2014年2月24日月曜日

Contributions of Orbitofrontal and Lateral Prefrontal Cortices to Economic Choice and the Good-to-Action Transformation

Xinying Cai, and Camillo Padoa-Schioppa
Neuron, 13 February 2014

サル電気生理。
「二種類のモノ(例:リンゴとミカン)のうち、どちらかを得る」という状況では、
(1)まず、「どちらが欲しいのか(例:ミカンが欲しい)」を決め、
(2)その後、「欲しいものを得るための行動(例:右手を伸ばすしてミカンをとる)」を行う、
必要がある。
外側前頭前野は上記二つの過程の両方に関わっている。

Previous work indicates that economic decisions can be made independently of the visuomotor contingencies of the choice task (space of goods). However, the neuronal mechanisms through which the choice outcome (the chosen good) is transformed into a suitable action plan remain poorly understood. Here we show that neurons in lateral prefrontal cortex reflect the early stages of this good-to-action transformation. Monkeys chose between different juices. The experimental design dissociated in space and time the presentation of the offers and the saccade targets associated with them. We recorded from the orbital, ventrolateral, and dorsolateral prefrontal cortices (OFC, LPFCv, and LPFCd, respectively). Prior to target presentation, neurons in both LPFCv and LPFCd encoded the choice outcome in goods space. After target presentation, they gradually came to encode the location of the targets and the upcoming action plan. Consistent with the anatomical connectivity, all spatial and action-related signals emerged in LPFCv before LPFCd.

2014年2月23日日曜日

Dopamine prediction error responses integrate subjective value from different reward dimensions

Armin Lak, William R. Stauffer, and Wolfram Schultz
PNAS vol. 111 no. 6 2343–2348, doi: 10.1073/pnas.1321596111

ドーパミン神経細胞の活動は「様々な種類の刺激/報酬(色々な種類のジュース、不確実性を含んだ選択肢など)」の主観的価値に関する予測誤差をコードしている。

Prediction error signals enable us to learn through experience. These experiences include economic choices between different rewards that vary along multiple dimensions. Therefore, an ideal way to reinforce economic choice is to encode a prediction error that reflects the subjective value integrated across these reward dimensions. Previous studies demonstrated that dopamine prediction error responses reflect the value of singular reward attributes that include magnitude, probability, and delay. Obviously, preferences between rewards that vary along one dimension are completely determined by the manipulated variable. However, it is unknown whether dopamine prediction error responses reflect the subjective value integrated from different reward dimensions. Here, we measured the preferences between rewards that varied along multiple dimensions, and as such could not be ranked according to objective metrics. Monkeys chose between rewards that differed in amount, risk, and type. Because their choices were complete and transitive, the monkeys chose “as if” they integrated different rewards and attributes into a common scale of value. The prediction error responses of single dopamine neurons reflected the integrated subjective value inferred from the choices, rather than the singular reward attributes. Specifically, amount, risk, and reward type modulated dopamine responses exactly to the extent that they influenced economic choices, even when rewards were vastly different, such as liquid and food. This prediction error response could provide a direct updating signal for economic values.

2014年2月20日木曜日

Dopamine dependency for acquisition and performance of Pavlovian conditioned response

Martin Darvas, Amanda M. Wunsch, Jeffrey T. Gibbs, and Richard D. Palmiter
PNAS February 18, 2014 vol. 111 no. 7 2764–2769

古典的条件づけにおける"Goal tracking"行動にも、ドーパミンの活動が不可欠である。

【背景】
刺激・報酬の連合を十分に学習させた後に刺激を呈示すると、「刺激に近付いていく個体」と「報酬(が出現する場所)に近付いていく個体」がいる。
前者は"sign tracking"、後者は"goal tracking"と呼ばれるが、「goal trackingにドーパミンが必要か否か」はよく分かっていなかった。
http://www.nature.com/nature/journal/v469/n7328/abs/nature09588.html

