Neuronal basis of tactile sense in the rat whisker system

Using their whiskers, rats have tactile capacities rivaling those of the human with our fingertips. We have carried out experiments to explore how neurons encode touch signals to build up a central representation. Touch signals begin with the receptors in the follicle of each whisker and can be traced to a columnar module in somatosensory cortex that is connected with the same whisker: the well-known whisker-to-column topography. We first examine the spatial organization or tactile information and find that the columnar topography acts as a framework for the organization of sensory information in behaving rats. Then, we consider the messages carried by neurons. Because rats can sweep their whiskers across surfaces to identify texture with very fine capacities, we ask what the brain representation of texture is. We will present evidence that the surface features of an object induce vibrations in the whisker shaft with distinct kinetic "signatures." The brain encodes the kinetics of whisker vibration to achieve a reliable representation of texture.