Behne Nicole, Wendt Beate, Scheich Henning, Brechmann André
Leibniz Institute for Neurobiology, Magdeburg, Germany.
J Neurophysiol. 2006 Apr;95(4):2630-7. doi: 10.1152/jn.01201.2005. Epub 2006 Jan 25.
In a previous study, we hypothesized that the approach of presenting information-bearing stimuli to one ear and noise to the other ear may be a general strategy to determine hemispheric specialization in auditory cortex (AC). In that study, we confirmed the dominant role of the right AC in directional categorization of frequency modulations by showing that fMRI activation of right but not left AC was sharply emphasized when masking noise was presented to the contralateral ear. Here, we tested this hypothesis using a lexical decision task supposed to be mainly processed in the left hemisphere. Subjects had to distinguish between pseudowords and natural words presented monaurally to the left or right ear either with or without white noise to the other ear. According to our hypothesis, we expected a strong effect of contralateral noise on fMRI activity in left AC. For the control conditions without noise, we found that activation in both auditory cortices was stronger on contralateral than on ipsilateral word stimulation consistent with a more influential contralateral than ipsilateral auditory pathway. Additional presentation of contralateral noise did not significantly change activation in right AC, whereas it led to a significant increase of activation in left AC compared with the condition without noise. This is consistent with a left hemispheric specialization for lexical decisions. Thus our results support the hypothesis that activation by ipsilateral information-bearing stimuli is upregulated mainly in the hemisphere specialized for a given task when noise is presented to the more influential contralateral ear.
在之前的一项研究中，我们假设向一只耳朵呈现携带信息的刺激而向另一只耳朵呈现噪声的方法可能是确定听觉皮层（AC）半球特化的一种通用策略。在该研究中，我们通过表明当向对侧耳朵呈现掩蔽噪声时，右侧AC而非左侧AC的功能磁共振成像（fMRI）激活被显著增强，证实了右侧AC在频率调制方向分类中的主导作用。在此，我们使用一个假定主要在左半球进行处理的词汇判定任务来检验这一假设。受试者必须区分单耳呈现给左耳或右耳的伪词和自然词，同时另一只耳朵要么有要么没有白噪声。根据我们的假设，我们预期对侧噪声对左侧AC的fMRI活动有强烈影响。对于无噪声的对照条件，我们发现与同侧单词刺激相比，双侧听觉皮层在对侧单词刺激时的激活更强，这与对侧听觉通路比同侧听觉通路更具影响力一致。对侧噪声的额外呈现并未显著改变右侧AC的激活，而与无噪声条件相比，它导致左侧AC的激活显著增加。这与词汇判定的左半球特化一致。因此，我们的结果支持以下假设：当向更具影响力的对侧耳朵呈现噪声时，同侧携带信息的刺激所引起的激活主要在专门负责给定任务的半球中被上调。
