What is mental effort: a clinical perspective.

Although mental effort is a frequently used term, it is poorly defined and understood. Consequently, its usage is frequently loose and potentially misleading. In neuroscience research, the term is used to mean both the cognitive 'work' that is done in meeting task demands, and the subjective experience of performing that work. We argue that conflating these two meanings hampers progress in understanding cognitive impairments in neuropsychiatric conditions, because cognitive work and the subjective experience of it have distinct underlying mechanisms. We suggest that the most coherent and clinically useful perspective on mental effort is that it is a subjective experience. This makes a clear distinction between cognitive impairments arising from changes in the cognitive apparatus, as in dementia and brain injury, and those arising from subjective difficulties in carrying out the cognitive work, as in attention deficit hyperactivity disorder, depression, and other motivational disorders. We review recent advances in neuroscience research, suggesting the experience of effort has emerged to control task switches so as to minimise 'costs' relative to 'benefits.' We consider how these advances can contribute to our understanding of the experience of increased effort perception in clinical populations. This more specific framing of mental effort will offer a deeper understanding of the mechanisms of cognitive impairments in differing clinical groups, and will ultimately facilitate better therapeutic interventions.