During Pavlovian conditioning, pairing of a neutral conditioned stimulus (CS) with a reward leads to conditioned reward-approach responses (CRs) that are elicited by presentation of the CS. CR behaviors can be sign tracking, in which animals engage the CS, or goal tracking, in which animals go to the reward location. We investigated CR behaviors in mice with only ∼5% of normal dopamine in the striatum using a Pavlovian conditioning paradigm. These mice had severely impaired acquisition of the CR, which was ameliorated by pharmacological restoration of dopamine synthesis with L-dopa. Surprisingly, after they had learned the CR, its expression decayed only gradually in following sessions that were conducted without L-dopa treatment. To assess specific contributions of dopamine signaling in the dorsal or ventral striatum, we performed virus-mediated restoration of dopamine synthesis in completely dopamine-deficient (DD) mice. Mice with dopamine signaling only in the dorsal striatum did not acquire a CR, whereas mice with dopamine signaling only in in the ventral striatum acquired a CR. The CR in mice with dopamine signaling only in the dorsal striatum was restored by subjecting the mice to instrumental training in which they had to interact with the CS to obtain rewards. We conclude that dopamine is essential for learning and performance of CR behavior that is predominantly goal tracking. Furthermore, although dopamine signaling in the ventral striatum is sufficient to support a CR, dopamine signaling only in the dorsal striatum can also support a CR under certain circumstances.

2014年2月19日水曜日

Functional changes of the reward system underlie blunted response to social gaze in cocaine users

Katrin H. Preller, Marcus Herdener, Leonhard Schilbach, Philipp Stämpfli, Lea M. Hulka, Matthias Vonmoos, Nina Ingold, Kai Vogeley, Philippe N. Tobler, Erich Seifritz, and Boris B. Quednow
PNAS February 18, 2014 vol. 111 no. 7 2842–2847

コカイン常習者は社会性に様々な障害があるが、その神経科学的基盤は?
常習者は「社会的刺激に対する内側眼窩前頭野(mOFC)の活動」が弱い。

Social interaction deficits in drug users likely impede treatment, increase the burden of the affected families, and consequently contribute to the high costs for society associated with addiction. Despite its significance, the neural basis of altered social interaction in drug users is currently unknown. Therefore, we investigated basal social gaze behavior in cocaine users by applying behavioral, psychophysiological, and functional brain-imaging methods. In study I, 80 regular cocaine users and 63 healthy controls completed an interactive paradigm in which the participants’ gaze was recorded by an eye-tracking device that controlled the gaze of an anthropomorphic virtual character. Valence ratings of different eye-contact conditions revealed that cocaine users show diminished emotional engagement in social interaction, which was also supported by reduced pupil responses. Study II investigated the neural underpinnings of changes in social reward processing observed in study I. Sixteen cocaine users and 16 controls completed a similar interaction paradigm as used in study I while undergoing functional magnetic resonance imaging. In response to social interaction, cocaine users displayed decreased activation of the medial orbitofrontal cortex, a key region of reward processing. Moreover, blunted activation of the medial orbitofrontal cortex was significantly correlated with a decreased social network size, reflecting problems in real-life social behavior because of reduced social reward. In conclusion, basic social interaction deficits in cocaine users as observed here may arise from altered social reward processing. Consequently, these results point to the importance of reinstatement of social reward in the treatment of stimulant addiction.

2014年2月18日火曜日

Predicting risky choices from brain activity patterns

Sarah M. Helfinstein, Tom Schonberg, Eliza Congdon, Katherine H. Karlsgodt, Jeanette A. Mumford, Fred W. Sabb, Tyrone D. Cannon, Edythe D. London, Robert M. Bilder, and Russell A. Poldrack
PNAS February 18, 2014 vol. 111 no. 7 2470–2475

「認知制御に関わる脳部位の活動(fMRI信号)」から「リスク下の意思決定」を予測出来る。

Previous research has implicated a large network of brain regions in the processing of risk during decision making. However, it has not yet been determined if activity in these regions is predictive of choices on future risky decisions. Here, we examined functional MRI data from a large sample of healthy subjects performing a naturalistic risk-taking task and used a classification analysis approach to predict whether individuals would choose risky or safe options on upcoming trials. We were able to predict choice category successfully in 71.8% of cases. Searchlight analysis revealed a network of brain regions where activity patterns were reliably predictive of subsequent risk-taking behavior, including a number of regions known to play a role in control processes. Searchlights with significant predictive accuracy were primarily located in regions more active when preparing to avoid a risk than when preparing to engage in one, suggesting that risk taking may be due, in part, to a failure of the control systems necessary to initiate a safe choice. Additional analyses revealed that subject choice can be successfully predicted with minimal decrements in accuracy using highly condensed data, suggesting that information relevant for risky choice behavior is encoded in coarse global patterns of activation as well as within highly local activation within searchlights.

