UC San Diego

In our daily lives we have to process sensory information at different speeds and in a sensory specific manner. For example, if we go for a walk in the park we will need to be aware of the relatively slow pace of changes in the environment, but as we read this text we will need to process the characters that pass through our fovea in rapid succession. A child might be aware of her teacher starting or finishing a discussion, but only if she is interested will she follow the ongoing flow of details. Because of its anatomical characteristics and its well established role in the control of global brain activity, the neurotransmitter acetylcholine is likely to play a large role in such temporal processing of information. This work deals with two aspects of the sensory processing of time modulated stimuli, particularly as it relates to acetylcholine. Chapters 1 and 2 analyze acetylcholine's influence on an animal's ability to discriminate between time modulated flashes of light (chapter 1) or trains of sounds (chapter 2). Chapter 3 analyzes the influence of brain state, a phenomenon tightly related to cholinergic activity, on the neural processing of trains of sounds, both at the thalamic and cortical levels. Finally, chapter 4 undertakes the problem of the influence of mean neuronal firing rate on measures of neural representation. The mean firing rate in the thalamus differs dramatically between states, and analysis of correlative activity must take this into consideration. Our theoretical results can explain various aspects of the current literature on the subject