Abstract
Amblyopia is a visual disorder associated with disruptions of conjugate binocular vision in early life, which cause a loss in visual performance usually in one eye. Previous studies explored the neurophysiological basis of the amblyopic deficit using single-unit recordings, but the results incompletely explain the perceptual deficits. Advances in recording technology now allow us to examine activity simultaneously over larger areas of cortex. We recorded from V1 and V2 using 96-channel, multi-electrode arrays in anesthetized, amblyopic and control monkeys. Arrays were implanted in foveal and parafoveal cortex, recording single units and multiunit clusters representing eccentricities between 0.5˚ and 5˚. We characterized the response properties of the heterogeneous population of recorded neurons with local spectral reverse correlation (LSRC), a form of spike-triggered averaging (Nishimoto et al, J Neurosci 26:3269, 2006). We presented dense, ternary, dynamic white noise alternately to each eye in 5-min blocks. We reverse-correlated spike trains with the local 2D amplitude spectrum of the stimulus. On average, each array yielded 45 sites with significant spectra; we measured receptive field location, size, orientation and spatial frequency tuning, and eye dominance for each site. Neurons in amblyopic animals were dominated by the fellow eye, most strongly in the foveal representations. In anisometropes, sites driven by the fellow eye were tuned to higher spatial frequencies than those driven by the treated eye. In contrast, strabismic amblyopes and controls showed no difference in the distribution of preferred spatial frequencies between the eyes. Our multisite recordings allowed us to map the receptive field locations on the cortical surface in detail. We observed no differences in these maps among the tested animals or eyes. We conclude that the eye dominance and visual response properties of cortical neurons but not their retinotopic organization can be altered by experimental amblyopia.
Meeting abstract presented at VSS 2014