We observed robust coupling between the high-and low-frequency bands of ongoing electrical activity in the human brain. In particular, the phase of the low-frequency theta (4 to 8 hertz) rhythm modulates power in the high gamma (80 to 150 hertz) band of the electrocorticogram, with stronger modulation occurring at higher theta amplitudes. Furthermore, different behavioral tasks evoke distinct patterns of theta/high gamma coupling across the cortex. The results indicate that transient coupling between low-and high-frequency brain rhythms coordinates activity in distributed cortical areas, providing a mechanism for effective communication during cognitive processing in humans.Neuronal oscillations facilitate synaptic plasticity (1), influence reaction time (2), correlate with attention (3) and perceptual binding (4), and are proposed to play a role in transient, longrange coordination of distinct brain regions (5). Direct cortical recordings reveal that ongoing rhythms encompass a wide range of spatial and temporal scales-ultraslow rhythms less than 0.05 Hz coexist with fast transient oscillations 500 Hz or greater (1), with spatial coherence between these oscillations extending from several centimeters for the corticospinal tract (6) to the micrometer scale for subthreshold membrane oscillations in a single neuron (7). Exactly how these transient oscillations influence each other and coordinate processing at both the single-neuron and population levels remains unknown.Evidence for cross-frequency coupling, where one frequency band modulates the activity of a different frequency band, is more abundant in animal than human data. For example, the theta rhythm can modulate the firing rate and spike timing of a single neuron (8-11) as well as the gamma power of the intracortical local field potential (8,12,13). Task-related changes in theta power have been observed in humans (14-16), and cross-frequency coupling at frequencies up to 40 Hz has been detected at the scalp (17,18). However, given the difficulty in localizing electrical sources from scalp recordings alone (19), subdural electrodes that record directly from the human cortex are needed to address this question. Furthermore, subdural electrodes are ideal for studying activity in the recently described human high gamma band (HG) at 80 to 150 Hz. HG activity is modulated by sensory, motor, and cognitive events (20), is

A review of the literature investigating the neural origins of detection behavior in humans reveals two event-related potential components, P3a and P3b, each with a distinct neural organization and cognitive function. The P3a is involved in automatic novelty detection and characterized by a more anterior cortical distribution, whereas the P3b is concerned with volitional target detection and has a more posterior cortical distribution. Intracranial investigation, studies with patients with focal brain lesions, and functional neuroimaging (fMRI) studies converge with the scalp-recorded ERP data in suggesting that a widespread cortical network gives rise to both automatic and controlled detection behavior. The main regions consistently attributed to generating detection related brain activation include the temporal-parietal junction, medial temporal complex, and the lateral prefrontal cortex. The extant human and animal literature addressing the neural networks, neuropharmacological underpinnings, and behavioral signicance of "the P300" potential will be reviewed.

. High gamma activity in response to deviant auditory stimuli recorded directly from human cortex. J Neurophysiol 94: 4269 -4280, 2005. First published August 10, 2005 doi:10.1152/jn.00324.2005. We recorded electrophysiological responses from the left frontal and temporal cortex of awake neurosurgical patients to both repetitive background and rare deviant auditory stimuli. Prominent sensory event-related potentials (ERPs) were recorded from auditory association cortex of the temporal lobe and adjacent regions surrounding the posterior Sylvian fissure. Deviant stimuli generated an additional longer latency mismatch response, maximal at more anterior temporal lobe sites. We found low gamma (30 -60 Hz) in auditory association cortex, and we also show the existence of high-frequency oscillations above the traditional gamma range (high gamma, 60 -250 Hz). Sensory and mismatch potentials were not reliably observed at frontal recording sites. We suggest that the high gamma oscillations are sensory-induced neocortical ripples, similar in physiological origin to the well-studied ripples of the hippocampus.