2014年2月13日木曜日

Dissociation between Neural Signatures of Stimulus and Choice in Population Activity of Human V1 during Perceptual Decision-Making

Kyoung Whan Choe, Randolph Blake, and Sang-Hun Lee
J. Neurosci. 2014;34 2725-2743 Open Access
http://www.jneurosci.org/cgi/content/abstract/34/7/2725?etoc

知覚的意思決定。
一次視覚野(V1)は「意思決定」に関する情報を保持しているか?
→ 「知覚」とか分離可能な形で保持している.

Primary visual cortex (V1) forms the initial cortical representation of objects and events in our visual environment, and it distributes information about that representation to higher cortical areas within the visual hierarchy. Decades of work have established tight linkages between neural activity occurring in V1 and features comprising the retinal image, but it remains debatable how that activity relates to perceptual decisions. An actively debated question is the extent to which V1 responses determine, on a trial-by-trial basis, perceptual choices made by observers. By inspecting the population activity of V1 from human observers engaged in a difficult visual discrimination task, we tested one essential prediction of the deterministic view: choice-related activity, if it exists in V1, and stimulus-related activity should occur in the same neural ensemble of neurons at the same time. Our findings do not support this prediction: while cortical activity signifying the variability in choice behavior was indeed found in V1, that activity was dissociated from activity representing stimulus differences relevant to the task, being advanced in time and carried by a different neural ensemble. The spatiotemporal dynamics of population responses suggest that short-term priors, perhaps formed in higher cortical areas involved in perceptual inference, act to modulate V1 activity prior to stimulus onset without modifying subsequent activity that actually represents stimulus features within V1.

2014年2月12日水曜日

Cortical Correlates of Human Motion Perception Biases

Brett Vintch and Justin L. Gardner
J. Neurosci. 2014;34 2592-2604
http://www.jneurosci.org/cgi/content/abstract/34/7/2592?etoc

理研時代にものすごくお世話になった Justinの論文.
「動く物体のスピードを知覚する際に存在する偏り」とそれに対応する一次視覚野(V1)の活動。
デコーディング,forward-encoding解析などを使用。

Human sensory perception is not a faithful reproduction of the sensory environment. For example, at low contrast, objects appear to move slower and flicker faster than veridical. Although these biases have been observed robustly, their neural underpinning is unknown, thus suggesting a possible disconnect of the well established link between motion perception and cortical responses. We used functional imaging to examine the encoding of speed in the human cortex at the scale of neuronal populations and asked where and how these biases are encoded. Decoding, voxel population, and forward-encoding analyses revealed biases toward slow speeds and high temporal frequencies at low contrast in the earliest visual cortical regions, matching perception. These findings thus offer a resolution to the disconnect between cortical responses and motion perception in humans. Moreover, biases in speed perception are considered a leading example of Bayesian inference because they can be interpreted as a prior for slow speeds. Therefore, our data suggest that perceptual priors of this sort can be encoded by neural populations in the same early cortical areas that provide sensory evidence.

2014年2月10日月曜日

Neural Computations Underlying Arbitration between Model-Based and Model-free Learning

Sang Wan Lee, Shinsuke Shimojo, John P. O'Doherty
Neuron, Volume 81, Issue 3, 687-699, 5 February 2014

Neuron誌より、同僚のSangWanの論文。「モデル・フリー学習とモデル・ベースド学習、どちらを使うか」をどうやって決めているのか?という話。

There is accumulating neural evidence to support the existence of two distinct systems for guiding action selection, a deliberative “model-based” and a reflexive “model-free” system. However, little is known about how the brain determines which of these systems controls behavior at one moment in time. We provide evidence for an arbitration mechanism that allocates the degree of control over behavior by model-based and model-free systems as a function of the reliability of their respective predictions. We show that the inferior lateral prefrontal and frontopolar cortex encode both reliability signals and the output of a comparison between those signals, implicating these regions in the arbitration process. Moreover, connectivity between these regions and model-free valuation areas is negatively modulated by the degree of model-based control in the arbitrator, suggesting that arbitration may work through modulation of the model-free valuation system when the arbitrator deems that the model-based system should drive behavior.