title: Neural mechanisms underlying the reward-related enhancement of motivation when remembering episodic memories with high difficulty.
abstract: The motivation to receive rewards enhances episodic memories, and the motivation is modulated by task difficulty. In episodic retrieval, however, functional neuroimaging evidence regarding the motivation that mediates interactions between reward and task difficulty is scarce. The present fMRI study investigated this issue. During encoding performed without fMRI, participants encoded Japanese words using either deep or shallow strategies, which led to variation in difficulty level during subsequent retrieval. During retrieval with fMRI, participants recognized the target words in either high or low monetary reward conditions. In the behavioral results, a reward-related enhancement of memory was found only when the memory retrieval was difficult, and the rewarding effect on subjective motivation was greater in the retrieval of memories with high difficulty than those with low difficulty. The fMRI data showed that reward-related increases in the activation of the substantia nigra/ventral tegmental area (SN/VTA), medial temporal lobe (MTL), dorsomedial prefrontal cortex (dmPFC), and dorsolateral prefrontal cortex (dlPFC) were greater during the retrieval of memories with high difficulty than those with low difficulty. Furthermore, reward-related enhancement of functional connectivity between the SN/VTA and MTL and between the SN/VTA and dmPFC during the retrieval of memories with high difficulty was significantly correlated with reward-related increases of retrieval accuracy and subjective motivation. The reward-related enhancement of episodic retrieval and retrieval-related motivation could be most effective when the level of retrieval difficulty is optimized. Such reward-related enhancement of memory and motivation could be modulated by a network including the reward-related SN/VTA, motivation-related dmPFC, and memory-related MTL. Hum Brain Mapp 38:3428-3443, 2017. © 2017 Wiley Periodicals, Inc.
authors.affiliation: Department of Functional Brain Imaging, Institute of Development, Aging and Cancer (IDAC), Tohoku University, Sendai, 980-8575, Japan.|Department of Cognitive and Behavioral Sciences, Graduate School of Human and Environmental Studies, Kyoto University, Kyoto, 606-8501, Japan.
authors.forename: Yayoi
authors.identifier: http://orcid.org/0000-0001-8220-2981
authors.initials: Y
authors.lastname: Shigemune
authors.affiliation: Department of Functional Brain Imaging, Institute of Development, Aging and Cancer (IDAC), Tohoku University, Sendai, 980-8575, Japan.|Department of Cognitive and Behavioral Sciences, Graduate School of Human and Environmental Studies, Kyoto University, Kyoto, 606-8501, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Tsukiura
authors.affiliation: Creative Interdisciplinary Research Division, Frontier Research Institute for Interdisciplinary Science (FRIS), Tohoku University, Sendai, 980-8578, Japan.|Smart Ageing International Research Center (SAIRAC), Institute of Development, Aging and Cancer (IDAC), Tohoku University, Sendai, 980-8575, Japan.|Human and Social Response Research Division, International Research Institute of Disaster Science (IRIDeS), Tohoku University, Sendai, 980-8575, Japan.
authors.forename: Rui
authors.initials: R
authors.lastname: Nouchi
authors.affiliation: Department of Functional Brain Imaging, Institute of Development, Aging and Cancer (IDAC), Tohoku University, Sendai, 980-8575, Japan.
authors.forename: Toshimune
authors.initials: T
authors.lastname: Kambara
authors.affiliation: Department of Functional Brain Imaging, Institute of Development, Aging and Cancer (IDAC), Tohoku University, Sendai, 980-8575, Japan.|Smart Ageing International Research Center (SAIRAC), Institute of Development, Aging and Cancer (IDAC), Tohoku University, Sendai, 980-8575, Japan.
authors.forename: Ryuta
authors.initials: R
authors.lastname: Kawashima
keywords: dorsolateral prefrontal cortex; dorsomedial prefrontal cortex; episodic memory; fMRI; hippocampus; retrieval; reward; substantia nigra; task difficulty; ventral tegmental area