2013年11月26日火曜日

Regulation of dietary choice by the decision-making circuitry

Antonio Rangel
Nature Neuroscience 16, 1717–1724 (2013)

「ダイエット」について「脳神経システムと計算論」の観点から論じた総説論文。

To advance our understanding of how the brain makes food decisions, it is essential to combine knowledge from two fields that have not yet been well integrated: the neuro-computational basis of decision-making and the homeostatic regulators of feeding. This Review integrates these two literatures from a neuro-computational perspective, with an emphasis in describing the variables computed by different neural systems and how they affect dietary choice. We highlight what is unique about feeding decisions, the mechanisms through which metabolic and endocrine factors affect the decision-making circuitry, why making healthy food choices is difficult for many people, and key processes at work in the obesity epidemic.

2013年11月25日月曜日

What's better for me? Fundamental role for lateral habenula in promoting subjective decision biases

Colin M Stopper & Stan B Floresco
Nature Neuroscience (2013) doi:10.1038/nn.3587

Lateral habenula (LHb) の活動を抑制すると、「コスト(報酬の遅延や不確実性)と利益に基づく意思決定」ができなくなる。
一方、単なる報酬量の大小に基づく意思決定はできる。
→ LHbは「利益とコスト計算して選択肢の価値を評価する」ことに関わっている。

The lateral habenula (LHb) is believed to convey an aversive or 'anti-reward' signal, but its contribution to reward-related action selection is unknown. We found that LHb inactivation abolished choice biases, making rats indifferent when choosing between rewards associated with different subjective costs and magnitudes, but not larger or smaller rewards of equal cost. Thus, instead of serving as an aversion center, the evolutionarily conserved LHb acts as a preference center that is integral for expressing subjective decision biases.

2013年11月21日木曜日

Distinct contributions of the amygdala and parahippocampal gyrus to suspicion in a repeated bargaining game.

Bhatt MA, Lohrenz T, Camerer CF, Montague PR.
Proc Natl Acad Sci U S A. 2012 May 29;109(22):8728-33.

Bargaining GameのfMRI研究。
「他人の戦略をベイズ的に予想する」モデルを被験者の行動にフィット。
「他者の行動のバラつき」、「他者戦略推定の不確実性」がそれぞれ扁桃体と海馬で保持されている。

Humans assess the credibility of information gained from others on a daily basis; this ongoing assessment is especially crucial for avoiding exploitation by others. We used a repeated, two-person bargaining game and a cognitive hierarchy model to test how subjects judge the information sent asymmetrically from one player to the other. The weight that they give to this information is the result of two distinct factors: their baseline suspicion given the situation and the suspicion generated by the other person's behavior. We hypothesized that human brains maintain an ongoing estimate of the credibility of the other player and sought to uncover neural correlates of this process. In the game, sellers were forced to infer the value of an object based on signals sent from a prospective buyer. We found that amygdala activity correlated with baseline suspicion, whereas activations in bilateral parahippocampus correlated with trial-by-trial uncertainty induced by the buyer's sequence of suggestions. In addition, the less credible buyers that appeared, the more sensitive parahippocampal activation was to trial-by-trial uncertainty. Although both of these neural structures have previously been implicated in trustworthiness judgments, these results suggest that they have distinct and separable roles that correspond to their theorized roles in learning and memory.

2013年11月17日日曜日

Safety Signals in the Primate Amygdala

Rotem Genud-Gabai, Oded Klavir, and Rony Paz
J. Neurosci. 2013;33 17986-17994

扁桃体(Amygdala)のニューロンは「安全性/危険性」をコードしている。
扁桃体がうまく働かないと安全な状況と危険な状況がうまく区別できず、それが不安障害などの原因になっているのでは?

The ability to distinguish danger from safety is crucial for survival. On the other hand, anxiety disorders can result from failures to dissociate safe cues from those that predict dangerous outcomes. The amygdala plays a major role in learning and signaling danger, and recently, evidence accumulates that it also acquires information to signal safety. Traditionally, safety is explored by paradigms that change the value of a previously dangerous cue, such as extinction or reversal; or by paradigms showing that a safe cue can inhibit responses to another danger-predicting cue, as in conditioned-inhibition. In real-life scenarios, many cues are never paired or tested with danger and remain neutral all along. A detailed study of neural responses to unpaired conditioned-stimulus (CS−) can therefore indicate whether information on safety-by-comparison is also acquired in the amygdala. We designed a multiple-CS study, with CS− from both visual and auditory modalities. Using discriminative aversive-conditioning, we find that responses in the primate amygdala develop for CS− of the same modality and of a different modality from that of the aversive CS+. Moreover, we find that responses are comparable in proportion, sign (increase/decrease), onset, and magnitude. These results indicate that the primate amygdala actively acquires signals about safety, and strengthen the hypothesis that failure in amygdala processing can result in failure to distinguish dangerous cues from safe ones and lead to maladaptive behaviors.

