Project description:Accurate metacognitive judgments about an individual's performance in a mental task require the brain to have access to representations of the quality and difficulty of first-order cognitive processes. However, little is known about how accurate metacognitive judgments are implemented in the brain. Here, we combine brain stimulation with functional neuroimaging to determine the neural and psychological mechanisms underlying the frontopolar cortex's (FPC) role in metacognition. Specifically, we evaluate two-layer neural architectures positing that FPC enables metacognitive judgments by communicating with brain regions encoding first-order decision difficulty. In support of two-layer architectures of metacognition, we found that high-intensity transcranial alternating current stimulation (tACS; 4 mA peak-to-peak) over FPC impaired metacognitive accuracy; at the neural level, this impairment was reflected by reduced coupling between FPC and dorsolateral prefrontal cortex (DLPFC), particularly during difficult metacognitive judgments. We also evaluated conceptual accounts assuming that metacognition relies on self-directed mentalizing. However, we observed no influence of FPC tACS on mentalizing performance and only a weak overlap of the networks underlying metacognition and mentalizing. Together, our findings put the FPC at the center of a two-layer architecture that enables accurate evaluations of cognitive processes, mainly via the FPC's connectivity with regions encoding first-level task difficulty, with little contributions from mentalizing-related processes.
Project description:Brodmann's area 10 is one of the largest cytoarchitecturally defined regions in the human cerebral cortex, occupying the most anterior part of the prefrontal cortex [frontopolar cortex (FPC)], and is believed to sit atop a prefrontal hierarchy. The crucial contributions that the FPC makes to cognition are unknown. Rodents do not possess such [corrected] a FPC, but primates do, and we report here the behavioral effects of circumscribed FPC lesions in nonhuman primates. FPC lesions selectively impaired rapid one-trial learning about unfamiliar objects and unfamiliar objects-in-scenes, and also impaired rapid learning about novel abstract rules. Object recognition memory, shifting between established abstract behavioral rules, and the simultaneous application of two distinct rules were unaffected by the FPC lesion. The distinctive pattern of impaired and spared performance across these seven behavioral tasks reveals that the FPC mediates exploration and rapid learning about the relative value of novel behavioral options, and shows that the crucial contributions made by the FPC to cognition differ markedly from the contributions of other primate prefrontal regions.
Project description:Neuroimaging studies of working memory (WM) suggest that prefrontal cortex may assist sustained maintenance, but also internal manipulation, of stimulus representations in lower-level areas. A different line of research in the somatosensory domain indicates that neuronal activity in ventrolateral prefrontal cortex (VLPFC) may also represent specific memory contents in itself, however leaving open to what extent top-down control on lower-level areas is exerted, or how internal manipulation processes are implemented. We used functional imaging and connectivity analysis to study static maintenance and internal manipulation of tactile working memory contents after physically identical stimulation conditions, in human subjects. While both tasks recruited similar subareas in the inferior frontal gyrus (IFG) in VLPFC, static maintenance of the tactile information was additionally characterized by increased functional coupling between IFG and primary somatosensory cortex. Independently, during internal manipulation, a quantitative representation of the task-relevant information was evident in IFG itself, even in the absence of physical stimulation. Together, these findings demonstrate the functional diversity of activity within VLPFC according to different working memory demands, and underline the role of IFG as a core region in sensory WM processing.
Project description:In recent years, theoretical perspectives on posterior parietal function have evolved beyond the traditional visuospatial processing models to include more diverse cognitive operations, such as long-term and working memory. However, definitive neuropsychological evidence supporting the superior parietal lobule's purported role in working memory has been lacking. Here, we studied human brain lesion patients to determine whether the superior parietal lobule is indeed necessary for working memory. We assessed a wide range of memory functions in three participant groups: superior parietal lesions (n = 19), lesions not involving superior parietal cortex (n = 146), and no brain lesions (n = 55). Superior parietal damage was reliably associated with deficits on tests involving the manipulation and rearrangement of information in working memory, but not on working memory tests requiring only rehearsal and retrieval processes, nor on tests of long-term memory. These results indicate that superior parietal cortex is critically important for the manipulation of information in working memory.
Project description:Important decisions often involve choosing between complex environments that define future item encounters. Despite its importance for adaptive behavior and distinct computational challenges, decision-making research primarily focuses on item choice, ignoring environment choice altogether. Here we contrast previously studied item choice in ventromedial prefrontal cortex with lateral frontopolar cortex (FPl) linked to environment choice. Furthermore, we propose a mechanism for how FPl decomposes and represents complex environments during decision making. Specifically, we trained a choice-optimized, brain-naive convolutional neural network (CNN) and compared predicted CNN activation with actual FPl activity. We showed that the high-dimensional FPl activity decomposes environment features to represent the complexity of an environment to make such choice possible. Moreover, FPl functionally connects with posterior cingulate cortex for guiding environment choice. Further probing FPl's computation revealed a parallel processing mechanism in extracting multiple environment features.
