SummaryFast internally generated sequences of neural representations are suggested to support learning and online planning. However, these sequences have only been studied in the context of spatial tasks and never in humans. Here, we recorded magnetoencephalography (MEG) while human subjects performed a novel non-spatial reasoning task. The task required selecting paths through a set of six visual objects. We trained pattern classifiers on the MEG activity elicited by direct presentation of the visual objects alone and tested these classifiers on activity recorded during periods when no object was presented. During these object-free periods, the brain spontaneously visited representations of approximately four objects in fast sequences lasting on the order of 120 ms. These sequences followed backward trajectories along the permissible paths in the task. Thus, spontaneous fast sequential representation of states can be measured non-invasively in humans, and these sequences may be a fundamental feature of neural computation across tasks.

Subjects routinely control the vigor with which they emit motoric responses. However, the bulk of formal treatments of decision-making ignores this dimension of choice. A recent theoretical study suggested that action vigor should be influenced by experienced average reward rate and that this rate is encoded by tonic dopamine in the brain. We previously examined how average reward rate modulates vigor as exemplified by response times and found a measure of agreement with the first suggestion. In the current study, we examined the second suggestion, namely the potential influence of dopamine signaling on vigor. Ninety healthy subjects participated in a double-blind experiment in which they received one of the following: placebo, L-DOPA (which increases dopamine levels in the brain), or citalopram (which has a selective, if complex, effect on serotonin levels). Subjects performed multiple trials of a rewarded odd-ball discrimination task in which we varied the potential reward over time in order to exercise the putative link between vigor and average reward rate. Replicating our previous findings, we found that a significant fraction of the variance in subjects' responses could be explained by our experimentally manipulated changes in average reward rate. Crucially, this relationship was significantly stronger under L-Dopa than under Placebo, suggesting that the impact of average reward levels on action vigor is indeed subject to a dopaminergic influence.

Mindfulness training, which involves observing thoughts and feelings without judgment or reaction, has been shown to improve aspects of psychosocial well-being when delivered via in-person training programs such as mindfulness-based stress reduction (MBSR) and mindfulness-based cognitive therapy (MBCT). Less is known about the efficacy of digital training mediums, such as smartphone apps, which are rapidly rising in popularity. In this study, novice meditators were randomly allocated to an introductory mindfulness meditation program or to a psychoeducational audiobook control featuring an introduction to the concepts of mindfulness and meditation. The interventions were delivered via the same mindfulness app, were matched across a range of criteria, and were presented to participants as well-being programs. Affect, irritability, and two distinct components of stress were measured immediately before and after each intervention in a cohort of healthy adults. While both interventions were effective at reducing stress associated with personal vulnerability, only the mindfulness intervention had a significant positive impact on irritability, affect, and stress resulting from external pressure (between group Cohen’s d = 0.44, 0.47, 0.45, respectively). These results suggest that brief mindfulness training has a beneficial impact on several aspects of psychosocial well-being, and that smartphone apps are an effective delivery medium for mindfulness training.