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The Journal of Neuroscience, November 18, 2009, 29(46):14463-14471; doi:10.1523/JNEUROSCI.1786-09.2009

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Behavioral/Systems/Cognitive
Default Mode of Brain Activity Demonstrated by Positron Emission Tomography Imaging in Awake Monkeys: Higher Rest-Related than Working Memory-Related Activity in Medial Cortical Areas

Takashi Kojima,¹ Hirotaka Onoe,^1,2 Kazuo Hikosaka,^1,3 Ken-ichiro Tsutsui,⁴ Hideo Tsukada,⁵ and Masataka Watanabe¹

¹Department of Psychology, Tokyo Metropolitan Institute for Neuroscience, Fuchu, Tokyo, 183-8526, Japan, ²Functional Probe Research Laboratory, RIKEN Center for Molecular Imaging Research Science, Chuo-ku, Kobe, 650-0047, Japan, ³Department of Sensory Science, Faculty of Health Science and Technology, Kawasaki University of Medical Welfare, Kurashiki, 701-0193, Japan, ⁴Division of Systems Neuroscience, Tohoku University Graduate School of Life Sciences, Aoba-ku, Sendai, 980-8577, Japan, and ⁵Central Research Laboratory, Hamamatsu Photonics K.K., Hamakita-ku, Hamamatsu, 434-8601, Japan

Correspondence should be addressed to Masataka Watanabe, Department of Psychology, Tokyo Metropolitan Institute for Neuroscience, 2-6 Musashidai, Fuchu, Tokyo, 183-8526, Japan. Email: watanabe-ms{at}igakuken.or.jp

Human neuroimaging studies have demonstrated the presence of a "default system" in the brain, which shows a "default mode of brain activity," i.e., greater activity during the resting state than during an attention-demanding cognitive task. The default system mainly involves the medial prefrontal and medial parietal areas, including the anterior and posterior cingulate cortex. It has been proposed that this default activity is concerned with internal thought processes. Recently, it has been indicated that chimpanzees show high metabolic levels in these medial brain areas during rest. Correlated low-frequency spontaneous activity as measured by functional magnetic resonance imaging was observed between the medial parietal and medial prefrontal areas in the anesthetized monkey. However, there have been few attempts to demonstrate a default system that shows task-induced deactivation in nonhuman primates. We conducted a positron emission tomography study with [¹⁵O]H₂O to demonstrate a default mode of brain activity in the awake monkey sitting on a primate chair. Macaque monkeys showed higher level of regional blood flow in these medial brain areas as well as lateral and orbital prefrontal areas during rest compared with that under a working memory task, suggesting the existence of internal thought processes in the monkey. However, during rest in the monkey, the highest level of blood flow relative to that in other brain regions was observed not in the default system but in the dorsal striatum, suggesting that regions with the highest cerebral blood flow during rest may differ depending on the resting condition and/or species.

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Received April 10, 2009; revised Sept. 4, 2009; accepted Sept. 21, 2009.

Correspondence should be addressed to Masataka Watanabe, Department of Psychology, Tokyo Metropolitan Institute for Neuroscience, 2-6 Musashidai, Fuchu, Tokyo, 183-8526, Japan. Email: watanabe-ms{at}igakuken.or.jp

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