Abstract
Purpose :
Abnormally enhanced internal noise in the visual system of amblyopes is thought to prevent them from reliably detecting or discriminating visual stimuli. However, the neural origin of this elevated perceptual noiseis not known. In this study we examined the hypothesis that correlated spiking noise (noise correlation) is elevated in neighboring pairs of extrastriate cortical neurons of amblyopic monkeys.
Methods :
Five macaque monkeys were reared with a light-weight helmet containing a defocus lens (-3 or -10 diopter) for one eye between 3 and 12 weeks of age. Behavioral testing showed that these monkeys exhibited a wide range of depth of amblyopia.We quantified the spiking noise of V2 neurons in response to brief (640 ms) sine wave gratings that were optimized for orientation and spatial frequency for each neuron and repeated for 25 times. We calculated mean-matched fano factor (m-FF) and correlated noise for stimulus contrast of 0%, 10%, 25%, 50% and 80%. We also examined the nature of binocular interactions of these neurons using dichoptic sine wave gratings.
Results :
Both fano factor and correlated noise were significantly elevated in amblyopic neurons for low stimulus contrasts but not for higher contrasts. There was a moderate association between the level of spiking noise and behavioral impairment for individual monkeys. Also these contrast-dependent spiking irregularities were generally correlated with the level of binocular suppression in these V2 neurons.
Conclusions :
Our results show that correlated noise among nearby neurons is elevated in amblyopic V2 for low contrast stimuli, which may make visual performance of amblyopic monkeys more difficult for low visible target. The results also suggest that binocular suppression may play a significant role in developmentally altering the cortical circuits that control the level of spiking noise for a given neuron and for multiple nearby neurons.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.