School of Biomedical Engineering Science and Health Systems, Drexel University Philadelphia, PA, USA.
Front Syst Neurosci. 2012 Sep 26;6:67. doi: 10.3389/fnsys.2012.00067. eCollection 2012.
The gradual buildup of neural activity over experimentally imposed delay periods, termed climbing activity, is well documented and is a potential mechanism by which interval time is encoded by distributed cortico-thalamico-striatal networks in the brain. Additionally, when multiple delay periods are incorporated, this activity has been shown to scale its rate of climbing proportional to the delay period. However, it remains unclear whether these patterns of activity occur within areas of motor cortex dedicated to hindlimb movement. Moreover, the effects of behavioral training (e.g., motor tasks) under different reward conditions but with similar behavioral output are not well addressed. To address this, we recorded activity from the hindlimb sensorimotor cortex (HLSMC) of two groups of rats performing a skilled hindlimb press task. In one group, rats were trained only to a make a valid press within a finite window after cue presentation for reward (non-interval trained, nIT; n = 5), while rats in the second group were given duration-specific cues in which they had to make presses of either short or long duration to receive reward (interval trained, IT; n = 6). Using perievent time histogram (PETH) analyses, we show that cells recorded from both groups showed climbing activity during the task in similar proportions (35% IT and 47% nIT), however, only climbing activity from IT rats was temporally scaled to press duration. Furthermore, using single trial decoding techniques (Wiener filter), we show that press duration can be inferred using climbing activity from IT animals (R = 0.61) significantly better than nIT animals (R = 0.507, p < 0.01), suggesting IT animals encode press duration through temporally scaled climbing activity. Thus, if temporal intervals are behaviorally relevant then the activity of climbing neurons is temporally scaled to encode the passage of time.
实验性地强加的延迟期间逐渐增加的神经活动，称为爬升活动，已有充分的记录，并且是大脑中分布式皮质丘脑纹状体网络对间隔时间进行编码的潜在机制。此外，当多个延迟期被合并时，已经表明这种活动的速率与其延迟期成比例地攀升。然而，尚不清楚这些活动模式是否发生在专门用于后肢运动的运动皮层区域内。此外，在不同奖励条件下但具有相似行为输出的行为训练（例如运动任务）的效果尚未得到很好的解决。为了解决这个问题，我们记录了执行熟练后肢按压任务的两组大鼠的后肢感觉运动皮层（HLSMC）的活动。在一组中，仅对大鼠进行了训练，使其在提示后有限的窗口内做出有效按压即可获得奖励（非间隔训练，nIT；n = 5），而第二组大鼠则接受了特定持续时间的提示，他们必须进行短或长的按压才能获得奖励（间隔训练，IT；n = 6）。使用事件时间直方图（PETH）分析，我们表明，来自两组的记录细胞在任务中以相似的比例表现出爬升活动（35％IT 和 47％nIT），但是，只有 IT 大鼠的爬升活动才与按压持续时间进行了时间缩放。此外，使用单试解码技术（Wiener 滤波器），我们表明，使用 IT 动物的爬升活动可以推断按压持续时间（R = 0.61），明显优于 nIT 动物（R = 0.507，p <0.01），这表明 IT 动物通过时间缩放的爬升活动来编码按压持续时间。因此，如果时间间隔在行为上是相关的，则攀爬神经元的活动将按时间缩放以编码时间的流逝。
