老年人大脑听觉皮质脑磁图对刺激声频率和强度的反应

Effects of stimulus frequency and intensity on the magnetoencephalography in elderly people

目的:观察不同刺激声频率和强度对老年人脑磁图的影响,为老年人大脑听觉皮质脑磁图的测试提供理论依据。方法:选取32例2002-01/2005-01在河北省人民医院耳鼻咽喉科门诊就诊的健康受试者,年龄60～80岁。以306通道全头型脑磁图仪测试听阈上30dB的0.5,2,4kHz纯音,以及听阈上30dB和50dB的2kHz纯音所诱发的双侧大脑半球听觉皮质脑磁场M100,并与其MRI解剖影像信息叠加整合,得到大脑听觉皮质磁源性影像。分析比较相同强度3种不同频率纯音和同一频率不同强度纯音所诱发M100的潜伏期、波幅及其等电流偶极在X,Y,Z坐标轴的三维定位。结果:32例受试者均进入结果分析。①0.5,2和4kHz三种频率纯音声刺激所诱发的老年人大脑听觉皮质磁反应波M100潜伏期和波幅相同诱发侧别之间比较其差异有显著意义(P<0.01),其中又以处于语言频率的2kHz所诱发的M100潜伏期最短[同侧(110.3±8.9)ms;对侧(102.8±8.5)ms],波幅最大[同侧(16.7±4.2)nA;对侧(18.4±6.4)nA];而高频的4kHz所诱发的M100潜伏期最长[同侧(132.5±12.6)ms;对侧(120.7±10.1)ms],波幅最低[同侧(6.7±2.6)nA;对侧(8.6±3.7)nA]。②听阈上50dB的2kHz纯音较30dB的2kHz纯音诱发的老年人大脑听觉皮质M100潜伏期显著缩短[同侧(100.6±6.2),(110.3±6.5)ms;对侧(92.5±4.3),(102.8±5.6)ms;P均<0.01],波幅显著增加[同侧(22.3±4.4),(16.7±3.8)nA;对侧(26.5±6.4),(18.4±4.5)nA;P均<0.01]。两种强度2kHz纯音诱发的M100等电流偶极的位置在X,Y,Z轴均无显著变化(P>0.05)。结论:①老年人大脑听觉皮质的老化性退行性变是以感受较高频率声音的听觉皮质区域最早开始而且其退行性变的程度也最重。②增加刺激声强度仅能激活大脑听觉皮质更多数量的神经细胞,却不能改变大脑听觉皮质各种频率刺激声激活的区域和范围。③老年人大脑听觉皮质脑磁图的测试需要注意所选择的刺激声频率要包括各种频率的声音信息,测试较高频率刺激声诱发的脑磁图时声音强度不可过低。

AIM： To study the effects of different stimulus frequency and intensity on the magnetoencephalogrephy （MEG） in elderly people, and provide theoretic instruction for the auditory cortex MEG examination in the eldedy. METHODS： Thirty-two eldedy subjects （60-80 years old） were selected from the outpatients in the Department of Otorhinolaryngology of Hebei Provincial People＇s Hospital from January 2002 to January 2005. The auditory cortex magnetic field M100 of bilateral hemispheres elicited by 0,5, 2, 4 kHz pure tones at the same intensity of 30 dB super-threshold level and by 2 kHz pure tone at 30 dB and 50 dB super-threshold level were examined with 306-channel whole-head magnetometer. The auditory cortex magnetic source imaging was obtained by superimposing functional MEG data on structural magnetic resonance image. The latencies, amplitudes and the three-dimensional Iocalizations of equivalent current dipole on X, Y, Z coordinate axis of M100 evoked by different three frequencies pure tones at same level and by same frequency pure tone at different level were analyzed and compared respectively. RESULTS： All 32 subjects were involved in the result analysis. ①The latencies and amplitudes of the auditory cortex magnetic field M100 on the same evoked side were different significantly among 0.5 kHz, 2 kHz and 4 kHz stimulating frequencies pure tones （P 〈 0.01）. The latency was the shortest and the amplitude was the largest in the M100 evoked by 2 kHz pure tone [one side： （110.3±8.9） ms; opposite side： （102.8±8.5） ms; one side： （16.7±4.2） nA; opposite side： （18.4±6.4） hA]. The latency was the longest and the amplitude was the smallest in the M100 evoked by 4 kHz pure tone [one side： （132.5±12.6） ms; opposite side： （120.7±10.10） ms; one side： （6.7：P.2..6） nA; opposite side： （8.6±3.7） nA].②The M100 latency was significantly shorter and the M100 amplitude was significantly larger evoked by 2 kHz pure tone at 50 dB super-threshold level than that at 30 dB super-threshold level on the same evoked side [one side： （100.6±6.2）, （110.3± 6.5） ms; opposite side： （92.5±4.3）, （102.8±5.6） ms; P 〈 0.01; one side： （22,3±4.4）, （16.7±3.8） nA; opposite side： （26.5± 6.4）, （18.4±4.5） nA; P 〈 0.01]. The three-dimensional Iocalizations of equivalent current dipole on X, Y, Z coordinate axis of M100 were the same between the two stimulating intensity pure tones. CONCLUSION： ①The aging of auditory cortex in elderly people begins with the higher frequency tones reception areas of auditory cortex and the atrophic degree is the most obvious in the same area, ②More neural cells of auditory cortex can be activated but the areas of auditory cortex activated by different frequency tones cannot be enlarged by increasing the stimulating pure tone intensity. ③The various frequencies of stimulating tones should be included and the intensity of higher frequency stimulating tones should not be lower when examining the auditory cortex magnetic field in elderly subjects.