Bonsai Trees in Your Head: How the Pavlovian System Sculpts Goal-Directed Choices by Pruning Decision Trees

When planning a series of actions, it is usually infeasible to consider all potential future sequences; instead, one must prune the decision tree. Provably optimal pruning is, however, still computationally ruinous and the specific approximations humans employ remain unknown. We designed a new sequential reinforcement-based task and showed that human subjects adopted a simple pruning strategy: during mental evaluation of a sequence of choices, they curtailed any further evaluation of a sequence as soon as they encountered a large loss. This pruning strategy was Pavlovian: it was reflexively evoked by large losses and persisted even when overwhelmingly counterproductive. It was also evident above and beyond loss aversion. We found that the tendency towards Pavlovian pruning was selectively predicted by the degree to which subjects exhibited sub-clinical mood disturbance, in accordance with theories that ascribe Pavlovian behavioural inhibition, via serotonin, a role in mood disorders. We conclude that Pavlovian behavioural inhibition shapes highly flexible, goal-directed choices in a manner that may be important for theories of decision-making in mood disorders

Response time variability and response inhibition predict affective problems in adolescent girls, not in boys: the TRAILS study

The present study examines the relationship between neurocognitive functioning and affective problems through adolescence, in a cross-sectional and longitudinal perspective. Baseline response speed, response speed variability, response inhibition, attentional flexibility and working memory were assessed in a cohort of 2,179 adolescents (age 10–12 years) from the TRacking Adolescents’ Individual Lives Survey (TRAILS). Affective problems were measured with the DSM-oriented Affective Problems scale of the Youth Self Report at wave 1 (baseline assessment), wave 2 (after 2.5 years) and wave 3 (after 5 years). Cross-sectionally, baseline response speed, response time variability, response inhibition and working memory were associated with baseline affective problems in girls, but not in boys. Longitudinally, enhanced response time variability predicted affective problems after 2.5 and 5 years in girls, but not in boys. Decreased response inhibition predicted affective problems after 5 years follow-up in girls, and again not in boys. The results are discussed in light of recent insights in gender differences in adolescence and state–trait issues in depression

Cognitive performance in tests sensitive to frontal lobe dysfunction in the elderly depressed

SynopsisThe paper reports the profile of impairment across a variety of cognitive functions with special emphasis on tests sensitive to frontal lobe dysfunction, in 24 elderly depressed patients during and on recovery from mood disorder, compared with 15 age- and sex-matched controls. Traditional neuropsychological tests and a recently developed battery of computerized tests (CANTAB) were used. Impairments were found in the depressed group compared to controls and to themselves on recovery across all domains examined. The depressed group showed deficits on visuospatial recognition memory, attentional shifting at the extra-dimensional shift stage and in measures of both processing and motor speed without impaired accuracy in a visual search task. Impairments were also found on a planning task with disproportionately increased numbers of moves needed for more difficult problems and evidence of both slowed motor response and increased processing time once the task was commenced.Performance on recovery improved across all tasks. Comparisons were made with the performance of patients suffering from dementia of the Alzheimer type (DAT) and Parkinson's disease on similar tests. Response latencies in test performance were found to correlate with the number of episodes of depression suffered and with ventricular size on CT scan, as measured by computerized planimetry. On recovery, residual depression scores correlated with latency of test performance and with ventricular brain ratio. The results, thus, show that depression in the elderly is associated with a significant degree of deficit on tests sensitive to frontostriatal dysfunction. Some of the deficits appear specific to depression and some do not remit following clinical recovery. However, these impairments have to be interpreted in the context of a broad profile of cognitive deficit.</jats:p