Combined dynamics of EEG and evoked potentials

Abstract

This study is carried out on single (not averaged) recordings combining the spontaneous activity preceding the stimulus onset and the EP recorded upon acoustical stimulation. These recordings, which we call EEG-EPograms, are measured simultaneously from different subdural structures, such as the auditory cortex, medial geniculate nucleus, inferior colliculus, reticular formation and the hippocampus of the cat brain during the slow wave sleep stage. Using a combined analysis procedure (C.A.P.), the relevant frequency components of spontaneous EEG and EPs, recorded simultaneously from these brain nuclei, are analyzed according to the consistent selectivity bands depicted by the determined amplitude-frequency characteristics for the SWS-stage. In parallel with the results which we obtained for the waking stage, these analyses provide also the following information: (1) there is an important congruency in the time courses of simultaneous response components in common frequency bands, especially in the alpha and beta frequency ranges; (2) there exist significant coupling and synchrony between the evoked amplitude enhancements in the simultaneously recorded single response components; (3) the inter-nuclei coherency in the brain's electrical activity is enormously increased upon stimulation;(4) the evoked response magnitude can be predicted, with reasonable accuracy, from the spontaneous activity preceding the stimulus. All these findings are discussed with reference to those obtained for the waking stage.

Synchronous cortical gamma-band activity in task-relevant cognition

“…Sheer [12] demonstrated 40 Hz rhythms associated with focused cortical arousal and attention. Basar et al [13] published the ®rst results related to the human auditory 40 Hz response.…”

Different event-related patterns of gamma-band power in brain waves of fast- and slow-reacting subjects.

“…This is particularly true for v-band EEG frequencies higher) that are most commonly supposed to be associated with awareness or conscious perception (9)(10)(11)(12)(13)(14). In human subjects, --band activity is enhanced during intense vigilance and performance ofcognitive tasks (6,9,10,(15)(16)(17), suppressed during central anesthesia and slow wave sleep (11,12), and has been proposed to play essential roles in olfactory recognition, temporal integration, visual feature binding and segregation, and sensorimotor integration (18)(19)(20)(21)(22)(23)(24).…”

Links of Consciousness, Perception, and Memory by Means of Delta Oscillations of Brain

“…The curves are normalized in such a way that the amplitude at 0 Hz is equal to 1 (or 20 log 1 = 0). (Modified from Başar et al, 1979). …”

“…The area under the coherence functions is darkened only if the curve surpasses this level. In order to facilitate a comparison between the coherence values computed from spontaneous and evoked parts of the EEG, the respective coherence functions are presented adjacently as couples for all the pairings of recording electrodes (From Başar et al, 1979). …”