Patients suffering from neuropsychiatric disorders such as substance-related and addictive disorders exhibit altered decisionmaking patterns, which may be associated with their behavioral abnormalities. However, the neuronal mechanisms underlying such impairments are largely unknown. Using a gambling test, we demonstrated that methamphetamine (METH)-treated rats chose a highrisk/high-reward option more frequently and assigned higher value to high returns than control rats, suggestive of changes in decisionmaking choice strategy. Immunohistochemical analysis following the gambling test revealed aberrant activation of the insular cortex (INS) and nucleus accumbens in METH-treated animals. Pharmacological studies, together with in vivo microdialysis, showed that the insular neural system played a crucial role in decision-making. Moreover, manipulation of INS activation using designer receptor exclusively activated by designer drug technology resulted in alterations to decision-making. Our findings suggest that the INS is a critical region involved in decision-making and that insular neural dysfunction results in risk-taking behaviors associated with altered decision-making.decision-making | methamphetamine | insular cortex | DREADD | motivational value D ecision-making is a key activity of everyday life. Consequently, disturbances in the ability to make appropriate decisions or anticipate their possible consequences can result in massive social, medical, and financial problems. Decision-making depends on three temporally and partially functionally distinct sets of processes: (i) assessment and formation of preferences among possible options, (ii) selection and execution of an action, and (iii) experience or evaluation of the outcome (1). These processes are thought to require an extended neural network, mainly comprising glutamatergic, serotonergic, noradrenergic, and dopaminergic pathways in the frontostriatal and limbic loops, including the cingulate cortex, orbitofrontal cortex (OFC), insular cortex (INS), striatum (St), basal ganglia, and amygdala (2). Analysis of these processes helps to distinguish which aspects of decision-making are differentially affected in various neuropsychiatric disorders (1).Poor decision-making is a symptom of several neuropsychiatric diseases, such as depression, schizophrenia, Parkinson's disease, and drug dependence (1,(3)(4)(5). Pathological decision-making in neuropsychiatric disorders is associated with an inability to make profitable long-term decisions that incorporate expectations of future outcomes (6). Thus, pathological decision-making is recognized as a core problem in neuropsychiatric disorders, and a better understanding of the mechanisms underlying altered decisionmaking should provide insights that could lead to successful treatments for these diseases.A hallmark of addiction is continuous use of substances despite negative consequences or the absence of positive consequences (7). Addicts are less able to flexibly adapt their behavior to changes in reward contingenci...