Temporally coherent visual stimuli boost ocular dominance plasticity.

Does cortical plasticity depend on the temporal coherence of visual stimuli? We addressed this question by studying ocular dominance (OD) plasticity in mice that were stimulated by moving square wave gratings for 6 h/d during a period of monocular deprivation (MD). It turned out that 4 d of deprivation were sufficient to induce a saturated shift in plasticity in adult (older than postnatal day 100) mice. Seeking to determine the shortest effective period of stimulation, we further showed that even 2 d of deprivation and stimulation shifted OD at any age. This shift was achieved by a decline in deprived-eye input that was saturated within 2 d and did not change during 7 d of MD. However, after 2 weeks of MD, cortical activity induced by both eyes increased again and this increase did not depend on continued stimulation, suggesting a homeostatic mechanism. Starting stimulation 4 d before MD did not mask OD plasticity, showing that the effect is not merely due to the "stimulus-dependent response potentiation" described recently (Frenkel et al., 2006). These results are the first to demonstrate the influence of stimulus quality on cortical plasticity and that cortical responses can be changed within very short periods of time (merely 2 d).