Motor Control: Which Themes Do We Orchestrate?*

When we are confronted with a living system, whose design is mysterious and whose optimizations are obscure, it is no easy task--as Professor Stein reminds us--to arrive at an answer to the question he has posed in this paper. Stein's target article is an important contribution for two main reasons. The first, which we shall mention only in passing, is that it is likely to provide much debate on what the controlled variables might be; moreover, it will force those who find this a burning issue to put their cards on the table. The second, and we feel more important reason, is that the paper poses a question--"What muscle variable(s) does the nervous system control. .. ?"--whose very nature raises questions about the strategies neuroscience uses to investigate problems of control and coordination of movement. In our commentary we will focus on some of the (not so) implicit assumptions behind the question posed by Stein; if nothing else we hope to heighten sensi tivity to some of the issues involved and (perhaps) to force the neuroscientist to consider his/her epistemology.