Neuronal processing of task-specific afferent whisker information in the rat barrel cortex

点击翻译按钮获取中文摘要

Rats are highly skilled in discriminating objects and textures by palpatory movements of their vibrissae. We ask the question whether task-specific whisking strategies optimize perception, and if so, what the neuronal correlate of optimized perception is in whisker sensorimotor cortex. In the first funding period we set out to study the hypothesis that the conversion of a texture’s spatial frequency into a temporal frequency of neuronal activity on the tactile pathway by whisking determines the choice of whisking parameters. The methodological trick to exert the desired exact experimental control (despite whisker movements) was to realize a virtual reality environment. Head-fixed rats were trained to discriminate virtual grids in which, by virtue of real-time feedback of the whisker position, the whisker’s passing of each grid point was presented to the animal by an electrical microstimulation in its primary afferents. Providing strong evidence against our hypothesis, we found poor psychometric performance and a lack of systematic adaptation of whisking strategy. Matching this result, a novel passive discrimination task employing pulsatile whisker deflections, showed that NOT frequency but rather kinematic events (instantaneous amplitude or velocity) are decisive for vibrotactile discrimination. In previous biomechanical studies by others, kinematic events which are dependent on the roughness of the palpated texture had been described. These so-called ‘slips’ are due to the biomechanical elasticity of the whisker. Guided by these insights we modified our working hypothesis. We now propose to investigate whether it is the probability of occurrence and the kinematic characteristics of ‘slip’ events that is the variable to be optimized by active tactile perception. To this end, we will first perform biomechanical measurements to find out if slip probability and kinematic characteristics are dependent on relative movement of the whisker across a texture. Secondly, we ask whether rats performing a discrimination task will change their whisking pattern as predicted from the measured slip patterns and the resulting changes in discriminability. In a second project we will use the virtual texture discrimination task to exert highest experimental control and investigate in a more analytical way, whether and how defined slip patterns and their dependence on whisker movements affect the whisking strategies of rats. In all experiments, multi-electrode unit recordings will help to determine whether neuronal signals in the whisker motor cortex and the barrel column are processed in a task specific way and whether and how they reflect information about critical changes in the motor program.