2013年11月14日木曜日

Changing Social Norm Compliance with Noninvasive Brain Stimulation

C. C. Ruff, G. Ugazio, E. Fehr,
Science 25 October 2013: Vol. 342 no. 6157 pp. 482-484

ヒトの「社会規範の遵守」の神経基盤。
tDCSによって「右前頭前野背外側部(rDLPFC)」を刺激すると、被験者の「社会規範遵守に関する行動」が変化する。
一方、社会規範に関する「判断」は変わらない。

All known human societies have maintained social order by enforcing compliance with social norms. The biological mechanisms underlying norm compliance are, however, hardly understood. We show that the right lateral prefrontal cortex (rLPFC) is involved in both voluntary and sanction-induced norm compliance. Both types of compliance could be changed by varying the neural excitability of this brain region with transcranial direct current stimulation, but they were affected in opposite ways, suggesting that the stimulated region plays a fundamentally different role in voluntary and sanction-based compliance. Brain stimulation had a particularly strong effect on compliance in the context of socially constituted sanctions, whereas it left beliefs about what the norm prescribes and about subjectively expected sanctions unaffected. Our findings suggest that rLPFC activity is a key biological prerequisite for an evolutionarily and socially important aspect of human behavior.

2013年11月13日水曜日

Single-Neuron Mechanisms Underlying Cost-Benefit Analysis in Frontal Cortex

Takayuki Hosokawa, Steven W. Kennerley, Jennifer Sloan, and Jonathan D. Wallis
J. Neurosci. 2013;33 17385-17397

サルが報酬を得るために「努力が必要な課題」、「単に一定時間待てばよい課題」を行う。
前頭前野(OFC、DLPFC)の多くのニューロンが、「どちらの課題をやっているのか」という情報をコードしていた。
→ これらの部位は「意思決定における価値」ではなく「状況のカテゴリー分け」に関わっているのでは?

Effective decision-making requires consideration of costs and benefits. Previous studies have implicated orbitofrontal cortex (OFC), dorsolateral prefrontal cortex (DLPFC), and anterior cingulate cortex (ACC) in cost-benefit decision-making. Yet controversy remains about whether different decision costs are encoded by different brain areas, and whether single neurons integrate costs and benefits to derive a subjective value estimate for each choice alternative. To address these issues, we trained four subjects to perform delay- and effort-based cost-benefit decisions and recorded neuronal activity in OFC, ACC, DLPFC, and the cingulate motor area (CMA). Although some neurons, mainly in ACC, did exhibit integrated value signals as if performing cost-benefit computations, they were relatively few in number. Instead, the majority of neurons in all areas encoded the decision type; that is whether the subject was required to perform a delay- or effort-based decision. OFC and DLPFC neurons tended to show the largest changes in firing rate for delay- but not effort-based decisions; whereas, the reverse was true for CMA neurons. Only ACC contained neurons modulated by both effort- and delay-based decisions. These findings challenge the idea that OFC calculates an abstract value signal to guide decision-making. Instead, our results suggest that an important function of single PFC neurons is to categorize sensory stimuli based on the consequences predicted by those stimuli.

2013年11月8日金曜日

アメリカで歯医者 Vol. 1

ついにこの日がやってきてしまいました。
渡米一年を過ぎた秋の穏やかな日、突如として猛烈な歯痛に襲われました。
ロキソニンも効かず、一晩中眠れず、冗談じゃなくて「死んだ方がマシ!!!」と何度も思いました。

