Bimanual coordination: An unbalanced field of research

Using more than one limb to perform functional, goal-directed actions is arguably one of the most important abilities that human beings possess. In many everyday tasks, the hands, in particular, must be used to accomplish all manner of goals. From buttoning a shirt to opening a jam jar and driving to work, good bimanual coordination is of great utility. In addition to the tasks mentioned above, there are also other tasks involving the functional use of more than one limb, including walking or cycling and typing a report. With a little thought, it becomes apparent that there is at least one important difference between these categories of coordination tasks. On one hand, in some tasks the effectors must perform markedly different motor outputs that are bound together in some functionally defined and usually object-oriented manner (e.g., buttoning a shirt) yet, in others, the effectors produce very similar motor outputs but in a specific temporal order, which may or may not repeat itself periodically (e.g., walking and cycling compared to typing or drumming). In this short article, I will argue that the second category of coordination task and, in particular, cyclical coordination, has been studied extensively and, at least at the level of behavior, is relatively well understood. In contrast the former category of bimanual task is seldom studied and, even at the descriptive level, is rather poorly understood. One of the reasons for this may be the complexity of such tasks and the technical difficulties involved in attempting to study them. By highlighting some key studies, I hope to illustrate that such tasks can be fruitfully studied in the laboratory. Last, since the neural control processes underlying both classes of coordination task are not yet well known, I aim to draw attention to the potential value of the interventional technique of Transcranial Magnetic Stimulation (TMS) as a tool for investigating the functions of brain regions contributing to bimanual coordination.