Use of Visual Evoked Potentials to Assess Deficits in Contrast Sensitivity in Rats Following Neurotoxicant Exposures

Abstract

This chapter describes a procedure for recording pattern-elicited visual evoked potentials from experimental animals, focused primarily on pigmented rats. When recorded over a range of visual pattern contrast values, the results can be used to derive estimates of visual contrast threshold, contrast sensitivity, and contrast gain. Visual contrast is defined as the difference between the bright and dark regions of a visual pattern, adjusted for the overall luminance. Contrast encoding is an important feature of the neurological processes underlying spatial vision and is dependent on integrated processing within defined neurological circuits. This chapter describes procedures to measure contrast-related parameters that have been developed over years of experience and trial and error approaches. They involve electrophysiological recordings from visual cortex while animals view modulating visual patterns. The resulting evoked potentials are signal averaged, subjected to spectral analysis and interpreted relative to the contrast of the eliciting visual patterns. The resulting parameters include measurements of response amplitude, contrast threshold, contrast sensitivity, and contrast gain. The data from experimental animals are highly analogous to those from human subjects and have shown similar responsivity to neurotoxicant exposures.