2017年7月27日木曜日

Dissociation of Choice Formation and Choice-Correlated Activity in Macaque Visual Cortex

Robbe L.T. Goris, Corey M. Ziemba, Gabriel M. Stine, Eero P. Simoncelli and J. Anthony Movshon
Journal of Neuroscience 21 April 2017, 37 (20) 5195-5203;
DOI: https://doi.org/10.1523/JNEUROSCI.3331-16.2017

Responses of individual task-relevant sensory neurons can predict monkeys' trial-by-trial choices in perceptual decision-making tasks. Choice-correlated activity has been interpreted as evidence that the responses of these neurons are causally linked to perceptual judgments. To further test this hypothesis, we studied responses of orientation-selective neurons in V1 and V2 while two macaque monkeys performed a fine orientation discrimination task. Although both animals exhibited a high level of neuronal and behavioral sensitivity, only one exhibited choice-correlated activity. Surprisingly, this correlation was negative: when a neuron fired more vigorously, the animal was less likely to choose the orientation preferred by that neuron. Moreover, choice-correlated activity emerged late in the trial, earlier in V2 than in V1, and was correlated with anticipatory signals. Together, these results suggest that choice-correlated activity in task-relevant sensory neurons can reflect postdecision modulatory signals.

2017年7月26日水曜日

Effort-Based Reinforcement Processing and Functional Connectivity Underlying Amotivation in Medicated Patients with Depression and Schizophrenia

Ho Il Park, Boung Chul Lee, Jae-Jin Kim, Joong Il Kim and Min-Seung Koo
Journal of Neuroscience 10 March 2017, 2524-16; DOI: https://doi.org/10.1523/JNEUROSCI.2524-16.2017

Amotivation is a common phenotype of major depressive disorder and schizophrenia which are clinically distinct disorders. Effective treatment targets and strategies can be discovered by examining the dopaminergic reward network function underlying amotivation between these disorders. We conducted a functional MRI study in healthy human participants and medicated patients with depression and schizophrenia using an effort-based reinforcement task. We examined regional activations related to reward type (positive and negative reinforcement), effort level, and their composite value as well as resting-state functional connectivities within the meso-striatal-prefrontal pathway. We found that integrated reward and effort values of low effort-positive reinforcement and high effort-negative reinforcement were behaviorally anticipated and represented in the putamen and medial orbitofrontal cortex activities. Patients with schizophrenia and depression did not show anticipation-related and work-related reaction time reductions, respectively. Greater amotivation severity correlated with smaller work-related putamen activity changes according to reward type in schizophrenia and effort level in depression. Patients with schizophrenia showed feedback-related putamen hyperactivity of low effort compared to healthy controls and depressed patients. The strength of medial orbitofrontal-striatal functional connectivity predicted work-related reaction time reduction of high effort negative reinforcement in healthy controls and amotivation severity in both patients with schizophrenia and depression. Patients with depression showed deficient medial orbitofrontal-striatal functional connectivity compared to healthy controls and patients with schizophrenia. These results indicate that amotivations in depression and schizophrenia involve different pathophysiology in the prefrontal-striatal circuitry.

2017年7月25日火曜日

Opposite Effects of Recent History on Perception and Decision

Fritsche M, Mostert P, de Lange FP.
Curr Biol. 2017 Feb 20;27(4):590-595. doi: 10.1016/j.cub.2017.01.006.

Recent studies claim that visual perception of stimulus features, such as orientation, numerosity, and faces, is systematically biased toward visual input from the immediate past [1-3]. However, the extent to which these positive biases truly reflect changes in perception rather than changes in post-perceptual processes is unclear [4, 5]. In the current study we sought to disentangle perceptual and decisional biases in visual perception. We found that post-perceptual decisions about orientation were indeed systematically biased toward previous stimuli and this positive bias did not strongly depend on the spatial location of previous stimuli (replicating previous work [1]). In contrast, observers' perception was repelled away from previous stimuli, particularly when previous stimuli were presented at the same spatial location. This repulsive effect resembles the well-known negative tilt-aftereffect in orientation perception [6]. Moreover, we found that the magnitude of the positive decisional bias increased when a longer interval was imposed between perception and decision, suggesting a shift of working memory representations toward the recent history as a source of the decisional bias. We conclude that positive aftereffects on perceptual choice are likely introduced at a post-perceptual stage. Conversely, perception is negatively biased away from recent visual input. We speculate that these opposite effects on perception and post-perceptual decision may derive from the distinct goals of perception and decision-making processes: whereas perception may be optimized for detecting changes in the environment, decision processes may integrate over longer time periods to form stable representations.

