A recent shift in psychiatry and the neurosciences has been towards trying to decompose top-level phenotypes (symptoms) into intermediate biological markers (Cuthbert & Insel,
2013). Such measures may then, conceivably, act as intermediaries to better understand the relationships between genetic-environmental risk factors and the ultimate expression of psychiatric syndromes (Chamberlain, Stochl, Redden, & Grant,
2017). Neuropsychological tests relating to decision-making are likely to be relevant in this search, given that decision-making problems are suggested by the symptoms of substance and behavioral addictions and this premise formed the basis for the current narrative review. Our first hypothesis, namely that addictions are associated with decision-making impairments on cognitive tasks, was partly supported by our literature search. We found meta-analytic support, from the literature, for the existence of decision-making impairments in several types of substance use disorders (e.g. alcohol, opioid), and in gambling disorder. The magnitude of effect appeared larger and with lower heterogeneity in relation to gambling disorder. Evidence of decision-making deficits in other behavioral addictions (kleptomania, compulsive shopping, compulsive sexual behavior disorder) was partial only, with a poverty of data studies, highlighting the need for much more research into these neglected areas of mental health. Rather than refuting our hypothesis, rather our findings inform the need for more research in these settings. Furthermore, neurochemical systems and fronto-striatal circuitry underpinning decision-making (Clark et al.,
2008; Clark, Cools, & Robbins,
2004; Fellows & Farah,
2005; Preuschoff, Bossaerts, & Quartz,
2006; Simon et al.,
2011; Talbot, Watson, Barrett, & Cooper,
2006) are implicated in the pathophysiology of addictive disorders (Clark & Limbrick-Oldfield,
2013; de Ruiter, Oosterlaan, Veltman, van den Brink, & Goudriaan,
2012; Goudriaan, Yucel, & van Holst,
2014; Rogers et al.,
1999; Verdejo-Garcia, Chong, Stout, Yucel, & London,
2017). Thus, based on the evidence so far, these decision-making impairments observable in substance and gambling addictions may be linked with reductions in cortical grey matter (Ersche, Williams, Robbins, & Bullmore,
2013; Grant, Odlaug, & Chamberlain,
2015) coupled with functional abnormalities of the frontal cortices and basal ganglia (ventral and dorsal striatum: Luijten, Schellekens, Kuhn, Machielse, & Sescousse,
2017). Regions such as these are richly modulated by different neurochemical systems, which may provide a new vista on future treatment directions as well as helping to account for positive data for some glutamatergic agents and opioid antagonists.
Our second hypothesis, that treatments with efficacy in these disorders may act via modulation of fronto-striatal circuitry involved in decision-making was not directly addressable due to an absence of relevant data. Medications with the firmest evidence for treating addictions include those acting on the glutamatergic and opioid systems, which are known to play key roles in decision-making and fronto-striatal circuitry. However, few clinical trials in addiction had included objective cognitive measures of decision-making. There were some open-label pilot data suggesting that memantine may improve decision-making (impulsivity) in compulsive shopping and kleptomania (Grant et al.,
2012; Grant, Odlaug, Schreiber, et al.,
2013). To address this second hypothesis further would require future clinical trials for addictions that include not only traditional clinical outcome measures but also cognitive outcome measures.
It is seen from this selective overview of the existing addiction literature that while pharmacological treatments exist for the symptomatic treatment of addictions linked with decision-making impairments, it is not yet clearly established that objective improvements in decision-making on laboratory-based tasks are directly linked with symptomatic improvement. Because cognitive impairments germane to decision-making appear common in addictive disorders, it would be valuable for future clinical trials to include such measures alongside the more traditional symptom outcome measures (Goodie & Fortune,
2013; Grant, Chamberlain, Schreiber, Odlaug, & Kim,
2011). The current review enables recommendations to be drawn together for such future work, including the need to minimize heterogeneity by using highly validated reliable cognitive tasks, the need to take a translational approach in clinical trials by including imaging and cognitive measures, and the need for more research into behavioral addictions in general, several of which are extremely neglected from clinical and research perspectives. In addition to examining pharmacological and psychological treatments for decision-making deficits, brain modulatory techniques should also be investigated.