2013年6月26日水曜日

Connectivity profiles reveal the relationship between brain areas for social cognition in human and monkey temporoparietal cortex

Rogier B. Mars, Jérôme Sallet, Franz-Xaver Neubert, and Matthew F. S. Rushworth
PNAS June 25, 2013 vol. 110 no. 26 10806-10811

ヒトの社会性に重要な役割を果たすと考えられているTPJ、サルではどの脳領域に相当する?ヒトとサルの「安静時のfMRI機能的結合のパターン」から、(顔認知に関わる)mid-STSが有力だと分かった。

The human ability to infer the thoughts and beliefs of others, often referred to as “theory of mind,” as well as the predisposition to even consider others, are associated with activity in the temporoparietal junction (TPJ) area. Unlike the case of most human brain areas, we have little sense of whether or how TPJ is related to brain areas in other nonhuman primates. It is not possible to address this question by looking for similar task-related activations in nonhuman primates because there is no evidence that nonhuman primates engage in theory-of-mind tasks in the same manner as humans. Here, instead, we explore the relationship by searching for areas in the macaque brain that interact with other macaque brain regions in the same manner as human TPJ interacts with other human brain regions. In other words, we look for brain regions with similar positions within a distributed neural circuit in the two species. We exploited the fact that human TPJ has a unique functional connectivity profile with cortical areas with known homologs in the macaque. For each voxel in the macaque temporal and parietal cortex we evaluated the similarity of its functional connectivity profile to that of human TPJ. We found that areas in the middle part of the superior temporal cortex, often associated with the processing of faces and other social stimuli, have the most similar connectivity profile. These results suggest that macaque face processing areas and human mentalizing areas might have a similar precursor.

2013年6月25日火曜日

Prefrontal mechanisms of behavioral flexibility, emotion regulation and value updating

Peter H Rudebeck, Richard C Saunders, Anna T Prescott, Lily S Chau & Elisabeth A Murray
Nature Neuroscience (2013) doi:10.1038/nn.3440
Received 20 March 2013 Accepted 21 May 2013 Published online 23 June 2013

OFC(眼窩前頭前野)とその周辺を損傷すると、失敗しても行動を変えない、ヘビを怖がらない、食べ飽きたモノを選び続けてしまう、ことなどが知られていた。しかし、OFC「だけ」を厳密に損傷したサルでは三つ目のみが観察された。

つまり、OFCの本質的な機能は「自分の状態(例:ある食べ物に飽きた)に合わせて、選択肢の価値を変える」こと。
「これまでの研究が不注意でOFC以外の部分にもダメージを与えていた可能性を検証する」とか、けっこうきついことが書いてあるw

Two ideas have dominated neuropsychology concerning the orbitofrontal cortex (OFC). One holds that OFC regulates emotion and enhances behavioral flexibility through inhibitory control. The other ascribes to OFC a role in updating valuations on the basis of current motivational states. Neuroimaging, neurophysiological and clinical observations are consistent with either or both hypotheses. Although these hypotheses are compatible in principle, we present results supporting the latter view of OFC function and arguing against the former. We found that excitotoxic, fiber-sparing lesions confined to OFC in monkeys did not alter either behavioral flexibility, as measured by object reversal learning, or emotion regulation, as assessed by fear of snakes. A follow-up experiment indicated that a previously reported loss of inhibitory control resulted from damage to nearby fiber tracts and not from OFC dysfunction. Thus, OFC has a more specialized role in reward-guided behavior and emotion than has been thought, a function that includes value updating.

2013年6月17日月曜日

Repeated Cortico-Striatal Stimulation Generates Persistent OCD-Like Behavior

Susanne E. Ahmari, Timothy Spellman, Neria L. Douglass, Mazen A. Kheirbek, H. Blair Simpson, Karl Deisseroth, Joshua A. Gordon, René Hen
Science 7 June 2013: Vol. 340 no. 6137 pp. 1234-1239

Although cortico-striato-thalamo-cortical (CSTC) circuit dysregulation is correlated with obsessive compulsive disorder (OCD), causation cannot be tested in humans. We used optogenetics in mice to simulate CSTC hyperactivation observed in OCD patients. Whereas acute orbitofrontal cortex (OFC)–ventromedial striatum (VMS) stimulation did not produce repetitive behaviors, repeated hyperactivation over multiple days generated a progressive increase in grooming, a mouse behavior related to OCD. Increased grooming persisted for 2 weeks after stimulation cessation. The grooming increase was temporally coupled with a progressive increase in light-evoked firing of postsynaptic VMS cells. Both increased grooming and evoked firing were reversed by chronic fluoxetine, a first-line OCD treatment. Brief but repeated episodes of abnormal circuit activity may thus set the stage for the development of persistent psychopathology.

2013年6月13日木曜日

Foraging under Competition: The Neural Basis of Input-Matching in Humans

Dean Mobbs, Demis Hassabis, Rongjun Yu, Carlton Chu, Matthew Rushworth, Erie Boorman, and Tim Dalgleish
J. Neurosci. 2013;33 9866-9872
http://www.jneurosci.org/cgi/content/abstract/33/23/9866?etoc

Input-matching is a key mechanism by which animals optimally distribute themselves across habitats to maximize net gains based on the changing input values of food supply rate and competition. To examine the neural systems that underlie this rule in humans, we created a continuous-input foraging task where subjects had to decide to stay or switch between two habitats presented on the left and right of the screen. The subject's decision to stay or switch was based on changing input values of reward-token supply rate and competition density. High density of competition or low-reward token rate was associated with decreased chance of winning. Therefore, subjects attempted to maximize their gains by switching to habitats that possessed low competition density and higher token rate. When it was increasingly disadvantageous to be in a habitat, we observed increased activity in brain regions that underlie preparatory motor actions, including the dorsal anterior cingulate cortex and the supplementary motor area, as well as the insula, which we speculate may be involved in the conscious urge to switch habitats. Conversely, being in an advantageous habitat is associated with activity in the reward systems, namely the striatum and medial prefrontal cortex. Moreover, amygdala and dorsal putamen activity steered interindividual preferences in competition avoidance and pursuing reward. Our results suggest that input-matching decisions are made as a net function of activity in a distributed set of neural systems. Furthermore, we speculate that switching behaviors are related to individual differences in competition avoidance and reward drive.

