The significance of body part as tool errors in limb apraxia

When pantomiming to command, individuals with left hemisphere brain damage (LBD) often produce errors in which they use a body part as if it were the tool (BPT). Some clinicians question the significance of this type of error because subjects without brain damage at times also make BPT responses. We analyzed BPT errors in LBD and normal subjects who were reinstructed to modify the inappropriate BPT responses when they occurred. We also analyzed errors in normal subjects who were never reinstructed if a BPT occurred. Whereas LBD subjects who were reinstructed produced significantly more BPT errors than normals who were also reinstructed, LBD subjects were not different from normals who were not reinstructed. When reinstructed, normal control subjects correctly modified virtually all BPT errors, whereas LBD subjects did not modify BPT errors. These findings underscore the need for reinstruction when a BPT error occurs to determine whether it represents a true BPT error, a sign of limb apraxia.