After marijuana, amphetamines are the most widely used illicit drug class worldwide. A recent report estimates that methamphetamine causes about 895 deaths per year in the U.S. and is responsible for an annual economic burden of $23.5 billion. Negative reinforcement occurs when (a) an action is selected to avoid an aversive outcome or (b) an individual in an aversive state acts to end such a state and has been considered an important mechanism underlying compulsive drug-taking behavior. The aversive state or outcome is processed by the interoceptive system, which includes the insular cortex and signals """"""""how we feel"""""""". Risk- taking decision-making is among the key dysfunctional behaviors in drug addicted individuals. Yet, there have been no studies to examine the causal influence of altering interoception on risk-taking decision-making, i.e. """"""""how feeling bad affects the choices one makes"""""""". In response to the RFA, we bring together two experimental approaches to examine to how anticipating or experiencing an aversive state alters risk-taking behavior decision-making in methamphetamine dependent (MD) individuals. These approaches include (1) using aversive direct interoceptive stimulation and negatively valenced faces as non-interoceptive stimuli to modulate the state of the individual and (2) measuring the frequency of risky responses during a risk-taking task and the adjustment to errors during a two-choice prediction task. These approaches are combined with functional magnetic resonance imaging (fMRI) to examine how negative reinforcement mechanisms are implemented in the brain and to lay the groundwork for neural substrate specific treatment interventions.
Specific Aim 1 : To determine the behavioral effects of anticipating and experiencing an aversive and pleasant interoceptive stimulus and the impact of negatively and positively valenced faces on risky decision making in MD individuals, relative to comparison subjects.
Specific Aim 2 : To determine the brain activation differences associated with anticipating and experiencing an aversive and pleasant interoceptive stimulus and their impact on brain activation during risky decision making in MD individuals relative to comparison subjects.
Specific Aim 3 : To evaluate the plasticity of the behavioral and neuroimaging findings as a function of sustained abstinence in MD individuals. Based on a neural processing model, it is proposed that MD individuals exhibit two types of abnormalities: (1) an increased sensitivity to anticipating and experiencing aversive events and (2) a decreased flexibility to adjust their behavior when anticipating or experiencing an aversive event. Two experiments are proposed. First, the effect of breathing restriction and the effects of negatively valenced faces on the frequency of risky decision making will be examined in a behavioral and neuroimaging study of 30 recently abstinent (3-6 weeks) MD individuals and 30 healthy volunteers. Second, if - as we hypothesize - MD individuals fail to adjust their risk-taking behavior in response to negatively valenced faces, we will determine in another experiment the effect of anticipation of aversive interoceptive stimuli on risky choices. Alternatively, we will test the effect of aversive interoceptive stimuli on decision-making adjustments to errors during the two- choice prediction task. We have found recently that the activation pattern within the insular cortex change as a function of duration of drug use and/or abstinence. Thus, we will extend the cross-sectional study to include a 6 months follow-up to determine whether sustained abstinence is associated with an attenuation of the hypothesized behavioral and neural abnormalities. The results from these experiments will determine whether the interoceptive system itself is """"""""sensitized"""""""" or whether information from the interoceptive system, e.g. insular cortex, is not appropriately processed by other brain areas that are important for adjusting risk-taking and decision making, e.g. anterior cingulate and orbitofrontal cortex.
The basic brain and behavioral processes that cause the development and maintenance of methamphetamine dependence are poorly understood. Here, we will use brain imaging and behavioral experiments to address the question: do methamphetamine dependent individuals make poor decisions because they are overwhelmed by negative gut feelings? The answer to this question will help to develop specific interventions, e.g. to dampen the influence of negative gut feelings on decision-making or risk-taking and thereby increase the chance of abstinence.
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