2017年7月24日月曜日

Perceptual Decision Making in Rodents, Monkeys, and Humans

Hanks TD, Summerfield C.
Neuron. 2017 Jan 4;93(1):15-31. doi: 10.1016/j.neuron.2016.12.003.

Perceptual decision making is the process by which animals detect, discriminate, and categorize information from the senses. Over the past two decades, understanding how perceptual decisions are made has become a central theme in the neurosciences. Exceptional progress has been made by recording from single neurons in the cortex of the macaque monkey and using computational models from mathematical psychology to relate these neural data to behavior. More recently, however, the range of available techniques and paradigms has dramatically broadened, and researchers have begun to harness new approaches to explore how rodents and humans make perceptual decisions. The results have illustrated some striking convergences with findings from the monkey, but also raised new questions and provided new theoretical insights. In this review, we summarize key findings, and highlight open challenges, for understanding perceptual decision making in rodents, monkeys, and humans.

2017年7月20日木曜日

Mnemonic Training Reshapes Brain Networks to Support Superior Memory

Dresler M, Shirer WR, Konrad BN, Müller NC, Wagner IC, Fernández G, Czisch M, Greicius MD
Neuron. 2017 Mar 8;93(5):1227-1235.e6. doi: 10.1016/j.neuron.2017.02.003.

Memory skills strongly differ across the general population; however, little is known about the brain characteristics supporting superior memory performance. Here we assess functional brain network organization of 23 of the world's most successful memory athletes and matched controls with fMRI during both task-free resting state baseline and active memory encoding. We demonstrate that, in a group of naive controls, functional connectivity changes induced by 6 weeks of mnemonic training were correlated with the network organization that distinguishes athletes from controls. During rest, this effect was mainly driven by connections between rather than within the visual, medial temporal lobe and default mode networks, whereas during task it was driven by connectivity within these networks. Similarity with memory athlete connectivity patterns predicted memory improvements up to 4 months after training. In conclusion, mnemonic training drives distributed rather than regional changes, reorganizing the brain's functional network organization to enable superior memory performance.

2017年7月19日水曜日

Effects of Medial Orbitofrontal Cortex Lesions on Self-Control in Intertemporal Choice

Peters J, D'Esposito M
Curr Biol. 2016 Oct 10;26(19):2625-2628. doi: 10.1016/j.cub.2016.07.035.

Many decisions involve a trade-off between the temporal proximity of a reward and its magnitude. A range of clinical conditions are associated with poor self-control during such intertemporal choices, such that smaller rewards that are received sooner are preferred over larger rewards that are received later to a greater extent [1, 2]. According to a prominent neural model of self-control [3-6], subjective reward values are represented in the medial orbitofrontal cortex (mOFC) at the time of choice [7-9]. Successful self-control in this model is then thought to depend on a modulation of these mOFC value representations via the lateral prefrontal cortex (lPFC) [3, 6]. Here we directly tested three key predictions of this model in patients with lesions to the mOFC (n = 9) and matched controls (n = 19). First, we show that mOFC lesions disrupt choice-free valuation ratings. This finding provides causal evidence for a role of the mOFC in reward valuation and contrasts with the effects of lPFC disruption [6]. Second, we show that mOFC damage indeed decreases self-control during intertemporal choice, replicating previous findings [10]. Third, extending these previous observations, we show that the effect of mOFC damage on intertemporal choice depends on the actual self-control demands of the task. Our findings thus provide causal evidence for a role of mOFC in reward valuation and are compatible with the idea that mOFC damage affects self-control specifically under conditions that might normally require a modulation of mOFC value representations, e.g., by the lPFC.

