2015年7月15日水曜日

Reward Pays the Cost of Noise Reduction in Motor and Cognitive Control

Sanjay G. Manohar, Trevor T.-J. Chong, Matthew A.J. Apps, Amit Batla, Maria Stamelou, Paul R. Jarman, Kailash P. Bhatia, Masud Husain

Current Biology
Volume 25, Issue 13, p1707–1716, 29 June 2015

報酬を与えることで、被験者は(コストを掛けて)運動/知覚のノイズを軽減し、それが運動のスピードと正確さの両方を改善する。

Speed-accuracy trade-off is an intensively studied law governing almost all behavioral tasks across species. Here we show that motivation by reward breaks this law, by simultaneously invigorating movement and improving response precision. We devised a model to explain this paradoxical effect of reward by considering a new factor: the cost of control. Exerting control to improve response precision might itself come at a cost—a cost to attenuate a proportion of intrinsic neural noise. Applying a noise-reduction cost to optimal motor control predicted that reward can increase both velocity and accuracy. Similarly, application to decision-making predicted that reward reduces reaction times and errors in cognitive control. We used a novel saccadic distraction task to quantify the speed and accuracy of both movements and decisions under varying reward. Both faster speeds and smaller errors were observed with higher incentives, with the results best fitted by a model including a precision cost. Recent theories consider dopamine to be a key neuromodulator in mediating motivational effects of reward. We therefore examined how Parkinson’s disease (PD), a condition associated with dopamine depletion, alters the effects of reward. Individuals with PD showed reduced reward sensitivity in their speed and accuracy, consistent in our model with higher noise-control costs. Including a cost of control over noise explains how reward may allow apparent performance limits to be surpassed. On this view, the pattern of reduced reward sensitivity in PD patients can specifically be accounted for by a higher cost for controlling noise.

2015年7月14日火曜日

Single-trial spike trains in parietal cortex reveal discrete steps during decision-making

Kenneth W. Latimer, Jacob L. Yates, Miriam L. R. Meister, Alexander C. Huk, Jonathan W. Pillow
Science 10 July 2015: Vol. 349 no. 6244 pp. 184-187

知覚的意思決定において、LIPニューロンの活動は「連続的に徐々に蓄積される情報を反映している」とされていたが、むしろ「情報の蓄積に対して離散的(情報が蓄積するとジャンプが起きる)に反応する」ことが分かった。

Neurons in the macaque lateral intraparietal (LIP) area exhibit firing rates that appear to ramp upward or downward during decision-making. These ramps are commonly assumed to reflect the gradual accumulation of evidence toward a decision threshold. However, the ramping in trial-averaged responses could instead arise from instantaneous jumps at different times on different trials. We examined single-trial responses in LIP using statistical methods for fitting and comparing latent dynamical spike-train models. We compared models with latent spike rates governed by either continuous diffusion-to-bound dynamics or discrete “stepping” dynamics. Roughly three-quarters of the choice-selective neurons we recorded were better described by the stepping model. Moreover, the inferred steps carried more information about the animal’s choice than spike counts.

2015年7月13日月曜日

Oxytocin Mediates Entrainment of Sensory Stimuli to Social Cues of Opposing Valence

Han Kyoung Choe, Michael Douglas Reed, Nora Benavidez, Daniel Montgomery, Natalie Soares, Yeong Shin Yim, Gloria B. Choi
Neuron. Volume 87, Issue 1, 1 July 2015, Pages 152–163

オキシトシンは「刺激と社会的報酬(異性に近付ける)の連合学習」に重要な役割を果たす。

Meaningful social interactions modify behavioral responses to sensory stimuli. The neural mechanisms underlying the entrainment of neutral sensory stimuli to salient social cues to produce social learning remain unknown. We used odor-driven behavioral paradigms to ask if oxytocin, a neuropeptide implicated in various social behaviors, plays a crucial role in the formation of learned associations between odor and socially significant cues. Through genetic, optogenetic, and pharmacological manipulations, we show that oxytocin receptor signaling is crucial for entrainment of odor to social cues but is dispensable for entrainment to nonsocial cues. Furthermore, we demonstrate that oxytocin directly impacts the piriform, the olfactory sensory cortex, to mediate social learning. Lastly, we provide evidence that oxytocin plays a role in both appetitive and aversive social learning. These results suggest that oxytocin conveys saliency of social stimuli to sensory representations in the piriform cortex during odor-driven social learning.