Coherent 25- to 35-Hz oscillations in the sensorimotor cortex of awake behaving monkeys.

Abstract

Synchronous 25-to 35-Hz were observed in local field potentials and unit activ in sensorimotor cortex of awake rhesus monkeys. The osatory epiode occurred often when the monkeys retrieved raisins from a KIliver board or from unseen locations uin somatosenor feedback; they occurred less often during perfnce of repetitive wrist flexion and extension movements. The amplitude, duration, and frequency of oscillations were not directly related to movement prameters In behaviors studied so far. The occurrence of the ollations was not nenty related to bursts of activity in foren musces, but cycle-triggered averages of eectromyograms revealed synchronous modulationin flexor and extensor muscles. The phase of the osilations changed continuously om te surface to the deeper layers ofthe cortex, reversing their polarity completely at depths exceeding 800 gAm. The oscillations could become synchronized over a distane of 14 mm mediolaterally in precentral cortex. Coherent osciations could also occur at pre-and postcentral sites separated by an estimated tangential intracortical dstance of20 mm.Activity ofsingle units was commonly seen to burst in synchrony with field potential llatins. These (3,5) and awake monkeys (6). Such oscillations occurred coherently at widely separated visual sites within and across the two hemispheres (3,5,7,8). Electroencephalogram (EEG) oscillations 'in the range of 20-50 Hz also occur in the motor and somatosensory cortex, especially during focused attention prior to motor acts (2, 9, 10). Pericruciate oscillations near 40 Hz occurred in cats (2), and in baboons and squirrel monkeys slower oscillations around 18 Hz were recorded at specific sites in the sensory hand areas and in area 5 (9). Scalp EEGs recorded from humans reportedly show an increase in 40-Hz signal during focused attention (10). Although the "40-Hz" oscillations are prevalent in the cortex, their function and the underlying mechanisms remain objects of speculation (11-13).The occurrence of coherent oscillations in single or multiunit activity in response to somatosensory stimulation or specific motor acts has not been reported to date, although one study reported that somatosensory stimulation disrupted rhythmic activity in single units (14). Here, we report the occurrence and properties of synchronous 25-to 35-Hz oscillations in the sensorimotor cortex of awake behaving monkeys. Oscillations in LFPs were most prominent during the performance of motor tasks that required attention and sensorimotor integration. The activities of some units separated by distances of up to 14 mm were found to be synchronized with each other and with the LFP oscillations.

High gamma frequency oscillatory activity dissociates attention from intention in the human premotor cortex

“…We conclude that, at least in the present experimental paradigm, the spatial extent of the beta band modulations does not colocalize with the fMRI effects of the interaction analysis (Simon et al, 2002). The reason for this discrepancy could be due to the type of responsiveness of the beta rhythm to sensory stimuli: beta range oscillations are widely observed in the sensorimotor cortex in relation to motor behaviors in both humans ( Salmelin and Hari, 1994;Pfurtscheller and Lopes da Silva, 1999;Brovelli et al, 2002;Salenius and Hari, 2003) and nonhuman primates (Rougeul et al, 1979;Murthy and Fetz, 1992;Sanes and Donoghue, 1993;MacKay and Mendonca, 1995;Brovelli et al, 2004). In particular, power suppression in the beta band, known as event-related desynchronization (ERD), has been observed during tasks activating the sensorimotor cortex using both EEG (Pfurtscheller, 1981) and electrocorticographic (ECoG) techniques (Arroyo et al, 1993;Toro et al, 1994, Crone et al, 1998a.…”

GABAergic synchronization in the limbic system and its role in the generation of epileptiform activity

“…More recently, cortical inhibitory networks have also been proposed to play a critical role in the generation of faster activities that include oscillations in the low (i.e, beta-gamma oscillations at 20-80 Hz) and high frequency range (>80 Hz, so called ripples) (Buzsáki et al, 1992). Interestingly, both beta-gamma rhythms and ripples occurring in cortical areas (Gray et al, 1989;Murthy and Fetz, 1992;Singer and Gray, 1995), including those of the limbic system Chrobak and Buzsáki, 1998;Csicsvari et al, 1999Csicsvari et al, , 2003, have been implicated in higher brain processes such as attention, sensorimotor integration, consciousness, learning and memory (Girardeau et al, 2009;Montgomery and Buzsáki, 2007). Therefore, it has been suggested that these oscillatory rhythms represent the basic neuronal processing state of the brain (Basar et al, 1999).…”

Interaction between neocortical and hippocampal networks via slow oscillations

“…In the hippocampus, at least two distinct gamma generators have been identified: one depends on the perforant path input from the entorhinal cortex, whereas the other emerges in the CA3 region Csicsvari et al, 2003). Cortical neurons are phase-locked to the local gamma oscillation (Gray et al, 1989;Murthy and Fetz, 1992;Steriade et al, 1996;Csicsvari et al, 2003), which allows them to synchronize within a narrow temporal window. This phase-locking is brought about by volleys of inhibitory currents produced by local interneurons (Buzsáki et al, 1983;Csicsvari et al, 2003;Bragin et al, 1995a;Hasenstaub et al, 2005).…”