Neural reorganization following sensory loss: the opportunity of change

Abstract

There is growing evidence that sensory deprivation is associated with crossmodal neuroplastic changes in the brain. After visual or auditory deprivation, brain areas that are normally associated with the lost sense are recruited by spared sensory modalities. These changes underlie adaptive and compensatory behaviours in blind and deaf individuals. Although there are differences between these populations owing to the nature of the deprived sensory modality, there seem to be common principles regarding how the brain copes with sensory loss and the factors that influence neuroplastic changes. Here, we discuss crossmodal neuroplasticity with regards to behavioural adaptation after sensory deprivation and highlight the possibility of maladaptive consequences within the context of rehabilitation.

Figure 1. Summary of crossmodal neuroplasticity changes following sensory loss

Crossmodal recruitment of occipital visual cortex in the blind and auditory cortex in the deaf have been reported. (A) Occipital recruitment for tactile processing such as Braille reading, sound localization and verbal memory. (B) Recruitment of auditory and language-related areas for viewing sign language, peripheral visual processing and vibro-tactile stimulation.

Figure 2. Crossmodal neuroplasticity changes in the case of dual sensory loss (vision and hearing)

Localization of activation (revealed by fMRI) associated with identifying words through haptically presented American Sign Language (ASL) in both a prelingually deaf and early blind (A) and a hearing-sighted control (B) subject (for simplicity, only the left hemisphere is shown). Crossmodal networks associated with the identification of words (contrasted to non-words) include inferior frontal cortex activation within the left hemisphere (corresponding to Broca’s area, BA 44) in both subjects (white circle). The white dashed circle identifies activation within superior temporal language areas (including Wernicke’s area and superior temporal gyrus). The arrow indicates occipital cortex activation. Activation within occipital and temporal cortical areas seem to be specific to the combined loss of vision and hearing.

Figure 3. Effects of early visual deprivation in cats

Dark-rearing alters the distribution of sensory responsive neurons in the anterior ectosylvian sulcus (AES). A. Schematic drawing of the lateral surface of the adult cat cortex showing the location of the AES and the relative position of its three major subdivisions: SIV (fourth somatosensory area), FAES (auditory field of the AES) and AEV (anterior ectosylvian visual area). B. Distribution of sensory unresponsive, unisensory and multisensory mature AES neurons in normally reared and dark-reared animals. Abbreviations: VA, visual auditory; VS, visual somatosensory; AS, auditory-somatosensory; VAS, visual-auditory-somatosensory. Part A modified from . Part B data from reference .