Plasticity in Auditory Cortex after Receptor Damage: Excitatory and Inhibitory Processes

Abstract

Primary sensory cortex in the auditory, somatosensory and visual systems in adult animals shows a capacity for plasticity subsequent to receptor organ damage. Here I review our own work in this area, on auditory cortex contralateral to a lesioned cochlea. I review the conditions required to establish that the cortical change is plasticity and not simply the residue of prelesion responses. I demonstrate that loss of cortical surround inhibition does not, in itself, cause plasticity of auditory cortical maps, as hypothesized in other sensory systems. However, such loss of surround inhibition does lead to unmasking of new excitatory and inhibitory responses in single auditory cortical neurons and this has implications for the standard model for the structure of receptive fields of A1 neurons. I propose an alternative model for the receptive field structure.

Indexing terms:

• Plasticity
• Cortex
• Auditory
• Surround inhibition
• Receptive field

Additional information

Notes on contributors

R Rajan

Ramesh Rajan completed his PhD in 1985 at the University of Western Australia, under the supervision of Prof Brian Johnstone, on “The role of the efferent systems in altering temporary threshold shifts”. In 1986 he moved to the University of Canberra as a Lecturer, and in 1987 to Monash University as a Research Officer to work with Dr Lindsay Aitkin and Dr Dexter Irvine on auditory cortex and neural coding of sound source position and cues for sound source position. He became an independent researcher in 1991 with the award of a RD Wright Fellowship by the National Health and Medical Research Council (NHMRC), for work on “Plasticity in auditory cortex following cochlear damage” and on “Cochlear efferents and protection from loud sound-induced hearing damage”. In 1994 he gained an NHMRC Fellowship to work on “Surround Inhibition in Auditory Cortex and Its Role in Shaping Responses to Simple and Complex Stimuli”. He took up an academic position in 1995 in the Dept of Physiology at Monash University and has been there since, currently as a Senior Lecturer. His research interests more recently have focused on neural coding mechanisms in auditory cortex and at lower stations in the central auditory pathway, but he has maintained his interest in the cochlear efferents. Current work extends to study of the somatosensory cortex and of multi-modal sensory interactions in the cerebellum. He regularly writes in journals like Neurophysiology, Hearing Research, Cerebral Cortex, Neuroscience etc.