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Z. A. Hirji, F. Cortese, H. C. Goltz, D. O. Cheyne, A. M. Wong; Neural Correlates of Pattern Perception in Human Amblyopia: An MEG Study. Invest. Ophthalmol. Vis. Sci. 2009;50(13):4707.
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The neural basis of amblyopia remains elusive: there is contradictory evidence on whether visual deficits result primarily from dysfunction of early visual cortex (V1/V2) or extrastriate cortex. In this study, we investigated the roles of early and late visual cortical areas and their interactions in human amblyopes by using magnetoencephalography (MEG).
Prior to MEG recording, 2 adult amblyopes and 6 visually normal subjects performed a behavioural experiment in which subjects detected static Glass patterns (radial or rotational) monocularly. The signal strength (% of correlated dot-pairs) of the Glass patterns was varied to determine the level at which the subject perceived the pattern 80% of the time. During MEG recording, the signal strength of the Glass pattern was set at the previously measured 80% performance level so that the amblyopic and fellow eyes in patients with amblyopia and healthy eyes in normal controls were stimulated equally across subjects and stimulus conditions.
Behaviorally, Glass pattern perception by the amblyopic eyes produced slower response times and required higher signal strengths when compared to the fellow and healthy eyes. Using beamformer-based spatial filtering, brain activity maps revealed bilateral activation in early visual areas (V1/V2) shortly after visual presentation for both amblyopic and normal subjects. However, ~250 ms after visual presentation, stimulation of the amblyopic eye produced attenuated activity in the extrastriate lateral occipital complex (LOC) bilaterally, and different activity in the right inferior parietal area, when compared to the fellow and healthy eyes. In addition, time course analysis of the source waveforms at these brain locations revealed a different pattern of interaction between early and later visual areas when stimulating the amblyopic eye, than was observed for fellow and healthy eyes.
The neural basis of amblyopia may be related to an abnormal interaction between early visual (V1/V2) and extrastriate cortices.
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