2017年7月17日月曜日

Reversed Procrastination by Focal Disruption of Medial Frontal Cortex

Jha A, Diehl B, Scott C, McEvoy AW, Nachev P.
Curr Biol. 2016 Nov 7;26(21):2893-2898. doi: 10.1016/j.cub.2016.08.016.

An enduring puzzle in the neuroscience of voluntary action is the origin of the remarkably wide dispersion of the reaction time distribution, an interval far greater than is explained by synaptic or signal transductive noise [1, 2]. That we are able to change our planned actions-a key criterion of volition [3]-so close to the time of their onset implies decision-making must reach deep into the execution of action itself [4-6]. It has been influentially suggested the reaction time distribution therefore reflects deliberate neural procrastination [7], giving alternative response tendencies sufficient time for fair competition in pursuing a decision threshold that determines which one is behaviorally manifest: a race model, where action selection and execution are closely interrelated [8-11]. Although the medial frontal cortex exhibits a sensitivity to reaction time on functional imaging that is consistent with such a mechanism [12-14], direct evidence from disruptive studies has hitherto been lacking. If movement-generating and movement-delaying neural substrates are closely co-localized here, a large-scale lesion will inevitably mask any acceleration, for the movement itself could be disrupted. Circumventing this problem, here we observed focal intracranial electrical disruption of the medial frontal wall in the context of the pre-surgical evaluation of two patients with epilepsy temporarily reversing such hypothesized procrastination. Effector-specific behavioral acceleration, time-locked to the period of electrical disruption, occurred exclusively at a specific locus at the ventral border of the pre-supplementary motor area. A cardinal prediction of race models of voluntary action is thereby substantiated in the human brain.

2017年7月14日金曜日

Dynamical Representation of Dominance Relationships in the Human Rostromedial Prefrontal Cortex

Ligneul R, Obeso I, Ruff CC, Dreher JC
Curr Biol. 2016 Dec 5;26(23):3107-3115. doi: 10.1016/j.cub.2016.09.015.

Humans and other primates have evolved the ability to represent their status in the group's social hierarchy, which is essential for avoiding harm and accessing resources. Yet it remains unclear how the human brain learns dominance status and adjusts behavior accordingly during dynamic social interactions. Here we address this issue with a combination of fMRI and transcranial direct current stimulation (tDCS). In a first fMRI experiment, participants learned an implicit dominance hierarchy while playing a competitive game against three opponents of different skills. Neural activity in the rostromedial PFC (rmPFC) dynamically tracked and updated the dominance status of the opponents, whereas the ventromedial PFC and ventral striatum reacted specifically to competitive victories and defeats. In a second experiment, we applied anodal tDCS over the rmPFC to enhance neural excitability while subjects performed a similar competitive task. The stimulation enhanced the relative weight of victories over defeats in learning social dominance relationships and exacerbated the influence of one's own dominance over competitive strategies. Importantly, these tDCS effects were specific to trials in which subjects learned about dominance relationships, as they were not present for control choices associated with monetary incentives but no competitive feedback. Taken together, our findings elucidate the role of rmPFC computations in dominance learning and unravel a fundamental mechanism that governs the emergence and maintenance of social dominance relationships in humans.

2017年7月13日木曜日

Imbalanced Activity in the Orbitofrontal Cortex and Nucleus Accumbens Impairs Behavioral Inhibition

Meyer HC, Bucci DJ.
Curr Biol. 2016 Oct 24;26(20):2834-2839. doi: 10.1016/j.cub.2016.08.034.