2013年6月6日木曜日

The importance of mixed selectivity in complex cognitive tasks

Mattia Rigotti, Omri Barak, Melissa R. Warden, Xiao-Jing Wang, Nathaniel D. Daw, Earl K. Miller & Stefano Fusi
Nature 497, 585–590 (30 May 2013) | doi:10.1038/nature12160

Single-neuron activity in the prefrontal cortex (PFC) is tuned to mixtures of multiple task-related aspects. Such mixed selectivity is highly heterogeneous, seemingly disordered and therefore difficult to interpret. We analysed the neural activity recorded in monkeys during an object sequence memory task to identify a role of mixed selectivity in subserving the cognitive functions ascribed to the PFC. We show that mixed selectivity neurons encode distributed information about all task-relevant aspects. Each aspect can be decoded from the population of neurons even when single-cell selectivity to that aspect is eliminated. Moreover, mixed selectivity offers a significant computational advantage over specialized responses in terms of the repertoire of input–output functions implementable by readout neurons. This advantage originates from the highly diverse nonlinear selectivity to mixtures of task-relevant variables, a signature of high-dimensional neural representations. Crucially, this dimensionality is predictive of animal behaviour as it collapses in error trials. Our findings recommend a shift of focus for future studies from neurons that have easily interpretable response tuning to the widely observed, but rarely analysed, mixed selectivity neurons.

2013年6月5日水曜日

A causal link between prediction errors, dopamine neurons and learning

Elizabeth E Steinberg, Ronald Keiflin, Josiah R Boivin, Ilana B Witten, Karl Deisseroth & Patricia H Janak
Nature Neuroscience (2013) doi:10.1038/nn.3413

報酬予測誤差とドーパミン、学習の因果関係。「光遺伝学的手法でドーパミンニューロンの活動を制御した」、「(学習心理学で使われる)ブロッキング、消去という実験パラダイムを用いて学習への影響をちゃんと調べた」ところがポイント(らしい)。

ブロッキング:「刺激A→報酬」学習後に「刺激AX→報酬」を経験させても「Xと報酬の連合」は学習されない(「AX→報酬」では報酬予測誤差がゼロでドーパミンニューロンが活動しないので)。しかし、光刺激でドーパミンニューロンを(報酬と同時に)活動させると学習が行われる。

消去:「刺激A → 報酬」学習後に「刺激A → 無報酬」を経験させると、学習効果は消去される。しかし、光刺激でドーパミンニューロンを「報酬が来るはずのタイミング」で活動させるとその学習が消去されない。

これらの結果は「ドーパミン(報酬予測誤差)→ 学習」の因果関係を示す。

Situations in which rewards are unexpectedly obtained or withheld represent opportunities for new learning. Often, this learning includes identifying cues that predict reward availability. Unexpected rewards strongly activate midbrain dopamine neurons. This phasic signal is proposed to support learning about antecedent cues by signaling discrepancies between actual and expected outcomes, termed a reward prediction error. However, it is unknown whether dopamine neuron prediction error signaling and cue-reward learning are causally linked. To test this hypothesis, we manipulated dopamine neuron activity in rats in two behavioral procedures, associative blocking and extinction, that illustrate the essential function of prediction errors in learning. We observed that optogenetic activation of dopamine neurons concurrent with reward delivery, mimicking a prediction error, was sufficient to cause long-lasting increases in cue-elicited reward-seeking behavior. Our findings establish a causal role for temporally precise dopamine neuron signaling in cue-reward learning, bridging a critical gap between experimental evidence and influential theoretical frameworks.

2013年6月4日火曜日

A unified selection signal for attention and reward in primary visual cortex

Liviu Stănişor, Chris van der Togt, Cyriel M. A. Pennartz, and Pieter R. Roelfsema
PNAS May 28, 2013 vol. 110 no. 22 9136-9141

一次視覚野(V1)の神経活動は、ある刺激と他の刺激の相対的な「価値(その刺激に紐付けられている報酬の量)」にモジュレートされる。そのパターンは「注意」によるモジュレーションと非常によく似ており、実際、価値に強く影響されるニューロンほど注意にも強く影響される。

Stimuli associated with high rewards evoke stronger neuronal activity than stimuli associated with lower rewards in many brain regions. It is not well understood how these reward effects influence activity in sensory cortices that represent low-level stimulus features. Here, we investigated the effects of reward information in the primary visual cortex (area V1) of monkeys. We found that the reward value of a stimulus relative to the value of other stimuli is a good predictor of V1 activity. Relative value biases the competition between stimuli, just as has been shown for selective attention. The neuronal latency of this reward value effect in V1 was similar to the latency of attentional influences. Moreover, V1 neurons with a strong value effect also exhibited a strong attention effect, which implies that relative value and top–down attention engage overlapping, if not identical, neuronal selection mechanisms. Our findings demonstrate that the effects of reward value reach down to the earliest sensory processing levels of the cerebral cortex and imply that theories about the effects of reward coding and top–down attention on visual representations should be unified.