Probing the causal role of the frontopolar cortex in cognitive effort based decision-making using transcranial direct current stimulation in healthy participants and Parkinson patients with apathy
General, Cognitive and Mathematical Psychology
Developmental and Educational Psychology
Human Cognitive and Systems Neuroscience
Cognitive, Systems and Behavioural Neurobiology
Final Report Abstract
Over the last decade, interdisciplinary research across Psychology, Medicine, and Cognitive Neuroscience became increasingly interested in the motivational aspects of cognitive control, i.e., the question of how humans (and other animals) decide when, if, and how much mental resources should be applied in a given situation. Many studies have since found that individuals tend to avoid cognitive control exertion, if possible, as they perceive it as effortful and aversive. Based on recent work demonstrating that transcranial direct current stimulation (tDCS) over the right frontopolar cortex (FPC) increases people’s willingness to exert cognitive effort for reward, this project aimed at testing whether the proposed motivational capacity of the FPC generalizes to choice problems that do not provide explicit information about effort and reward, as is common in many real-life situations. To this end, we collected data from 50 young, healthy individuals in a fully crossed, double-blind within subject design. Participants received either anodal (excitatory) or sham stimulation of the FPC while completing a novel effort-based foraging task that involves continuously choosing between harvesting a tree for a gradually declining amount of apples (i.e., rewards) or completing a cognitively demanding computer task to travel to a new, replenished tree. Previous work has shown that individuals stay longer at a given tree if travelling requires more compared to less mental effort, effectively reducing the rate at which they receive reward to avoid the cost of travelling. Results from this study indicate that stimulating the FPC reduced the difference in effort costs between low and high effort trials in the foraging task. Specifically, while we saw the expected “over-harvesting” of apples under sham stimulation, participants displayed more similar exit thresholds (i.e., number of apples at which they choose to leave a tree) between trial types under anodal tDCS. Our findings support the hypothesis of a generalized, causal role of the FPC in effortbased decision making, which has important implications for theories aimed at mapping out the neural substrates of these processes. Furthermore, our study indicates that the non-invasive stimulation of the right FPC might be a useful tool to potentially treat more severe forms of impaired motivation, such as apathy and anhedonia which are common in many psychiatric and neurological conditions. To test this, we had initially proposed a second study that would have used the same experimental design in patients with Parkinson’s Disease (PD). Unfortunately, due to the unexpected onset of the COVID-19 pandemic, we were not able to collect these data, as all research activities, especially those including in-person testing of vulnerable samples, were heavily restricted for the majority of the funding period. However, we were able to work on and publish several other studies that are closely related to the theme of the funded project. In one experiment, we used electroencephalography (EEG) to investigate neural signatures of reward processing following effort exertion. We found enhanced amplitudes in the Reward Positivity (RewP), a feedback-induced event-related potential (ERP) and increased reward-related delta band activity after exertion of high compared to low effort, indicating that exerted effort may enhance reward signals retrospectively (while usually reducing subjective reward value prospectively). Furthermore, in a pharmacological study in PD patients, we were able to show that patients OFF medication avoid effort exertion more strongly compared to ON medication in situations that do not involve any effort-related incentives, demonstrating that PD may specifically affect effort processing in addition to its known effects on reward sensitivity. Finally, we were able to conduct several online experiments that will contribute to the conceptual discussion about the construct of cognitive effort and its role in basic and translational research. Data from these studies are currently analyzed and will be published in the near future.
Publications
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Cognitive effort exertion enhances electrophysiological responses to rewarding outcomes. Cerebral Cortex, 32(19), 4255-4270.
Bogdanov, Mario; Renault, Héléna; LoParco, Sophia; Weinberg, Anna & Otto, A Ross
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Dopaminergic medication increases motivation to exert cognitive control by reducing subjective effort costs in Parkinson’s patients. Neurobiology of Learning and Memory, 193, 107652.
Bogdanov, Mario; LoParco, Sophia; Otto, A. Ross & Sharp, Madeleine
