Behavioral Modulation of Tactile Responses in the Rat Somatosensory System

Abstract

We investigated the influence of four different behavioral states on tactile responses recorded simultaneously via arrays of microwires chronically implanted in the vibrissal representations of the rat ventral posterior medial nucleus (VPM) of the thalamus and the primary somatosensory cortex (SI). Brief (100 microsecond) electrical stimuli delivered via a cuff electrode to the infraorbital nerve yielded robust sensory responses in VPM and SI during states of quiet immobility. However, significant reductions in tactile response magnitude and latency were observed in VPM and SI during large-amplitude, exploratory movements of the whiskers (at approximately 4-6 Hz). During small-amplitude, 7-12 Hz whisker-twitching movements, a significant reduction in SI response magnitude and an increase in VPM and SI response latencies were observed as well. When pairs of stimuli with interstimulus intervals <100 msec were delivered during quiet immobility, the response to the second stimulus in the pair was reduced and occurred at a longer latency compared with the response to the first stimulus. In contrast, during large-amplitude whisker movements and general motor activity, paired stimuli yielded similar sensory responses at interstimulus intervals >25 msec. These response patterns were correlated with the amount and duration of postexcitatory firing suppression observed in VPM and SI during each of these behaviors. On the basis of these results, we propose that sensory responses are dynamically modulated during active tactile exploration to optimize detection of different types of stimuli. During quiet immobility, the somatosensory system seems to be optimally tuned to detect the presence of single stimuli. In contrast, during whisker movements and other exploratory behaviors, the system is primed to detect the occurrence of rapid sequences of tactile stimuli, which are likely to be generated by multiple whisker contacts with objects during exploratory activity.

Goal-directed whisking increases phase-locking between vibrissa movement and electrical activity in primary sensory cortex in rat

“…Changes in coherence between unit activity in motor cortex, as opposed to sensory cortex in the present work, and the underlying tremor in motoneuron output have been observed for hand muscles in monkey during a precision grip task (33,34). Although the underlying mechanism for either effect is unknown, modulators of cortical excitability could increase the extent of phase-locking, perhaps controlled by thalamic-induced gain control (35) or synchrony across cortex (36,37). Past studies have shown that attention can regulate the timing or synchrony of neuronal responses in sensory cortex, as opposed to the rate of spiking.…”

Input-specific effects of acetylcholine on sensory and intracortical evoked responses in the “barrel cortex” in vivo

“…Interestingly however, during these active states, the frequency-dependent depression was almost abolished (Fanselow & Nicolelis, 1999). This suggests that the somatosensory system is able to modulate the effectiveness of tactile information in o~der to optimize the transfer of information depending upon the behavioral state ofthe animal.…”

“…Short-term plasticity of thalamocortical pathways can he dynamically modulated with behavioral state (Castro-Alamancos " Connors, 1996a;Fanselow & Nicolelis, 1999). For example, stimulating the ventrolateral nucleus of the thalamus at frequencies ranging from 7-14 Hz causes an enhanced response for each successive stimulus, relative to the tirst (Castro-Alamancos &- Connors, 1996a,-b, cl.…”

Characterization of sustained BOLD activation in the rat barrel cortex and neurochemical consequences

“…Neurons of the whisker barrel system in the rodent primary somatosensory cortex are known to encode external events in time and space and thus offer an excellent model to study BOLD activation processes (de Celis Alonso et al, 2012;Lu et al, 2003;Yang et al, 1996Yang et al, , 1997. The rat barrel cortex can also be reliably and reproducibly activated through trigeminal nerve (TGN) stimulation (Nielsen and Lauritzen, 2001;Just et al, 2010;Fanselow and Nicolelis, 1999). BOLD responses to short TGN stimulations (30 s) were characterized as a function of stimulus frequency and current intensity (Just et al, 2010) showing robust and reproducible BOLD activation of the primary somatosensory barrel field cortex (S1BF).…”