When is the brain ready for mental actions? Readiness potential for mental calculations

While the preparatory neural mechanisms of real and imagined body movements have been extensively studied, the underpinnings of self-initiated, voluntary mental acts are largely unknown. Therefore, using electroencephalography (EEG), we studied the time course and patterns of changes in brain activity associated with purely mental processes which start on their own, without an external or interoceptive stimulation. We compared EEG recordings for decisions to perform mental operations on numbers, imagined finger movements, and actual finger movements. In all three cases, we found striking similarities in slow negative shifts of brain electrical activity lasting around 1 s and, therefore, characteristic for readiness potential. These results show that the brain not only needs time to be ready for a purely mental task but also that a required preparatory interval involves neural changes analogical to the ones observed before intentional body movements. As such, the readiness potential represents a universal process of unconscious preparatory brain activity preceding any, including purely mental, voluntary action.