Homeostatic plasticity in human extrastriate cortex following a simulated peripheral scotoma.

ABSTRACT

Neuroimaging and patient work over the past decade have indicated that, following retinal deafferentation, the human visual cortex undergoes a large-scale and enduring reorganization of its topography such that the classical retinotopic organization of deafferented visual cortex remaps to represent non-classical regions of visual space. Such long-term visual reorganization is proposed to occur through changes in the functional balance of deafferented visual circuits that engage more lasting changes through activity-dependent neuroplasticity. Here, we investigated the short-term changes in functional balance (short-term plasticity; homeostatic plasticity) that occur within deafferented human visual cortices. We recorded electroencephalogram (EEG) while observers were conditioned for 6 s with a simulated retinal scotoma (artificial scotoma) positioned 8.0° in the periphery. Visual evoked potentials (VEPs) evoked by the onset of sinusoidal visual probes that varied in their tilt were used to examine changes in cortical excitability within and around cortical representations of the simulated scotoma. Psychophysical orientation functions obtained from discrimination of visual probe tilt were used to examine alterations in the stimulus selectivity within the scotoma representations. Consistent with a mechanism of homeostatic disinhibition, an early extrastriate component of the VEP (the early phase P1) exhibited increased amplitude following the condition with a simulated scotoma relative to a stimulus-matched control condition. This increased visual cortical response was associated with a reduction in the slope of the psychophysical orientation function, suggesting a broader tuning of neural populations within scotoma representations. Together, these findings support a mechanism of disinhibition in promoting visual plasticity and topographical reorganization.