Dissociable substrates for body motion and physical experience in the human action observation network

An action observation network (AON) that responds to the observation of human actions has been identified in the premotor cortex, inferior parietal lobule (IPL), superior temporal sulcus (STS) and supplementary motor area of the human brain (Grafton et al., 1996; Rizzolatti et al., 1996b; Buccino et al., 2001; Gre`zes & Decety, 2001; Jeannerod, 2001; Rizzolatti & Craighero, 2004; Zentgraf et al., 2005; Cross et al., 2006; Molnar-Szakacs et al., 2006). This network is believed to contain mirror neurons (Rizzolatti & Craighero, 2004; Iacoboni & Mazziotta, 2007), and several different functions have been proposed for it, including action prediction (Prinz, 1997, 2006; Kilner et al., 2007; Schu¨tz-Bosbach & Prinz, 2007), action understanding (Rizzolatti et al., 1996b, 2001; Rizzolatti & Fadiga, 1998), inferring the intention of others (Fogassi et al., 2005; Hamilton & Grafton, 2006; Kilner et al., 2006), and social cognition (Iacoboni & Dapretto, 2006). Some components of the AON also have a role in motor control (Brown et al., 2006; Catmur et al., 2007; Borroni et al., 2008) and motor planning (Grafton & Hamilton, 2007; Williams et al., 2007). Previous imaging studies of this network with healthy individuals have not directly compared these functions in the same experiments to differentiate between them or to determine whether different components of the AON might serve specific functions. One unsettled issue is whether or not this network responds preferentially to observation of actions performed by other humans, or whether it responds in the same way to symbolic cues to action. Moreover, if the AON has a specific role in action prediction and action understanding, then manipulating the degree to which an action can be easily understood should also affect the level of activity in the AON. One way this can be evaluated is by varying the amount of direct experience one has in performing the observed action. In this study, we used a novel dance training paradigm to determine if activity within the AON is driven by action embodiment or by the form of the action stimuli. If the AON is dedicated to biological action understanding, we might expect it to show a preference for stimuli that feature biological motion, as recent data suggest (e.g. Brass et al., 2000; Tai et al., 2004; Kessler et al., 2006). Brass et al. (2000) were among the first to report that participants were measurably faster to imitate finger movements that were performed by another person compared with those that were cued by a spatial cue. Kessler et al. (2006) used whole-head magnetoencephalography to monitor participants’ brain activity while they performed a finger-tapping movement. Movements were cued by a video of a finger tapping (biological movement condition) compared Correspondence: Dr E. S. Cross, at *present address below. E-mail: *Present address: Max Planck Institute for Human Cognitiv