Robert Wood Johnson Medical School
Neuromodulation and cognitive effort
Cognitive control is effortful, causing people to avoid demanding tasks, and undermining their goal-directed behavior. Yet the nature of effort costs, and the systems biasing decisions to exert or withhold effort are largely unknown. Striatal dopamine promotes physical effort for reward, by increasing sensitivity to reward benefits and decreasing sensitivity to effort costs. In the first part of my talk, I will discuss evidence that, as with physical action, striatal dopamine boosts motivation for cognitive effort as well. In a study combining [18F]-DOPA PET imaging of dopamine synthesis capacity with dopamine transport blocker methylphenidate, the D2 agent sulpiride, and placebo, we find that greater striatal dopamine signaling biases participants to choose harder working memory tasks to earn more money over easier tasks for less money. Moreover, gaze-informed drift diffusion modeling supports the inference that dopamine signaling increases willingness to exert effort by making people more sensitive to the benefits, and less sensitive to the costs of cognitive work.
In the second part of this talk, I consider a novel hypothesis about the nature of effort costs. Namely, that subjective cognitive effort is a phenomenological readout of divergence from criticality in the brain. Brains at rest exhibit emergent properties indicative of a dynamical system near a critical point – regulated by the balance of cortical excitation to inhibition. These properties are monotonically suppressed with increasing cognitive load, reflecting increasing divergence from criticality. Importantly, because criticality maximizes functional flexibility and information processing capacity, divergence implies computational costs. In my talk, I will discuss the rationale for the hypothesis linking subjective effort and criticality. I will also discuss a first study examining subjective cognitive effort and critical dynamics in EEG data while participants perform various levels of the N-back working memory task.