というわけで、悪名高い「アメリカの歯医者」へGO…

ここで、歯痛時の状況諸々を確認。
渡米前に日本で、四週連続の親不知抜歯も含めて歯の治療は終えてきました(つもりでした…)。
また、職場の歯科治療保険には加入していました(アメリカでは通常の医療保険と歯科保険は別です)。
加入している保険は「Delta Dental PPO」。
「PPOなので自由に医者を選べる」+「カバー率は最初の診断や定期健診は100%、簡単な治療は80%、根幹治療やブリッジなど高価なものは50%」と、(アメリカの基準では)まあまあ悪くない保険です。
注1:他にも色々と細かい条件はあります。
注2:お分かりのように、アメリカの歯科保険では「健診や簡単な治療ほどカバー率が高い」です。なので、みんな幼い頃から普段のメンテナンスに熱心です。
注3:保険料は大学(ボス)と折半で月15ドルくらいです。

痛くて切羽詰まっていたのでじっくりと歯医者を選ぶ余裕もなく、ラボの同僚お薦めの歯医者へアポを入れる。
ネットでは「アポは数週間後しか取れなかった」とか色々書いてあってガクブルでしたが、すんなり翌日のアポが取れました。
選んだのはここ↓
http://www.pasadenafamilydental.com/
治療は始まったばかりですが、普通っぽいです。
他との比較はできませんが、特に不満はないですね。
(治療が終わったら、続編を書きます。たぶん…)

最初は色々と書類書き。
・保険証
・身分証明書(免許証でOK)
・SSN(番号が分かればOK)
が必要でした。
それらの情報を基に、受付の人が保険会社に電話して加入状況を確認。

その後は、分厚い同意書を渡され、それを熟読。コンピュータの画面上でサインをしました。

そしていよいよ診察室へ。
念入りにレントゲンを撮られる。
(アメリカの歯医者では診察椅子に座ったままレントゲンを撮ります。楽でいい!)
その後、ドクターが登場して、色々と質問される。

そして運命の宣告。
ドクター曰く、
・日本で処置したブリッジの下の歯に大きな虫歯があり、根幹治療が必要。
・当然、ブリッジも作り直す必要がある。
そして、総額は3000ドル!30万円!
保険で色々カバーされるけど、1300ドル程度の支払いが必要…ホントに凹みます。

何が高いって、ブリッジが高いみたいです…
まず、仮のモノを作って一ヶ月ほど試し、その後に本物を作るらしいです。
ちなみに普通の被せ物(クラウン)なら、合計で1000ドル強、実際の支払いも500ドル強で済むらしいです…

治療自体は、まずは根幹治療からスタート。
日本と同じような感じでした。
麻酔 → 歯を削る → 根幹を掃除 → 薬を詰めて仮止めをするという感じで、一時間弱で終わりました。
その日は痛み止めを飲みましたが、翌日には痛みも納まり全く問題なかったです。

最後に、料金(今回の根幹治療の分)を払って終了でした。
疲れた。。。

というわけで治療はまだまだ続きます。
歯科保険、絶対に入っておいた方が良いですよ!!!

追伸:
そうそう、そう言えば、処方箋をもらって薬局に抗生物質と痛み止めを買いに行ったのですが、医療保険(歯科保険ではなく)が効きました。
保険証を持って行った方が吉です。

2013年11月7日木曜日

Atypical Combinations and Scientific Impact

Brian Uzzi, Satyam Mukherjee, Michael Stringer, Ben Jones,
Science 25 October 2013: Vol. 342 no. 6157 pp. 468-472

あらゆる分野の研究論文、17,900,000篇を調査。
インパクトのある研究論文は「既存の知見」を基盤に「新規の知見」を報告している(新しい知見だけではダメ)ことが分かった。

Novelty is an essential feature of creative ideas, yet the building blocks of new ideas are often embodied in existing knowledge. From this perspective, balancing atypical knowledge with conventional knowledge may be critical to the link between innovativeness and impact. Our analysis of 17.9 million papers spanning all scientific fields suggests that science follows a nearly universal pattern: The highest-impact science is primarily grounded in exceptionally conventional combinations of prior work yet simultaneously features an intrusion of unusual combinations. Papers of this type were twice as likely to be highly cited works. Novel combinations of prior work are rare, yet teams are 37.7% more likely than solo authors to insert novel combinations into familiar knowledge domains.

