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

Abstract

Vibration-related neurons in monkey primary somatosensory cortex (SI) discharge rhythmically when vibratory stimuli are presented. It remains unclear how functional information carried by vibratory inputs is coded in rhythmic neuronal activity. In the present study, we compared neuronal activity during wrist movements in response to two sets of cues. In the first, movements were guided by vibratory cue only (VIB trials). In the second, movements were guided by simultaneous presentation of both vibratory and visual cues (COM trials). SI neurons were recorded extracellularly during both wrist extensions and flexions. Neuronal activity during the instructed delay period (IDP) and the early reaction time period (RTP) were analyzed. A total of 96 cases from 48 neurons (each neuron contributed two cases, one each for extension and flexion) showed significant vibration entrainment during the early RTPs, as determined by circular statistics (Rayleigh test). Of these, 50 cases had cutaneous (CUTA) and 46 had deep (DEEP) receptive fields. The CUTA neurons showed lower firing rates during the IDPs and greater firing rate changes during the early RTPs when compared with the DEEP neurons. The CUTA neurons also demonstrated decreases in activity entrainment during VIB trials when compared with COM trials. For the DEEP neurons, the difference of entrainment between VIB and COM trials was not statistically significant. The results suggest that somatic vibratory input is coded by both the firing rate and the activity entrainment of the CUTA neurons in SI. The results also suggest that when vibratory inputs are required for successful task completion, the activity of the CUTA neurons increases but the entrainment degrades. The DEEP neurons may be tuned before movement initiation for processing information encoded by proprioceptive afferents.

Cutaneous stimulation of the digits and lips evokes responses with different adaptation patterns in primary somatosensory cortex

“…Under this assumption, motor control of orofacial movements during speech and of digits during fine manipulation would be dependent on continuous monitoring of superficial and deep mechanoreceptive sensory input. Single-neuron recordings in behaving monkeys have shown that the primary somatosensory area in particular may indeed play an important role in orofacial (Lin et al, 1994; Sessle et al, 2005) and hand/digit motor control (Liu et al, 2008; Gardner et al, 2007; Salimi et al, 1999; Wannier et al, 1991). Whereas the transient tactile inputs to the digits during active exploration or manipulation of small objects likely require fast integration over brief temporal intervals, tactile input to the lips associated with orofacial behaviors repeats and must be eventually maintained and integrated in primary sensory cortices or higher order cortical areas over slightly longer intervals.…”

Motor Planning under Unpredictable Reward: Modulations of Movement Vigor and Primate Striatum Activity

“…Two adult male rhesus monkeys ( Macaca mulatta : E, N) were trained to make wrist flexion and extension movements in response to vibratory or visual go-cues (Lebedev and Nelson, 1995 , 1999 ; Liu et al, 2008 ). The monkeys were cared for in accordance with the National Research Council Guide for the Care and Use of Laboratory Animals.…”

“…Once an animal reached a stable daily performance level (∼2000 rewarded trials per experimental session), it was prepared for recording. A stainless steel recording chamber was surgically implanted over the skull to allow for extracellular recordings of the activity of basal ganglia neurons by using platinum–iridium microelectrodes with impedances of 1–2 MΩ (see Gardiner and Nelson, 1992 ; Liu et al, 2008 ). Transdural penetrations began no sooner than 1 week after the chamber implantation.…”

“…Transdural penetrations began no sooner than 1 week after the chamber implantation. In each recording session, a microelectrode was lowered into the striatum and the activity of single units was amplified, discriminated, and stored in a computer by conventional means (Lebedev and Nelson, 1995 ; Liu et al, 2008 ). Neuronal receptive fields (RFs) were examined by lightly touching punctuate skin surfaces, manipulating joints, and palpating muscles.…”

Neostriatal Neuronal Activity Correlates Better with Movement Kinematics under Certain Rewards

“…Experimental protocols were approved by the Animal Care and Use Committee of The University of Tennessee Health Science Center, Memphis. Detailed descriptions of the experimental apparatus have been provided elsewhere (Gardiner and Nelson, 1992 ; Lebedev and Nelson, 1995 ; Liu et al, 2005 , 2008 ). A brief description is provided below.…”