Brains adapt to new situations by retuning their neurons. The most common form of neuronal
adaptation, typically observed with repetitive stimulations of passive sensory organs, is depression
(responses gradually decrease until stabilized). We studied cortical adaptation when stimuli are
acquired by active movements of the sensory organ. In anesthetized rats, artificial whisking was
induced at 5 Hz, and activity of individual neurons in layers 2-5 was recorded during whisking in
air (Whisking condition) and whisking against an object (Touch condition). Response strengths were
assessed by spike counts. Input-layer responses (layers 4 and 5a) usually facilitated during the
whisking train, whereas superficial responses (layer 2/3) usually depressed. In layers 2/3 and 4,
but not 5a, responses were usually stronger during touch trials than during whisking in air.
Facilitations were specific to the protraction phase; during retraction, responses depressed in all
layers and conditions. These dynamic processes were accompanied by a slow positive wave of activity
progressing from superficial to deeper layers and lasting for approximately 1 s, during the transient
phase of response. Our results indicate that, in the cortex, adaptation does not depend only on the
level of activity or the frequency of its repetition but rather on the nature of the sensory information
that is conveyed by that activity and on the processing layer. The input and laminar specificities
observed here are consistent with the hypothesis that the paralemniscal layer 5a is involved in the
processing of whisker motion, whereas the lemniscal barrels in layer 4 are involved in the processing
of object identity.