Cross-modal and compensatory plasticity in adult deafened cats: a longitudinal PET study

Although much is known about the cerebral neural plasticity that occurs after deafness, it is unclear how much time is required for its development or what other cortical changes may consequently occur. This study provides a longitudinal assessment of cerebral cortical neural plasticity, as manifested in adult deafened cats. A total of 5 male cats were subjected to whole cortex analysis of glucose metabolic activity via 2-deoxy-2[(18)F] fluoro-D-glucose (FDG) micro-positron emission tomography (PET). The imaging was performed at the baseline state of normal hearing and then at 4, 9, 24, and 33 months after the induction of deafness. We compared glucose metabolism between the normal hearing state and each deafened state by using voxel-based statistical analysis (P<0.005). Significant changes were observed in the primary auditory (A1) and primary visual (V1) cortices. A bilateral metabolic decrease was observed in A1 areas and in temporal auditory fields, the extent of which was significantly increased at Month 9. Then it was declined at Month 24. And finally it was disappeared by Month 33. Auditory cortical plasticity subsequent to deafness was thus demonstrated. Furthermore, a significant metabolic upsurge occurred in bilateral occipital areas at Month 33. This increase, involving bilateral occipital and thalamic areas of V1, suggests compensatory hyperactivity of the visual cortex after deafness.