Instituto de Fisiología Celular-Neurociencias, Universidad Nacional Autónoma de México, 04510 Mexico City, Mexico.
Proc Natl Acad Sci U S A. 2012 Dec 18;109(51):21093-8. doi: 10.1073/pnas.1219636110. Epub 2012 Dec 3.
The sensory thalamus is classically viewed as a relay station of sensory information to cortex, but recent studies suggest that it is sensitive to cognitive demands. There are, however, few experiments designed to test whether this is so. We addressed this problem by analyzing the responses of single neurons recorded in the somatosensory thalamus while trained monkeys reported a decision based on the comparison of two mechanical vibration frequencies applied sequentially to one fingertip. In this task, monkeys must hold the first stimulus frequency (f1) in working memory and compare it to the current sensory stimulus (f2) and must postpone the decision report until a cue triggers the decision motor report, i.e., whether f2 > f1 or f2 < f1. We found that thalamic somatosensory neurons encoded the stimulus frequency either in their periodicity and firing-rate responses, but only during the stimulus periods and not during the working memory and decision components of this task. Furthermore, correlation analysis between behavior and stimulus coding showed that only the firing rate modulations accounted for the overall psychophysical performance. However, these responses did not predict the animal's decision reports on individual trials. Moreover, the sensitivity to changes in stimulus frequency was similar when the monkeys performed the vibrotactile discrimination task and when they were not required to report discrimination. These results suggest that the somatosensory thalamus behaves as a relay station of sensory information to the cortex and that it is insensitive to the cognitive demands of the task used here.
经典观点认为感觉丘脑是感觉信息向皮层传递的中继站，但最近的研究表明，它对认知需求敏感。然而，很少有实验旨在检验这是否属实。我们通过分析在训练猴子报告基于比较施加到一个指尖的两个机械振动频率的决策时记录的感觉丘脑中的单个神经元的反应来解决这个问题。在这个任务中，猴子必须在工作记忆中保持第一个刺激频率（f1），并将其与当前的感觉刺激（f2）进行比较，并且必须等到提示触发决策运动报告，即 f2>f1 还是 f2<f1 时才报告决策。我们发现，丘脑感觉神经元以其周期性和放电率反应来编码刺激频率，但仅在刺激期间，而不在该任务的工作记忆和决策部分。此外，行为与刺激编码之间的相关分析表明，只有放电率调制才能解释整体心理物理性能。然而，这些反应并不能预测动物在个别试验中的决策报告。此外，当猴子执行振动触觉辨别任务时，以及当它们不需要报告辨别时，对刺激频率变化的敏感性相似。这些结果表明，感觉丘脑表现为感觉信息向皮层传递的中继站，并且对这里使用的任务的认知需求不敏感。
