Redwood Neuroscience
Title "Active sensing: object
localization in rats"
Ehud
Ahissar
The Weizmann Institute,
(currently on Sabbatical at
UCSF)
Abstract:
Mammals acquire much of their sensory information by
actively moving their sensory organs. Rats, in particular, scan their
surrounding environment with their whiskers. This form of active sensing
induces specific patterns of temporal encoding of sensory information, which
are based on a conversion of space into time via sensor movement. We
investigate the ways in which object location is encoded by the whiskers and
decoded by the brain. We recorded from first-order neurons located in the
trigeminal ganglion (TG) of anesthetized rats during epochs of artificial
whisking induced by electrical stimulation of the facial motor nerve. We found
that TG neurons encode the three positional coordinates with different codes.
The horizontal coordinate (along the backward-forward axis) is encoded by two
encoding schemes, both relying on the firing times of one type of TG neurons,
the "Contact cell". The radial coordinate (from face outward) is
encoded primarily by the firing magnitude of another type of TG neurons, the
"Pressure cell". The vertical coordinate (from ground up) is encoded
by the identity of activated neurons. The decoding schemes of at least some of
these sensory cues, our data suggest, are also active: cortical representations
are generated by a thalamic comparison of cortical expectations with incoming
sensory data. The main part of my talk will be devoted to these results. If
time will permit I would like to discuss with you the plausibility of a
somewhat similar process in vision: active vision via fixational
eye movements.