Project 4

Effects of d-amphetamine on emotional modulation of the startle reflex in healthy volunteers

A number of major theories of the motivational substrates underlying substance use posit that the mesolimbic dopamine system is central to addictive processes. However, theories differ in the way in which dopamine may be involved. Some theories posit that dopamine is a so-called “pleasure” neurotransmitter, with hedonic aspects of stimuli mediated by dopamine release in the nucleus accumbens. Other theorists disagree, arguing that dopamine is involved in “incentive” effects; that is, dopamine subserves “wanting”, not “liking”. Yet other theorists argue that dopamine mediates effects of both hedonic and aversive stimuli, and its actions are better characterised as being “arousal-like”. Hedonic stimuli decrease the effect of startling stimuli on the startle reflex, whereas aversive stimuli increase the effect of startling stimuli. Arousal potentiates the effects of both. Thus, the effect of amphetamine on the modulation of the startle response can differentiate between