Vibration-entrained and premovement activity in monkey primary somatosensory cortex

Abstract

1. Primary somatosensory cortical (SI) neurons exhibit characteristic activity before the initiation of movements. This premovement activity (PMA) may result from centrally generated as well as from peripheral inputs. We examined PMA for 55 SI neurons (10, 13, 28, and 4 in areas 3a, 3b, 1, and 2, respectively) with activity that was entrained to vibrotactile stimulation (i.e., was temporally correlated with the stimulus). We sought to determine whether the temporal characteristics of vibration-entrained discharges would change throughout the reaction time period, and, if they did, whether these changes might be accounted for by central inputs. 2. Monkeys made wrist flexions and extensions in response to sinusoidal vibration (27, 57, or 127 Hz) of their palms. Vibration remained on until the animal moved at least 5 degrees from the initial hold position. Mean firing rate (MFR), a measure of the level of activity, was derived from the number of spikes per vibratory cycle. The correlation between the vibration and the neuronal firing was described by the mean phase (MP) of the vibratory cycle at which spikes occurred. The degree of entrainment was quantified as synchronicity (Synch), a statistical parameter that could change from 0 for no entrainment to 1 for responses at a constant phase. 3. Premovement MFR increases (activation) and decreases (suppression) were observed. Moreover, two changes in MFR often were observed for the same neuron (2-event PMA). Many MFR shifts, especially the first in the two-event PMA, preceded electromyographic (EMG) onset. The pre-EMG MFR shifts more often had the same sign both for flexion and extension movements rather than having opposite signs. However, with equal frequency, post-EMG PMA events had the same or opposite sign for different movement directions. We suggest that the pre-EMG PMA has an origin different from movement-related peripheral reafference. 4. Premovement activation was accompanied by shifts of MP corresponding to earlier responses to the ongoing vibratory stimulus and by decreases of response Synch. Premovement suppression was not associated with consistent shifts of MP and Synch. We suggest that during premovement activation, asynchronous (uncorrelated with vibration) signals are integrated with the vibratory input. These asynchronous signals may make neurons more likely to discharge and to do so earlier with respect to the vibratory stimulus. The asynchronous component may also disrupt the vibration-entrained activity pattern.(ABSTRACT TRUNCATED AT 400 WORDS)

Primate Reaching Cued by Multichannel Spatiotemporal Cortical Microstimulation

“…Increases in the frequency of microstimulation may not affect the total number of spikes firing in a predictable way, as excitatory periods begin to interfere with inhibitory periods. However, certain temporal patterns (Mountcastle et al, 1969(Mountcastle et al, , 1990Lebedev et al, 1994) can be faithfully reproduced by cortical neurons. Indeed, during microstimulation, neuronal responses of cortical cells are clearly entrained to microstimulation pulses (Butovas and Schwarz, 2003), which provides a tool to deliver to the brain a variety of temporally patterned signals.…”

Monkey primary somatosensory cortical activity during the early reaction time period differs with cues that guide movements

“…Transdural penetrations were made daily into postcentral somatosensory areas, as well as precentral motor cortices. Neuronal activity was discriminated by a template-matching Multispike Detector (Alpha Omega Engineering, Nazareth, Israel), was time-stamped relative to the animal's behavior, and was stored in a computer (Nelson 1988;Nelson et al 1991;Lebedev et al 1994). Wrist position was digitized at 100 Hz and stored along with the digital records of neuronal activity.…”

“…The characteristics of vibration-entrained neurons in SI have been studied under a number of conditions (Mountcastle et al 1969;Nelson et al 1991Nelson et al , 2002Lebedev et al 1994;Lebedev and Nelson 1995;Salinas et al 2000;Romo and Salinas 2003). Two classes of SI neurons are thought to play essential roles in the sense of flutter-vibration: the glabrous quickly adapting (QA) neurons and the Pacinian (PC) neurons (Mountcastle et al 1969).…”

“…Vibratory stimuli can be used to guide motor tasks in behaviorally trained monkeys (Nelson et al 1991(Nelson et al , 2002Lebedev et al 1994;Lebedev and Nelson 1995;Salinas et al 2000;Romo and Salinas 2003). Extracellular recordings in task-performing monkeys reveal some taskrelated activity that is vibration-entrained, suggesting that the entrained activity may code functionally significant information conveyed by vibratory inputs.…”

“…The patterns of neuronal activity evoked in SI vary depending on the modality of sensory stimulation. One characteristic discharge pattern is the rhythmic neuronal activity in response to somatic vibratory stimuli (Mountcastle et al 1969;Nelson et al 1991Nelson et al , 2002Lebedev et al 1994;Lebedev and Nelson 1995;Salinas et al 2000;Romo and Salinas 2003). To some extent, vibration-entrained activity reflects the frequency of vibratory inputs, although some SI neurons may be sensitive to lower frequencies while others are sensitive to higher frequencies.…”