Low Dopamine D2/D3 Receptor Availability is Associated with Steep Discounting of Delayed Rewards in Methamphetamine Dependence.

BackgroundIndividuals with substance use disorders typically exhibit a predilection toward instant gratification with apparent disregard for the future consequences of their actions. Indirect evidence suggests that low dopamine D2-type receptor availability in the striatum contributes to the propensity of these individuals to sacrifice long-term goals for short-term gain; however, this possibility has not been tested directly. We investigated whether striatal D2/D3 receptor availability is negatively correlated with the preference for smaller, more immediate rewards over larger, delayed alternatives among research participants who met DSM-IV criteria for methamphetamine (MA) dependence.MethodsFifty-four adults (n = 27 each: MA-dependent, non-user controls) completed the Kirby Monetary Choice Questionnaire, and underwent positron emission tomography scanning with [(18)F]fallypride.ResultsMA users displayed steeper temporal discounting (p = 0.030) and lower striatal D2/D3 receptor availability (p < 0.0005) than controls. Discount rate was negatively correlated with striatal D2/D3 receptor availability, with the relationship reaching statistical significance in the combined sample (r = -0.291, p = 0.016) and among MA users alone (r = -0.342, p = 0.041), but not among controls alone (r = -0.179, p = 0.185); the slopes did not differ significantly between MA users and controls (p = 0.5).ConclusionsThese results provide the first direct evidence of a link between deficient D2/D3 receptor availability and steep temporal discounting. This finding fits with reports that low striatal D2/D3 receptor availability is associated with a higher risk of relapse among stimulant users, and may help to explain why some individuals choose to continue using drugs despite knowledge of their eventual negative consequences. Future research directions and therapeutic implications are discussed

On the biomedicalization of alcoholism

The shift in the prevailing view of alcoholism from a moral paradigm towards a biomedical paradigm is often characterized as a form of biomedicalization. We will examine and critique three reasons offered for the claim that viewing alcoholism as a disease is morally problematic. The first is that the new conceptualization of alcoholism as a chronic brain disease will lead to individualization, e.g., a too narrow focus on the individual person, excluding cultural and social dimensions of alcoholism. The second claim is that biomedicalization will lead to stigmatization and discrimination for both alcoholics and people who are at risk of becoming alcoholics. The third claim is that as a result of the biomedical point of view, the autonomy and responsibility of alcoholics and possibly even persons at risk may be unjustly restricted. Our conclusion is that the claims against the biomedical conceptualization of alcoholism as a chronic brain disease are neither specific nor convincing. Not only do some of these concerns also apply to the traditional moral model; above that they are not strong enough to justify the rejection of the new biomedical model altogether. The focus in the scientific and public debate should not be on some massive “biomedicalization objection” but on the various concerns underlying what is framed in terms of the biomedicalization of alcoholism

Model-based functional neuroimaging using dynamic neural fields: An integrative cognitive neuroscience approach

A fundamental challenge in cognitive neuroscience is to develop theoretical frameworks that effectively span the gap between brain and behavior, between neuroscience and psychology. Here, we attempt to bridge this divide by formalizing an integrative cognitive neuroscience approach using dynamic field theory (DFT). We begin by providing an overview of how DFT seeks to understand the neural population dynamics that underlie cognitive processes through previous applications and comparisons to other modeling approaches. We then use previously published behavioral and neural data from a response selection Go/Nogo task as a case study for model simulations. Results from this study served as the ‘standard’ for comparisons with a model-based fMRI approach using dynamic neural fields (DNF). The tutorial explains the rationale and hypotheses involved in the process of creating the DNF architecture and fitting model parameters. Two DNF models, with similar structure and parameter sets, are then compared. Both models effectively simulated reaction times from the task as we varied the number of stimulus–response mappings and the proportion of Go trials. Next, we directly simulated hemodynamic predictions from the neural activation patterns from each model. These predictions were tested using general linear models (GLMs). Results showed that the DNF model that was created by tuning parameters to capture simultaneously trends in neural activation and behavioral data quantitatively outperformed a Standard GLM analysis of the same dataset. Further, by using the GLM results to assign functional roles to particular clusters in the brain, we illustrate how DNF models shed new light on the neural populations’ dynamics within particular brain regions. Thus, the present study illustrates how an interactive cognitive neuroscience model can be used in practice to bridge the gap between brain and behavior

Explaining away behavior: Scientific analysis and the transformation of acts into occurrences

In ordinary person perception, observers make a distinction between voluntary and involuntary behaviors. Generally, social accountability is restricted to those behaviors that are considered voluntary. Scientific explanations of behavior can at times undermine the conception that the explained behavior is voluntary. In light of the great many recent advances in the sciences that target human behavior, this is an increasingly important issue. The experiments reported below examine the tendency of explanations to devoluntarize behavior as well as impact related judgments such as blame worthiness and deserved punishment. The following three aspects of explanations were manipulated: (1) the prevalence of the behavior given the explanatory antecedent, (2) the deterrability of the behavior given the explanatory antecedent, and (3) the type of explanatory antecedent cited--physiological or experiential. The effects of the first two factors on the degree of devoluntarization were both statistically significant though surprisingly minor. The type of explanation cited had a large and highly reliable effect, and was the only independent variable to reliably effect all dependent measures related to volition. Devoluntarization appears to depend not on the certainty with which the explained behavior is shown to follow from antecedents, but rather on the explanation\u27s effectiveness at getting subjects to adopt an object attributional framework

Explaining away behavior: Scientific analysis and the transformation of acts into occurrences

In ordinary person perception, observers make a distinction between voluntary and involuntary behaviors. Generally, social accountability is restricted to those behaviors that are considered voluntary. Scientific explanations of behavior can at times undermine the conception that the explained behavior is voluntary. In light of the great many recent advances in the sciences that target human behavior, this is an increasingly important issue. The experiments reported below examine the tendency of explanations to devoluntarize behavior as well as impact related judgments such as blame worthiness and deserved punishment. The following three aspects of explanations were manipulated: (1) the prevalence of the behavior given the explanatory antecedent, (2) the deterrability of the behavior given the explanatory antecedent, and (3) the type of explanatory antecedent cited--physiological or experiential. The effects of the first two factors on the degree of devoluntarization were both statistically significant though surprisingly minor. The type of explanation cited had a large and highly reliable effect, and was the only independent variable to reliably effect all dependent measures related to volition. Devoluntarization appears to depend not on the certainty with which the explained behavior is shown to follow from antecedents, but rather on the explanation\u27s effectiveness at getting subjects to adopt an object attributional framework