J Neurosci 2010 Jun 30; 30(26): 8935-52
Temporal and spatial characteristics of vibrissa responses to motor commands.
Simony E, Bagdasarian K, Herfst L, Brecht M, Ahissar E, Golomb D.
A mechanistic description of the generation of whisker movements is essential for
understanding the control of whisking and vibrissal active touch. We explore how facial-
motoneuron spikes are translated, via an intrinsic muscle, to whisker movements. This is
achieved by constructing, simulating, and analyzing a computational, biomechanical model of
the motor plant, and by measuring spiking to movement transformations at small and large
angles using high-precision whisker tracking in vivo. Our measurements revealed a
supralinear summation of whisker protraction angles in response to consecutive
motoneuron spikes with moderate interspike intervals (5 ms < Deltat < 30 ms). This behavior
is explained by a nonlinear transformation from intracellular changes in Ca(2+) concentration
to muscle force. Our model predicts the following spatial constraints: (1) Contraction of a
single intrinsic muscle results in movement of its two attached whiskers with different
amplitudes; the relative amplitudes depend on the resting angles and on the attachment
location of the intrinsic muscle on the anterior whisker. Counterintuitively, for a certain range
of resting angles, activation of a single intrinsic muscle can lead to a retraction of one of its
two attached whiskers. (2) When a whisker is pulled by its two adjacent muscles with similar
forces, the protraction amplitude depends only weakly on the resting angle. (3) Contractions
of two adjacent muscles sums up linearly for small amplitudes and supralinearly for larger
amplitudes. The model provides a direct translation from motoneuron spikes to whisker
movements and can serve as a building block in closed-loop motor-sensory models of active
touch.