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Bioengineering Seminar Series: Robert Rogers
Wednesday, April 9, 2008
2:00 p.m.-3:00 p.m.
0408 Animal Science/Agricultural Eng. Bldg.
For More Information:
Professor Ben Shapiro
benshap@eng.umd.edu

Nervous System Slight of Hand: How the respiratory control system retains information while losing accuracy

Presented by Robert Rogers
Assistant Professor
Department of Electrical & Computer Engineering
University of Delaware

The nervous system uses spike trains, the temporal pattern of action potentials, as a means of rapid intercellular communication. The cardiovascular and respiratory control systems use feedback signals, in the form of spike trains generated by various mechanosensory and chemosensory afferent neurons, to control cardiac output, vascular resistance, and respiratory effort. The control system performance is limited by the information carried in the spike trains of these neurons. One set of mechanoreceptors, slowly adapting pulmonary stretch receptors (PSRs), have sensory endings in the walls of the pulmonary tree, and provide the central nervous system with information regarding the rate and depth of breathing--information that is used to both augment and terminate inspiration. In order to quantify the information carried by the average firing rates of individual PSR responses, we applied information theoretic analysis to PSR spike trains produced in response to a continuous, dynamic, physiologically-relevant stimulus. The analysis uses three free variables: the stimulus and response discretization levels, and the integration or observation time window width. Using this method, we demonstrate that mutual information saturates as a function of window width, and does so well before the CNS produces a reflexive change in the relevant motor output. In addition, up to 38% of the theoretical maximum information is carried by the spike count of PSRs. In a follow-up study, we applied this approach to pump cells, which are second-order cells in this system which receive monosynaptic input from PSRs. We determined that although their responses are slightly less reliable at higher stimulus values, they carry statistically equivalent amounts of information in their spike trains as PSRs, because the probability distribution of naturalistic stimuli are heavily skewed towards regimes where their encoding is extremely consistent. Thus, we conclude that the nervous system performance does not suffer from the "noise" associated with spatial and temporal synaptic integration because it takes advantage of the fact that very little time is spent exposed to stimulus amplitudes associated with diminished information. In future studies, we are examining the potential for information to be carried in the pattern (rather than number) of PSR action potentials, with surprising results.

This Event is For: Clark School • Graduate • Faculty • Post-Docs

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