2013年9月25日水曜日

Neural Correlates of Interval Timing in Rodent Prefrontal Cortex

Jieun Kim, Jeong-Wook Ghim, Ji Hyun Lee, and Min Whan Jung
J. Neurosci. 2013;33 13834-13847
http://www.jneurosci.org/cgi/content/abstract/33/34/13834?etoc

【背景】
脳はどのように「時間情報」を処理しているのか?
線形?対数スケール?などなど、よく分かっていない。
先行研究により、「前頭葉内側部(mPFC)の働きを阻害すると、時間情報の処理に障害が起こる」ことが知られている。

【手法、結果】
この研究では、ラットを対象とした電気生理学的手法を用いて、mPFCと時間情報処理の関係を詳細に調べた。
その結果、「mPFCのニューロンは時間の情報を対数スケールで保持している」ことが分かった。
→ mPFCが主観的な時間を表す「こころの中の時計」の役割を果たしているのでは?

Time interval estimation is involved in numerous behavioral processes, but its underlying neural mechanisms remain unclear. In particular, it has been controversial whether time is encoded on a linear or logarithmic scale. Based on our previous finding that inactivation of the medial prefrontal cortex (mPFC) profoundly impairs rat's ability to discriminate time intervals, we investigated how the mPFC processes temporal information by examining activity of mPFC neurons in rats performing a temporal bisection task. Many mPFC neurons dconveyed temporal information based on monotonically changing activity profiles over time with negative accelerations, so that their activity profiles were better described by logarithmic than linear functions. Moreover, the precision of time-interval discrimination based on neural activity was lowered in proportion to the elapse of time, but without proportional increase in neural variability, which is well accounted for by logarithmic, but not by linear functions. As a population, mPFC neurons conveyed precise information about the elapse of time with their activity tightly correlated with the animal's choice of target. These results suggest that the mPFC might be part of an internal clock in charge of controlling interval-timing behavior, and that linearly changing neuronal activity on a logarithmic time scale might be one way of representing the elapse of time in the brain.

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