神経符号における時間的精度と自然な視覚の時間スケール

Correlation between neural spike trains increases with firing rate

de la Rocha J, Doiron B, Shea-Brown E, Josi K, Reyes A.

Nature. 2007 Aug 16;448(7155):802-6.

• たとえ入力間の相関が不変のままでも、発火率の上昇に伴ってスパイク列出力間の相関は増大するが、スパイク列の変動にはほとんど影響を受けない。
• 出力相関と発火率との関係はロバストで入力の変化によって影響を受けにくい

新奇な刺激に触れることが発達に重要

Programming social, cognitive, and neuroendocrine development by early exposure to novelty

Tang AC, Akers KG, Reeb BC, Romeo RD, McEwen BS.

Proc Natl Acad Sci U S A. 2006 Oct 9; [Epub ahead of print]

Mildly stressful early life experiences can potentially impact a broad range of social, cognitive, and physiological functions in humans, nonhuman primates, and rodents. Recent rodent studies favor a maternal-mediation hypothesis that considers maternal-care differences induced by neonatal stimulation as the cause of individual differences in offspring development. Using neonatal novelty exposure, a neonatal stimulation paradigm that dissociates maternal individual differences from a direct stimulation effect on the offspring, we investigated the effect of early exposures to novelty on a diverse range of psychological functions using several assessment paradigms. Pups that received brief neonatal novelty exposures away from the home environment showed enhancement in spatial working memory, social competition, and corticosterone response to surprise during adulthood compared with their home-staying siblings. These functional enhancements in novelty-exposed rats occurred despite evidence that maternal care was directed preferentially toward home-staying instead of novelty-exposed pups, indicating that greater maternal care is neither necessary nor sufficient for these early stimulation-induced functional enhancements. We suggest a unifying maternal-modulation hypothesis, which distinguishes itself from the maternal-mediation hypothesis in that (i) neonatal stimulation can have direct effects on pups, cumulatively leading to long-term improvement in adult offspring; and (ii) maternal behavior can attenuate or potentiate these effects, thereby decreasing or increasing this long-term functional improvement.

幼少期の経験がどう発達に影響するかについて。従来の Maternal-Mediation Hypothesis は親からのケアの違いが発達に影響をもたらすと考えていたが、新奇な刺激に触れることのほうが種々の発達(空間的ワーキングメモリ、社会競争、コルチコステロン反応)に重要である、という知見。親からのケアは発達初期の刺激誘発性の機能強化においては、必要条件でも充分条件でもない。著者らの Maternal-Modulation Hypothesis: (i)新生児期の刺激は直接発達に作用し、累積的に長期の向上をもたらす (ii)親の行動はこうした効果を調整し、長期の機能向上を増強もしくは減弱する。


　
新生児が何に触れるか、という要因と、親がどうケアするか、というのは発達において別のファクターであり、直接作用するのは前者である、という。

扁桃体の活動がワーキングメモリ課題と関連

Individual differences in amygdala activity predict response speed during working memory

Schaefer A, Braver TS, Reynolds JR, Burgess GC, Yarkoni T, Gray JR

J Neurosci. 2006 Oct 4;26(40):10120-8

　

The human amygdala has classically been viewed as a brain structure primarily related to emotions and dissociated from higher cognition. We report here findings suggesting that the human amygdala also has a role in supporting working memory (WM), a canonical higher cognitive function. In a first functional magnetic resonance imaging (fMRI) study (n = 53), individual differences in amygdala activity predicted behavioral performance in a 3-back WM task. Specifically, higher event-related amygdala amplitude predicted faster response time (RT; r = -0.64), with no loss of accuracy. This relationship was not contingent on mood state, task content, or personality variables. In a second fMRI study (n = 21), we replicated the key finding (r = -0.47) and further showed that the correlation between the amygdala and faster RT was specific to a high working memory load condition (3-back) compared with a low working memory load condition (1-back). These results support models of amygdala function that can account for its involvement not only in emotion but also higher cognition.

扁桃体 amygdala の活動がワーキングメモリ課題における反応時間と負の相関 (つまり活動が高いほど反応時間が短い) を持つ。この相関は負荷の高い課題を行っている場合 (3バック課題) にだけ見られた。扁桃体は感情のみならず高次認知機能にも関わっている。



BOLD信号と反応時間の個人差との相関を取るわけだけれど、n=53 てのはなかなかすごい。このくらいやれば信頼性は充分かな。

人間の脳におけるフレーム、バイアス、合理的意思決定

Frames, biases, and rational decision-making in the human brain

De Martino B, Kumaran D, Seymour B, Dolan RJ.

Science. 2006 Aug 4;313(5787):684-7.

　

Human choices are remarkably susceptible to the manner in which options are presented. This so-called "framing effect" represents a striking violation of standard economic accounts of human rationality, although its underlying neurobiology is not understood. We found that the framing effect was specifically associated with amygdala activity, suggesting a key role for an emotional system in mediating decision biases. Moreover, across individuals, orbital and medial prefrontal cortex activity predicted a reduced susceptibility to the framing effect. This finding highlights the importance of incorporating emotional processes within models of human choice and suggests how the brain may modulate the effect of these biasing influences to approximate rationality.

