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Background Previously we showed that working memory training decreased the discounting of future rewards in stimulant addicts without affecting a Go/NoGo task. While a relationship between delay discounting and working memory is consistent with other studies, the unique brain regions of plausible causality between these two abilities have yet to be determined. Methods Activation likelihood estimation (ALE) meta-analyses were performed on foci from studies of delay discounting (DD = 449), working memory (WM = 452), finger tapping (FT = 450), and response inhibition (RI = 450). Activity maps from relatively less (FT) and more (RI) demanding executive tasks were contrasted with maps of DD and WM. Overlap analysis identified unique functional coincidence between DD and WM. Results The anterior cingulate cortex was engaged by all tasks. FT largely engaged motor-related brain areas. In addition to motor-related areas, RI engaged frontal brain regions. The right lateral prefrontal cortex was engaged by RI, DD and WM and was contrasted out of overlap maps. A functional cluster in the posterior portion of the left lateral prefrontal cortex emerged as the largest location of unique overlap between DD and WM. Conclusions A portion of the left lateral prefrontal cortex is a unique location where delay discounting and working memory processes overlap in the brain. This area, therefore, represents a therapeutic target for improving behaviors that rely on the integration of the recent past with the foreseeable future.

Chronic marijuana users (MJ Users) perform poorly on the Iowa Gambling Task (IGT), a complex decision-making task in which monetary wins and losses guide strategy development. This study sought to determine if the poor performance of MJ Users was related to differences in brain activity while evaluating wins and losses during the strategy development phase of the IGT. MJ Users (16) and Controls (16) performed a modified IGT in an MRI scanner. Performance was tracked and functional activity to early wins and losses was examined. While the MJ Users continued to perform poorly at the end of the task, there was no difference in group performance during the initial strategy development phase. During this phase, before the emergence of behavioral differences, Controls exhibited significantly greater activity in response to losses in the anterior cingulate cortex, medial frontal cortex, precuneus, superior parietal lobe, occipital lobe and cerebellum as compared to MJ Users. Furthermore, in Controls, but not MJ Users, the functional response to losses in the anterior cingulate cortex, ventral medial prefrontal cortex and rostral prefrontal cortex positively correlated with performance over time. These data suggest MJ Users are less sensitive to negative feedback during strategy development.

Hand preferences for a coordinated bimanual task were assessed in 109 chimpanzees (Pan troglodytes). Hand preference was evaluated for 4 test sessions using bouts and frequencies of hand use to compare the sensitivity of each level of analysis in evaluating individual variation in handedness. Overall, significant population-level right-handedness was found using several different measures of hand use. Handedness indices based on bouts and frequencies were highly and significantly correlated. Moreover, hand preferences were consistent across tests despite efforts to situationally bias preference during each test. Taken together, these data do not support the view that bouts are a better level of analysis for evaluating hand preference. The results further suggest that hand preferences for coordinated bimanual actions are not influenced by situational factors and may reflect an inherent specialization of the left hemisphere for motor skill.The issue of whether nonhuman primates exhibit population-level handedness has been a topic of historical and recent debate (Ettlinger, 1988;Fagot & Vauclair, 1991;MacNeilage, StuddertKennedy, & Lindblom, 1987;Marchant & McGrew, 1991;Ward & Hopkins, 1993;Warren, 1980 NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript sample display the same directional bias in hand use. The historical view held that handedness was bimodally distributed in nonhuman species including primates (Warren, 1980), but this view has recently been challenged by a host of behavioral Studies (see Bradshaw & Rogers, 1993;Hook-Costigan & Rogers, 1997;Hopkins, 1996;Hopkins & Morris, 1993;Lehman, 1993;Ward, Milliken, & Stafford, 1993, for reviews). Of specific interest to this article is the evidence of population-level right-handedness in chimpanzees and other great apes. Some have argued that there is a 2:1 ratio of right-to left-handed individuals (Corballis, 1997;Hopkins, 1999b;Hopkins & Pearson, 2000). In contrast, others have argued that the evidence is weak for population-level right-handedness in apes and that some Studies reporting evidence of population-level right-handedness are methodologically or statistically flawed (McGrew & Marchant, 1997).Presently, the debate over whether great apes (and other nonhuman primates) exhibit population-level hand preference centers on two issues, both of which are subject to different interpretation. One issue is whether population-level right-handedness is restricted to captive populations of apes, and this issue is not addressed in this article. The second issue, which is addressed in this article, is whether the use of frequencies contrasted with bouts of lateralized behavior reflects the same or different manifestations of lateral bias at the individual and population level. Specifically, Marchant (1994,1997), as well as others (Boesch, 1991;Byrne & Byrne, 1991), have argued that bouts are a better measure of laterality in hand use than the use of the raw frequencies. The central premise of this argument, outlined by McGrew and ...

Population-level right-handedness has historically been considered a hallmark of human evolution. Even though recent studies in chimpanzees (Pan troglodytes) have demonstrated population-level right-handedness for certain behaviors, some have questioned the validity and consistency of these findings by arguing that reported laterality effects are specific to certain colonies of apes and to those chimpanzees reared by humans. The authors report evidence of population-level right-handedness in 3 separate colonies of chimpanzees. Moreover, handedness in the 3 colonies was unrelated to the proportion of subjects that were raised by humans. This is the strongest evidence to date that population-level handedness is evident in chimpanzees and is not an artifact of human rearing.