Injury- and Use-Related Plasticity in Adult Auditory Cortex

Abstract

After restricted cochlear lesions in adult animals the frequency selectivity of neurons in the cortical region deprived of its normal input by the lesion is changed such that the region is occupied by expanded representations of adjacent (perilesion) frequencies. These changes reflect a dynamic process of reorganization (plasticity) and are not explicable as passive consequences of the lesion. Analogous plasticity of cortical frequency selectivity and organization is seen following behavioural training that enhances the significance of particular acoustic stimuli. The occurrence of injury- and use-related auditory cortical plasticity gives rise to a number of questions relating to the mechanisms involved, the perceptual consequences and functional significance of such plastic changes, and their implications for the central processing of input from prosthetic devices. Evidence relating to these issues is briefly summarized in this review, and the directions of future research are considered.

Perceptual training improves syllable identification in new and experienced hearing aid users

“…In cats with high-frequency hearing loss, neurons in auditory cortex originally tuned to high frequencies alter their tuning to process inputs from intact nearby portions of the cochlea [2,22]. Similar neuroplastic changes occur in humans with SNHL: difference limens for frequency are altered in a manner consistent with a neuroplastic expansion of the representation of sounds below the high-frequency hearing loss and the correspondingly reduced representation of higher frequencies [23].…”

Auditory-Processing Malleability

“…Thus, the perception of simple attributes of sound (pitch, duration) and complex ones (sound patterns, speech sounds) improves with training. Improved perception is accompanied by changes in the auditory cortex, similar to those induced by environmental experience and injury (Irvine et al, 2001). A typical result is that following active training on a task (e.g., discriminating one sound from another) with a particular target stimulus (e.g., a tone of a given frequency; a speech sound discriminable based on a specific cue such as voicing; a location cue), participants can distinguish stimuli they previously could not.…”

“…This means that even in adult animals, higher levels of the auditory system will change their function in response to the type of information received from the auditory periphery. When information related to certain frequencies is no longer received, its representation in the cortex is also lost (Irvine, Rajan, & Brown, 2001). Similar changes, known as cortical-map plasticity, occur following training.…”

The mechanisms of tinnitus: Perspectives from human functional neuroimaging

“…A maladaptive response to this loss of input causes expansion of the tonotopic map so that this affected portion now becomes responsive to the adjacent frequency at which hearing threshold is normal -the lesion-edge frequency ( Figure 7). Of relevance for human neuroimaging studies, animal research has shown that a restricted cochlear lesion in adult animals drives neuroplastic changes in the frequency gradient within primary auditory cortex (Robertson and Irvine, 1989;Kaas, 1991, Rajan et al, 1993Schwaber et al 1993;Irvine et al, 2001). One theory of TI proposes that it is a consequence of such cortical reorganisation (e.g., Salvi et al, 2000a).…”