The Enduring Outcomes of Stress During Neurodevelopment Dynamically Impact Food Reward Responsiveness and Valuation: A Meta-Analysis of Pre-Clinical Evidence
Early Life Stress , Meta-Analysis , Reward , Rodents
Early life stress (ELS), broadly defined as stress occurring prior to the onset of adulthood, increases risk of reward-processing pathology in later life. Pre-clinical research using rodent models provide a means for examining the enduring effects of ELS on reward-related behaviours in a causal manner. Evidence from pre-clinical research varies; some studies suggest that ELS reduces behavioural indices of reward processing in later life, whereas others observe heightened reward processing behaviours following ELS. An emerging hypothesis is that these diverging outcomes might reflect unique reward-related subconstructs being differentially influenced by ELS, differences in type of ELS, age at ELS, or sex. To address these variable findings, I conducted a meta-analysis investigating the enduring effects of ELS on reward-related behaviours with a focus on food reward. The systematic literature search was conducted with a focus on studies employing ELS in rodents and examining responses to food reward in adulthood. Specifically, studies reporting data from paradigms measuring initial responsiveness to food reward (i.e., sucrose preference and sucrose reactivity tests), reward satiation (i.e., food intake paradigms), and effort (i.e., progressive ratio tests for food reward). This search yielded 2234 studies, 71 of which met inclusion criterion. The meta-analysis suggested the effects of ELS vary by the reward-related subconstruct tested. ELS rodents demonstrated decreased initial reward responsiveness, which was moderated by the type of ELS incurred, but not age at ELS or sex. ELS also decreased indices of reward satiation in adult rodents, which was dependent on the age at ELS, but not the type of ELS. Surprisingly, the effects of ELS on effort to obtain a food reward yielded non-significant results. Taken together, these data demonstrate the importance of investigating reward-related behaviours in a subconstruct specific manner and provide insights into the manners by which ELS might dynamically influence reward-related outcomes.