The game motoneurons play

We offer a new game-theoretical approach to analyze the developmental competition between motoneurons (motor-neurons) that innervate the same muscle. The size principle--stating that motoneurons with successively higher activation thresholds innervate successively larger portions of muscle--is thought to result from this competition. However, it was not known how. We define a game in which motoneurons "compete" to innervate a maximal number of muscle-fibers. Their strategies are their activity levels. We resolve an existing paradox of contradictory experimental data regarding the role of activity in this competition, explain the emergence of the size principle, and provide new experimentally testable predictions. We conclude that the time of winnings has a competitive value, such that it is better to win more in later competitions. This conclusion has implications for economical systems.