It has been argued whether internal representations are encoded using a universal
('the neural code') or multiple codes. Here, we review a series of experiments that
demonstrate that tactile encoding of object location via whisking employs an
orthogonal, triple-code scheme. Rats, and other rodents, actively move the whiskers
back and forth to localize and identify objects. Neural recordings from primary
sensory afferents, along with behavioral observations, demonstrate that vertical
coordinates of contacted objects are encoded by the identity of activated afferents,
horizontal coordinates by the timing of activation and radial coordinates by the intensity
of activation. Because these codes are mutually independent, the three-dimensional
location of an object could, in principle, be encoded by individual afferents during
single whisker-object contacts. One advantage of such a same-neuron-different-codes scheme
over the traditionally assumed same-code-different-neurons scheme is a reduction of code
ambiguity that, in turn, simplifies decoding circuits.