Role of somatosensory feedback from tools in realizing movements by patients with ideomotor apraxia

In order to investigate the underlying mechanism of ideomotor apraxia, we studied 9 patients who could not mime using tools despite the ability to manipulate actual tools normally. In all the mime tasks, visually presented tools or model gestures by examiners were fundamentally ineffectual in improving the patients' performances. Even the remarkable improvement demonstrated when using actual tools disappeared immediately after the subjects took their hands off them. In a further experiment, 4 of the 9 patients were required to pretend to use tools while holding a stick, resulting in significant improvements or normal miming. These findings suggest that the somatosensory feedback continuously supplied from a handheld tool is a crucial component in enabling patients with ideomotor apraxia to actually use tools.