2.2.2. Neural bases of empathy

We started our survey of the relevant literature by searching for “empathy fMRI” and “empathic fMRI” on Pubmed (https://www.ncbi.nlm.nih.gov/pubmed/) (see Figure S2). After duplicate removal, a preliminary pool of 721 studies was first screened by title, and then by abstract. While the methodological selection criteria were the same as above (1–5), here we selected only studies reporting brain activations interpreted by the authors as related to empathic processing. To this purpose, we selected only:

6. studies aimed to elicit an affective sharing and brain activity interpreted by the authors in terms of empathic resonance, rather than mentalizing (i.e., representation, and attribution of mental states);7. studies aimed to elicit the isomorphic experience of another's affective state. Put differently, in these studies participants were supposed to know and “feel into” another's experience. These studies employed mostly visual, and to a lesser extent auditory or textual, stimuli conveying emotional situations which participants attended passively, or evaluated on various dimensions, without a direct involvement. Namely, we selected studies requiring participants to attend to another person's emotional state, and performing contrasts aimed to elicit brain activations interpreted by the authors in terms of empathic processing, that is:a) direct comparison between emotional stimuli and baseline/control stimuli (e.g., pain > no pain or emotion > neutral in others);b) direct comparison between an empathy task and a control task (e.g., brain activations highlighted by the contrast between rating and counting painful stimuli);c) correlation with trait empathy as measured by self‐report questionnaires (e.g., Baron‐Cohen and Wheelwright's (2004) Empathy Quotient (EQ));d) correlation with valence rating (e.g., pain or unpleasantness ratings);e) observing other's exclusion, compared with inclusion, during interactive games (e.g., cyberball game; Williams, Cheung, & Choi, 2000).

Within the studies fulfilling these criteria, we retained only the contrasts between conditions differing in terms of the requirement to share another's emotional state. Thus, while mentalizing task required to develop an abstract representation of characters' (affective and cognitive) mental states, only in empathy task participants were supposed to “feel into” another's feelings (emotions, pain, compassion, etc.).

Starting from an initial screening of 721 titles and abstracts, 631 papers deemed as potentially relevant were fully reviewed based on the aforementioned selection criteria (see Figure S2). We thus excluded: 57 review or meta‐analysis articles; 33 studies employing techniques other than fMRI; 11 studies using ROIs or SVC; 6 studies explicitly focused on mentalizing; 51 studies focused on children or aging populations; 28 studies not reporting all the required information; 204 studies focused on clinical populations and 161 studies that did not focus on empathic processing.

We included studies fulfilling the above criteria regardless of: (a) sensory modality (e.g., visual or auditory), (b) experimental paradigm (e.g., comprehension or attentional tasks), and (c) stimulus type (e.g., videos, photos, and verbal materials). Our aim was indeed to pool across different experimental paradigms to ensure both generalizability and consistency of results, within the requirement of an empathic processing inherent in our research question (Radua & Mataix‐Cols, 2012). This selection phase resulted in 80 studies fulfilling our criteria.

We then expanded our search for other potentially relevant studies by carefully examining both the studies quoting, and those quoted by, each of these papers, alongside previously published meta‐analyses on the neural bases of empathic processing (Del Casale et al., 2017; Gu et al., 2012; Lamm, Decety, & Singer, 2011; Timmers et al., 2018; Wu et al., 2019). This second phase highlighted 10 further studies fitting our search criteria. Overall, this procedure led to include in the ALE meta‐analysis 90 previously published studies (see Table S2), resulting from 90 experiments (individual comparisons reported) with 2,230 subjects and 1,355 activation foci.