ABSTRACT

Many perceptual studies focus on the brain’s capacity to discriminate between stimuli. However, our normal experience of the world also involves integrating multiple stimuli into a single perceptual event. Neural mechanisms such as lateral inhibition are believed to enhance local differences between sensory inputs from nearby regions of the receptor surface. However, this mechanism would seem dysfunctional when sensory inputs need to be combined rather than contrasted. Here, we investigated whether the brain can strategically regulate the strength of suppressive interactions that underlie lateral inhibition between finger representations in human somatosensory processing. To do this, we compared sensory processing between conditions that required either comparing or combining information. We delivered two simultaneous tactile motion trajectories to index and middle fingertips of the right hand. Participants had to either compare the directions of the two stimuli, or to combine them to form their average direction. To reveal preparatory tuning of somatosensory cortex, we used an established event-related potential design to measure the interaction between cortical representations evoked by digital nerve shocks immediately before each tactile stimulus. Consistent with previous studies, we found a clear suppression between cortical activations when participants were instructed to compare the tactile motion directions. Importantly, this suppression was significantly reduced when participants had to combine the same stimuli. These findings suggest that the brain can strategically switch between a comparative and a combinative mode of somatosensory processing, according to the perceptual goal, by preparatorily adjusting the strength of a process akin to lateral inhibition.

摘要

许多感知研究集中在大脑区分刺激的能力上。然而，我们对世界的正常体验也涉及将多种刺激整合到一个单一的感知事件中。神经机制如侧向抑制被认为会增强来自受体表面附近区域的感觉输入之间的局部差异。然而，当感觉输入需要组合而不是对比时，这种机制似乎功能失调。在这里，我们调查了大脑是否可以战略性地调节人类体感处理中手指表征之间横向抑制的抑制相互作用的强度。为此，我们比较了需要比较或组合信息的条件之间的感觉处理。我们将两条同时的触觉运动轨迹传送到右手的食指和中指尖。参与者必须要么比较两种刺激的方向，要么将它们结合起来形成它们的平均方向。为了揭示体感皮层的准备调整，我们使用已建立的事件相关电位设计来测量在每次触觉刺激之前由数字神经休克诱发的皮层表征之间的相互作用。与以往的研究一致，当参与者被指示比较触觉运动方向时，我们发现皮质激活之间存在明显的抑制。重要的是，当参与者必须结合相同的刺激时，这种抑制显着降低。这些发现表明，根据知觉目标，大脑可以通过预先调整类似于侧向抑制的过程强度，在体感处理的比较模式和组合模式之间进行战略性切换。