Kaur Jaspreet, Komi Salif A, Dmytriyeva Oksana, Houser Grace A, Bonfils Madelaine C A, Berg Rune W
Department of Neuroscience, Faculty of Health and Medical Sciences, University of Copenhagen, Blegdamsvej 3, 2200, Copenhagen, Denmark.
Novo Nordisk Foundation Center for Basic Metabolic Research, University of Copenhagen, Blegdamsvej 3B, 2200, Copenhagen, Denmark.
Sci Rep. 2025 May 23;15(1):17903. doi: 10.1038/s41598-025-01695-8.
While the movement of rodents can be paused by optogenetic stimulation of a brainstem nucleus, the pedunculopontine nucleus (PPN), it is unknown whether this response has a functional purpose. The arrest appears conspicuously similar to fear-induced freezing behavior and could constitute a general halting mechanism for movement without an emotional component. Further, it is unclear to what extent brain activity is affected by the evoked motor arrest. Here, we investigate this phenomenon by engaging a distinct brain activity, the hippocampal theta rhythm. The theta rhythm is prominent during locomotor activity, absent under normal immobile situations, yet present under vigilant states like fear-induced freezing. Specifically, we ask whether the PPN-induced motor arrest has the same effect on the theta rhythm as if the animal would perform a volitional arrest, which results in the disappearance of the theta rhythm, or whether it would cause a continuation of the theta rhythm as would be expected by a fear-induced motor arrest. An alternative hypothesis is that the theta rhythm represents an ongoing intention to move rather than the movement itself. To distinguish between these two possibilities, we recorded the hippocampal brain rhythm before and during movement arrest induced by optogenetic stimulation of the PPN in rats. The PPN-induced motor arrest was associated with a clear obstruction of the ongoing theta activity. The timescale of movement arrest was less than 200 ms, similar to the obstruction of the theta rhythm. Since fear and behavioral freezing are associated with hippocampal theta rhythm, which we did not see during PPN stimulation, we suggest that induced motor arrest occurs without an associated emotional component. Further, our experiments reveal that the theta rhythm during motor activity does not represent an intention, but rather the ongoing sensory-motor state.
虽然通过对脑干核团脚桥核（PPN）进行光遗传学刺激可以使啮齿动物的运动暂停，但尚不清楚这种反应是否具有功能目的。这种静止状态与恐惧引起的僵住行为明显相似，可能构成一种没有情感成分的运动普遍停止机制。此外，尚不清楚诱发的运动停止对大脑活动的影响程度。在此，我们通过引入一种独特的大脑活动——海马θ节律来研究这一现象。θ节律在运动活动期间很突出，在正常静止状态下不存在，但在恐惧引起的僵住等警觉状态下存在。具体而言，我们要问的是，PPN诱导的运动停止对θ节律的影响，是否与动物主动停止运动时相同，主动停止运动会导致θ节律消失；或者是否会像恐惧诱导的运动停止那样导致θ节律持续。另一种假设是，θ节律代表的是持续的运动意图而非运动本身。为了区分这两种可能性，我们记录了大鼠在接受PPN光遗传学刺激诱导运动停止之前和期间的海马脑节律。PPN诱导的运动停止与正在进行的θ活动明显受阻有关。运动停止的时间尺度小于200毫秒，与θ节律受阻情况相似。由于恐惧和行为僵住与海马θ节律有关，而我们在PPN刺激期间未观察到这种情况，我们认为诱导的运动停止发生时没有相关的情感成分。此外，我们的实验表明，运动活动期间的θ节律并不代表一种意图，而是代表正在进行的感觉运动状态。
