Dopamine precursor depletion affects performance and confidence judgements when events are timed from an explicit, but not an implicit onset.

Dopamine affects processing of temporal information, but most previous work has tested its role in prospective tasks, where participants know in advance when the event to be timed starts. However, we are often exposed to events whose onset we do not know in advance. We can evaluate their duration after they have elapsed, but mechanisms underlying this ability are still elusive. Here we contrasted effects of acute phenylalanine and tyrosine depletion (APTD) on both forms of timing in healthy volunteers, in a within-subject, placebo-controlled design. Participants were presented with a disc moving around a circular path and asked to reproduce the duration of one full revolution and to judge their confidence in performance. The onset of the revolution was either known in advance (explicit onset) or revealed only at the end of the trial (implicit onset). We found that APTD shortened reproduced durations in the explicit onset task but had no effect on temporal performance in the implicit onset task. This dissociation is corroborated by effects of APTD on confidence judgements in the explicit task only. Our findings suggest that dopamine has a specific role in prospective encoding of temporal intervals, rather than the processing of temporal information in general.

Dopamine Precursor Depletion in Healthy Volunteers Impairs Processing of Duration but Not Temporal Order.

Studies in animals and humans have implicated the neurotransmitter dopamine in duration processing. However, very few studies have examined dopamine's involvement in other forms of temporal processing such as temporal order judgments. In a randomized within-subject placebo-controlled design, we used acute phenylalanine/tyrosine depletion (APTD) to reduce availability of the dopamine precursors tyrosine and phenylalanine in healthy human volunteers. As compared to a nutritionally balanced drink, APTD significantly impaired the ability to accurately reproduce interval duration in a temporal reproduction task. In addition, and confirming previous findings, the direction of error differed as a function of individual differences in underlying dopamine function. Specifically, APTD caused participants with low baseline dopamine precursor availability to overestimate the elapse of time, whereas those with high dopamine availability underestimated time. In contrast to these effects on duration processing, there were no significant effects of APTD on the accuracy of discriminating the temporal order of visual stimuli. This pattern of results does not simply represent an effect of APTD on motor, rather than perceptual, measures of timing because APTD had no effect on participants' ability to use temporal cues to speed RT. Our results demonstrate, for the first time in healthy volunteers, a dopaminergic dissociation in judging metrical (duration) versus ordinal (temporal order) aspects of time.

Pill or needle? Determinants of the preference for long-acting injection over oral treatment in people facing chronic illness.

Although long-acting injection (LAI) is presented as first line treatment option for patients with psychosis, negative attitudes toward this galenic negatively impact the selection of this treatment option. However, these negative attitudes may not be confined to patients but also observed in the general population. A web-based study on 1807 participants was conducted during which participants imagined that they had a particular chronic illness based on clinical vignettes (mental illnesses: schizophrenia, depression; somatic illnesses: multiple sclerosis, rheumatoid arthritis). The frequency of relapse and the intensity of symptoms were experimentally manipulated in the vignettes. Participants rated their subjective distress associated with each vignette, their belief in the effectiveness of treatment, and their treatment preference regarding medication. We examined under which conditions LAI was preferred over pills. Statistical analyses were performed using Bayesian methods. Results showed that participants preferred LAI over pills in 40.5% to 50.8% of cases. LAI was more preferred for illnesses with low frequency of relapse, low subjective distress, and for somatic than for mental illnesses. The perceived advantage for LAI over pills and the belief about the better efficiency of LAI were the main factors that drove the preference for LAI. Keeping in mind some advantages of LAI, the public negative representations of injections might partially influence patients' prejudices against LAI. These attitudes should be named and discussed with the patients when LAI seems to represent a relevant therapeutic option.