Differential coding of absolute and relative aversive value in the Drosophila brain.

Animals use prior experience to assign absolute (good or bad) and relative (better or worse) value to new experience. These learned values guide appropriate later decision making. Even though our understanding of how the valuation system computes absolute value is relatively advanced, the mechanistic underpinnings of relative valuation are unclear. Here, we uncover mechanisms of absolute and relative aversive valuation in Drosophila. Three types of punishment-sensitive dopaminergic neurons (DANs) respond differently to electric shock intensity. During learning, these punishment-sensitive DANs drive intensity-scaled plasticity at their respective mushroom body output neuron (MBON) connections to code absolute aversive value. In contrast, by comparing the absolute value of current and previous aversive experiences, the MBON-DAN network can code relative aversive value by using specific punishment-sensitive DANs and recruiting a specific subtype of reward-coding DANs. Behavioral and physiological experiments revealed that a specific subtype of reward-coding DAN assigns a "better than" value to the lesser of the two aversive experiences. This study therefore highlights how appetitive-aversive system interactions within the MB network can code and compare sequential aversive experiences to learn relative aversive value.

The effectiveness of physical exercise as an intervention to reduce depressive symptoms following traumatic brain injury: A meta-analysis and systematic review.

Alongside the obvious health benefits, physical exercise has been shown to have a modest anti-depressant effect for people in the general population. To the authors' knowledge, there are no current literature reviews or meta-analyses available exploring this effect for people with a traumatic brain injury (TBI). A systematic review of intervention studies utilising physical exercise and mood outcome measures for a TBI population was performed in November 2016. Baseline and outcome data were extracted for the nine studies which met the inclusion criteria. Effect sizes were calculated for the three controlled trials and six uncontrolled trials and entered into the meta-analysis. Consistent with research in non-brain injury populations, the current meta-analysis identified a small to medium effect size of physical exercise on reducing depressive symptoms in people with a TBI. This would support further rigorous trials to provide additional evidence for the efficacy of physical exercise interventions for people with TBI. Limitations of the current meta-analysis and clinical implications are discussed.