Encoding and recoding of object location in whisking rats

Ehud Ahissar

Department of Neurobiology, The Weizmann Institute of Science, Rehovot, Israel.

Rats use their large facial hairs (whiskers) to detect, localize and identify objects in their proximal three-dimensional (3D) space. Our data indicate that object location in 3D is encoded in an orthogonal scheme: each primary-afferent can signal object location by a spatial (labeled-line) code for the vertical axis (along whisker arcs), a temporal code for the horizontal axis (along whisker rows), and an intensity code for the radial axis (from the face out). Since these codes are mutually independent, the 3D location of an object could in principle be encoded by individual afferents during single whisker-object contacts. One advantage of such same-neuron-different-codes scheme over the traditionally assumed same-code-different-neurons scheme is a reduction of code ambiguity which in turn simplifies decoding circuits. The recoding of these signals as reliable representations in the thalamocortical network appears to be based on an iterative convergence process of several (~4) whisking cycles, involving fast bottom-up and slow top-down waves via the thalamus and somatosensory cortices (S1 and S2) and multiple neural codes.