Focal striatum lesions impair cautiousness in humans.

Functional neuroimaging data indicate the dorsal striatum is engaged when people are required to vary the cautiousness of their decisions, by emphasizing the speed or accuracy of responding in laboratory-based decision tasks. However, the functional contribution of the striatum to decision making is unknown. In the current study we tested patients with focal ischemic lesions of the dorsal striatum and matched non-lesion control participants on a speed-accuracy tradeoff (SAT) task. Analysis using a computational model of response selection in a competitive and time-pressured context indicated that the decisions of patients with striatal lesions were less cautious than those of matched controls. This deficit was most prominent when the accuracy of decisions was emphasized. The results are consistent with the hypothesis that the striatum plays an important role in strategically setting response caution, an essential function for flexible behavior.

Early evidence affects later decisions: why evidence accumulation is required to explain response time data.

Models of decision making differ in how they treat early evidence as it recedes in time. Standard models, such as the drift diffusion model, assume that evidence is gradually accumulated until it reaches a boundary and a decision is initiated. One recent model, the urgency gating model, has proposed that decision making does not require the accumulation of evidence at all. Instead, accumulation could be replaced by a simple urgency factor that scales with time. To distinguish between these fundamentally different accounts of decision making, we performed an experiment in which we manipulated the presence, duration, and valence of early evidence. We simulated the associated response time and error rate predictions from the drift diffusion model and the urgency gating model, fitting the models to the empirical data. The drift diffusion model predicted that variations in the evidence presented early in the trial would affect decisions later in that same trial. The urgency gating model predicted that none of these variations would have any effect. The behavioral data showed clear effects of early evidence on the subsequent decisions, in a manner consistent with the drift diffusion model. Our results cannot be explained by the urgency gating model, and they provide support for an evidence accumulation account of perceptual decision making.

Bromocriptine does not alter speed-accuracy tradeoff.

Being quick often comes at the expense of being accurate. This speed-accuracy tradeoff is a central feature of many types of decision making. It has been proposed that dopamine plays an important role in adjusting responses between fast and accurate behavior. In the current study we investigated the role of dopamine in perceptual decision making in humans, focusing on speed-accuracy tradeoff. Using a cued version of the random dot motion task, we instructed subjects to either make a fast or an accurate decision. We investigated decision making behavior in subjects who were given bromocriptine (a dopamine receptor agonist) or placebo. We analyzed the behavioral data using two accumulator models, the drift diffusion model, and the linear ballistic accumulator model. On a behavioral level, there were clear differences in decision threshold between speed and accuracy focus, but decision threshold did not differ between the drug and placebo sessions. Bayesian analyses support the null hypothesis that there is no effect of bromocriptine on decision threshold. On the neural level, we replicate previous findings that the striatum and pre-supplementary motor area are active when preparing for speed, compared with accurate decisions. We do not find an effect of bromocriptine on this activation. Therefore, we conclude that bromocriptine does not alter speed-accuracy tradeoff.

Observed and self-experienced conflict induce similar behavioral and neural adaptation.

In adapting our behavior to a rapidly changing environment, we also tune our behavior to that of others. To investigate the neural bases of such adaptive mechanisms, we examined how individuals adjust their actions after decision-conflicts observed in others compared to self-experienced conflicts. Participants responded to the color of a stimulus, while its spatial position elicited either a conflicting or a congruent action. Participants were required either to respond to stimuli themselves or to observe the response of another participant. We studied the difference between interference effects following conflicting or congruent stimuli, an effect known as conflict adaptation. Consistent with earlier reports, we found that the implementation of reactive control, following congruent trials, was accompanied by activation of the right inferior frontal cortex. Individual differences in the efficacy of response inhibition covaried with the level of activation in that region. Sustaining proactive control, following incongruent trials, activated the left lateral prefrontal cortex. Most importantly, adaptive controls induced by decision-conflicts observed in others, as well as the associated prefrontal activations, were comparable to those induced by self-experienced conflicts. We show that in both behavioral and neural terms we adapt to conflicts happening to others just as if they happened to us.

The Lantern: an ultra-light micro-drive for multi-tetrode recordings in mice and other small animals.

In vivo electrophysiological recordings from groups of distinguishable neurons in behaving mice is a technique with a rapidly growing appeal, particularly because it can be combined with gene targeting techniques. This methodology is deemed essential for achieving a flexible and versatile coupling of molecular-genetic manipulations with behavioral and system level analyses of the nervous system. One major obstacle in obtaining this technological integration is the relatively high weight and bulk size of the available implantable devices for ensemble recordings as compared to the size of the animal. This imposes considerable physical stress on the animals and may prevent them from performing complex behavioral tasks for more than a few minutes. We developed a novel micro-drive which allows independent day-to-day positioning of up to 6 tetrodes in the mouse brain, with an extremely reduced weight and size. The system is based on an "exoskeleton" as its structural element, and allows a completely rectilinear path of the electrodes inside the drive and into the brain. Tests showed that mice can tolerate the chronically implanted device very well up to 12 weeks after implantation, while exhibiting normal behavior. Cell yields and stability obtained with this drive in two different brain areas (the hippocampus and orbitofrontal cortex) were comparable to those of traditional recording systems, usually applied to rats. The device may greatly expand possibilities to combine gene targeting and ensemble recording techniques, in behaviorally varied as well as cognitively demanding settings.

Your conflict matters to me! Behavioral and neural manifestations of control adjustment after self-experienced and observed decision-conflict.

In everyday life we tune our behavior to a rapidly changing environment as well as to the behavior of others. The behavioral and neural underpinnings of such adaptive mechanisms are the focus of the present study. In a social version of a prototypical interference task we investigated whether trial-to-trial adjustments are comparable when experiencing conflicting action tendencies ourselves, or simulate such conflicts when observing another player performing the task. Using behavioral and neural measures by means of event-related brain potentials we showed that both own as well as observed conflict result in comparable trial-to-trial adjustments. These adjustments are found in the efficiency of behavioral adjustments, and in the amplitude of an event-related potential in the N2 time window. In sum, in both behavioral and neural terms, we adapt to conflicts happening to others just as if they happened to ourselves.