老化對於噪音環境中傾聽言語時大腦活化之影響： 以功能性磁振攝影研究中樞型老年性聽障

Aging Effects of Auditory Cortical Activation during Speech listening in Noise: A Study of Central Presbycusis Using fMRI

黃俊豪(Juen-Haur Hwang)

指導教授 ： 林凱南

共同指導教授 ： 劉殿楨

國立臺灣大學/醫學院/臨床醫學研究所/碩士(2006年)

https://doi.org/10.6342/NTU.2006.01158

摘要

人類聽覺系統隨著年紀的增長，有兩種不同的退化表現：一種是聽覺閥值敏感度降低，另一種是分辨語言的能力下降。語言聽知覺的障礙，除了受到週邊聽覺系統損傷的影響，也會因為聽覺中樞的退化而加重症狀。此外，在言語訊號被干擾的情況下，例如有背景噪音或同時有多種言語刺激，老年人會比年輕人更難去感受並分辨，使得聽覺障礙更加嚴重，此一現象可能是聽覺中樞在處理與整合聽覺刺激的系統，產生異常或退化。
本實驗採用十二名年齡大於60歲、慣用右手、週邊聽力檢查正常之健康老年人。對照組為十二名，慣用右手、健康、無聽力障礙年齡、年齡介於21歲至31歲之年輕人。這些受試者皆以國語為慣用語之本國人。每位受試者接受功能性核磁共振腦部掃描，造影同時接受雙耳聲音刺激，刺激聲音分為兩種情況：一是單純連續語句刺激(音量約為70分貝)，另一是連續語句加上寬頻噪音(訊造比約差5分貝)。分別取得2種刺激情況下之影像資料。之後，依群組合成分析法(group analysis)，將所有影像資料加以SPM2軟體統計分析，資料經過空間修飾後(spatial smoothing with filters)，以family-wise corrected P閾值小於0.01，以及在heighT閾值為4.80的情況下，空間常數的cluster number大於30，認為有意義的活化區域。最後，比較老年人和年輕人，在不同情況下大腦活化模式之異同。並將〝連續語句加上寬頻噪音〞減去〝單純連續語句〞刺激之影像資料，當作在寬頻噪音下，專注傾聽時聽覺系統之額外活化區域。
結果顯示，年輕人與老年人在無寬頻噪音干擾下，言語聽辨檢查結果與大腦活化模式類似，只有在兩側上顳迴的後部，也就是planum temporale區域，活化強度較弱；當有寬頻噪音干擾時，老年人的言語聽辨檢查結果比年輕人差，老年人的大腦活化模式，在左側大腦半球有些不連續的現象，而且，活化範圍明顯比年輕人小，尤其是兩側上顳迴前部與後部，以及兩側中顳迴區域。活化強度方面，無論年輕人或老年人，在寬頻噪音干擾下，聽覺皮質活化空間叢聚常數，與局部平均最大活化強度，都比無寬頻噪音干擾時小，此種現象在老年人比較嚴重，不過，活化空間叢聚常數，變化差異較大，而局部平均最大活化強度，差異較小。
另外，在背景噪音下，專注傾聽時聽覺系統之額外活化區域方面，年輕人在左側被殼，右側上顳迴前部等處，以及右側丘腦pulvinar處有明顯活化，而老年人只有兩側的丘腦內背核有活化。另外，本實驗並未發現腦幹部位的聽覺傳出系統有明顯活化，雖然如此，我們無法排除聽覺傳出系統在噪音干擾下進行言語聽知覺的角色。
結論：中樞型老年性聽障，初期的病變位置主要在兩側上顳迴前部與後部，以及中顳迴上部。而且，在寬頻噪音下進行言語聽知覺時，老年人由上而下的機制，也比年輕人差。

關鍵字

老化 ； 言語聽知覺 ； 噪音 ； 功能性核磁共振造影

並列摘要

The aging human auditory system is manifested by deterioration of two critical dimension of hearing, namely, reduction in threshold sensitivity and reduction in the ability to understand speech. The deterioration in speech perception ability results not only from the problems of peripheral hearing organs but also affected by the degeneration of central auditory system. Further more, the elderly listener’s difficulties increase dramatically more than the young listeners whenever the speech message is degraded. These difficulties may due to a central integrative and synthesizing hearing disability that reflects a progressive deterioration of the CNS.
Twelve subjects aged over 61 with normal peripheral hearing will be included in this study. Another twelve young subjects aged between 21 and 31 will serve as control. Functional MRI will be performed while these subjects were listening to
speech (both in quiet and in noise) binaurally using a Bruker’s 3T scanner. A
pre-recorded continuous discourse is used as the speech signal. The same signal plus a background white noise (S/N ratio: + 5 dB) serve as the hearing in noise counterpart.
Results showed that the SDS and activation patterns were very similar between young adults and elderly people during speech listenig, but the SDS and extent of activation decreased obviously in both groups durning speech listening in white noise, especially in elderly people. The reduced activation was mainly located in the anterior and posterior parts of superior temporal gyrus of both hemispheres, especially in the left side. The IWV of auditory cortex was smaller in elderly subjects than in young subjects, so as to the cluster levels and the voxel levels, especially in cluster levels. In addition, the ratio of the noise-induced masking effect in IWV was much greater in elderly subjects than in young subjects. Both of the cluster levels and voxle levels, especially in cluster levels, were also decreased greatly in elderly subjects.
Furthermore, compared to speech listening alone, the activation increased in the left putamen, the anterior part of the right STG (BA 38), pulvinar of right thalamus, right claustrum and left caudate tail during speech listening in noise in younger adults. However, only medial dorsal nuclei of the thalamus of both hemispheres were additionally activated during speech listening in white noise in elderly subjects.
To conclude, the early changes of central presbycusis maily located in anterior and posterior parts of the superior temporal gyrus, and suprior part of the middle temporal gysus of both hemispheres. Top-down mechanism during speech listening in noise were reduced in elderly subjects.

並列關鍵字

aging ； speech perception ； noise ； functional magnetic resonance imaging

參考文獻

Bailey BJ等。Head & Neck Surgery Otolaryngology。2001年，第 三版，第1625、1629、1637頁，LWW出版。

Dallos P等。The cochlea。1996年，第436頁，Springer出版。

International Organization for standards: Acoustics, 1990. Determination of occupational noise exposure and estimation of noise-induced hearing impairment. Geneva, International Organization for standards, 1999.

Kaplan & Sadock。Comprehensive textbook of psychiatry。 1999年，第7版，第18、690頁。

Schuknecht HF等。 Pathology of the ear. 1974年，Cambridge, Harvard University Press。