UC San Diego

Animals perceive their surroundings both through sensory systems that transduce environmental features and through motor systems that control how those features are received. This perception, distinct from its building blocks of sensation and motion, is constructed in the nervous system by the integration of modalities. While the neural substrates of this construct are often studied by reducing perceptual systems into more simple sensory and motor components, this dissertation takes the complementary approach of studying such active sensory processes by considering the simple rat vibrissa model system in which these components are integrated to create spatial perception. We develop a conceptual and behavioral framework for the study of these integration processes in three main parts. ChapterĨI introduces the rat vibrissae and divides earlier behavioral experiments in the system into two categories of environmental features, texture and location. After brief observations on texture processing, we focus on the question of spatial perception and build on previous work demonstrating that sensory and motor streams are intermixed in the vibrissa system. We then develop a quantitative approximation of vibrissa motion to categorize potential algorithms for decoding the position of environmental objects. ChapterĨII presents an aside in which we consider evidence for frequency mixing in the rat and other nervous systems. We describe an algorithm that can isolate particular components from the mixing that results from neuronal thresholds. This mixing computation is offered as a potential substrate for the phase difference algorithms described in ChapterĨI. ChapterĨV develops the main experimental work of the dissertation. Rats are challenged with a psychophysical test of their ability to discriminate object location using only vibrissa tactile cues through a single vibrissa. The ability of animals to perform this task with this restricted sensory apparatus constrains the algorithms discussed in ChapterĨI and argues that the rat brain in fact integrates sensory and motor streams to inform perception. ChapterṼ concludes the dissertation with a brief demonstration of electrophysiological techniques that characterize neural activity over cortical large areas. Through experiments such as these, our single vibrissa results can be related to the function of the complete vibrissa array