, 2007). It is thus likely that the increase in prefrontal activation for Acheulean–Oldowan reflects the greater temporal and relational complexity of Acheulean toolmaking actions, which, to a greater extent than Oldowan flaking, are organized into flexible and internally variable action chunks, such as ‘platform preparation’ vs. ‘primary flake removal’ (Pelegrin, 2005; Stout, 2011). No significant prefrontal activation BTK inhibitor libraries was observed for Oldowan–Control, in keeping with previous conclusions regarding the relative simplicity

of Oldowan action sequences (Stout & Chaminade, 2007; Stout et al., 2008). On this interpretation, the anterior inferior parietal cortex and the inferior frontal sulcus form a parieto-frontal circuit involved in representing episode-specific intentions, causal relations and multi-component action sequences during toolmaking observation. The apparent abstraction (Hamilton & Grafton, 2006; Badre & D’Esposito, 2009) of causal/intentional processing in this circuit may be compared with a proposed ‘intermediate’

level representing ‘intentions in action’ as goal-oriented sequences of motor commands and predicted outcomes (de Vignemont & Haggard, 2008). Varying expertise across subject groups was associated with qualitative shifts Navitoclax nmr in the set of brain regions activated in response to Acheulean compared with Oldowan stimuli (Fig. 4; Table 3). These differences suggest a functional reorganization (Kelly & Garavan, 2005) involving the adoption of different cognitive strategies for action understanding. Naïve subjects show activation in core motor resonance structures together with the ventral prefrontal cortex, as expected for a low-level strategy of novel action understanding

through kinematic simulation. Trained subjects show strong, statistically indistinguishable responses to both Oldowan and Acheulean stimuli, perhaps reflecting the particular social context and motivational set associated with training. Finally, Expert subjects display activation in the medial prefrontal cortex, a classic ‘mentalizing’ region, suggesting a relatively high-level, inferential strategy of intention reading. One Suplatast tosilate cluster exclusive to technologically Naïve subjects occurred in the pars opercularis of the left posterior inferior frontal gyrus (Fig. 4, left). Pars opercularis is another core component of the putative human mirror neuronal system (Rizzolatti & Craighero, 2004), which, in contrast with the performance-monitoring functions of the anterior inferior parietal cortex described above, is thought to be responsible for the generation of the kinematic models used to execute (Fagg & Arbib, 1998) or simulate (Carr et al., 2003; Grafton & Hamilton, 2007; Kilner et al., 2007) motor acts.