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Abstract

ntroduction. Electrophysiological studies (Chino, Calford, Heinen, Gilbert, Kaas, Rosa) suggest that adult V1 visual field maps reorganize after de-afferentiation. The reported electrophysiological reorganization appears inconsistent with cytochrome oxidase staining patterns after similar de-afferentiation (Horton amp;amp; Hocking, J Neurosci 1998). We are measuring macaque V1 responses with functional magnetic resonance imaging (fMRI) and electrophysiology to clarify the extent of V1 reorganization.
Methods. A retinal photocoagulation laser (GYC-2000, NIDEK) was used to lesion 5-8 degree homonymous visual field locations in four adult rhesus macaques. The retinal lesion creates a de-afferentiated V1 zone referred to as the lesion projection zone, or LPZ (Schmid et al., Cerebral Cortex 1996). As expected, following the lesion we found little or no response to visual stimulation inside the LPZ using functional magnetic resonance imaging (fMRI) at 4.7T in the anesthetized macaque preparation (Logothetis et al., Nat Neurosci 1999). The extent of V1 reorganization was quantified by repeatedly measuring the visual modulation in the BOLD signal near the border of the LPZ.
Results. Over the course of seven months, we found very little, if any, increase in BOLD activity within the LPZ apart from that expected by reduced retinal swelling. The boundary of the LPZ remained stable to within 1 mm. The stable scotoma persisted in the BOLD response in all four animals tested. Parallel electrophysiological experiments are in progress in these animals, allowing direct comparison between BOLD measurements and single unit responses.