Functional Hearing Difficulties in Blast-Exposed Service Members With Normal to Near-Normal Hearing Thresholds.

OBJECTIVES: Estimated prevalence of functional hearing and communication deficits (FHCDs), characterized by abnormally low speech recognition and binaural tone detection in noise or an abnormally high degree of self-perceived hearing difficulties, dramatically increases in active-duty service members (SMs) who have hearing thresholds slightly above the normal range and self-report to have been close to an explosive blast. Knowing the exact nature of the underlying auditory-processing deficits that contribute to FHCD would not only provide a better characterization of the effects of blast exposure on the human auditory system, but also allow clinicians to prescribe appropriate therapies to treat or manage patient complaints. DESIGN: Two groups of SMs were initially recruited: (1) a control group (N = 78) with auditory thresholds ≤20 dB HL between 250 and 8000 Hz, no history of blast exposure, and who passed a short FHCD screener, and (2) a group of blast-exposed SMs (N = 26) with normal to near-normal auditory thresholds between 250 and 4000 Hz, and who failed the FHCD screener (cutoffs based on the study by Grant et al.). The two groups were then compared on a variety of audiometric, behavioral, cognitive, and electrophysiological measures. These tests were selected to characterize various aspects of auditory system processing from the cochlear to the cortex. A third, smaller group of blast-exposed SMs who performed within normal limits on the FHCD screener were also recruited (N = 11). This third subject group was unplanned at the onset of the study and was added to evaluate the effects of blast exposure on hearing and communication regardless of performance on the FHCD screener. RESULTS: SMs in the blast-exposed group with FHCD performed significantly worse than control participants on several metrics that measured peripheral and mostly subcortical auditory processing. Cognitive processing was mostly unaffected by blast exposure with the exception of cognitive tests of language-processing speed and working memory. Blast-exposed SMs without FHCD performed similarly to the control group on tests of peripheral and brainstem processing, but performed similarly to blast-exposed SMs with FHCD on measures of cognitive processing. Measures derived from EEG recordings of the frequency-following response revealed that blast-exposed SMs who exhibited FHCD demonstrated increased spontaneous neural activity, reduced amplitude of the envelope-following response, poor internal signal to noise ratio, reduced response stability, and an absent or delayed onset response, compared with the other two participant groups. CONCLUSIONS: Degradation in the neural encoding of acoustic stimuli is likely a major contributing factor leading to FHCD in blast-exposed SMs with normal to near-normal audiometric thresholds. Blast-exposed SMs, regardless of their performance on the FHCD screener, exhibited a deficit in language-processing speed and working memory, which could lead to difficulties in decoding rapid speech and in understanding speech in challenging speech communication settings. Further tests are needed to align these findings with clinical treatment protocols being used for patients with suspected auditory-processing disorders.

The efficacy and practicality of the Neurotrack Cognitive Battery assessment for utilization in clinical settings for the identification of cognitive decline in an older Japanese population.

Introduction: Japan has the largest aging population with 33% of the population over the age of 60 years. The number of Japanese adults with dementia is estimated to be approximately 4.6 million, comprising nearly 15% of the older adult population. It is critical to administer cognitive assessments early in the disease state that have high reliability and low user burden to detect negative cognitive changes as early as possible; however, current preclinical AD detection methods are invasive, time-consuming, and expensive. A number of traditional and digital cognitive assessments are also available, but many of these tests are time-consuming, taxing to the user, and not widely scalable. The purpose of this study was to incorporate a digital cognitive assessment battery into a standard clinical assessment performed within a Japanese-based neuropsychology clinic to assess the diagnostic accuracy and the relationship between the digital Neurotrack Cognitive Assessment Battery (N-CAB) to traditional cognitive assessments. Methods: Healthy individuals and probable Alzheimer's patients completed the N-CAB, as well as two traditional cognitive assessments, the Mini Mental Status Exam (MMSE) and the Revised Hasegawa's Dementia Scale (HDS-R). Results: Our results demonstrate the Image Pairs hand-response phase of the N-CAB had the highest diagnostic accuracy with 95% sensitivity and 89% specificity to probable Alzheimer's disease. This was closely followed by the Symbol Match assessment, with a 96% sensitivity and 74% specificity to probable Alzheimer's disease. Additionally, Symbol Match and Path Points used in combination resulted in a sensitivity of 94%, specificity of 90%; a model with all N-CAB assessments resulted in a sensitivity and specificity of 100%. All N-CAB assessments had moderate to strong and significant correlations with the MMSE and HDS-R. Discussion: Together, this suggests that the N-CAB assessment battery may be an appropriate alternative for the clinical screening of cognition for earlier detection of Alzheimer's disease.