Prentice award lecture 2011: removing the brakes on plasticity in the amblyopic brain

Abstract

Experience-dependent plasticity is closely linked with the development of sensory function. Beyond this sensitive period, developmental plasticity is actively limited; however, new studies provide growing evidence for plasticity in the adult visual system. The amblyopic visual system is an excellent model for examining the "brakes" that limit recovery of function beyond the critical period. While amblyopia can often be reversed when treated early, conventional treatment is generally not undertaken in older children and adults. However, new clinical and experimental studies in both animals and humans provide evidence for neural plasticity beyond the critical period. The results suggest that perceptual learning and video game play may be effective in improving a range of visual performance measures and importantly the improvements may transfer to better visual acuity and stereopsis. These findings, along with the results of new clinical trials, suggest that it might be time to reconsider our notions about neural plasticity in amblyopia.

Figure 1

Vernier acuity vs. Snellen acuity for the non-preferred eye for the entire sample of McKee, Levi and Movshon. The crosses show the normal observers. The dots show the amblyopic eyes of aniometropic (green), strabismic (blue) and mixed (i.e., both stabismic and anisometropic – red) subjects.

Figure 2

The improvement in Vernier acuity (squares – left ordinate) and Snellen acuity (circles – right ordinate) in an anisometropic amblyope following PL; after Levi, Polat & Hu. Each Vernier threshold represents 125 trials.

Figure 3

The improvement in performance (expressed as a factor along the abscissa) following PL on different tasks from previous studies (ordinate). Improvement on the trained task is shown by the gray bars and in Snellen acuity by the black bars. The results are ordered on the improvement on the trained task, from least (top) to most (bottom).

Figure 4

The effect of age (top) and duration (bottom) on the improvement (trained task - gray; Snellen acuity – black) in performance following PL.

Figure 5

The improvement in Snellen acuity in the amblyopic eye following videogame play (diamonds and triangles) or patching (gray circle); after Li et al. For comparison, the effect of PL over the same time course is shown (small squares from Figure 4).

Figure 6

Stereoacuity before (abscissa) and after PL (monocular PL shown by solid black symbols; dichoptic PL by gray symbols) or Video game play (open diamond).