Cochlear Implant Results in Older Adults with Post-Lingual Deafness: The Role of “Top-Down” Neurocognitive Mechanisms

To date, no clear specific cognitive predictors of speech perception outcome in older adult cochlear implant (CI) users have yet emerged. The aim of this prospective study was to increase knowledge on cognitive and clinical predictors of the audiological outcome in adult cochlear implant users. A total of 21 patients with post-lingual deafness, who were candidates for cochlear implantation, were recruited at the Department of Ear, Nose and Throat, University of Torino (Italy) and subjected to a pre-operatory neuropsychological assessment (T0) and an audiological examination after 12 months of implantation (T12). Patients who, at T12, had a 60 dB verbal recognition above 80%, were younger (z = −2.131, p = 0.033) and performed better in the Verbal Semantic Fluency Test at T0 (z = −1.941, p = 0.052) than subjects who had a 60 dB verbal recognition at T12 below 80%. The most significant predictors of the CI audiological outcome at T12 were age (β = −0.492, p = 0.024) and patients’ TMT-A performance at baseline (β = −0.486, p = 0.035). We conclude that cognitive processing speed might be a good predictor of the level of speech understanding in older adult patients with CI after one year of implantation

Cerebral lateralization of language in deaf children and adults with cochlear implant (CI): a neurofunctional study with transcranial doppler ultrasound (fTCD)

Severe to profound sensorineural hearing loss (SNHL) is a pathological condition, that affects about 1-3/1000 newborns, but as shown by several studies on humans and animals, can be considered a scientific opportunity for understanding the role of auditory stimuli in neuroplasticity. In the late decades the advent of Cochlear Implantation (CI) has also permitted further investigation on how stimuli restoration can affect neuroplasticity in previously deprived subjects. This issue has been studied in terms of timing of restoration (age of implantation) and side of stimulation (afferented ear), and effects on auditory perception and language development in the case of humans. Within this theoretical frame, the present study focuses on language lateralization, measured through functional Transcranial Doppler ultrasonography (fTCD), a non invasive technique, that quantifies a Lateralization Index (LI) detecting blood flow during language performance. At this aim, 3 different groups of subjects were evaluated by fTCD: (i) 36 children with prelingual profound bilateral SNHL with monolateral CI (and 24 control subjects with normal hearing); they were also evaluated in language achievement (PPVT, TCGB, Inpe high and low frequencies, GASS and language composite score); (ii) 11 children with profound congenital unilateral hearing loss (UHL) (and 11 control subjects with normal hearing bilaterally); they were evaluated on verbal and non verbal development (PPVT, TROG2, IQ, PRI, WMI, PSI, VCI, VMI); (iii) 6 adults with preverbal profound bilateral SNHL, evaluated before and after CI. The results show that (i) left dominance is maintained, even if bilateral representation for language appears more frequent in children with monolateral CI; children with right ear implanted or left LI show better language performance. (ii) left activation was confirmed in children with right UHL while it was not confirmed in those with left UHL. Performance on verbal test were significantly better in children with right hearing. (iii) No significant changes LI were observed in adults, after implantation. On the basis of the present study neuroplasticity of auditory and language circuits appears to be a complex phenomenon in which some biological constraints for left dominance for language are confirmed, but other factors, such as age of reafferentation, and side of afference can play roles, that have still to be clearly understood. Furthermore the present study brings some support to the right ear advantage hypothesis and this should be taken into account while choosing the ear to be implanted, in the case of unilateral CI. From this point of view the right implant could be considered the first choice in monolateral or sequenced implantation. fTDC for LI evaluation can be considered in the case of late diagnosed deafness before implantation

The timecourse of multisensory speech processing in unilaterally stimulated cochlear implant users revealed by ERPs.

A cochlear implant (CI) is an auditory prosthesis which can partially restore the auditory function in patients with severe to profound hearing loss. However, this bionic device provides only limited auditory information, and CI patients may compensate for this limitation by means of a stronger interaction between the auditory and visual system. To better understand the electrophysiological correlates of audiovisual speech perception, the present study used electroencephalography (EEG) and a redundant target paradigm. Postlingually deafened CI users and normal-hearing (NH) listeners were compared in auditory, visual and audiovisual speech conditions. The behavioural results revealed multisensory integration for both groups, as indicated by shortened response times for the audiovisual as compared to the two unisensory conditions. The analysis of the N1 and P2 event-related potentials (ERPs), including topographic and source analyses, confirmed a multisensory effect for both groups and showed a cortical auditory response which was modulated by the simultaneous processing of the visual stimulus. Nevertheless, the CI users in particular revealed a distinct pattern of N1 topography, pointing to a strong visual impact on auditory speech processing. Apart from these condition effects, the results revealed ERP differences between CI users and NH listeners, not only in N1/P2 ERP topographies, but also in the cortical source configuration. When compared to the NH listeners, the CI users showed an additional activation in the visual cortex at N1 latency, which was positively correlated with CI experience, and a delayed auditory-cortex activation with a reversed, rightward functional lateralisation. In sum, our behavioural and ERP findings demonstrate a clear audiovisual benefit for both groups, and a CI-specific alteration in cortical activation at N1 latency when auditory and visual input is combined. These cortical alterations may reflect a compensatory strategy to overcome the limited CI input, which allows the CI users to improve the lip-reading skills and to approximate the behavioural performance of NH listeners in audiovisual speech conditions. Our results are clinically relevant, as they highlight the importance of assessing the CI outcome not only in auditory-only, but also in audiovisual speech conditions

Tinnitus & Cochlear Implants

A cochlear implant is an electronic device that can help to restore hearing in patients who have severe bilateral sensorineural hearing loss. This thesis aims to obtain more insight into the number of patients that might benefit from cochlear implantation concerning tinnitus. We did two questionnaire studies, which showed that the prevalence of tinnitus in cochlear implant patients is 51-66%. The tinnitus severity is generally mild to moderate. Cochlear implantation reduces tinnitus in an important part of the patients (56-75%), but in a small part of the patients (0-28%) cochlear implantation has a negative influence on tinnitus. However, in the patients who show tinnitus deterioration the tinnitus handicap does not increase and in the patients who show tinnitus onset after implantation the tinnitus handicap is mild. Based on the questionnaire studies we created a prognostic model that showed that the lower the preoperative tinnitus handicap and the preoperative hearing handicap, the higher the chance that cochlear implantation will worsen tinnitus. This result suggests that preoperative screening with tinnitus- and hearing handicap questionnaires could be meaningful. Further, we performed a study in which we explored single electrode stimulation to reduce tinnitus perception. We found that the effect of single-electrode stimulation on tinnitus is relatively small in comparison to the effect of full-array stimulation, but in some cases sustained single electrode stimulation may be beneficial for tinnitus management