Abstract
Purpose:
Ocular dominance is an extensively studied form of neural plasticity. Several recent studies have demonstrated that a degree of eye dominance plasticity occurs in adults after one eye is patched for as little as 2.5 hours. Over these timescales, the patched eye, rather than the unpatched eye, becomes stronger in subsequent binocular viewing. However, little is known about the site and nature of the underlying processes. In this study, we examine the mechanisms underlying this eye dominance plasticity in adults by measuring steady-state visual evoked potentials (SSVEPs) as an index of the neural contrast response in early visual areas.
Methods:
The experiment consisted of three consecutive stages: a pre-patching EEG recording (14 minutes), a monocular patching stage (2.5 hours) and a post-patching EEG recording (14 minutes; started immediately after the removal of the patch). During the patching stage, a transparent patch (i.e. a diffuser, which transmits light but not pattern) was placed in front of one randomly selected eye. During the EEG recording stage, we measured contrast response functions for each eye to obtain an estimate of the contrast-dependence of the patching-induced changes.
Results:
We found that patching one eye with a diffuser for 2.5 hours in adult humans increased the neural response to stimuli in the patched eye, whilst the responses from the unpatched eye remained the same. Such phenomena occurred under both monocular and dichoptic viewing conditions.
Conclusions:
We interpret this eye dominance plasticity in adult human visual cortex as homeostatic intrinsic plasticity regulated by an increase of contrast-gain in the patched eye.