Brain Plasticity Can Predict the Cochlear Implant Outcome in Adult-Onset Deafness.

Area of Science:

• Neuroscience
• Auditory Neuroscience
• Neuroplasticity

Background:

• Sensory plasticity in adult-onset deafness is less understood than in developmental deafness.
• Auditory deprivation in adults can lead to brain reorganization, but its impact on cochlear implant outcomes is unclear.

Purpose of the Study:

• To investigate brain reorganization in adults with postlingual deafness using glucose metabolism.
• To determine the clinical relevance of this reorganization for cochlear implant (CI) outcomes.
• To compare adult brain plasticity with findings in congenitally deaf children.

Main Methods:

• ¹⁸F-FDG-PET scans were used to measure glucose metabolism in 37 postlingually deafened adults and 39 normal-hearing controls.
• Speech perception outcomes were assessed 1 year after cochlear implantation using a phoneme identification test.
• Metabolic activity in auditory and visual pathways, as well as medial frontal cortices, was analyzed.

Main Results:

• Deaf adults showed hypometabolism in auditory pathways (inferior colliculus, superior temporal gyri) compared to controls.
• Visual cortex metabolism was elevated in deaf individuals, suggesting cross-modal sensory compensation.
• Auditory cortex hypometabolism in deaf adults did not predict speech perception recovery after CI, unlike in children.
• Higher metabolism in visual association areas correlated negatively with speech perception outcomes.
• Preserved metabolic activity in medial frontal cortices was associated with better speech performance.

Conclusions:

• The adult auditory cortex is relatively resistant to cross-modal plasticity following deafness.
• Visual processing and cognitive control appear to be more significant prognostic markers for CI success in adults.
• Findings highlight differences in neuroplasticity between adult and developmental deafness.