Contemporary models of behavioral regulation maintain that balanced activity between cognitive control areas (prefrontal cortex, PFC) and subcortical reward-related regions (nucleus accumbens, NAC) mediates the selection of appropriate behavioral responses, whereas imbalanced activity (PFC < NAC) results in maladaptive behavior [1-6]. Imbalance can arise from reduced engagement of PFC (via fatigue or stress [7]) or from excessive activity in NAC [8]. Additionally, a concept far less researched is that an imbalance can result from simultaneously low PFC activity and high NAC activity. This occurs during adolescence, when the maturation of PFC lags behind that of NAC and NAC is more functionally active compared to adulthood or pre-adolescence [2, 5, 9, 10]. Accordingly, activity is disproportionately higher in NAC than in PFC, which may contribute to impulsivity and risk-taking exhibited by adolescents [5, 6, 10-12]. Despite having explanatory value, support for this notion has been solely correlational. Here, we causally tested this using chemogenetics to simultaneously decrease neural activity in the orbitofrontal cortex (OFC) and increase activity in NAC in adult rats, mimicking the imbalance during adolescence. We tested the effects on negative occasion setting, an important yet understudied form of inhibitory learning that may be particularly relevant during adolescence. Rats with combined manipulation of OFC and NAC were impaired in learning to use environmental cues to withhold a response, an effect that was greater than that of either manipulation alone. These findings provide direct evidence that simultaneous underactivity in OFC and overactivity in NAC can negatively impact behavioral control and provide insight into the neural systems that underlie inhibitory learning.

2017年7月10日月曜日

Dissociation of Choice Formation and Choice-Correlated Activity in Macaque Visual Cortex

Robbe L.T. Goris, Corey M. Ziemba, Gabriel M. Stine, Eero P. Simoncelli and J. Anthony Movshon
Journal of Neuroscience 21 April 2017, 37 (20) 5195-5203;
DOI: https://doi.org/10.1523/JNEUROSCI.3331-16.2017

Responses of individual task-relevant sensory neurons can predict monkeys' trial-by-trial choices in perceptual decision-making tasks. Choice-correlated activity has been interpreted as evidence that the responses of these neurons are causally linked to perceptual judgments. To further test this hypothesis, we studied responses of orientation-selective neurons in V1 and V2 while two macaque monkeys performed a fine orientation discrimination task. Although both animals exhibited a high level of neuronal and behavioral sensitivity, only one exhibited choice-correlated activity. Surprisingly, this correlation was negative: when a neuron fired more vigorously, the animal was less likely to choose the orientation preferred by that neuron. Moreover, choice-correlated activity emerged late in the trial, earlier in V2 than in V1, and was correlated with anticipatory signals. Together, these results suggest that choice-correlated activity in task-relevant sensory neurons can reflect postdecision modulatory signals.

2017年7月5日水曜日

Interaction of Instrumental and Goal-Directed Learning Modulates Prediction Error Representations in the Ventral Striatum

Guo R, Böhmer W, Hebart M, Chien S, Sommer T, Obermayer K, Gläscher J.
J Neurosci. 2016 Dec 14;36(50):12650-12660.

Goal-directed and instrumental learning are both important controllers of human behavior. Learning about which stimulus event occurs in the environment and the reward associated with them allows humans to seek out the most valuable stimulus and move through the environment in a goal-directed manner. Stimulus-response associations are characteristic of instrumental learning, whereas response-outcome associations are the hallmark of goal-directed learning. Here we provide behavioral, computational, and neuroimaging results from a novel task in which stimulus-response and response-outcome associations are learned simultaneously but dominate behavior at different stages of the experiment. We found that prediction error representations in the ventral striatum depend on which type of learning dominates. Furthermore, the amygdala tracks the time-dependent weighting of stimulus-response versus response-outcome learning. Our findings suggest that the goal-directed and instrumental controllers dynamically engage the ventral striatum in representing prediction errors whenever one of them is dominating choice behavior.

2017年7月3日月曜日

Decoding Spontaneous Emotional States in the Human Brain

Kragel PA, Knodt AR, Hariri AR, LaBar KS.
PLoS Biol. 2016 Sep 14;14(9):e2000106. doi: 10.1371/journal.pbio.2000106.

Pattern classification of human brain activity provides unique insight into the neural underpinnings of diverse mental states. These multivariate tools have recently been used within the field of affective neuroscience to classify distributed patterns of brain activation evoked during emotion induction procedures. Here we assess whether neural models developed to discriminate among distinct emotion categories exhibit predictive validity in the absence of exteroceptive emotional stimulation. In two experiments, we show that spontaneous fluctuations in human resting-state brain activity can be decoded into categories of experience delineating unique emotional states that exhibit spatiotemporal coherence, covary with individual differences in mood and personality traits, and predict on-line, self-reported feelings. These findings validate objective, brain-based models of emotion and show how emotional states dynamically emerge from the activity of separable neural systems.