Prediction of Responses to Periodic and Aperiodic Stimuli in the Rat Barrel Cortex

Roxanna M. Webber and Garrett B. Stanley
Division of Engineering and Applied Sciences
Harvard University

---

Neurons in the barrel cortex exhibit prolonged suppression following stimlulus-evoked excitation. We have probed the temporal time course of this suppression by investigating the OFF responses of cells using ramp and hold deflections of the primary whisker with widths ranging between 20 and 200 ms. Single unit, extracellular recordings were obtained from female Sprague-Dawley rats anesthetized with sodium pentobarbital. Previously, we have shown that the time course of the suppression could be used to predict the steady state frequency response characteristics of neurons in layer 4. Steady state frequency response characteristics are intimately linked to the adaptation properties of cells. We therefore deflected primary whiskers with a 50% duty cycle ramp and hold stimulus at frequencies between 1 and 16 Hz to determine the extent to which the prolonged suppression can explain observed adaptation to periodic stimuli. Preliminary results show that the time course of response suppression is able to partially predict the transient adaptive behavior of neurons. Although periodic stimulation is critical in characterizing the response properties of the pathway, it is also important to understand the neuronal response to aperiodic stimuli that could reflect more naturalistic deflection patterns experienced as the whisker brushes across objects of different textures. We deflected the primary whisker with an aperiodic stimulus with random times between the ON and OFF edges of the stimulus, ranging from 15 to 250 ms. The functional suppression determined from the pulse width study was also able to predict the general response pattern of neurons to an aperiodic stimulus. This suggests that the post-excitatory suppression plays a role in determining the response characteristics of barrel neurons across a wide range of stimuli.