Okada Ken-ichi, Kobayashi Yasushi
Graduate School of Frontier Biosciences, Osaka University, 1-4 Yamadaoka, Suita, 563-0871, Japan; Center for Information and Neural Networks (CiNet), National Institute of Information and Communications Technology, Osaka University, Osaka, Japan.
Eur J Neurosci. 2014 Aug;40(4):2641-51. doi: 10.1111/ejn.12632. Epub 2014 May 27.
Fixational saccades are small, involuntary eye movements that occur during attempted visual fixation. Recent studies suggested that several cognitive processes affect the occurrence probability of fixational saccades. Thus, there might be an interaction between fixational saccade-related motor signals and cognitive signals. The pedunculopontine tegmental nucleus (PPTN) in the brainstem has anatomical connections with numerous saccade-related and limbic areas. Previously, we reported that a group of PPTN neurons showed transient phasic bursts or a pause in activity during large visually guided and spontaneous saccades, and also showed sustained tonic changes in activity with task context. We hypothesised that single PPTN neurons would relay both fixational saccade-related and task context-related signals, and might function as an interface between the motor and limbic systems. We recorded the activity of PPTN neurons in behaving monkeys during a reward-biased task, and analysed neuronal activity for small fixational saccades during visual fixation, and compared it with the activity for large visually guided targeting saccades and large spontaneous saccades during intertrial intervals. A population of PPTN neurons exhibited a fixational saccade-related phasic increase in activity, and the majority of them also showed activity modulation with large targeting saccades. In addition, a group of these neurons showed a task-related tonic increase in activity during the fixation period, and half of them relayed the saccade signal only when the neuron exhibited higher tonic activity during the task execution period. Thus, fixational saccade-related signals of PPTN neurons overlap with tonic task-related signals, and might contribute to the cognitive modulation of fixational saccades.
注视性眼跳是在试图进行视觉注视时发生的小幅度、非自主性眼球运动。最近的研究表明，几种认知过程会影响注视性眼跳的发生概率。因此，注视性眼跳相关的运动信号与认知信号之间可能存在相互作用。脑干中的脚桥被盖核（PPTN）与众多与眼跳相关和边缘系统区域存在解剖学联系。此前，我们报告称，一组PPTN神经元在大型视觉引导和自发眼跳期间表现出短暂的相位性爆发或活动暂停，并且在任务背景下活动也会出现持续的紧张性变化。我们假设单个PPTN神经元会传递与注视性眼跳相关和与任务背景相关的信号，并且可能作为运动系统和边缘系统之间的接口发挥作用。我们在行为学猴子执行奖励偏向任务期间记录了PPTN神经元的活动，分析了视觉注视期间小幅度注视性眼跳的神经元活动，并将其与试验间隔期间大型视觉引导靶向眼跳和大型自发眼跳的活动进行了比较。一群PPTN神经元表现出与注视性眼跳相关的相位性活动增加，并且其中大多数在大型靶向眼跳时也表现出活动调制。此外，这些神经元中有一组在注视期表现出与任务相关的紧张性活动增加，并且其中一半仅在任务执行期神经元表现出较高紧张性活动时才传递眼跳信号。因此，PPTN神经元的注视性眼跳相关信号与紧张性任务相关信号重叠，并且可能有助于注视性眼跳的认知调制。
