical and research purposes. At one end are action potentials in a single axon or currents within a single dendrite, and at the other end is the activity measured by the scalp EEG.
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Just as the activity in a computer can be perceived on multiple different levels, from the activity of individual transistors to the function of applications, so can the electrical activity of the brain be described on relatively small to relatively large scales. Electroencephalography (EEG) is the measurement of electrical activity produced by the brain as recorded from electrodes placed on the scalp and displayed as a electrocardiogram.