Auditory cortical plasticity: does it provide evidence for cognitive processing in the auditory cortex?

The past 20 years have seen substantial changes in our view of the nature of the processing carried out in auditory cortex. Some processing of a cognitive nature, previously attributed to higher-order "association" areas, is now considered to take place in auditory cortex itself. One argument adduced in support of this view is the evidence indicating a remarkable degree of plasticity in the auditory cortex of adult animals. Such plasticity has been demonstrated in a wide range of paradigms, in which auditory input or the behavioural significance of particular inputs is manipulated. Changes over the same time period in our conceptualization of the receptive fields of cortical neurons, and well-established mechanisms for use-related changes in synaptic function, can account for many forms of auditory cortical plasticity. On the basis of a review of auditory cortical plasticity and its probable mechanisms, it is argued that only plasticity associated with learning tasks provides a strong case for cognitive processing in auditory cortex. Even in this case the evidence is indirect, in that it has not yet been established that the changes in auditory cortex are necessary for behavioural learning and memory. Although other lines of evidence provide convincing support for cognitive processing in auditory cortex, that provided by auditory cortical plasticity remains equivocal.