A signal detection analysis of neural coding efficacies in the receptor potentials and action potentials of the Limulus lateral eye

Zixi Cheng, Purdue University

Abstract

Neural signals have spatio-temporal characteristics that differ from their stimuli in form. Two coding theories address this: Multiple Meaning Theory says that neural signal patterns make statements about combinations of stimulus properties. The Task Dependence Hypothesis holds that different features (i.e., neural codes) mediate performance in different behavioral tasks. This thesis addressed these questions by characterizing intracellular responses of single photoreceptors and spike generating optic nerve cells in Limulus lateral eyes. Light adaptation and flash intensity were varied. Efficacies were objectively measured for six codes by Signal Detection Theory (TSD). The results are: (A) Both adaptation state and intensity affect efficacy. (B) As light adaptation reduces detection sensitivity, TSD-discrimination acuity increases. (C) For graded receptor potentials (RPs), code efficacies are significantly different with Area $\geq$ Peak = Mean $\geq$ Duration-End = Slope = Duration-Drop. (D) For all-or-none spike potentials (APs), Area = Peak $\geq$ Mean $\geq$ Slope Duration-End = Duration-Drop. RP efficacies quantitatively compare with AP's as follows: (A) More proximal efficacies all decline. (B) The decline is code dependent. (C) The code which transmits best between cells does not have the highest efficacy within a cell. Arbitrary code characterizations are therefore incomplete. This particularly applies to the mean code, often the sole AP code (as average spike rate). Use of that code alone would have underestimated detectability. Moreover, the efficacy of the nervous system's representation of the environment now seems to depend on both code type and neural function. Because the best between-cell-transmission code is not the best within a cell, the Task Dependence Hypothesis was extended to say that: Different neural codes may mediate performance in different behavioral tasks because different codes may serve different neural functions. This assumes that different behavioral tasks depend on various neural functions to relatively different degrees.

Degree

Ph.D.

Advisors

Wasserman, Purdue University.

Subject Area

Psychobiology|Physiological psychology|Anatomy & physiology|Animals|Neurology

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