Scalp-recorded optical signals make sound processing in the auditory cortex visible
Scalp-recorded optical signals make sound processing in the auditory cortex visible
复制标题
DOI：
10.1006/nimg.1999.0495
复制
发表时间：
1999-11-01
期刊：
影响因子：
5.7
通讯作者：
Näätänen, R
中科院分区：
文献类型：
--
作者：
Rinne, T;Gratton, G;Näätänen, R
使用现代脑成像方法可以详细研究人类听觉皮质的功能。例如，正电子发射断层扫描(PET；Lauter等人，1985)、功能磁共振成像(fMRI；Wessinger等人，1997)和脑磁图(Meg；Romani等人，1982)已经证明了听觉皮质中的立位组织。因此，这些方法，特别是功能磁共振成像，能够在毫米尺度上绘制涉及听觉处理的大脑区域。然而，fMRI在编码和分析声音信息时无法跟踪中枢听觉系统的细微时间动力学，因为它的时间分辨率受到血流动力学变化特性的限制，至少落后神经活动几百毫秒。相比之下，脑磁图提供了有关中枢听觉处理的时间细节信息(Lutkenhöner和Steinsträter，1998)，但在将同时激活的相邻声源彼此分开方面存在严重问题，并且不能指示激活区域的范围和模式。本文报道了第一个与事件相关的光信号(Eros；Gratton和Fabiani，1998)。使用这种新的非侵入性皮质激活测量方法，我们能够在时间和空间上定位声音检测和变化检测这两个最重要的听觉功能的神经元发生器(Näätänen，1992)。EROS方法在一次测量中结合了高空间和高时间分辨率(Gratton和Fabiani，1998)。在Eros记录中，强度调制的近红外线光源和探测器被放置在头皮上，彼此相距几厘米。光源发出的低强度光通过皮肤、骨骼和大脑扩散，一些光子离开头部，到达探测器。空间上的高分辨率信号是通过根据光子的飞行时间来选择的；那些花费类似时间通过介质的光子很可能遵循相对相似的路径。EROS是一种测量光的调制包络相移的方法，当光子在脑组织中移动时，脑组织被神经激活进行光学修改。与神经电活动相比，脑组织中的一些光学变化与持续时间相对较长的各种血流动力学现象有关(Cannestra等人，1996)。此外，与神经元激活相关的光散射也有快速的变化(Cohen，1972；Frostig等人，1990；Malonek和Grinvald，1996)，这在性爱中得到了反映。在细胞水平上，散射变化的物理原因尚不完全清楚，但已经提出了一些因素，如穿过细胞膜的离子电流(Cohen，1972；Stepnowski等人，1991)以及神经和神经胶质细胞的肿胀(Andrew和MacVicar，1994)。以前已经证明，由相同的视觉刺激引起的电和光反应的时间进程是相似的，而且，由EROS指示的激活轨迹与由fMRI指示的对应(Gratton等人，1997)。然而，到目前为止，还没有关于性激素对听觉刺激的报道。在目前的研究中，我们测量了当受试者被呈现音调点点时，听觉皮质的性欲。我们还获得了一些结果，澄清了当这些重复的音调偶尔缩短持续时间时，听觉皮质如何检测声音的变化。我们记录了6名听力正常的健康受试者(年龄21-41岁，3名女性)的性欲。以恒定的400ms…向受试者呈现丰富的和声(5ms上升和下降时间)
The functioning human auditory cortex can be studied in detail with modern brain-imaging methods. For example, positron emission tomography (PET; Lauter et al., 1985), functional magnetic resonance imaging (fMRI; Wessinger et al., 1997), and magnetoencephalography (MEG; Romani et al., 1982) have demonstrated tonotopic organization in the auditory cortex. Thus, these methods, especially fMRI, are able to map brain areas involved in auditory processing on a millimeter scale. However, fMRI is not able to track the finegrained temporal dynamics of the central auditory system in encoding and analyzing sound information because its time resolution is limited by the properties of the hemodynamic changes, lagging neural activity at least by several hundred milliseconds. In contrast, MEG provides temporally detailed information on central auditory processing (Lutkenhöner and Steinsträter, 1998) but has severe problems in separating simultaneously activated adjacent sources from each other and cannot indicate the extent and pattern of the activated area. The present paper reports the first event-related optical signals (EROS; Gratton and Fabiani, 1998) from the functioning human auditory cortex. Using this novel noninvasive measure of cortical activation, we were able to locate, in both time and space, neuronal generators for two of the most important auditory functions, sound detection and change detection (Nä ä tä nen, 1992). The EROS method combines both high spatial and high temporal resolution in a single measure (Gratton and Fabiani, 1998). In an EROS recording, a source of intensity-modulated near-infrared light and a detector are placed on the scalp a few centimeters apart from each other. The low-intensity light emitted by the source diffuses through the skin, bone, and brain, and some photons exit the head, reaching the detector. A spatially high-resolution signal is achieved by selecting the photons on the basis of their time of flight; those photons that take similar amounts of time to migrate through the medium are likely to follow relatively similar paths. EROS is a measure of phase-shifts in the modulation envelope of the light as the photons migrate through the brain tissue, which is optically modified by neural activation. Some of the optical changes in the brain tissue are related to various hemodynamic phenomena lasting relatively long times compared with neural electric activity (Cannestra et al., 1996). In addition, there are also rapid changes in light scattering associated with neuronal activation (Cohen, 1972; Frostig et al., 1990; Malonek and Grinvald, 1996) that are reflected in EROS. At the cellular level, the physical cause of the scattering changes is not entirely clear but factors such as ion currents across the cell membrane (Cohen, 1972; Stepnowski et al., 1991) and the swelling of the neural and glial cells have been suggested (Andrew and MacVicar, 1994). Previously it has been shown that the time courses of the electric and optic responses evoked by the same visual stimulation are similar and, further, that the loci of activation indicated by EROS correspond to those indicated by fMRI (Gratton et al., 1997). So far no EROS to auditory stimulation has been reported, however. In the present study, we measured EROS from the auditory cortex when subjects were presented with tone pips. We also obtained results clarifying how the auditory cortex detects sound change when these repetitive tones are occasionally shortened in duration. We recorded EROS from six healthy subjects (ages 21–41, 3 females) with normal hearing. Subjects were presented with harmonically enriched tones (5-ms rise and fall times) at constant 400-ms …