Deprivation-induced plasticity in the early central circuits of the rodent visual, auditory, and olfactory systems: a systematic review and meta-analysis of the literature

Activity-dependent neuronal plasticity is crucial for animals to adapt to dynamic sensory environments. Traditionally, research on activity dependent-plasticity has used sensory deprivation approaches in animal models, and it has focused on its effects in primary sensory cortices. However, emerging evidence emphasizes the importance of activity-dependent plasticity both in the sensory organs and in sub-cortical regions where cranial nerves relay information to the brain. Additionally, a critical question arises: do different sensory modalities share common cellular mechanisms for deprivation-induced plasticity at these central entry-points? Furthermore, does the duration of deprivation correlate with specific plasticity mechanisms? This study aims to systematically review and meta-analyse research papers that investigated visual, auditory, or olfactory deprivation in rodents. Specifically, it explores the consequences of sensory deprivation in homologous regions at the first central synapse after the cranial nerve: vision--lateral geniculate nucleus and superior colliculus; audition-- ventral and dorsal cochlear nucleus; olfaction--olfactory bulb. The systematic search yielded 91 research papers (39 vision, 22 audition, 30 olfaction), revealing significant heterogeneity in publication trends, experimental methods of inducing deprivation, measures of deprivation-induced plasticity, and reporting, across the three sensory modalities. Nevertheless, despite these methodological differences, commonalities emerged when correlating the plasticity mechanisms with the duration of the sensory deprivation. Following short-term deprivations (up to 1 day) all three systems showed reduced activity levels and increased disinhibition. Medium-term deprivation (1 day to a week) induced greater glial involvement and synaptic remodelling. Long-term deprivation (over a week) predominantly led to macroscopic structural changes including tissue shrinkage and apoptosis. These findings underscore the importance of standardizing methodologies and reporting practices. Additionally, they highlight the value of cross-modals synthesis for understanding how the nervous system, including peripheral, pre-cortical, and cortical areas, respond to and compensate for sensory inputs loss.