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Abstract:
Visual cortex has the capacity to reorganize in response to changes in sensory input. Early studies of visual deprivation (Blakemore, Hubel, LeVay) suggested that stimulus driven reorganization occurs only during a critical period in early development. Recent electrophysiological studies (Gilbert, Kaas, Chino, Rosa, Heinen) suggest that the visual system of adult mammals may undergo significant reorganization after de-afferentiation. There is an ongoing debate regarding the nature and extent of this reorganization (Horton, DeAngelis).
Here we describe measurements of cortical reorganization after inducing a 5-8o homonymous scotoma in the retinas of adult rhesus macaques with a photocoagulation laser (GYC-2000, NIDEK). We used 4.7T functional magnetic resonance imaging (fMRI) in the anesthetized macaque preparation (Logothetis et al., Nat Neurosci 1999) to track the changes in visual field maps in early cortical areas. FMRI is appealing as it is noninvasive, provides global coverage of the visual areas, and facilitates comparison with human studies. By comparing the activation patterns seen as a function of time after induction of the scotoma we aim to outline the temporal course of cortical reorganization. Preliminary results, based on one monkey, reveal a localized cortical region within V1 (~1.2x2.5cm2) whose signal response is strongly diminished by the lesion. Further, it appears that the fraction of area V1 silenced by the scotoma changes in time.
