A temporal difference account of avoidance learning

Phasic excitation of dopamine neurons in ventral VTA by noxious stimuli

Midbrain dopamine neurons play central roles in reward processing. It is widely assumed that all dopamine neurons encode the same information. Some evidence, however, suggests functional differences between subgroups of dopamine neurons, particularly with respect to processing nonrewarding, aversive stimuli. To directly test this possibility, we recorded from and juxtacellularly labeled individual ventral tegmental area (VTA) dopamine neurons in anesthetized rats so that we could link precise anatomical position and neurochemical identity with coding for noxious stimuli. Here, we show that dopamine neurons in the dorsal VTA are inhibited by noxious footshocks, consistent with their role in reward processing. In contrast, we find that dopamine neurons in the ventral VTA are phasically excited by footshocks. This observation can explain a number of previously confusing findings that suggested a role for dopamine in processing both rewarding and aversive events. Taken together, our results indicate that there are 2 functionally and anatomically distinct VTA dopamine systems.

Social predictors of psychotic experiences: specificity and psychological mechanisms

It has become widely accepted that the psychotic disorders are endpoints of atypical developmental trajectories indexed by abnormal emotional and cognitive development early in life. However, the role of environmental factors in determining these trajectories has received relatively little attention. In this article, we argue that (1) the influence of environment on psychosis can best be understood if we focus on specific types of psychotic experiences such as hallucinations and delusions, (2) these symptoms are the products of specific cognitive biases and deficits, and (3) the development of these particular patterns of cognitive functioning is influenced by specific kinds of environmental adversity. This approach is at variance with more conventional approaches because it suggests that each type of experience, rather than being the manifestation of a common underlying illness process, is a product of a specific set of causal variables. Importantly, these variables include environmental determinants, although not to the exclusion of endogenous factors such as neurodevelopmental impairment or genetic vulnerability. We discuss the implications of this approach for neurobiological and genetic research into psychosis, as well as clinical practice.