Impact of Cochlear Implantation on Neurocognitive Subdomains in Adult Cochlear Implant Recipients

Introduction: Age-related hearing loss affects about one-third of the population worldwide. Studies suggest that hearing loss may be linked to cognitive decline and auditory rehabilitation may improve cognitive functions. So far, the data are limited, and the underlying mechanisms are not fully understood. The study aimed to analyze the impact of cochlear implantation on cognition in a large homogeneous population of hearing-impaired adults using a comprehensive non-auditory cognitive assessment with regard to normal-hearing (NH) subjects. Material and Methods: Seventy-one cochlear implant (CI) candidates with a postlingual, bilateral severe or profound hearing loss aged 66.3 years (standard deviation [SD] 9.2) and 105 NH subjects aged 65.96 years (SD 9.4) were enrolled. The computer-based neurocognitive tool applied included 11 subtests covering attention (M3), short- and long-term memory (recall and delayed recall), working memory (0- and 2-back, Operation Span [OSPAN] task), processing speed (Trail Making Test [TMT] A), mental flexibility (TMT B), inhibition (cFlanker and iFlanker), and verbal fluency. CI patients underwent a neurocognitive testing preoperatively as well as 12 months postoperatively. Impact of hearing status, age, gender, and education on cognitive subdomains was studied. Additionally, after controlling for education and age, cognitive performance of CI subjects (n = 41) was compared to that of NH (n = 34). Results: CI users achieved significantly better neurocognitive scores 12 months after cochlear implantation than before in most subtests (M3, [delayed] recall, 2-back, OSPAN, iFlanker, and verbal fluency; all p < 0.05) except for the TMT A and B. A significant correlation could be found between the postoperative improvement in speech perception and in the attentional task M3 (p = 0.01). Hearing status (p = 0.0006) had the strongest effect on attention, whereas education had a high impact on recall (p = 0.002), OSPAN (p = 0.0004), and TMT A (p = 0.005) and B (p = 0.003). Inhibition was mainly age-dependent with better results in younger subjects (p = 0.016). Verbal fluency was predicted by gender as females outperformed men (p = 0.009). Even after controlling for age and education NH subjects showed a significantly better performance than CI candidates in the recall (p = 0.03) and delayed recall (p = 0.01) tasks. Postoperatively, there was no significant difference between the 2 groups anymore. Conclusion: Impact of cochlear implantation on neurocognitive functions differs according to the cognitive subdomains. Postoperatively, CI recipients performed as good as age- and education-matched NH subjects.