AUDIOLOGY & SPEECH-LANGUAGE PATHOLOGY 청각 및 언어 병리학 분야 1위 (25개중) 저널이면서,
OTORHINOLARYNGOLOGY 이비인후과 분야 1위 (43개중) 저널인
Hearing Research에 논문이 온라인 게재 됐습니다. (2016년 10월 8일)
청각 분야에서 '이명'이 중추신경계와 말초신경계 모두의 원인에 기인한다는 것을 밝힌 뇌파 연구입니다.
Although a peripheral auditory (bottom-up) deficit is an essential prerequisite for the generation of tinnitus, central cognitive (top-down) impairment has also been shown to be an inherent neuropathological mechanism. Using an auditory oddball paradigm (for top-down analyses) and a passive listening paradigm (for bottom-up analyses) while recording electroencephalograms (EEGs), we investigated whether top-down or bottom-up components were more critical in the neuropathology of tinnitus, independent of peripheral hearing loss. We observed significantly reduced P300 amplitudes (reflecting fundamental cognitive processes such as attention) and evoked theta power (reflecting top-down regulation in memory systems) for target stimuli at the tinnitus frequency of patients with tinnitus but without hearing loss. The contingent negative variation (reflecting top-down expectation of a subsequent event prior to stimulation) and N100(reflecting auditory bottom-up selective attention) were different between the healthy and patient groups. Interestingly, when tinnitus patients were divided into two subgroups based on their P300 amplitudes, their P170 and N200 components, and annoyance and distress indices to their tinnitus sound were different. EEG theta-band power and its Granger causal neurodynamic results consistently support a double dissociation of these two groups in both top-down and bottom-up tasks. Directed cortical connectivity corroborates that the tinnitus network involves the anterior cingulate and the parahippocampal areas, where higher-order top-down control is generated. Together, our observations provide neurophysiological and neurodynamic evidence revealing a differential engagement of top-down impairment along with deficits in bottom-up processing in patients with tinnitus but without hearing loss.
Figure 1. Experimental design. (A) A task flow diagram with a series of auditory stimuli comprising both rarely presented target sounds (with a 20% occurrence probability) and frequently presented standard sounds (with an 80% occurrence probability). White bars and the letter ‘S’ indicate standard stimuli, and black bars and the letter ‘T’ represent target stimuli. The auditory stimuli were presented to participants using binaural insert earphones (depicted as red and blue boxes with connected lines). The frequency of the standard sound is 500 Hz, and that of the target is 8 kHz for healthy participants and an individual tinnitus pitch-matched frequency for patients with tinnitus. Each stimulus was presented for 200 ms with variable inter-stimulus intervals (ISI: 1300 to 1700 ms). During the oddball task (B: for top-down analyses), participants were instructed to perform a sound-discrimination task by pressing a button. In contrast, during the passive listening task (C: for bottom-up analyses), participants were instructed to watch a silent movie without responding to the presented auditory sounds. In both the oddball and passive listening tasks, the same series of auditory stimuli (with 80 target and 320 standard stimuli) were used.