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One of the most salient and well-recognized features of human goal-directed behavior is our limited ability to conduct multiple demanding tasks at once. Previous work has identified overlap between task processing pathways as a limiting factor for multitasking performance in neural architectures. This raises an important question: insofar as shared representation between tasks introduces the risk of cross-talk and thereby limitations in multitasking, why would the brain prefer shared task representations over separate representations across tasks? We seek to answer this question by introducing formal considerations and neural network simulations in which we contrast the multitasking limitations that shared task representations incur with their benefits for task learning. Our results suggest that neural network architectures face a fundamental tradeoff between learning efficiency and multitasking performance in environments with shared structure between tasks.

International audience

The adaptive regulation of the trade-off between pursuing a known reward (exploitation) and sampling lesser-known options in search of something better (exploration) is critical for optimal performance. Theory and recent empirical work suggest that humans use at least two strategies for solving this dilemma: a directed strategy in which choices are explicitly biased toward information seeking, and a random strategy in which decision noise leads to exploration by chance. Here we examined the hypothesis that random exploration is governed by the neuromodulatory locus coeruleus-norepinephrine system. We administered atomoxetine, a norepinephrine transporter blocker that increases extracellular levels of norepinephrine throughout the cortex, to 22 healthy human participants in a double-blind crossover design. We examined the effect of treatment on performance in a gambling task designed to produce distinct measures of directed exploration and random exploration. In line with our hypothesis we found an effect of atomoxetine on random, but not directed exploration. However, contrary to expectation, atomoxetine reduced rather than increased random exploration. We offer three potential explanations of our findings, involving the non-linear relationship between tonic NE and cognitive performance, the interaction of atomoxetine with other neuromodulators, and the possibility that atomoxetine affected phasic norepinephrine activity more so than tonic norepinephrine activity.

Recent studies have begun to elucidate the neural correlates of evidence accumulation in perceptual decision making. Few of them have used a combined modeling-electrophysiological approach to studying evidence accumulation. We introduce a novel multivariate approach to EEG analysis with which we can perform a comprehensive search for neural correlates of dynamics predicted by the drift diffusion model. We show that the dynamics of evidence accumulation are correlated with de- creases in the 4–9 Hz theta band over the course of a trial. The rate of decrease in this band correlates with individual differ- ences in fitted drift diffusion model parameters.