Focal or unilateral slow-wave disturbances are common, however, particularly in patients developing lateralized aura or neurologic deficits in association with their attacks. In uncomplicated cases, the EEG is usually normal, or shows only minor nonspecific changes between and during migrainous attacks. Aminoff, in Aminoff's Electrodiagnosis in Clinical Neurology (Sixth Edition), 2012 HeadacheĮlectroencephalography has little relevance to the diagnosis of migraine.
More sophisticated experimental designs and methods of signal analysis have revealed robust connections to detailed cognitive events. Modern signal analyses allow for identification of distinct sleep stages or quantitative measures of the depth of anesthesia. For example, states of deep sleep, coma, or anesthesia are mostly associated with very slow EEG oscillations and larger amplitudes. Oscillations of scalp voltage tell a very limited but important part of the story of brain functioning. EEG monitors the state of consciousness of patients in clinical work or experimental subjects in basic research. Human ‘mind-measures’ are easily obtained at the large scale of scalp recordings. Luckily, these large-scale estimates provide important measures of brain dysfunction for clinical work and cognition or behavior for basic scientific studies. Each scalp electrode records electrical activity at large scales, measuring electric currents (or potentials) generated in cortical tissue containing about 30 million to 500 million neurons. In both clinical and research studies, EEG is nearly always recorded from electrodes placed on the scalp.
ECoG recordings are usually obtained only over a very limited portion of the cortex, areas which vary widely across individuals, partly guided by EEG recordings of epileptic activity using electrodes placed on the scalp prior to surgery. These recordings are called electrocorticograms (ECoGs). Intracranial recordings in humans are mostly limited to patients with intractable epilepsy, often in preparation for brain surgery. However, there are significant limitations to intracranial EEG recording for studies of cognition and behavior. Such intracranial recordings provide measures of cortical dynamics at small spatial scales, dependent on electrode size. EEG is the only widely available technology with sufficient temporal resolution to follow these quick dynamic changes.ĮEG can be recorded using electrodes placed inside the skull to study nonhuman mammals or human epilepsy patients. Cortical processes involve electrical signaling between neurons that change over many times in the 10 ms (0.01 s) range. The outer brain layer is the cerebral cortex, believed to be largely responsible for cognition: perception, memory, thinking, emotions, actions, and behaviors. Human electroencephalography (EEG) provides a convenient, but often opaque, ‘window on the mind,’ allowing observations of electrical processes near the brain surface. Nunez, in Encyclopedia of Human Behavior (Second Edition), 2012 Window on the Mind
#Eeg definition portable
Traditionally, EEG is performed in well-controlled laboratory settings however, portable monitoring and long-term monitoring have also become common with recent advances in technology. EEG is also used in a variety of research protocols.
EEG can be used in clinical settings to diagnose CNS pathology and is included in PSG, along with multiple other physiological parameters to distinguish sleep and wake, and to identify sleep stages. EEG can also differentiate between wakefulness, sleep, coma, and CNS silence (brain death). When used in polysomnography (PSG), EEG allows for both microanalysis (e.g., specific frequencies and waveforms) and macroanalysis (e.g., whether the patient is awake or asleep, whether pathologies are present) of sleep. Other analyses include describing the morphology and temporal distribution of events. EEG allows for analysis of data in terms of both time (i.e., frequency) and voltage (i.e., amplitude) domains. EEG recording requires care and attention to detail regarding electrode application, equipment preparation, and the recognition and elimination of artifact. It is the only measure that allows differentiation within the spectrum of consciousness. Casseres, in Encyclopedia of Sleep, 2013 AbstractĮlectroencephalography (EEG) provides a window into the dynamic function of the central nervous system (CNS).