2014年3月31日月曜日

Changing value through cued approach: an automatic mechanism of behavior change

Tom Schonberg, Akram Bakkour, Ashleigh M Hover, Jeanette A Mumford, Lakshya Nagar, Jacob Perez & Russell A Poldrack
Nature Neuroscience 17, 625–630 (2014)

「ある商品を見せられると同時に音が鳴り,素早くボタンを押すことが求められる」という実験課題.
それだけで、その商品に対する主観的価値(評価)が上昇する.
また,価値をコードしている脳部位(vmPFC:前頭前野内腹側部)の活動もそれに対応して変化する.

It is believed that choice behavior reveals the underlying value of goods. The subjective values of stimuli can be changed through reward-based learning mechanisms as well as by modifying the description of the decision problem, but it has yet to be shown that preferences can be manipulated by perturbing intrinsic values of individual items. Here we show that the value of food items can be modulated by the concurrent presentation of an irrelevant auditory cue to which subjects must make a simple motor response (i.e., cue-approach training). Follow-up tests showed that the effects of this pairing on choice lasted at least 2 months after prolonged training. Eye-tracking during choice confirmed that cue-approach training increased attention to the cued items. Neuroimaging revealed the neural signature of a value change in the form of amplified preference-related activity in ventromedial prefrontal cortex.

2014年3月24日月曜日

The Good, the Bad, and the Just: Justice Sensitivity Predicts Neural Response during Moral Evaluation of Actions Performed by Others

Keith J. Yoder and Jean Decety
J. Neurosci. 2014;34 4161-4166

質問紙で測定した「Justice Sensitivity(日本語訳は?)」は、道徳判断課題中の「右・側頭頭頂接合部(rTPJ)、背側前頭前野(dlPFC、dmPFC)」における脳活動と相関する。

Morality is a fundamental component of human cultures and has been defined as prescriptive norms regarding how people should treat one another, including concepts such as justice, fairness, and rights. Using fMRI, the current study examined the extent to which dispositions in justice sensitivity (i.e., how individuals react to experiences of injustice and unfairness) predict behavioral ratings of praise and blame and how they modulate the online neural response and functional connectivity when participants evaluate morally laden (good and bad) everyday actions. Justice sensitivity did not impact the neuro-hemodynamic response in the action-observation network but instead influenced higher-order computational nodes in the right temporoparietal junction (rTPJ), right dorsolateral and dorsomedial prefrontal cortex (rdlPFC, dmPFC) that process mental states understanding and maintain goal representations. Activity in these regions predicted praise and blame ratings. Further, the hemodynamic response in rTPJ showed a differentiation between good and bad actions 2 s before the response in rdlPFC. Evaluation of good actions was specifically associated with enhanced activity in dorsal striatum and increased the functional coupling between the rTPJ and the anterior cingulate cortex. Together, this study provides important knowledge in how individual differences in justice sensitivity impact neural computations that support psychological processes involved in moral judgment and mental-state reasoning.

2014年3月20日木曜日

Dorsal Raphe Neurons Signal Reward through 5-HT and Glutamate

Zhixiang Liu, Jingfeng Zhou, Yi Li, Fei Hu, Yao Lu, Ming Ma, Qiru Feng, Ju-en Zhang, Daqing Wang, Jiawei Zeng, Junhong Bao, Ji-Young Kim, Zhou-Feng Chen, Salah El Mestikawy, Minmin Luo
Neuron, Volume 81, Issue 6, 1360-1374, 19 March 2014

光遺伝学(オプトジェネティクス)。
中脳背側縫線核(midbrain dorsal raphe nucleus)に存在するセロトニン・ニューロンは報酬に反応する。
(従来の理論研究では「セロトニン・ニューロンは(ドーパミンニューロンとは逆に)報酬ではなく罰に反応する」と考えられていた。)

The dorsal raphe nucleus (DRN) in the midbrain is a key center for serotonin (5-hydroxytryptamine; 5-HT)-expressing neurons. Serotonergic neurons in the DRN have been theorized to encode punishment by opposing the reward signaling of dopamine neurons. Here, we show that DRN neurons encode reward, but not punishment, through 5-HT and glutamate. Optogenetic stimulation of DRN Pet-1 neurons reinforces mice to explore the stimulation-coupled spatial region, shifts sucrose preference, drives optical self-stimulation, and directs sensory discrimination learning. DRN Pet-1 neurons increase their firing activity during reward tasks, and this activation can be used to rapidly change neuronal activity patterns in the cortex. Although DRN Pet-1 neurons are often associated with 5-HT, they also release glutamate, and both neurotransmitters contribute to reward signaling. These experiments demonstrate the ability of DRN neurons to organize reward behaviors and might provide insights into the underlying mechanisms of learning facilitation and anhedonia treatment.