Inferior Parietal Lobule Supports Decision Making under Uncertainty in Humans

University of Minnesota, Department ofPsychology & Center for Cognitive Sciences, Minneapolis, MN,USAThe optimal responses for many decisions faced by humans are illdeﬁned, yet we are able to choose well by associating choices withoutcomes, and employing this information in decision making.Previous studies suggest that the parietal cortex is involved in‘‘uncertain’’ decision making, yet uncertainty is confounded withincreased difﬁculty and attention. Here we aim to dissociate therole of parietal cortex in decision making and attention. Usingfunctional magnetic resonance imaging we measured brain activitywhile participants played a ‘‘matching-pennies’’ game. We foundthat the inferior parietal lobule is involved in decision making underuncertainty, showing higher activity when the decision wasuncertain rather than certain and when humans were given trial-by-trial feedback on choice outcomes than when they were not.Crucially, increasing attentional load with secondary tasks reducedinferior parietal activity when decisions were made under un-certainty, suggesting that general attention does not drive itsactivation. This pattern was consistent for visual or auditoryfeedback, and for direct (symbols representing wins and losses) orindirect (only the opponent’s choices were shown) feedback. Itcontrasted with results from medial superior frontal gyrus, whichwas driven primarily by increased attentional load. We suggest thatdecision making under uncertainty is dissociable from generalattention in the brain.Keywords: attention, decision making, inferior parietal lobule, rewardIntroductionDecision making sometimes involves straightforward, objectivecriteria, such as determining the direction of a moving object,even if made in the presence of perceptual noise (Shadlen andNewsome 2001), whereas at other times it is inherentlyuncertain, as when we gamble on a roll of the dice, theweather on a particular day, or the behavior of another agent.Much research in decision making has confronted the formertype, by having participants categorize, discriminate, or detecta signal among noise (Heekeren et al. 2004). Increasingly,researchers are exploring the neural machinery underlyinguncertain decision making (Barraclough et al. 2004; Dorris andGlimcher 2004; Sugrue et al. 2004; Glimcher 2005). Whenchoices are uncertain, humans must often take into accountmany sources of evidence, especially previous experience(Sutton and Barto 1998; Feltovich 2000; Camerer 2003). Thus,the historical association of rewards and punishments withchoices becomes a key element in decision making. Here, weexamine the role of inferior parietal lobule (IPL) in supportingdecision making under uncertainty, as distinct from rule-baseddecision making, general attention, and executive functions.Decision making under uncertainty is construed broadly, toinclude processes that compute action-reward associations,opponent and environment modeling, and the integration ofthese factors into a ﬁnal choice.Previous research has located several frontal and parietalregions that are more active during uncertain decision makingthan certain, rule-based decision making. Some regions, in-cluding the inferior parietal cortex, show activity that is gradedin proportion to relative feedback about previous choiceoutcomes (Paulus et al. 2001; Nickerson 2002; Miller et al.2005). For example, Huettel, Song, and McCarthy presentedcontexts that represented with varying degrees of certaintywhich of 2 responses were ‘‘correct.’’ Blood oxygenation level--dependent (BOLD) responses in regions of parietal cortex(among others) were higher for less certain than more certainchoices (Huettel et al. 2005). However, parietal cortex issensitive to increased attentional effort and task demandsunder a broad range of cognitive tasks (Kanwisher andWojciulik 2000; Shuman and Kanwisher 2004). Increasedactivation in the presence of uncertainty may simply reﬂectgreater attentional demands under uncertain than certainconditions. At present, it is unknown whether parietal regionssingled out for involvement in uncertain decision making showspecialization for calculations that support optimal decisions ofthis type, or whether they simply reﬂect increased attentionaldemands (Bechara et al. 1998; Maunsell 2004).Miller et al. (2005) attempted to dissociate decision makingunder uncertainty from attentional demands by subtractingactivity in an N-back working memory task from those in anuncertain decision-making task. The subtraction left noactivation in IPL, casting doubts on its speciﬁc role in decisionmaking. However, this subtraction contrasted 2 very differenttasks, in which a number of variables were altered, clouding theinterpretation of this contrast.In the present study we sought to clarify the role of IPL indecision making under uncertainty using functional magneticresonance imaging (fMRI). We asked whether activity in IPLreﬂects increased attentional demands associated with in-creased decision uncertainty, or whether it reﬂects the in-volvement of this region in either calculating choices on thebasis of feedback from prior trials, or tracking the associationsbetween choices and feedback. We manipulated as directly aspossible the overall effort required of the participants acrossdifferent attentional conditions and under different feedbackconditions.Inouranalysis,wecontrastBOLDactivationpatternsin IPL to those in the medial superior frontal gyrus (mSFG),anotherregionwhichhasanindeterminateroleinattentionanddecision making (Carter et al. 2000; Duncan and Owen 2000;Walton et al. 2003; Rushworth et al. 2004). These 2 regionsprovide us with a clear and compelling contrast.