2013年11月6日水曜日

War, space, and the evolution of Old World complex societies

Peter Turchin, Thomas E. Currie, Edward A. L. Turner, and Sergey Gavrilets
PNAS October 8, 2013 vol. 110 no. 41 16384-16389

ヒトの社会の発展を実際の地形上でシミュレーションしてみましたよ、という研究。

How did human societies evolve from small groups, integrated by face-to-face cooperation, to huge anonymous societies of today, typically organized as states? Why is there so much variation in the ability of different human populations to construct viable states? Existing theories are usually formulated as verbal models and, as a result, do not yield sharply defined, quantitative predictions that could be unambiguously tested with data. Here we develop a cultural evolutionary model that predicts where and when the largest-scale complex societies arose in human history. The central premise of the model, which we test, is that costly institutions that enabled large human groups to function without splitting up evolved as a result of intense competition between societies—primarily warfare. Warfare intensity, in turn, depended on the spread of historically attested military technologies (e.g., chariots and cavalry) and on geographic factors (e.g., rugged landscape). The model was simulated within a realistic landscape of the Afroeurasian landmass and its predictions were tested against a large dataset documenting the spatiotemporal distribution of historical large-scale societies in Afroeurasia between 1,500 BCE and 1,500 CE. The model-predicted pattern of spread of large-scale societies was very similar to the observed one. Overall, the model explained 65% of variance in the data. An alternative model, omitting the effect of diffusing military technologies, explained only 16% of variance. Our results support theories that emphasize the role of institutions in state-building and suggest a possible explanation why a long history of statehood is positively correlated with political stability, institutional quality, and income per capita.

2013年11月4日月曜日

Neural Estimates of Imagined Outcomes in the Orbitofrontal Cortex Drive Behavior and Learning

Yuji K. Takahashi, Chun Yun Chang, Federica Lucantonio, Richard Z. Haney, Benjamin A. Berg, Hau-Jie Yau, Antonello Bonci, Geoffrey Schoenbaum
Neuron, Volume 80, Issue 2, 507-518, 16 October 2013

眼窩前島皮質(OFC)のニューロンは「想像した報酬(Imagined Outcomes)」をコード。
また、そのコーディングの強さから、報酬学習のパフォーマンスを予測出来る。

Imagination, defined as the ability to interpret reality in ways that diverge from past experience, is fundamental to adaptive behavior. This can be seen at a simple level in our capacity to predict novel outcomes in new situations. The ability to anticipate outcomes never before received can also influence learning if those imagined outcomes are not received. The orbitofrontal cortex is a key candidate for where the process of imagining likely outcomes occurs; however, its precise role in generating these estimates and applying them to learning remain open questions. Here we address these questions by showing that single-unit activity in the orbitofrontal cortex reflects novel outcome estimates. The strength of these neural correlates predicted both behavior and learning, learning that was abolished by temporally specific inhibition of orbitofrontal neurons. These results are consistent with the proposal that the orbitofrontal cortex is critical for integrating information to imagine future outcomes.

2013年11月3日日曜日

A Critical Role for the Hippocampus in the Valuation of Imagined Outcomes

Maël Lebreton, Maxime Bertoux, Claire Boutet, Stéphane Lehericy, Bruno Dubois, Philippe Fossati, Mathias Pessiglione
PLoS Biol 11(10): e1001684. doi:10.1371/journal.pbio.1001684

将来の状況を詳細に思い浮かべると、将来の報酬を高く評価する。
さらに、その傾向は海馬の活動で説明できる。

Many choice situations require imagining potential outcomes, a capacity that was shown to involve memory brain regions such as the hippocampus. We reasoned that the quality of hippocampus-mediated simulation might therefore condition the subjective value assigned to imagined outcomes. We developed a novel paradigm to assess the impact of hippocampus structure and function on the propensity to favor imagined outcomes in the context of intertemporal choices. The ecological condition opposed immediate options presented as pictures (hence directly observable) to delayed options presented as texts (hence requiring mental stimulation). To avoid confounding simulation process with delay discounting, we compared this ecological condition to control conditions using the same temporal labels while keeping constant the presentation mode. Behavioral data showed that participants who imagined future options with greater details rated them as more likeable. Functional MRI data confirmed that hippocampus activity could account for subjects assigning higher values to simulated options. Structural MRI data suggested that grey matter density was a significant predictor of hippocampus activation, and therefore of the propensity to favor simulated options. Conversely, patients with hippocampus atrophy due to Alzheimer's disease, but not patients with Fronto-Temporal Dementia, were less inclined to favor options that required mental simulation. We conclude that hippocampus-mediated simulation plays a critical role in providing the motivation to pursue goals that are not present to our senses.