Evidence for interacting but decoupled controls of decisions and movements in nonhuman primates.

Many recent studies indicate that control of decisions and actions is integrated during interactive behavior. Among these, several carried out in humans and monkeys conclude that there is a coregulation of choices and movements. Another perspective, based on human data only, proposes a decoupled control of decision duration and movement speed, allowing, for instance, trading decision duration for movement duration when time pressure increases.

Atomoxetine and reward size equally improve task engagement and perceptual decisions but differently affect movement execution.

Our ability to engage and perform daily activities relies on balancing the associated benefits and costs. Rewards, as benefits, act as powerful motivators that help us stay focused for longer durations. The noradrenergic (NA) system is thought to play a significant role in optimizing our performance.

Impact of decision and action outcomes on subsequent decision and action behaviours in humans.

Speed-accuracy trade-off adjustments in decision-making have been mainly studied separately from those in motor control. In the wild, however, animals coordinate their decision and action, often deciding while acting. Recent behavioural studies support this view, indicating that animals, including humans, trade decision time for movement time to maximize their global rate of reward during experimental sessions.

Integrated neural dynamics of sensorimotor decisions and actions.

Recent theoretical models suggest that deciding about actions and executing them are not implemented by completely distinct neural mechanisms but are instead two modes of an integrated dynamical system. Here, we investigate this proposal by examining how neural activity unfolds during a dynamic decision-making task within the high-dimensional space defined by the activity of cells in monkey dorsal premotor (PMd), primary motor (M1), and dorsolateral prefrontal cortex (dlPFC) as well as the external and internal segments of the globus pallidus (GPe, GPi). Dimensionality reduction shows that the four strongest components of neural activity are functionally interpretable, reflecting a state transition between deliberation and commitment, the transformation of sensory evidence into a choice, and the baseline and slope of the rising urgency to decide.

Hasty sensorimotor decisions rely on an overlap of broad and selective changes in motor activity.

Humans and other animals are able to adjust their speed-accuracy trade-off (SAT) at will depending on the urge to act, favoring either cautious or hasty decision policies in different contexts. An emerging view is that SAT regulation relies on influences exerting broad changes on the motor system, tuning its activity up globally when hastiness is at premium. The present study aimed to test this hypothesis.

Dissociating the Impact of Movement Time and Energy Costs on Decision-Making and Action Initiation in Humans.

Recent theories and data suggest that adapted behavior involves economic computations during which multiple trade-offs between reward value, accuracy requirement, energy expenditure, and elapsing time are solved so as to obtain rewards as soon as possible while spending the least possible amount of energy. However, the relative impact of movement energy and duration costs on perceptual decision-making and movement initiation is poorly understood. Here, we tested 31 healthy subjects on a perceptual decision-making task in which they executed reaching movements to report probabilistic choices.

Reducing behavioral dimensions to study brain-environment interactions.

Movement vigor provides a window on action valuation. But what is vigor, and how to measure it in the first place? Strikingly, many different co-varying vigor-related metrics can be found in the literature. I believe this is because vigor, just like the neural circuits that determine it, is an integrated, low-dimensional parameter.

Trading accuracy for speed over the course of a decision.

Humans and other animals often need to balance the desire to gather sensory information (to make the best choice) with the urgency to act, facing a speed-accuracy tradeoff (SAT). Given the ubiquity of SAT across species, extensive research has been devoted to understanding the computational mechanisms allowing its regulation at different timescales, including from one context to another, and from one decision to another. However, animals must frequently change their SAT on even shorter timescales-that is, over the course of an ongoing decision-and little is known about the mechanisms that allow such rapid adaptations.

Humans sacrifice decision-making for action execution when a demanding control of movement is required.

A growing body of evidence suggests that decision-making and action execution are governed by partly overlapping operating principles. Especially, previous work proposed that a shared decision urgency/movement vigor signal, possibly computed in the basal ganglia, coordinates both deliberation and movement durations in a way that maximizes the reward rate. Recent data support one aspect of this hypothesis, indicating that the urgency level at which a decision is made influences the vigor of the movement produced to express this choice.

Microstimulation of dorsal premotor and primary motor cortex delays the volitional commitment to an action choice.

Humans and other animals are faced with decisions about actions on a daily basis. These typically include a period of deliberation that ends with the commitment to a choice, which then leads to the overt expression of that choice through action. Previous studies with monkeys have demonstrated that neural activity in sensorimotor areas correlates with the deliberation process and reflects the moment of commitment before movement initiation, but the causal roles of these regions are challenging to establish.

Decision urgency invigorates movement in humans.

Recent work in highly trained monkeys suggests that decision-making and motor control are linked processes whose regulation by urgency allows reward rate optimization. However, such urgency-based mechanism might be species-specific and/or a consequence of practice. Here I show that the unified regulation hypothesis exists in naïve human subjects.

