What's to lose and what's to learn: development under auditory deprivation, cochlear implants and limits of cortical plasticity.
Sensory and environmental manipulations affect the development of sensory systems. Higher-order auditory representations (auditory categories or "objects") evolve with experience and via top-down influences modify representations in early auditory areas. During development of a functional auditory system, the capacity for bottom-up reorganizations is successively less well expressed due to a molecular change in synaptic properties. It is, however, complemented by top-down influences that direct and modulate the residual (adult) capacity for circuit reorganization. In a deprived condition, this developmental step is substantially affected. As higher-order representations cannot be established in absence of auditory experience, the developmental decrease in capacity for "bottom-up regulated" reorganizations (as repeatedly demonstrated in also in deprived sensory systems) cannot be complemented by an increasing influence of top-down modulations. In consequence, the ability to learn is compromised in sensory deprivation, resulting in a sensitive period for recovery.
Kral
Andrej
A
Laboratory of Auditory Neuroscience, Department of Neurophysiology and Pathophysiology, University of Hamburg School of Medicine, Germany. a.kral@uke.de
Eggermont
Jos J
JJ
D000818:Animals; D001303:Auditory Cortex / Q000254:growth & development* / Q000503:physiopathology*; D001306:Auditory Pathways / Q000254:growth & development / Q000503:physiopathology; D003054:Cochlear Implants; D003638:Deafness / Q000151:congenital / Q000503:physiopathology* / Q000628:therapy; D006801:Humans; D007859:Learning Disabilities / Q000209:etiology / Q000503:physiopathology*; D009473:Neuronal Plasticity / Q000502:physiology*; D020127:Recovery of Function / Q000502:physiology; D012683:Sensory Deprivation / Q000502:physiology*; D009435:Synaptic Transmission / Q000502:physiology