Simulation of the vibrissal brainstem loop reveals effects of sensory feedback on whisking and active touch

The vibrissa sensory-motor system is organized as nested
loops. In the lowest order loop in the brainstem, sensory
S114 J Mol Neurosci (2011) 45 (Suppl 1):S1–S137
neurons in the trigeminal nucleus project to the motoneurons in the facial nucleus. Retrograde axonal tracing show
both excitatory and inhibitory projections to the facial
nucleus. We ask: what is the role of excitatory and
inhibitory sensory feedback to the facial nucleus in
controlling whisker movements? We explore this issue
using a simplified model of the loop, which includes
motoneuron pool driven by external CPG that control
whisker movements (Simony et al., in press) via intrinsic
and extrinsic muscles, and receive inhibitory and excitatory
sensory feedback driven by various cell types of the trigeminal
ganglion (TG). We show that synaptic adaptation in the loop
(Nquyen et al., 2005) leads to stabilization of whisking
amplitude, and that the magnitude of the effect of sensory
feedback peaks around 35 ms from protraction onset. Our
preliminary results suggest that experimentally observed
whisking "stuttering" or "pumps" in free-air (Towal et al.,
2008) or upon object contact (Deutsch et al., this meeting) can
be explained by the brainstem loop. Our analysis suggests
that the frequency of rhythmic whisking (e.g., Gao et al. 2001)
is controlled by higher sensory feedback loop that includes the
CPG whereas the brainstem loop directly controls muscle force.