Motor cortex disruption delays motor processes but not deliberation about action choices.

Decisions about actions typically involve a period of deliberation that ends with the commitment to a choice and the motor processes overtly expressing that choice. Previous studies have shown that neural activity in sensorimotor areas, including the primary motor cortex (M1), correlates with deliberation features during action selection. However, the causal contribution of these areas to the decision process remains unclear.

Thirst for Intention? Grasping a Glass Is a Thirst-Controlled Action.

Every day and every hour, we feel we perform numerous voluntary actions, i.e., actions under the control of our will.

The Urge to Decide and Act: Implications for Brain Function and Dysfunction.

Humans and other animals are motivated to act so as to maximize their subjective reward rate. Here, we propose that reward rate maximization is accomplished by adjusting a context-dependent "urgency signal," which influences both the commitment to a developing action choice and the vigor with which the ensuing action is performed. We review behavioral and neurophysiological data suggesting that urgency is controlled by projections from the basal ganglia to cerebral cortical regions, influencing neural activity related to decision making as well as activity related to action execution.

The Basal Ganglia Do Not Select Reach Targets but Control the Urgency of Commitment.

Prominent theories of decision making suggest that the basal ganglia (BG) play a causal role in deliberation between action choices. An alternative hypothesis is that deliberation occurs in cortical regions, while the BG control the speed-accuracy trade-off (SAT) between committing to a choice versus continuing to deliberate. Here, we test these hypotheses by recording activity in the internal and external segments of the globus pallidus (GPi/GPe) while monkeys perform a task dissociating the process of deliberation, the moment of commitment, and adjustment of the SAT.

Trial-to-trial adjustments of speed-accuracy trade-offs in premotor and primary motor cortex.

Unlabelled: Recent studies have shown that activity in sensorimotor structures varies depending on the speed-accuracy trade-off (SAT) context in which a decision is made. Here we tested the hypothesis that the same areas also reflect a more local adjustment of SAT established between individual trials, based on the outcome of the previous decision. Two monkeys performed a reaching decision task in which sensory evidence continuously evolves during the time course of a trial.

Modulation of Premotor and Primary Motor Cortical Activity during Volitional Adjustments of Speed-Accuracy Trade-Offs.

Recent work suggests that while animals decide between reaching actions, neurons in dorsal premotor (PMd) and primary motor (M1) cortex reflect a dynamic competition between motor plans and determine when commitment to a choice is made. This competition is biased by at least two sources of information: the changing sensory evidence for one choice versus another, and an urgency signal that grows over time. Here, we test the hypothesis that the urgency signal adjusts the trade-off between speed and accuracy during both decision-making and movement execution.

Evidence against perfect integration of sensory information during perceptual decision making.

Perceptual decision making is often modeled as perfect integration of sequential sensory samples until the accumulated total reaches a fixed decision bound. In that view, the buildup of neural activity during perceptual decision making is attributed to temporal integration. However, an alternative explanation is that sensory estimates are computed quickly with a low-pass filter and combined with a growing signal reflecting the urgency to respond and it is the latter that is primarily responsible for neural activity buildup.

How to discriminate conclusively among different models of decision making?

A popular and successful class of decision-making models (the "evidence accumulator" models) has been recently challenged by a new hypothesis called the urgency-gating model. Hawkins et al. (J Neurophysiol 114: 40-47, 2015) used a sophisticated curve-fitting procedure to show that these models are discriminable and thus testable in constant evidence tasks.

The urgency-gating model can explain the effects of early evidence.

In a recent report, Winkel, Keuken, van Maanen, Wagenmakers & Forstmann (Psychonomics Bulletin and Review 21(3): 777-784, 2014) show that during a random-dot motion discrimination task, early differences in motion evidence can influence reaction times (RTs) and error rates in human subjects. They use this as an argument in favor of the drift-diffusion model and against the urgency-gating model. However, their implementation of the urgency-gating model is incomplete, as it lacks the low-pass filter that is necessary to deal with noisy input such as the motion signal used in their experimental task.

Context-dependent urgency influences speed-accuracy trade-offs in decision-making and movement execution.

Speed-accuracy tradeoffs (SATs) exist in both decision-making and movement control, and are generally studied separately. However, in natural behavior animals are free to adjust the time invested in deciding and moving so as to maximize their reward rate. Here, we investigate whether shared mechanisms exist for SAT adjustment in both decisions and actions.

Deliberation and commitment in the premotor and primary motor cortex during dynamic decision making.

Neurophysiological studies of decision making have primarily focused on decisions about information that is stable over time. However, during natural behavior, animals make decisions in a constantly changing environment. To investigate the neural mechanisms of such dynamic choices, we recorded activity in dorsal premotor (PMd) and primary motor cortex (M1) while monkeys performed a two-choice reaching task in which sensory information about the correct choice was changing within each trial and the decision could be made at any time.