Distinct brain signatures of content and structure violation during action observation

Sentences, musical phrases and goal-directed actions are composed of elements that are linked by specific rules to form meaningful outcomes. In goal-directed actions including a non-canonical element or scrambling the order of the elements alters the action's content and structure, respectively. In the present study we investigated event-related potentials of the electroencephalographic (EEG) activity recorded during observation of both alterations of the action content (obtained by violating the semantic components of an action, e.g. making coffee with cola) and alterations of the action structure (obtained by inverting the order of two temporally adjacent pictures of sequences depicting daily life actions) interfering with the normal flow of the motor acts that compose an action. Action content alterations elicited a bilateral posterior distributed EEG negativity, peaking at around 400 ms after stimulus onset similar to the ERPs evoked by semantic violations in language studies. Alteration of the action structure elicited an early left anterior negativity followed by a late left anterior positivity, which closely resembles the ERP pattern found in language syntax violation studies. Our results suggest a functional dissociation between the processing of action content and structure, reminiscent of a similar dissociation found in the language or music domains. Importantly, this study provides further support to the hypothesis that some basic mechanisms, such as the rule-based structuring of sequential events, are shared between different cognitive domains.