几百毫秒到几秒范围内的时间信息处理涉及小脑和基底神经节。在这一章中,我们介绍了最近对非人灵长类动物的研究。在本章前半部分的研究中,当视觉提示(时间产生任务)开始后经过一定时间后,训练猴子进行眼球运动。动物必须根据固定点的颜色报告从几百毫秒到几秒钟的时间流逝。在这项任务中,扫视潜伏期随要测量的时间长度而变化,并且从一个试验到另一个试验显示出随机变异性。在相同条件下的试验变异性与瞳孔直径以及小脑深部核和运动丘脑的准备活动密切相关。当被要求报告亚秒间隔时,这些大脑区域的失活会延迟扫视。这些结果表明,内部状态,随着每次试验的变化,可能会引起小脑神经元活动的波动,从而产生自定时的变化。当测量不同的时间间隔时,小脑的准备活动总是在运动前大约500毫秒开始,无论被测量的时间间隔的长度。然而,纹状体的准备活动在整个强制延迟期间持续进行,可以达到2秒,活动的增加速度不同。此外,在纹状体,时间测量前的视觉反应和低频振荡活动因预期时间间隔的长度而改变.这些结果表明,网络的状态,包括纹状体,随着预期时机的变化,这导致了准备活动的不同时间过程。因此,基底神经节似乎负责测量几百毫秒到几秒范围内的时间,而小脑负责调节亚秒范围内的自我定时变异性。本章的后半部分介绍了与周期性时序相关的研究。在与定期交替的目标同步的眼睛运动期间,小脑核中的不同神经元表现出与运动时间相关的活动,预测刺激时机,和同步的时间误差。其中,例如,与目标外观相关联的活动在同步运动期间特别增强,并且可以表示刺激序列的时间结构的内部模型。我们还考虑了在没有运动的情况下感知周期性定时的神经机制。在感知节奏的过程中,我们预测下一次刺激的时机,并将注意力集中在那一刻。在缺失的怪球范例中,受试者必须检测到定期重复刺激的遗漏。当应用于人类时,结果表明,预测每个刺激时间的最快时间限制约为0.25s(4Hz)。在执行这项任务的猴子中,小脑核中的神经元,纹状体,运动丘脑表现出周期性活动,根据大脑区域的不同,有不同的时间过程。由于记录部位的电刺激或失活会改变对刺激遗漏的反应时间,这些神经元活动必须参与周期性的时间处理。未来的研究需要阐明节律感知的机制,似乎是通过皮质-小脑和皮质-基底神经节途径处理的。
Temporal information processing in the range of a few hundred milliseconds to seconds involves the cerebellum and basal ganglia. In this chapter, we present recent studies on nonhuman primates. In the studies presented in the first half of the chapter, monkeys were trained to make eye movements when a certain amount of time had elapsed since the onset of the visual cue (time production task). The animals had to report time lapses ranging from several hundred milliseconds to a few seconds based on the color of the fixation point. In this task, the saccade latency varied with the time length to be measured and showed stochastic variability from one trial to the other. Trial-to-trial variability under the same conditions correlated well with pupil diameter and the preparatory activity in the deep cerebellar nuclei and the motor thalamus. Inactivation of these brain regions delayed saccades when asked to report subsecond intervals. These results suggest that the internal state, which changes with each trial, may cause fluctuations in cerebellar neuronal activity, thereby producing variations in self-timing. When measuring different time intervals, the preparatory activity in the cerebellum always begins approximately 500 ms before movements, regardless of the length of the time interval being measured. However, the preparatory activity in the striatum persists throughout the mandatory delay period, which can be up to 2 s, with different rate of increasing activity. Furthermore, in the striatum, the visual response and low-frequency oscillatory activity immediately before time measurement were altered by the length of the intended time interval. These results indicate that the state of the network, including the striatum, changes with the intended timing, which lead to different time courses of preparatory activity. Thus, the basal ganglia appear to be responsible for measuring time in the range of several hundred milliseconds to seconds, whereas the cerebellum is responsible for regulating self-timing variability in the subsecond range. The second half of this chapter presents studies related to periodic timing. During eye movements synchronized with alternating targets at regular intervals, different neurons in the cerebellar nuclei exhibit activity related to movement timing, predicted stimulus timing, and the temporal error of synchronization. Among these, the activity associated with target appearance is particularly enhanced during synchronized movements and may represent an internal model of the temporal structure of stimulus sequence. We also considered neural mechanism underlying the perception of periodic timing in the absence of movement. During perception of rhythm, we predict the timing of the next stimulus and focus our attention on that moment. In the missing oddball paradigm, the subjects had to detect the omission of a regularly repeated stimulus. When employed in humans, the results show that the fastest temporal limit for predicting each stimulus timing is about 0.25 s (4 Hz). In monkeys performing this task, neurons in the cerebellar nuclei, striatum, and motor thalamus exhibit periodic activity, with different time courses depending on the brain region. Since electrical stimulation or inactivation of recording sites changes the reaction time to stimulus omission, these neuronal activities must be involved in periodic temporal processing. Future research is needed to elucidate the mechanism of rhythm perception, which appears to be processed by both cortico-cerebellar and cortico-basal ganglia pathways.