This case study provides evidence, that DBS affecting the NAcc/BSTM/VP region has an impact on reward processing. Behaviorally, the patient showed a tendency towards more risky behavior when the stimulator was turned off. A similar behavioral pattern is known from Parkinson patients treated with drugs affecting dopaminergic D2/D3 receptors 
known to give rise to a number of impulse control disorders 
but also from studies with healthy young subjects receiving dopaminergic D2/D3 agonists 
. Thus, one might speculate that DBS in the NAcc normalizes reward processing and reduces impulsive choices in patients with chronic alcohol abuse. However, this interpretation has to be substantiated by further experiments, since a re-examination outside the PET-scanner four month later did not result in a full replication of the behavioral results . While the pattern of risky choices still remained by trend, the reaction times showed an inverse pattern of results. Thus, we are not able to rule out any order effects entirely, although this had been the re-examination's intention. The question remains why the behavioral results could not be fully replicated.
Importantly, robust and statistically significant changes in the PET activation maps were observed that were more pronounced with stimulators turned on. Specifically, monetary rewards (compared to losses) led to an activation of the paracingulate cortex and the temporal poles. The paracingulate cortex integrates affective and motor information in behavioral control and adaptation 
in particular in economic decisions 
and receives input from the NAcc 
. Functionally, the paracingulate cortex can be divided into two sections: the dorsal part, which is known to be involved in the processing of cognitive control, and the rostral part, which is related to the processing of affective information in behavioral control tasks 
. The increased activity in the rostral part of the paracingulate cortex under active DBS is pointing to an involvement of emotional processes in behavioral adaptation and control in the win condition. The participation of emotional processes is known to be essential for effective adaptation and control of behavior 
. The absence of rCBF changes in this part of the paracingulate cortex under deactivated DBS suggests that without active DBS this integrative function is not involved. In conjunction with the observed behavioral data this implies that DBS in the NAcc complex seems to improve behavioral adaption. The temporal poles receive input from all three senses 
and, as part of the paralimbic circuitry and the parahippocampal cortex, are interconnected to the amygdala, the orbitofrontal cortex, and the hippocampus 
. Accordingly, the temporal poles are often described as a multimodal convergence zone integrating sensory input, memory and emotion in order to bind emotional information across sensory domains 
. This temporal pole function forms the basis for more complex cognitions like autobiographical memory 
or the processing of self-referential information 
. Self-referential information is needed for evaluative judgment 
, and results - successful decisions and adequate self-attribution assumed - in self-conscious emotions like joy or pride 
. As indicated by the increased rCBF changes, these mechanisms are likely triggered to a greater extent in runs with an excess of win-trials. Again, the differences between win and loss trials are more pronounced for the DBS-on than for the DBS-off condition, indicating that under active DBS positive outcomes of choices increase self-referential processing. Accordingly, DBS effects may facilitate the selective ascription of positive outcome to one's own behavior. By contrast, for the runs with more loss trials greater activation was seen in the precuneus and hippocampus. The latter has been implicated in reward based learning and decision making processes 
. The processing of reward related contextual aspects in the hippocampus 
improves and facilitates predictions about upcoming events 
. As Coricelli and colleagues 
have shown, hippocampal and parahippocampal areas also support the affective evaluation of the outcome of a decision. The hippocampal activations observed in the loss condition under active DBS suggest an increased involvement of these evaluation processes. The precuneus has been tightly linked to evidence accumulation in decision making situations 
, in particular in unpredictable situations 
. Accordingly, the precuneus is also reported to be active during risky decisions 
and the identification of risk 
. With respect to the present investigation active NAcc-DBS seems to increase activation in cortical areas which are necessary for identifying situations that are (potentially) disadvantageous.
Interestingly, no blood flow changes were observed in the DBS target area. This might be caused by the partial volume effect in PET imaging, which results in an underestimation of the activity in small structures like the NAcc or BSTM 
To sum up, under stimulator on conditions, brain areas were seen activated under active DBS that have been previously linked to aspects of behavioral control and decision making. Importantly, under deactivated DBS most of these activations were no longer seen with the exception of the right temporal pole. This said, it has to stressed that the present PET and behavioral data are coming from a single case and thus have to be interpreted with caution. Due to ethical reasons it was not practicable to examine the patient a second time and accordingly potential order effects cannot be ruled out. However, the reported results fit well to the literature and provide a first glimpse at the impact of DBS on the neural underpinnings of decision making and cognitive control. Together with the behavioral effect towards more risky behavior this suggests that behavioral control is impaired with the stimulator turned off. Future investigations have to examine the hypothesis that enhanced behavioral control is likely to contribute to the clinical effect of DBS in the NAcc.
Despite the known limitations of single case reports we conclude that DBS in the NAcc improves behavioral control in decision making processes by activating areas related to processing of self-referential information, integration of emotional information and updating of contextual information. While further investigations are needed to substantiate this finding, this mechanism might contribute to the efficacy of DBS in addiction.