Project description:The frontopolar cortex (FPC) contributes to tracking the reward of alternative choices during decision making, as well as their reliability. Whether this FPC function extends to reward gradients associated with continuous movements during motor learning remains unknown. We used anodal transcranial direct current stimulation (tDCS) over the right FPC to investigate its role in reward-based motor learning. Nineteen healthy human participants practiced novel sequences of finger movements on a digital piano with corresponding auditory feedback. Their aim was to use trialwise reward feedback to discover a hidden performance goal along a continuous dimension: timing. We additionally modulated the contralateral motor cortex (left M1) activity, and included a control sham stimulation. Right FPC-tDCS led to faster learning compared to lM1-tDCS and sham through regulation of motor variability. Bayesian computational modelling revealed that in all stimulation protocols, an increase in the trialwise expectation of reward was followed by greater exploitation, as shown previously. Yet, this association was weaker in lM1-tDCS suggesting a less efficient learning strategy. The effects of frontopolar stimulation were dissociated from those induced by lM1-tDCS and sham, as motor exploration was more sensitive to inferred changes in the reward tendency (volatility). The findings suggest that rFPC-tDCS increases the sensitivity of motor exploration to updates in reward volatility, accelerating reward-based motor learning.
Project description:Neuroimaging and lesion studies have implicated specific prefrontal cortex locations in subjective memory awareness. Based on this evidence, a rostrocaudal organization has been proposed whereby increasingly anterior prefrontal regions are increasingly involved in memory awareness. We used theta-burst transcranial magnetic stimulation (TBS) to temporarily modulate dorsolateral versus frontopolar prefrontal cortex to test for distinct causal roles in memory awareness. In three sessions, participants received TBS bilaterally to frontopolar cortex, dorsolateral prefrontal cortex, or a control location prior to performing an associative-recognition task involving judgments of memory awareness. Objective memory performance (i.e., accuracy) did not differ based on stimulation location. In contrast, frontopolar stimulation significantly influenced several measures of memory awareness. During study, judgments of learning were more accurate such that lower ratings were given to items that were subsequently forgotten selectively following frontopolar TBS. Confidence ratings during test were also higher for correct trials following frontopolar TBS. Finally, trial-by-trial correspondence between overt performance and subjective awareness during study demonstrated a linear increase across control, dorsolateral, and frontopolar TBS locations, supporting a rostrocaudal hierarchy of prefrontal contributions to memory awareness. These findings indicate that frontopolar cortex contributes causally to memory awareness, which was improved selectively by anatomically targeted TBS.
Project description:Bipolar and major depressive disorders are essentially relapsing and remitting disorders of affect with nearly full recovery between episodes. Although the underlying molecular mechanisms remain unclear, myelin-related abnormalities have long been suspected. Here, using novel statistical analysis, we show that subtle but significant abnormalities exist in the composition of fatty acids (FAs), including docosapentaenoic acid (22:5n-3), one of the omega-3 polyunsaturated FAs, found in the post-mortem frontopolar cortex (FPC) of subjects with bipolar or major depressive disorders, although not in those with schizophrenia. These abnormalities were all aggravated in a myelin level-dependent manner, suggesting their close relationship with myelination. Animal studies have further revealed that chronic antidepressant treatment induces robust changes in brain FA metabolism, but contributes only part of the abnormalities found in the affective disorder brains. These findings indicate that the pathophysiology of affective disorders involves an unknown type of perturbed myelination in the FPC that may serve as a novel diagnostic and therapeutic target.
Project description:The explore-exploit dilemma occurs anytime we must choose between exploring unknown options for information and exploiting known resources for reward. Previous work suggests that people use two different strategies to solve the explore-exploit dilemma: directed exploration, driven by information seeking, and random exploration, driven by decision noise. Here, we show that these two strategies rely on different neural systems. Using transcranial magnetic stimulation to inhibit the right frontopolar cortex, we were able to selectively inhibit directed exploration while leaving random exploration intact. This suggests a causal role for right frontopolar cortex in directed, but not random, exploration and that directed and random exploration rely on (at least partially) dissociable neural systems.
Project description:Decision making and learning in a real-world context require organisms to track not only the choices they make and the outcomes that follow but also other untaken, or counterfactual, choices and their outcomes. Although the neural system responsible for tracking the value of choices actually taken is increasingly well understood, whether a neural system tracks counterfactual information is currently unclear. Using a three-alternative decision-making task, a Bayesian reinforcement-learning algorithm, and fMRI, we investigated the coding of counterfactual choices and prediction errors in the human brain. Rather than representing evidence favoring multiple counterfactual choices, lateral frontal polar cortex (lFPC), dorsomedial frontal cortex (DMFC), and posteromedial cortex (PMC) encode the reward-based evidence favoring the best counterfactual option at future decisions. In addition to encoding counterfactual reward expectations, the network carries a signal for learning about counterfactual options when feedback is available-a counterfactual prediction error. Unlike other brain regions that have been associated with the processing of counterfactual outcomes, counterfactual prediction errors within the identified network cannot be related to regret theory. Furthermore, individual variation in counterfactual choice-related activity and prediction error-related activity, respectively, predicts variation in the propensity to switch to profitable choices in the future and the ability to learn from hypothetical feedback. Taken together, these data provide both neural and behavioral evidence to support the existence of a previously unidentified neural system responsible for tracking both counterfactual choice options and their outcomes.