Bilateral reorganization of posterior temporal cortices in post‐lingual deafness and its relation to cochlear implant outcome

Abstract

Post-lingual deafness induces a decline in the ability to process phonological sounds or evoke phonological representations. This decline is paralleled with abnormally high neural activity in the right posterior superior temporal gyrus/supramarginal gyrus (PSTG/SMG). As this neural plasticity negatively relates to cochlear implantation (CI) success, it appears important to understand its determinants. We addressed the neuro-functional mechanisms underlying this maladaptive phenomenon using behavioral and functional magnetic resonance imaging (fMRI) data acquired in 10 normal-hearing subjects and 10 post-lingual deaf candidates for CI. We compared two memory tasks where subjects had to evoke phonological (speech) and environmental sound representations from visually presented items. We observed dissociations in the dynamics of right versus left PSTG/SMG neural responses as a function of duration of deafness. Responses in the left PSTG/SMG to phonological processing and responses in the right PSTG/ SMG to environmental sound imagery both declined. However, abnormally high neural activity was observed in response to phonological visual items in the right PSTG/SMG, i.e., contralateral to the zone where phonological activity decreased. In contrast, no such responses (overactivation) were observed in the left PSTG/SMG in response to environmental sounds. This asymmetry in functional adaptation to deafness suggests that maladaptive reorganization of the right PSTG/SMG region is not due to balanced hemispheric interaction, but to a specific take-over of the right PSTG/SMG region by phonological processing, presumably because speech remains behaviorally more relevant to communication than the processing of environmental sounds. These results demonstrate that cognitive long-term alteration of auditory processing shapes functional cerebral reorganization. Hum Brain Mapp 00:000-000,

Physiology, Psychoacoustics and Cognition in Normal and Impaired Hearing

“…They found that, when doing a rhyming task with written words, CI users with later good speech understanding showed an activation pattern that was consistent with them using the normal phonological pathway to do the task, whereas those with poor outcomes used a pathway normally associated with lexical-semantic understanding (Lazard et al 2010). They further compared activity evoked by speech and non-speech imageries in the right and left posterior superior temporal gyrus/supramarginal gyrus (PSTG/SMG) (Lazard et al 2013). These areas are normally specialised for phonological processing in the left hemisphere and environmental sound processing in the right hemisphere.…”

Representing sounds and spellings: Phonological decline and compensatory working memory in acquired hearing impairment

“…With lower WMC, the option to engage working memory processing to compensate for phonological decline is likely to be relatively reduced as fewer resources are available for careful phonological analyses. Resorting to a whole word, lexico-semantic based route to word phonology may then be an alternative way to compensate for degraded representations (Lazard et al, 2010;Lazard et al, 2012). Such a strategy is likely to interfere with rhyme judgment but enhance recall via increased attendance to semantic rather than phonological features (Craik & Tulving, 1975;Morris, Bransford, & Franks, 1977;.…”

“…The reorganization likely reflects an increased responsiveness to visual stimuli in the left temporal cortex together with recruitment of the right temporal cortex for phonological processing (Lazard et al, 2011;Lazard et al, 2010;Lazard et al, 2012). While fMRI studies have indicated topographical changes in phonological processing following acquired HI, the time-course of these changes has not been examined previously.…”

“…For example, Lee et al (2007) found evidence of cross-modal plasticity in the form of an enhanced receptiveness to visual linguistic input in the auditory speech regions of the brain in deafened adults. It has been suggested that if the left lateralized temporal regions that are normally devoted to phonological processing become more responsive to visual linguistic information, the right lateralized auditory areas that are otherwise involved in processing of environmental sounds may in turn be recruited for the processing of phonology (Lazard, Lee, Truy, & Giraud, 2012). Recruitment of auditory areas for visual processing following hearing loss may even interfere with auditory speech recognition by affecting the ability to segregate conflicting auditory and visual information (Champoux, Lepore, Gagne, & Theoret, 2009).…”

Hearing Aid Use in Older Adults With Postlingual Sensorineural Hearing Loss: Protocol for a Prospective Cohort Study (Preprint)

“…In normal hearing older adults, lip and word reading broadly activate the abovementioned dorsal articulatory and spectrotemporal/phonological analysis networks, with the exception of the primary auditory cortices due to diminished auditory function [25]. SNHL adults engage a similar network, but exhibit greater amplitudes in the attendant structures, especially the prefrontal and premotor cortices, and recruit additional structures including the right posterior temporal lobe [21,[26][27][28], which is normally only activated by actual sounds [25].…”