A possible role for primary motor cortex during action observation

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Abstract
Social interaction depends on the ability to infer beliefs and intentions in the minds of others. Little is known about the neural basis of our ability to “read” the intentions of others, but a likely candidate is the mirror-neuron system (MNS). Mirror neurons discharge not only during action execution but also during action observation. It is this property that makes these neurons a possible neural substrate for action understanding. The notion that actions are intrinsically linked to perception was proposed by William James, who suggested that “every mental representation of a movement awakens to some degree the actual movement which is its object” (1). The implication is that observing, imagining, preparing, or in any way representing an action excites the motor program used to execute that same action (2, 3). Mirror neurons were originally discovered in macaque monkeys (4). However, a variety of subsequent studies have found homologous areas in the human brain that are similarly activated when observing and executing movements (5–7). Of particular relevance here is that studies employing electroencephalography or magnetoencephalography have shown a modulation of cortical oscillatory activity at both ≈10 and ≈20 Hz during periods of movement observation that is similar to that observed during movement execution (8, 9). The work of Caetano et al. (10) in this issue of PNAS focuses on modulations of such oscillatory activity, recorded from human subjects by using magnetoencephalography, when executing an action (banging a drum), as well as when observing the action (seeing someone else bang a drum) or hearing the action (hearing the sound …