Neural correlates of cross-modal plasticity in partial hearing loss: A mini-review

Cross-modal plasticity is an adaptive process where sensory neurons that have lost input from one sensory modality begin to respond to another modality, such as in deafness when auditory neurons begin to respond to visual stimulation. Research in cross-modal plasticity in the auditory system has mainly focused on extreme forms of sensory loss like total deafness, especially when occurring at birth or early in life. However, hearing loss is more common in adulthood and only partly affects hearing function to mild or moderate degrees. Fewer research studies have focused on cross-modal plasticity under these conditions. Our objective was to review evidence for cross-modal plasticity to evaluate if findings derived from populations with deafness extend to populations with partial hearing loss. We conclude that cross-modal plasticity occurs in adult-onset partial hearing loss and is likely to recruit cognitive systems. However, cross-modal effects are not clearly separate from intra-modal contributions. It is also unclear if cross-modal plasticity in partial hearing loss confers a behavioural advantage, or if it is influenced by age and cognitive decline.