Bereitschaftsfield in supplementary and cingulate motor areas and primary motor cortex: Job sharing in preparation, intention and execution of voluntary action

Erdler M., Beisteiner R., Mayer D., Lindinger G., Milakara D., and Deecke L.
Department of Clinical Neurology, Medical University, Vienna, Austria and Ludwig Boltzmann Institute for Functional Brain Topography, Vienna, Austria

While the 'expectancy wave' or Contingent Negative Variation (CNV) occurs in conjunction with a reaction time experiment to exogenous stimuli, volitional self-initiated acts are endogenous and are preceded by the Bereitschaftspotential (BP). Thus, the CNV paradigm is associated with re-actions, while the BP paradigm is associated with actions. Both, CNV and BP, have two components an early and a late one. The early component is termed BP1 and lasts from the very beginning of the BP (1-2 s or more prior to movement onset) to about 0.5 s prior to movement onset. The late component is termed BP2 and lasts from 0.5 s to shortly before movement. BP1 is symmetrical even for unilateral movement, while BP2 shows a characteristic contralateral dominance. For simple movements, BP1 starts about 1 or 1.5 sec prior to the onset of movement; for complex movements, onset time is even longer, up to 3 s. For simple movements, the BP is positive in frontal leads and negative in central and parietal leads. According to the theory of the EEG, negativity can be related to activity of the cortical areas under study, while positivity is related to inactivity. The BP paradigm (voluntary movement paradigm) investigates internally produced movement, that is willed actions. For these volitional movements one can envisage an 'act of will' necessary to self-initiate the movement. This certainly is a 'frontal act', and the decision of 'when to move' is thought to be elaborated by the mesial fronto-central cortex (CMA and SMA).