Gesture errors in left and right hemisphere damaged patients: a behavioural and anatomical study

Objective. Erroneous gesture execution is at the core of motor cognition difficulties in apraxia. While a taxonomy of errors may provide important information about the nature of the disorder, classifications are currently often inconsistent. This study aims to identify the error categories which distinguish apraxic from non-apraxic patients. Method. Two groups of mixed and bucco-facial apraxic patients were compared to non-apraxic, left and right hemisphere damaged patients in tasks tapping the ability to perform transitive and intransitive limb and mouth actions. The errors were analysed and classified into 6 categories relating to content, configuration or movement, spatial or temporal parameters and unrecognisable actions. Results. Although all these error typologies may be observed, the most indicative of mixed apraxia relate to content and configuration, while configuration and unrecognisable/destructured action errors seem to be typical of bucco-facial apraxia. Spatial errors are similar in both apraxic and right brain damaged, non-apraxic patients. A lesion mapping analysis of left-brain damaged patients demonstrates that the error categories (except for spatial errors) are all associated with the fronto-parietal network. Tellingly, content errors are also associated with fronto-insular lesions and movement errors with damage to the paracentral territory (precentral and postcentral gyri). Spatial errors more frequently involve ventral frontal lesions. Conclusions. Bucco-facial and mixed apraxic patients make different types of errors in different types of actions. Not all errors are equally indicative of apraxia. In addition, the various error categories are associated with at least partially different neural correlates.