Radboud University Nijmegen, Donders Institute for Brain, Cognition and Behaviour, NL 6500 HE, Nijmegen, The Netherlands.
J Neurosci. 2011 Nov 16;31(46):16864-71. doi: 10.1523/JNEUROSCI.3404-11.2011.
Single-unit recordings have shown that the brain uses multiple reference frames in spatial processing. The brain could use this neural architecture to implicitly create multiple modes of representation at the population level, with each reference frame weighted as a function of task demands. Using magnetoencephalography, we tested this hypothesis by studying the reference frames in rhythmic neuronal synchronization--a population measure--during tactile remapping for saccades. Human subjects fixated either to the left or right of the body midline, while a tactile stimulus was applied to an invisible fingertip, located either left or right of fixation. After a variable delay, they looked at the remembered stimulus location. Results show a transient body-centered, stimulus-induced gamma-band response (70-90 Hz) in somatosensory areas, contralateral to the stimulated hand. Concurrently, a gamma-band response occurred in posterior parietal cortex (PPC), contralateral to the gaze-centered location of the stimulus, even though the stimulus was not seen. The temporal overlap of these early representations suggests that there is a fast bottom-up sensory-induced remapping in PPC, taking into account the relative positions of eyes and hand. The gaze-centered representation in PPC was sustained in a high gamma range (85-115 Hz) and increased in power closer to the initiation of the saccade. Lower-frequency rhythms (alpha, beta) showed body-centered power modulations in somatosensory areas in anticipation of the stimulus and a mixture of reference frames in PPC after stimulus presentation. We conclude that oscillatory activity reflects the time-varying coding of information in body- and gaze-centered reference frames during tactile remapping for saccades.
单细胞记录表明，大脑在空间处理中使用多个参考系。大脑可以利用这种神经结构在群体水平上隐式地创建多个表示模式，每个参考系的权重作为任务需求的函数。我们使用脑磁图通过研究在扫视的触觉重映射过程中，节律性神经元同步的参考系（群体测量）来检验这一假设。人类被试者注视身体中线的左侧或右侧，同时将触觉刺激施加到看不见的指尖上，该指尖位于注视点的左侧或右侧。经过可变的延迟后，他们会看着记忆中的刺激位置。结果显示，在感觉区域中出现了短暂的以身体为中心的、由刺激诱导的伽马带反应（70-90Hz），与受刺激的手相对应。同时，在与注视中心位置相对应的顶后皮质（PPC）中也发生了伽马带反应，即使刺激未被看到。这些早期表现的时间重叠表明，在 PPC 中存在快速的由下至上的感觉诱导重映射，考虑到眼睛和手的相对位置。在 PPC 中，以注视为中心的表示在高伽马范围内（85-115Hz）持续存在，并在接近扫视开始时增加功率。较低频率的节律（α、β）在感觉区域中显示出以身体为中心的功率调制，以预测刺激，并且在刺激呈现后，PPC 中出现了混合的参考系。我们得出结论，振荡活动反映了在扫视的触觉重映射过程中，信息在以身体和注视为中心的参考系中的时变编码。
