A tapping test in apraxia.

An enigma in understanding the mechanism of motor apraxia is why patients with disease restricted to the left hemisphere cannot imitate motions with the left hand despite intact visual motor apparatus. Liepmann suggested that motor memories are stored in the left hemisphere and that in apraxia these engrams are either destroyed or separated from the right hemisphere. If Liepmann's hypothesis is correct, then, in addition to poor performance on commands and imitation, there should be poor performance in a motor task. To ascertain if there is a motor defect of the non-paretic hand of apraxic patients, twenty apraxic patients were given a rapid finger tapping test and their performance was compared with the left hand performance of aphasic right hemiparetic non-apraxic controls. The aptaxic group performed this task significantly slower than the control group, thereby giving support to Liepmann's hypothesis of apraxia.