Division of Brain Biology, National Institute for Basic Biology, Okazaki, Japan.
PLoS One. 2011;6(9):e25283. doi: 10.1371/journal.pone.0025283. Epub 2011 Sep 26.
Animals can make faster behavioral responses to multisensory stimuli than to unisensory stimuli. The superior colliculus (SC), which receives multiple inputs from different sensory modalities, is considered to be involved in the initiation of motor responses. However, the mechanism by which multisensory information facilitates motor responses is not yet understood. Here, we demonstrate that multisensory information modulates competition among SC neurons to elicit faster responses. We conducted multiunit recordings from the SC of rats performing a two-alternative spatial discrimination task using auditory and/or visual stimuli. We found that a large population of SC neurons showed direction-selective activity before the onset of movement in response to the stimuli irrespective of stimulation modality. Trial-by-trial correlation analysis showed that the premovement activity of many SC neurons increased with faster reaction speed for the contraversive movement, whereas the premovement activity of another population of neurons decreased with faster reaction speed for the ipsiversive movement. When visual and auditory stimuli were presented simultaneously, the premovement activity of a population of neurons for the contraversive movement was enhanced, whereas the premovement activity of another population of neurons for the ipsiversive movement was depressed. Unilateral inactivation of SC using muscimol prolonged reaction times of contraversive movements, but it shortened those of ipsiversive movements. These findings suggest that the difference in activity between the SC hemispheres regulates the reaction speed of motor responses, and multisensory information enlarges the activity difference resulting in faster responses.
动物对多感觉刺激的行为反应比单一感觉刺激更快。上丘（SC）接收来自不同感觉模态的多个输入，被认为参与运动反应的启动。然而，多感觉信息促进运动反应的机制尚不清楚。在这里，我们证明多感觉信息调节 SC 神经元之间的竞争，以引发更快的反应。我们在大鼠执行听觉和/或视觉刺激的双选择空间辨别任务时，从 SC 进行多单位记录。我们发现，在运动开始之前，大量 SC 神经元表现出与刺激模态无关的方向选择性活动。逐次相关分析表明，许多 SC 神经元的运动前活动随着对反向运动的更快反应速度而增加，而另一群神经元的运动前活动随着对同侧运动的更快反应速度而减少。当同时呈现视觉和听觉刺激时，用于反向运动的一群神经元的运动前活动增强，而用于同侧运动的另一群神经元的运动前活动减弱。使用 muscimol 单侧失活 SC 会延长反向运动的反应时间，但会缩短同侧运动的反应时间。这些发现表明，SC 半球之间的活动差异调节运动反应的反应速度，多感觉信息扩大了导致更快反应的活动差异。
