Modulation of anticipatory brain activity as a function of action complexity

Stimulus-driven actions are preceded by preparatory brain activity that can be expressed by event-related potentials (ERP). Literature on this topic has mainly focused on simple actions, such as the finger keypress, finding activity in frontal, parietal, and occipital areas detectable up to two seconds before the stimulus onset. However, little is known about the preparatory brain activity when the action complexity increases, and specific brain areas designated to achieve movement integration intervene. The main aim of this paper is to identify the time course of preparatory brain activity associated with actions of increasing complexity using ERP analysis and a visuomotor discrimination task. Motor complexity was manipulated by asking nineteen volunteers to provide their response by simply pressing a key or by adding to the keypress arm extensions (reaching) alone, or in combination with a standing step (involving the whole body). Results showed that these actions of increasing levels of complexity appear to be associated with different patterns of preparatory brain activity. Specifically, the simple keypress was characterized by the largest motor excitatory preparation in premotor areas paralleled by the largest prefrontal inhibitory/attentional control. Reaching presented a dominant parietal preparation confirming the role of these integration areas in reaching actions toward a goal. Stepping was characterized by localized activity in the bilateral dorsomedial parieto-occipital areas attributable to sensory readiness, for the approaching stimulus. In conclusion, the brain is able to optimally anticipate any stimulus-driven action modulating the activity in the brain areas specialized in the preparation of that action type.