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Overview
We consider how animals extract a stable picture of the world from the blur of inputs obtained with their actively moving sensors.
We work with the vibrissa sensorimotor system of rat; these animals palpate the world in front of them as they navigate and identify objects (top figure).
Anatomy
The anatomy consists of a hierarchy of nested closed loops that can
support coherent rhythmic electrical signaling. Two of these loops,
at the thalamic and neocortical levels, appear to act as a phase-locked
servo that is hypothesized to control vibrissa motion (bottom
figure; sites of electrical measurement and the nature of the
spike signals are noted).
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Experiments
At the level of the brainstem, we previously identified the nature
of sensorimotor feedback involved in vibrissa contact. In particular,
the results from in vivo and in vitro experiments
show that contact results in a positive signal that further drives
the mystacial musculature. Ultimately, the system adapts and feedback
diminishes.
At the level of the neocortex, we previously identified the nature
and origin of reference signals for vibrissa position in both
primary sensory and motor cortices. These signals are essential
determinates of the absolute position of the vibrissae in head-centered
coordinates. Further, the motor pathway exhibits signatures of
a servo-control system, alluded to above, i.e., the signal in
motor cortex captures only the fundamental frequency of a rhythmic
input, brainstem motoneurons act as tuned filters, and exploratory
whisking per se can be spectrally pure. These data, together with
our behavioral evidence that rats with only a single vibrissa
can detrect the angle of contact, define a means to fuse reference
and contact signals to code vibrissa position in head-centered
coordinates.
Ongoing projects address: (i) Detailed muscular control of the
vibrissae; (ii) Modularity and interaction of brainstem nuclei;
(iii) Electrophysiological correlates of vibrissa contact and
the fusion of contact and position signals; (iv) Intracellular
mechanisms for the nonlinear mixing of rhythmic signals in neocortex;
(v) Sensory feedback in cortical control of exploratory whisking;
and (vi) Arousal and cholinergic input in the control of whisking.
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