The conventional theory of apraxia has primarily focused on the left hemisphere since Liepmann’s initial model. However, the role of the right hemisphere has not been given sufficient attention. Specifically, the involvement of the right hemisphere in praxis may be crucial for apraxia rehabilitation. Despite a lack of high-quality research clarifying its effective approach, considering the role of the right hemisphere in rehabilitation settings might prove beneficial.

Here, we propose a supplementary role of the right hemisphere and its corresponding auxiliary function of the left-hand during praxis, especially in tool use. Traditional examinations of apraxia have mainly focused on the activities of the dominant hand, namely the right hand, clarifying the role of the left hemisphere. For instance, when assessing the tool-use action of cutting paper with scissors, evaluations have been conducted through pantomime or the actual use of the tool, observing the subject's ability to correctly handle and manipulate the scissors with the right hand. However, everyday actions typically require the involvement of both hands. Moreover, in clinical settings, instances of inadequate auxiliary use of the left hand are not uncommonly observed in patients with apraxia.

The coordinated movement of the right hand, responsible for the primary action, and the left hand, acting as the auxiliary hand, is basically simultaneous. For example, during scissor manipulation, we typically begin by having the left-hand hold and position the paper before grasping the scissors with the right hand. Subsequently, the left hand guides the paper during cutting with the right hand. Surprisingly, the left hand even moves ahead of the right hand. In such instances, the activation of the primary motor area in the right hemisphere must be involved during the movement of the left hand. However, the traditional theory of apraxia suggests that the neural basis for the act of "cutting paper" is located in the parietal lobe of the left hemisphere. This raises questions: How is the auxiliary use of the left hand developed in the context of brain mechanisms? How is the connection from the parietal lobe in the left hemisphere to the primary motor area of the right hemisphere established? Moreover, when observing movements related to preparing the left hand's actions, it even seems plausible that the involvement of the right hemisphere occurs at the very early stage of the action.

Considering the involvement of the right hemisphere in praxis holds additional practical significance for apraxia rehabilitation. This is particularly relevant for apraxia patients with paralysis in the right upper extremity who must rely on their intact left hand for daily activities. Therefore, from a rehabilitation perspective, it becomes crucial to elucidate the role of the right hemisphere in praxis.

Despite the long-established view on praxis, motor actions inherently engage both hands or even the entire body. In the context of apraxia, we propose reconsidering the mechanism of action not as confined to the left hemisphere but as a function of the entire brain, including the right hemisphere.