December 2016

As detailed above, interoception is strongly related to reward, urge, and craving, and alliesthesia emphasizes that through interoceptive processing these constructs are dependent on the pre-existing internal state of the individual, which may undergo positive/negative alliesthetic changes. Thus, three components appear critical for how an individual responds to drugs: (1) the internal or homeostatic state as signaled via afferents converging to the insular cortex; (2) the cognitive state of the individual, which includes a “contextualized” representation of the interoceptive state (Shipp, 2005); and (3) the learned associations of the external stimulus (e.g. the drug of choice) with previous outcomes including predicted internal states. These components clearly differ across individuals who are initially exposed to drugs and those who have been taking drugs for years.

In particular, negative alliesthesia refers to the notion that repeated administration of a stimulus will affect the internal milieu in such a way that the rewarding aspects of the stimulus are attenuated (e.g., the second or third piece of chocolate does not feel as good as the first). In contrast, positive alliesthesia is observed if the repeated administration (or omission) of a stimulus changes the internalmilieu in such a way as to increase its rewarding aspects. For example, fasting can enhance the subjective pleasantness of food images (Stoeckel et al., 2007). These phenomena can also be observed in animals. Specifically, pre-feeding has been associated with negative alliesthesia (Zhao and Cabanac, 1994), whereas food restriction was found to increase the sensory reward derived from alcohol, which is an example of positive alliesthesia (Soderpalm and Hansen, 1999). Based on the alliesthesia construct, some investigators proposed a dynamic, homeostatic hypothesis of pleasure regulation (Cabanac et al., 2002).