Congenital deafness affects the functional and anatomical properties of the auditory system (Kral et al, 2019, Ann Rev Neurosci). It has been suggested that congenital deafness affects predominantly corticocortical functional connections within but also beyond the auditory system (the connectome model of deafness, Kral et al, 2016, Lancet Neurol). This may lead to increased risk of cognitive deficits in deaf children. Indeed, so-called induced responses, indicative of corticocortical interactions, were reduced in the auditory cortex of congenitally deaf cats (Yusuf et al, 2017, Brain). Here Dr Kral’s group directly investigated effective connectivity between primary and secondary areas of congenitally deaf cats (CDC).
In adult hearing cats (HC) and CDCs, responses to acoustic and electric stimulation (through a cochlear implant) were compared. Recordings were in the primary auditory field (A1) and the higher order posterior auditory field (PAF) using multielectrode arrays. Penetrations were histologically reconstructed. For effective connectivity pairwise phase consistency, weighted phase-lag index and nonparametric Granger causality were determined and compared. Additionally, spike-field coherence was computed between different recording sites.
CDCs demonstrated a substantially reduced stimulus-related corticocortical coupling in the connectivity measures used. Largest deficits were observed in sensory-related top-down interactions, in the alpha and beta band (Yusuf et al, 2021, Front Neurosci). Furthermore, spike-field coherence revealed a decoupling of supragranular and infragranular layers in A1 (Yusuf et al, 2022, Front Syst Neurosci), likely responsible for dystrophic changes in the deep cortical layers (Berger et al, 2017, J Comp Neurol). The data document that corticocortical interactions are dependent on developmental hearing experience. These observations suggests that the congenitally deaf brain cannot incorporate top-down prediction information into auditory processing and thus have a deficient predictive processing.