灰鼠下丘近场记录未观察到掩蔽级差(Masking Level Difference)现象

No evidence of MLD in near - field recording from chinchilla IC

目的 以往的实验中采用近场电极记录方法发现了听皮层电位的掩蔽级差(Masking level difference,MLD)样改变,本实验采用同样技术观察下丘的MLD是否存在。方法6只健康成年灰鼠,手术植入右侧下丘电极,术后恢复期7-10天,然后在无麻醉状态下进行下丘电位的测试。短纯音条件的测试(500 Hz短纯音)共设:双耳同相纯青(b0),双耳反相纯音(bπ),左耳纯音(le)和右耳纯音(re)四个条件,用以观察纯音本身参数对实验的影响。MLD条件的测试(500 Hz短纯音+白噪声)共设:双耳同相噪声反相纯音(n0sπ),双耳同相噪声同相纯音(n0s0),双耳同相噪声左耳纯音(n0sl),左耳噪声左耳纯音(nlsl),双耳同相噪声右耳纯音(n0sr)和右耳噪声右耳纯音(nrsr)六个条件。结果 纯音条件组的右侧声刺激(re)得到较弱的诱发电位。MLD条件组中下丘电位的噪声掩蔽阈,潜伏期和振幅的分析未发现各组数据间有明显差异。结论 采用近电场电极记录方法不能发现下丘的MLD样活动,但能发现皮层的MLD样活动。研究结果支持MLD完成于脑干以上水平的观点。

Objective A previous study found the evidence of masking level difference (MID) in chinchilla auditory cortex (AC) by using a near- field electrode recording technique. The present study aims at searching for MID in chinchilla inferior colliculus (IC) by using similar techniques. Methods Six healthy adult chinchillas were surgically implanted with the right IC electrode and recovered for 7-10 days. The 1C potentials were recorded in unanesthetized animals that were passively restrained. For a toneburst series, a 500 Hz toneburst was presented to both ears heterophasically (brr) and homophasically (b0), left ear (le) and rightear (re). The purpose of the test was to evaluate the effects of toneburst parameters on the IC potentials. MID series test (500 Hz toneburst plus broadband noise) consisted of six paradigms: binaural noise in phase and binaural toneburst out of phase (n0sπ); binaural noise and tone burst in phase (n0s0); binaural noise in phase and left ear tone burst (n0sl); left ear noise and tone burst (nlsl);binaural noise in phase and right ear toneburst (n0sr); and right ear noise and toneburst (nrsr) .Results For the toneburst series, ipisilateral stimuli (re) produced weaker responses. For the MID series, IC masked thresholds, and OC response latencies and amplitudes did not show obvious differences among the different MID conditions. Conclusions The near- field electrode recording technique found no evidence of MID - like activity from the chinchilla IC, despite previous results showed MID - like activities from AC. These data support the hypothesis that the neural basis of MID occurs rostral to the brainstem.