イントロより。
｢合理的意思決定に関する最も基本的な信条は、選択肢の提示のされ方に拘わらず、論理的に一貫性のある決定が行われる、というものだ。この前提は "extensionality" もしくは "invariance" として知られ、ゲーム理論の公理 axiom となっている。しかし、人間の意思決定が｢記述不変 description-invariant｣なものである、という主張は数ある経験的データの前に危機にさらされている。カーネマン Kahneman とツベルスキー Tversky はこの合理的意思決定からの逸脱を最初に記述し、プロスペクト理論のキー概念として｢フレーム効果 framing effect｣と名付けた。｣
　
で、情報が不完全だったり、複雑すぎるときには、アルゴリズムに従うよりも、ヒューリスティックスや経験則 "rule of thumb(!)" に従って意思決定する。そして、こういったフレーム効果は情動系に裏打ちさらたシステマティックなバイアスに依るのではないか、という議論がなされてきた。しかし" the underlying neurobiological biasis is not understood"　となるわけか。
　
論文の詳細は下のレビュー参照。
　
関連コメント

The emotional brain weighs its options
Miller G.
Science. 2006 Aug 4;313(5787):600-1.

　
ご専門の方のレビュー
http://d.hatena.ne.jp/./buzzz/20060913

関係節付加における統語的プライミング/語彙にドライヴされる統語的プライミング

本日の神経心理学勉強会より。

Syntactic priming of relative clause attachments: persistence of structural configuration in sentence production

Scheepers C.

Cognition. 2003 Oct;89(3):179-205.

　

Three sentence completion experiments will be reported in which participants had to generate German equivalents of "the servant of the actress who..." (NP-of-NP-RC) constructions. Target fragments (which were unconstrained as to whether the relative pronoun permitted high or low attachment) were preceded by constrained prime fragments, which were either structurally congruent with the targets (Experiments 1 and 2) or structurally incongruent with the targets (anaphoric adverbial clauses rather than relative clauses (RCs), Experiment 3). While the first two experiments established reliable repetition of RC attachments between primes and targets, Experiment 3 failed to obtain a significant priming effect, indicating that RC attachment priming is dependent on a syntactic overlap between primes and targets. The results suggest a tendency of language producers to retain hierarchical syntactic relations over consecutive trials. Current models of syntactic priming in production do not offer an explanatory mechanism for this kind of observation as they presently stand.

Lexically-driven syntactic priming.

Melinger A, Dobel C.

Cognition. 2005 Nov;98(1):B11-20. Epub 2005 May 31.

　

Syntactic priming studies demonstrate that exposure to a particular syntactic structure leads speakers to reproduce the same structure in subsequent utterances. Explanations for this phenomenon rely on either the retrieval of morphosyntactic features associated with the verb in the prime sentence or the preservation of the mapping between message and word sequences in the prime sentence. Two experiments test the featural account of syntactic priming. We used single word primes to investigate the dative alternation in German (Experiment 1) and Dutch (Experiment 2). Native speakers read ditransitive verbs that are restricted either to the prepositional (dative) or double object construction, followed by pictures that can be described with either structure. We find that a single verb in isolation is sufficient to bias speakers' production preferences supporting lexically-driven accounts of syntactic priming.

頭頂葉における学習依存性の運動方向カテゴリー表現

Experience-dependent representation of visual categories in parietal cortex
Freedman DJ, Assad JA.
Nature. 2006 Sep 7;443(7107):85-8. Epub 2006 Aug 27.

　
LIP のニューロンは、視覚刺激の運動方向をカテゴリーの構成要素に従って符号化する。また、学習によって符号化の表現も変化する。MT野ではほとんどカテゴリー化はなされない。LIP は視覚運動の方向選択性を、行動への関連性・意味を持った抽象的な表現に変換しているのでは。
　
関連

Walk the line: parietal neurons respect category boundariesFerrera VP, Grinband J.
Nature Neuroscience. 2006; 9:1207-1208

ヒトの聴覚ミラー・ニューロン、そして共感力

Empathy and the somatotopic auditory mirror system in humans
Gazzola V, Aziz-Zadeh L, Keysers C.
Curr Biol. 2006 Sep 19;16(18):1824-9.

　
How do we understand the actions of other individuals if we can only hear them? Auditory mirror neurons respond both while monkeys perform hand or mouth actions and while they listen to sounds of similar actions . This system might be critical for auditory action understanding and language evolution . Preliminary evidence suggests that a similar system may exist in humans . Using fMRI, we searched for brain areas that respond both during motor execution and when individuals listened to the sound of an action made by the same effector. We show that a left hemispheric temporo-parieto-premotor circuit is activated in both cases, providing evidence for a human auditory mirror system. In the left premotor cortex, a somatotopic pattern of activation was also observed: A dorsal cluster was more involved during listening and execution of hand actions, and a ventral cluster was more involved during listening and execution of mouth actions. Most of this system appears to be multimodal because it also responds to the sight of similar actions. Finally, individuals who scored higher on an empathy scale activated this system more strongly, adding evidence for a possible link between the motor mirror system and empathy.
　
猿の聴覚ミラーニューロンは行為を行うときも、他個体の同様の行為の音を聞いたときも活動する。ヒトでも同様の活動が左半球の側頭-頭頂-運動前野サーキットで見られた。運動前野では体部位表現があり、背側では腕の運動に関する音、腹側では口の運動に関する音に対して反応を示した。これらは運動を視覚で捉えたときにも同様の活動を示したので、マルチモーダルなものだと考えられる。ちなみに共感度テストで高い点を示した者はこれらの活動が強かったため、ミラー・システムと共感とのリンクが示唆される。