Abstract
Purpose: :
Extrastriate visual cortex of sub-human primates has been rarely explored with respect to the neural basis of amblyopia. Here we investigated how brief periods of unrestricted vision during early monocular form deprivation that are known for reducing the depth of resulting amblyopia affect the development of neuronal responses in Visual Area 2 (V2) of macaque monkeys.
Methods: :
Infant monkeys were reared with a helmet containing a diffuser in front of one eye and a plano lens in the fellow eye between 3 and 18 weeks of age. The rearing regimen included a daily period of unrestricted vision for 0, 1, 2, or 4 hours during the 12-hour deprivation period. When the monkeys were at least 18 months of age, behavioral testing was conducted to measure the depth of amblyopia. Around 4 years of age, microelectrode recording experiments were conducted in V2.
Results: :
One hour of unrestricted vision during the deprivation period slightly decreased the severity of form deprivation amblyopia. With the introduction of 2 hours of daily unrestricted vision, the depth of amblyopia was cut by 50% while 4 hours of unrestricted vision prevented the development of amblyopia. The primary effects of brief periods of unrestricted vision on V2 development were 1) reductions in ocular dominance shifts away from the deprived eye that were generally proportional to the duration of the unrestricted vision, and 2) reductions in the prevalence and the magnitude of binocular suppression.
Conclusions: :
The perceptual effects of daily brief periods of unrestricted vision during early monocular form deprivation (reduction in the depth of amblyopia) are associated with preserving the functional connections from the deprived eye and lowering the impact of binocular suppression in the early stages of cortical processing.
Keywords: amblyopia • visual cortex • visual development