Electroencephalogram (EEG) represents voltage differences (or oscillations) between two locations on the cerebral cortex that are recorded at the scalp. These recordings capture neural activity between the thalamus and the cortex. A set of electrodes held onto the scalp allow analysis systems to collect and analyze these brainwaves. We use a stretch cap to painlessly collect signals from up to 64 sites at a time. From this mix of ongoing EEG, brainwave potentials are collected. These are coordinated brain responses to visual, auditory, or somatosensory trigger events that can be analyzed using signal averaging techniques.
Event-related potentials (ERPs) are components of the scalp-recorded EEG. This non-invasive technology records the brain's electrical signals that are time-locked to selected tasks/stimuli. ERPs are the averaged responses time-locked to the experimental trigger event. The ERP components, negative and/or positive fluctuations in the ERP waveforms (e.g., the N1, P2, N2 and P3 peaks), reflect the brain activation that is consistently coordinated in response to the triggering events in experimental tasks.
Event-related oscillations (EROs) are components of the EEG studied in the frequency, rather than time, domain. The frequency range of background EEG oscillations is commonly divided into five bands: delta (less than 4 Hz), theta (4 - 8 Hz), alpha (8 - 13 Hz), beta (13 - 30 Hz) and gamma (greater than 30 Hz). Each of these oscillations is thought to have a functional significance and has been associated with specific brain states. For example, alpha frequency band has been associated with a state of relaxation, while theta activity is observed during some sleep states, and during quiet focusing.
These ERP/ERO responses have high temporal resolution (~1 ms) and can reveal rapid changes in sensory and cognitive brain responses to selected tasks as well as subtle differences between subject groups. These analyses provide an exciting complement to the excellent spatial resolution of brain activities provided by fMRI. Thus, we are developing neuropsychological paradigms that can be used in both EEG and fMRI environments, with the goal of acquiring EEG simultaneously with fMRI recordings.
Icahn School of Medicine at Mount Sinai
The Leon and Norma Hess Center for Science and Medicine
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