Harnessing brain plasticity to improve binocular vision in amblyopia: An evidence-based update.

Amblyopia is a developmental visual disorder resulting from atypical binocular experience in early childhood that leads to abnormal visual cortex development and vision impairment. Recovery from amblyopia requires significant visual cortex neuroplasticity, i.e. the ability of the central nervous system and its synaptic connections to adapt their structure and function. There is a high level of neuroplasticity in early development and, historically, neuroplastic responses to changes in visual experience were thought to be restricted to a "critical period" in early life. However, as our review now shows, the evidence is growing that plasticity of the adult visual system can also be harnessed to improve vision in amblyopia. Amblyopia treatment involves correcting refractive error to ensure clear and equal retinal image formation in both eyes, then, if necessary, promoting the use of the amblyopic eye by hindering or reducing visual input from the better eye through patching or pharmacologic therapy. Early treatment in children can lead to visual acuity gains and the development of binocular vision in some cases; however, many children do not respond to treatment, and many adults with amblyopia have historically been untreated or undertreated. Here we review the current evidence on how dichoptic training can be used as a novel binocular therapeutic approach to facilitate visual processing of input from the amblyopic eye and can simultaneously engage both eyes in a training task that requires binocular integration. It is a novel and promising treatment for amblyopia in both children and adults.

Spatial localization of sound elicits early responses from occipital visual cortex in humans.

Much evidence points to an interaction between vision and audition at early cortical sites. However, the functional role of these interactions is not yet understood. Here we show an early response of the occipital cortex to sound that it is strongly linked to the spatial localization task performed by the observer. The early occipital response to a sound, usually absent, increased by more than 10-fold when presented during a space localization task, but not during a time localization task. The response amplification was not only specific to the task, but surprisingly also to the position of the stimulus in the two hemifields. We suggest that early occipital processing of sound is linked to the construction of an audio spatial map that may utilize the visual map of the occipital cortex.

Time, number and attention in very low birth weight children.

Premature birth has been associated with damage in many regions of the cerebral cortex, although there is a particularly strong susceptibility for damage within the parieto-occipital lobes (Volpe, 2009). As these areas have been shown to be critical for both visual attention and magnitudes perception (time, space, and number), it is important to investigate the impact of prematurity on both the magnitude and attentional systems, particularly for children without overt white matter injuries, where the lack of obvious injury may cause their difficulties to remain unnoticed. In this study, we investigated the ability to judge time intervals (visual, audio and audio-visual temporal bisection), discriminate between numerical quantities (numerosity comparison), map numbers onto space (numberline task) and to maintain visuo-spatial attention (multiple-object-tracking) in school-age preterm children (N29). The results show that various parietal functions may be more or less robust to prematurity-related difficulties, with strong impairments found on time estimation and attentional task, while numerical discrimination or mapping tasks remained relatively unimpaired. Thus while our study generally supports the hypothesis of a dorsal stream vulnerability in children born preterm relative to other cortical locations, it further suggests that particular cognitive processes, as highlighted by performance on different tasks, are far more susceptible than others.