Vibration-entrained and premovement activity in monkey primary somatosensory cortex. Lebedev, A, M., Denton, J. M., & Nelson, R. J. J. Neurophysiology, 72(4):1654-73, 1994.
abstract   bibtex   
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.
@article{ Lebedev_etal94,
  author = {Lebedev, M. A and Denton, J. M. and Nelson, R. J.},
  title = {Vibration-entrained and premovement activity in monkey primary somatosensory
	cortex},
  journal = {J. Neurophysiology},
  year = {1994},
  volume = {72},
  pages = {1654-73},
  number = {4},
  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.},
  en_number = {14.2:42}
}

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