Debugging the Neural Code

Document Type

Presentation Abstract

Presentation Date

4-12-2007

Abstract

What is the meaning associated with a single action potential in a neural spike train? The answer depends on the way the question is formulated. One general approach toward formulating this question involves estimating the average stimulus waveform that leads up to each spike generated by a nerve cell: presumably, the mean of all of these pre-spike waveforms is a good estimate of the "best stimulus" or "optimal feature" for that neuron. Many different algorithms have been used to obtain such estimates, ranging from spike-triggered averaging of stimuli to correlation-based extraction of "stimulus-reconstruction" kernels or spatiotemporal receptive fields. We demonstrate that all of these approaches miscalculate the stimulus feature selectivity of a neuron. Their errors arise from the manner in which the stimulus waveforms are aligned to one another during the calculations. Specifically, the waveform segments are locked to the precise time of spike occurrence, ignoring the intrinsic "jitter" in the stimulus-to-spike latency. We present an algorithm that takes this jitter into account. " Dejittered" estimates of the feature selectivity of a neuron are more accurate (i.e., provide a better estimate of the mean waveform eliciting a spike) and more precise (i.e., have smaller variance around that waveform) than estimates obtained using standard techniques. Moreover, this approach yields an explicit measure of spike-timing precision and, therefore, and estimate of the "temporal resolution" of a neuron.

These results will be discussed within the context of our group's general research into the functional organization and operation of one specific sensory system: the cricket cercal system. This system functions as a low-frequency, near-field extension of the cricket's auditory system, and mediates the detection, localization and identification of signals generated by predators, mates and competitors. The sense organ for this system consists of a pair of antenna-like 'cerci' at the rear of the cricket's body, each of which is covered with approximately 1000 mechanosensory hairs. Each of these hairs is innervated by a single receptor neuron. The working hypothesis is that the anatomical, biomechanical and neurophysiological characteristics of the cerci are optimized for the sensory processing operations they mediate. The group of researchers working on this general project include four MSU faculty (2 neurophysiologists and 2 applied mathematicians), 5 grad students and 1 postdoc, and a slew of advanced undergrads.

Additional Details

Cosponsored by the Center for Structural & Functional Neuroscience

Thursday, 12 April 2007
4:10 p.m. in Math 109

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