An altered neural response to reward may contribute to alcohol problems among late adolescents with an evening chronotype

Abstract

Evening chronotypes not only differ from morning-types in their sleep and circadian timing, but they are prone to problematic outcomes involving reward function, including affective disturbance, sensation seeking, and substance involvement. We explored the neural mechanisms underlying these chronotype differences by comparing the neural response to reward in morning- and evening-types. Using a monetary reward fMRI paradigm, we compared the neural response to reward in 13 morning-types and 21 evening-types (all 20 y/o males). Region-of-interest (ROI) analyses focused on the medial prefrontal cortex (mPFC) and ventral striatum (VS), comparing the chronotype groups in these ROIs during anticipation and outcome conditions, and adjusting for time of scan. Chronotype groups were also compared on measures of sensation-seeking, substance involvement, and sleep quality. Evening-types reported significantly greater levels of alcohol dependence and worse sleep quality. Furthermore, evening-types showed an altered neural response to reward relative to morning-types, specifically, reduced mPFC reactivity during reward anticipation and increased VS reactivity during win outcome. In turn, less activation in the mPFC region in response to reward was associated with greater alcohol consumption, while increased activation in the VS in response to reward was associated with more symptoms of alcohol dependence. Increased reward-related problems among evening-types may be accompanied by altered neural responses to reward.

Keywords: Adolescence; Alcohol abuse; Brain imaging; Chronotype; Circadian rhythms; Sleep.

Figure 1

Chronotype differences in the neural response to the anticipation (1A) and outcome (1B) of monetary reward. Results are based on two-tailed t-tests run in SPM8, covarying for the time of scan, and masked for regions of interest in the medial prefrontal cortex (mPFC) and ventral striatum (VS). Evening-types displayed less mFPC activity during reward anticipation compared to morning-types (1A). Evening-types displayed more VS activity during win outcome compared to morning-types (1B).

Figure 2

Medial prefrontal cortex (mPFC) activity during anticipation of monetary reward correlated with the alcohol consumption scale on the ADCQ (2A) and ventral striatal (VS) activity during the win outcome of monetary reward correlated with scores on the Alcohol Dependence Scale (2B). Results are based on regression analysis in SPM8, masked either for the mPFC cluster in which Evening-types displayed less mPFC activity during reward anticipation (see Figure 1A), or for the VS cluster in which Evening-types displayed greater VS activity during win outcome (see Figure 1B), respectively. Open diamonds = Morning-types; filled diamonds = Evening-types.