ALE meta-analysis of action observation and imitation in the human brain

Abstract

Over the last decade, many neuroimaging studies have assessed the human brain networks underlying action observation and imitation using a variety of tasks and paradigms. Nevertheless, questions concerning which areas consistently contribute to these networks irrespective of the particular experimental design and how such processing may be lateralized remain unresolved. The current study aimed at identifying cortical areas consistently involved in action observation and imitation by combining activation likelihood estimation (ALE) meta-analysis with probabilistic cytoarchitectonic maps. Meta-analysis of 139 functional magnetic resonance and positron emission tomography experiments revealed a bilateral network for both action observation and imitation. Additional subanalyses for different effectors within each network revealed highly comparable activation patterns to the overall analyses on observation and imitation, respectively, indicating an independence of these findings from potential confounds. Conjunction analysis of action observation and imitation meta-analyses revealed a bilateral network within frontal premotor, parietal, and temporo-occipital cortex. The most consistently rostral inferior parietal area was PFt, providing evidence for a possible homology of this region to macaque area PF. The observation and imitation networks differed particularly with respect to the involvement of Broca's area: whereas both networks involved a caudo-dorsal part of BA 44, activation during observation was most consistent in a more rostro-dorsal location, i.e., dorsal BA 45, while activation during imitation was most consistent in a more ventro-caudal aspect, i.e., caudal BA 44. The present meta-analysis thus summarizes and amends previous descriptions of the human brain networks related to action observation and imitation.

Fig. 1

Significant meta-analysis results for action observation, summarized over all effectors. All results are displayed on the left and right lateral surface view of the MNI single subject template. pMTG posterior middle temporal gyrus, SMA supplementary motor area (hidden within the interhemispheric fissure); BA 44, 45: Broca's area (Amunts et al., 1999); BA 6: lateral premotor cortex (Geyer 2004); SI: primary somatosensory cortex (BA 2, Grefkes et al., 2001); 7A: superior parietal area (Scheperjans et al., 2008a,b); PFt: inferior parietal area (Caspers et al., 2006, 2008); hIP3: intraparietal area (Scheperjans et al., 2008a,b); V5: extrastriate visual area (Malikovic et al., 2007).

Fig. 2

Significant meta-analysis results for (A) observation of hand actions, (B) observation of right hand actions, (C) observation of non-hand actions, (D) observation of face actions, and (E) contrast analysis between observation of hand actions and observation of non-hand actions (colour-coding of respective contrasts within the figure). For other conventions, see Fig. 1.

Fig. 3

Significant meta-analysis results for (A) observation of hand actions with instruction ‘passively observe,’ (B) observation of hand actions with instruction ‘observe to imitate,’ and (C) contrast analysis between both categories (colour-coding of respective contrasts within the figure). For other conventions, see Fig. 1.

Fig. 4

Significant meta-analysis results for (A) observation of object-related hand actions, (B) observation of non-object-related hand actions, and (C) contrast analysis between both categories (colour-coding of respective contrasts within the figure). For other conventions, see Fig. 1.

Fig. 5

Significant meta-analysis results for action imitation. MI: primary motor cortex (areas 4a, 4p; Geyer et al., 1996). For other conventions, see Fig. 1.

Fig. 6

Significant meta-analysis results for (A) imitation of hand actions, and (B) imitation of right hand actions, and (C) imitation of non-object-related hand actions. For other conventions, see Fig. 1.

Fig. 7

Significant results for (A) the conjunction and (B) the contrast analysis between the main categories action observation and action imitation (colour-coding of respective contrasts within the figure). For other conventions, see Fig. 1.