Active perception of virtual texture frequency in the whisker-related sensorimotor system of the rat

by Petya Georgieva

Institution: Universität Tübingen
Year: 2014
Record ID: 1108168
Full text PDF: http://hdl.handle.net/10900/51653


Rats are able to sample their surroundings for tactile discrimination purposes by performing series of whisker deflections. In this perceptual state, called active perception, the animal chooses how to best manipulate its mobile sensors (the whiskers) based on the incoming sensory information it receives via these sensors, so as to perform better at the task at hand. On the other end of the perceptual spectrum lies passive perception which can be described as a “wake-up” call to investigate the surroundings if a sensation was received which was not expected by the subject. During active perception each deflection leads to a mechanical stress at the base of the whisker. Additionally, the touch of any object which the whisker finds along its path also leads to whisker deflections and hence whisker vibrations. These combined vibrations are termed the vibrotactile signal. The nature of the vibrotactile signal is highly complex and it is still not known which of its physical parameters are used by the animal for discrimination. Moreover, it is not yet clear if the tactile system of the rat integrates over this signal to reduce its complexity or if the animals have access to instantaneous kinematic parameters such as minute details of the whisker trajectory. Some of the possible parameters which the animals could use for performing tactile discrimination include the temporal frequency of the signal (i.e. its spectral information), its intensity (i.e. the mean speed of the signal) or instantaneous kinematic features (such as details of the whisker trajectory). In this work I established a new psychophysical Go/No-Go paradigm for spatial frequency discrimination using actively whisking head fixed rats in a virtual environment where a natural stimulus is replaced by electrical microstimulation of the ascending sensory pathway. The major advantage of replacing natural stimuli such as textures with electrical stimulation is the greater level of stimulus control achieved from trial to trial. The initial goal of the project was to investigate the differences in neuronal activation in the barrel and motor cortex arising in active versus passive perception. For the purpose I wanted to train animals to discriminate sets of virtual grids with defined line spacing first in an active case- where the animal has to sweep its whisker in space and receive an electrical pulse in the primary somatosensory cortex each time a grid line is crossed, and then in a passive case- in which the same animal is retrained to keep its whiskers still and the stimulation patterns from the active case are replayed in the cortex. To my great surprise, even after extensive training none of the experimental animals was able to discriminate between a set of two virtual grids with significantly different spatial frequencies. Thus I was unable to proceed towards my initial goal and show that the motor program of the animal would be changed in order to optimize sensory percept in active versus passive case. Instead, I provided the animals with an additional…