Cook et al. argue that mirror neurons originate in sensorimotor associative learning and that their function is determined by their origin. Both these claims are hard to accept. It is here suggested that a major role in the origin of the mirror mechanism is played by top-down connections rather than by associative learning.

A comparative fMRI study by Peeters et al. (2009) provided evidence that a specific sector of left inferior parietal lobule is devoted to tool use in humans, but not in monkeys. We propose that this area represents the neural substrate of the human capacity to understand tool use by using causal reasoning.

In this study, we first briefly review the basic properties of a particular set of neurons that discharge both when the individuals execute a specific action and when they observe another individual doing a similar action. These neurons are called mirror neurons. We then show that mirror neurons mediate our capacity to understand actions done by others. In the second part of the study we discuss the role of the mirror mechanism in intention understanding. We conclude with a review of recent data suggesting that a deficit in the mirror neuron mechanism may underlie some aspects of autism.

The evolutionary continuity between the prespeech functions of premotor cortex and its new linguistic functions, the main thesis of MacNeilage's target article, is confirmed by the recent discovery of “mirror” neurons in monkeys and a corresponding action-observation/action-execution matching system in humans. Physiological data (and other considerations) appear to indicate, however, that brachiomanual gestures played a greater role in language evolution than MacNeilage would like to admit.