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

老鼠在通过触须的触感运动辨别物体和质地方面非常熟练。我们提出的问题是，任务特定的拂动策略是否优化感知，如果是这样，优化感知的神经元关联是在须感觉运动皮层。在第一个资助期，我们开始研究一个假设，即通过拂动将纹理的空间频率转换为触觉通路上神经元活动的时间频率决定了拂动参数的选择。实现所需的精确实验控制（尽管须运动）的方法技巧是实现虚拟现实环境。头部固定的大鼠被训练来区分虚拟网格，在虚拟网格中，由于须位置的实时反馈，须经过的每个网格点通过电微刺激在其主要传入中呈现给动物。提供强有力的证据反对我们的假设，我们发现不良的心理测量表现和缺乏系统的适应搅拌策略。与这一结果相匹配的是，一种采用脉冲晶须偏转的新型被动识别任务表明，运动事件（瞬时振幅或速度）对振动触觉识别起决定性作用，而不是频率。在以前由其他人进行的生物力学研究中，已经描述了依赖于触诊纹理粗糙度的运动学事件。这些所谓的“滑动”是由于须的生物力学弹性。在这些见解的指导下，我们修改了我们的工作假设。我们现在建议研究是否“滑动”事件的发生概率和运动学特征是主动触觉感知优化的变量。为此，我们将首先进行生物力学测量，以找出滑动概率和运动学特征是否依赖于晶须在纹理中的相对运动。其次，我们询问执行辨别任务的大鼠是否会根据测量到的滑动模式和由此产生的判别性变化来预测其搅拌模式。在第二个项目中，我们将使用虚拟纹理辨别任务来施加最高的实验控制，并以更分析的方式研究定义的滑动模式及其对须运动的依赖是否以及如何影响大鼠的须运动策略。在所有实验中，多电极单元记录将有助于确定须状运动皮层和桶状柱中的神经元信号是否以特定任务的方式处理，以及它们是否以及如何反映运动程序中关键变化的信息。

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.