5. Critical need for the study of individual differences in
sleep-reward circuitry
There is significant overlap between the neural circuitry controlling
the motivation for reward and the circuitry controlling sleep-wake
states (Fig. 1). Given the many points of interaction between these
systems, it is easy to see why these behavioral states are so closely
intertwined, and how acute or chronic sleep disturbances can cause such
profound changes in the consumption of food, drugs, and alcohol.
Individual differences are a major concern for the study of both
addiction and sleep disorders. There is tremendous individual variation
in how these conditions develop, the effects they have on health and
social functioning, and how they respond to treatment. Rodents show
natural phenotypic differences in the degree to which food-paired cues
engage mesolimbic dopaminergic activity and elicit incentive
motivational states. These individual differences have a strong genetic
component, and are associated with other behavioral traits that are
frequently comorbid with addictive tendencies. By taking advantage of
these individual differences, it may be possible to determine whether
certain sleep patterns represent an underlying predisposing factor for
addictive behavior. For example, a predisposition for poor quality or
fragmented sleep, prior to any drug or reward exposure, may be one of
several traits that are part of an addictive phenotype. Disordered sleep
may cause certain individuals to experience greater attraction to
incentive cues when they are first encountered (leading to
sign-tracking), which may then be exacerbated by further cue exposure or
by the sleep deficits that can result from the comsumption of drugs or
alcohol. Another possibility is that baseline sleep characteristics do
not differ between STs and GTs, but the hyper-responsive mesolimbic
circuitry that underlies sign-tracking may render STs especially
vulnerable to the negative effects of sleep deprivation on
reward-seeking behavior. In either case, the ST/GT model could provide a
better understanding of how the neural pathways mediating sleep and
motivation interact with each other, and ultimately lead to treatment
strategies for substance use disorders that are more closely tailored to
the unique needs of each invidual.