Mental Effort: Brain and Autonomic Correlates in Health and Disease

Abstract

Mental effort is an embodied process for the short-term deployment of attentional, cognitive and affective resources. The engagement of mental effort involves whole brain shifts in the activation and functional connectivity of sensory and integrative brain regions. Concurrent changes in bodily internal physiology are mediated by cortically driven modulation of subcortical and brainstem homeostatic centres. Within the brain, there is typically engagement of components of the salience network including (sympathetic visceromotor) dorsal anterior cingulate cortex and (viscerosensory) bilateral insula cortex. There is also commonly a disengagement of the default mode network (‘antisympathetic’ ventromedial prefrontal cortex and posterior cingulate/precuneus) regions. The bidirectional impact of these changes on bodily states of preparedness is mediated neurally via midbrain and brainstem centres. The accompanying state of autonomic arousal is proposed to facilitate goal-directed cognitive processes and underpin feelings of perceived difficulty, control and achievement. Mental effort also elicits more task-specific involvement of executive frontoparietal centres and sensory cortices, while the achievability and control of sustained effort feeds back into affective circuitry. Clinical disorders of effort accompany inflammation-induced stereotyped sickness responses and span developmental, ‘functional’ and degenerative psychiatric diagnostic boundaries. Fatigue states, inattentiveness and diminished motivational drive suggest discrete dimensions through which effort is compromised. Mental effort is ultimately tied to top-down predictions and the value associated with active more precise inferences about future behavioural outcomes.