Elizabeth O'Nions

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.

Serotonin transporter genotype modulates subgenual response to fearful faces using an incidental task

This study assessed the impact of serotonin transporter genotype (5-HTTLPR) on regional responses to emotional faces in the amygdala and subgenual cingulate cortex (sgACC), while subjects performed a gender discrimination task. Although we found no evidence for greater amygdala reactivity or reduced amygdala–sgACC coupling in short variant 5-HTTLPR homozygotes (s/s), we observed an interaction between genotype and emotion in sgACC. Only long variant homozygotes (la/la) exhibited subgenual deactivation to fearful versus neutral faces, whereas the effect in s/s subjects was in the other direction. This absence of subgenual deactivation in s/s subjects parallels a recent finding in depressed subjects [Grimm, S., Boesiger, P., Beck, J., Schuepbach, D., Bermpohl, F., Walter, M., et al. Altered negative BOLD responses in the default-mode network during emotion processing in depressed subjects. Neuropsychopharmacology, 34, 932–943, 2009]. Taken together, the findings suggest that subgenual cingulate activity may play an important role in regulating the impact of aversive stimuli, potentially conferring greater resilience to the effects of aversive stimuli in la/la subjects. Using dynamic causal modeling of functional magnetic resonance imaging data, we explored the effects of genotype on effective connectivity and emotion-specific changes in coupling across a network of regions implicated in social processing. Viewing fearful faces enhanced bidirectional excitatory coupling between the amygdala and the fusiform gyrus, and increased the inhibitory influence of the amygdala over the sgACC, although this modulation of coupling did not differ between the genotype groups. The findings are discussed in relation to the role of sgACC and serotonin in moderating responses to aversive stimuli [Dayan, P., & Huys, Q. J., Serotonin, inhibition, and negative mood. PLoS Comput Biol, 4, e4, 2008; Mayberg, H. S., Liotti, M., Brannan, S. K., McGinnis, S., Mahurin, R. K., Jerabek, P. A., et al. Reciprocal limbic–cortical function and negative mood: Converging PET findings in depression and normal sadness. Am J Psychiatry, 156, 675–682, 1999].

Pathological demand avoidance: Exploring the behavioural profile

‘Pathological Demand Avoidance’ is a term increasingly used by practitioners in the United Kingdom. It was coined to describe a profile of obsessive resistance to everyday demands and requests, with a tendency to resort to ‘socially manipulative’ behaviour, including outrageous or embarrassing acts. Pathological demand avoidance is thought to share aspects of social impairment with autism spectrum disorders, but autism spectrum disorder–appropriate strategies, such as routine and repetition, are described as unhelpful. Outrageous acts and lack of concern for their effects draw parallels with conduct problems and callous-unemotional traits. However, reward-based techniques, effective with conduct problems and callous-unemotional traits, seem not to work in pathological demand avoidance. Despite increasing interest and controversy over the pathological demand avoidance label, there is only one published study to date. We present the first systematic comparison of the behavioural profile of children receiving the term pathological demand avoidance (N = 25) to children with autism spectrum disorders (N = 39) or conduct problems and callous-unemotional traits (N = 28), using parent-report indices of psychopathology. The pathological demand avoidance group displayed comparable levels of autistic traits and peer problems to the autism spectrum disorders group and anti-social traits approaching those seen in the conduct problems and callous-unemotional traits group. Emotional symptoms in pathological demand avoidance exceeded both comparison groups. Findings highlight the extreme behavioural impairment associated with pathological demand avoidance and the need to explore whether behavioural overlap reflects a similar neurocognitive basis to existing groups.

Pathological Demand Avoidance in a population-based cohort of children with epilepsy: four case studies.

Childhood epilepsy is associated with a range of neurobehavioural comorbidities including Attention-Deficit/Hyperactivity Disorder (ADHD), Autism Spectrum Disorder (ASD), motor impairments and emotional problems. These difficulties frequently have a greater impact on quality of life than seizures. Pathological Demand Avoidance (PDA) is a term increasingly in use in the UK and Europe to describe behaviours associated with an extreme resistance to demands and requests and the need to be in control in social interactions. In a population-based group of 85 children with epilepsy, four (5%) were identified as displaying significant symptoms of PDA, were assessed using the Extreme Demand Avoidance Questionnaire (EDA-Q) and are described in detail. As well as significant symptoms of PDA, the four children met criteria for a range of neurobehavioural disorders; all four had cognitive impairment (IQ<85) and met DSM-IV-TR criteria for ADHD. Three, in addition, met criteria for ASD and Developmental Coordination Disorder (DCD) and two for Oppositional Defiant Disorder (ODD). All four experienced their first seizure before 5 years of age. School and parent reports indicated very significant functional impairment and management concerns, particularly with respect to complying with everyday demands. Symptoms of PDA should be considered when evaluating neurobehavioural comorbidity in childhood epilepsy.