Symmetrical effects of amphetamine and alpha-flupenthixol on conditioned punishment and conditioned reinforcement: contrasts with midazolam

Killcross, A.S., Everitt, B.J., & Robbins, T.W. (1997). Symmetrical effects of amphetamine and alpha-flupenthixol on conditioned punishment and conditioned reinforcement: contrasts with midazolam. Psychopharmacology, 129, 141-152.

There is evidence to suggest that forebrain dopaminergic systems are likely to be involved in both appetitive and aversive motivation. These authors studied the effects of dopamine (DA) agents on conditioned punishment (aversive learning) and conditioned reinforcement (appetitive learning) paradigms using DA agonists and antagonists injected systemically. In conditioned punishment, a Pavlovian CS predicting punishment is added to an instrumental bar-pressing paradigm, but only on one of the bars. Normal animals will adjust their bar-pressing away from this lever. (Note: These authors, however, implemented a punishment procedure by presenting a CS and shock upon bar-press, rather than a conditioned punishment procedure which would only present the CS upon bar-press). In conditioned reinforcement, a CS predicting reward is added to the instrumental bar-pressing paradigm on one of the bars. Animals will naturally come to favor this bar paired with the appetitive CS.

DA agonists increased the effect of a punishing CS, causing the animals to further decrease their bar pressing. DA agonists also enhanced the effect of an appetitive CS, increasing bar pressing. DA antagonists, on the other hand, decreased the effect of a punishing CS. They also reduced the effect of an appetitive CS. Thus, it appears dopaminergic agents modulate the behavioral impact of both appetitively and aversively motivated conditioned stimuli on instrumental performance. Systemic benzodiazepene administration was also explored with results showing a selective impact on aversively-motivated stimuli (i.e. no effect on the appetitive CS).

Parallel incentive processing: an integrated view of amygdala function

Balleine, B.W. & Killcross, S. (May 2006). Parallel incentive processing: an integrated view of amygdala function. Trends in Neuroscience, Vol. 29, 272-279.

Although the amygdala has been long studied for its involvement in emotional learning and memory, the exact nature of its involvement is still disputed. Historically, a serial model has predominated, with the lateral nucleus detecting threatening stimuli and the central nucleus initiating expression of defensive behaviors and other bodily responses associated with fear reactivity. However, in this paper Balleine and Killcross opine perhaps it's time to consider alternative models, and propose a model which, based on appetitive conditioning studies, has the basolateral and central nuclei operating independently and in parallel to mediate incentive processes in both appetitive and aversive situations. They suggest the basolateral nucleus encodes emotional events with reference to their particular sensory features, while the central nucleus provides affective significance to processing, motivating or inciting responses and actions.