Nonlinear Spatiotemporal Encoding in the Rat Vibrissa System
Garrett B. Stanley, Roxanna M. Webber, and Alireza S. Boloori
Division of Engineering and Applied Sciences
Harvard University
Cells in the barrel cortex respond to vibrissa deflection with a brief
excitatory component and a longer suppressive component. The response
to a given deflection is thus scaled due to suppression induced by a
preceding deflection, causing the neuronal response to be linked to the
temporal properties of the peripheral stimulus. A paired-deflection
stimulus was used to characterize the post-excitatory suppression and a
three-deflection stimulus was used to investigate the nonlinear response
to patterns of whisker deflections. The post-excitatory suppression was
not dependent upon a sensory-evoked action potential to the first deflection,
implying that it is likely a subthreshold property of the network.
The suppression induced by a deflection served to suppress both the
excitatory and suppressive components of a subsequent neuronal response,
thus effectively disinhibiting it. Two different response properties were
observed in the recorded cells. Approximately 65% responded to a vibrissa
deflection with an excitatory component followed by a suppressive component
and 35% responded with excitation, suppression, and a subsequent rebound
in excitation. Based on these observations of post-excitatory dynamics,
a prediction method was used to estimate neuronal responses to more complex
stimulus trains. Using the second-order representation obtained from the
paired-deflection stimulus, responses to general periodic deflection
patterns were well predicted. A higher cut-off frequency was predicted
for rebound cells as compared to cells not exhibiting rebound excitation,
consistent with experimental observations. The method also predicted
the response of neurons to a random aperiodic deflection pattern.
Furthermore, similar predictions in the spatial domain were confirmed
through a paired-vibrissa probe. The temporal structure of cortical
dynamics following a deflection, therefore, dictates the response to
more complex temporal patterns, which are more representative of
stimuli encountered under natural conditions.
This work was supported by an NSF graduate research fellowship to R. M.
Webber, the Whitaker Foundation, and the Whitehall Foundation.