Abstract
Imagination is an internally-generated process, where one can make oneself or other people appear as protagonists of a scene. How does the brain tag the protagonist of an imagined scene as being oneself or someone else? Crucially, during imagination, neither external stimuli nor motor feedback are available to disentangle imagining oneself from imagining someone else. Here, we test the hypothesis that an internal mechanism based on the neural monitoring of heartbeats could distinguish between self and other. 23 participants imagined themselves (from a first-person perspective) or a friend (from a third-person perspective) in various scenarios, while their brain activity was recorded with magnetoencephalography and their cardiac activity was simultaneously monitored. We measured heartbeat-evoked responses, i.e. transients of neural activity occurring in response to each heartbeat, during imagination. The amplitude of heartbeat-evoked responses differed between imagining oneself and imagining a friend, in the precuneus and posterior cingulate regions bilaterally. Effect size was modulated by the daydreaming frequency scores of participants but not by their interoceptive abilities. These results could not be accounted for by other characteristics of imagination (e.g., the ability to adopt the perspective, valence or arousal), nor by cardiac parameters (e.g., heart rate) or arousal levels (e.g. arousal ratings, pupil diameter). Heartbeat-evoked responses thus appear as a neural marker distinguishing self from other during imagination.
Highlights
The ability to imagine is one of the most intriguing mental activities (Schacter et al, 2007; Suddendorf et al, 2009)
Imagining oneself was rated as being significantly more arousing than imagining the other (Arousal: Self: 3.4±0.1, Other: 3±0.1, t(22)=4.10, p=0.0005, Bayes Factor (BF)=549.3 – decisive evidence for H1; uncorrected p-‐value)
heartbeat-‐evoked responses (HERs) amplitude differs between self and other We compared the amplitude of HERs occurring during imagination of self with the amplitude of HERs occurring during imagination of other, for heartbeats (T-‐peaks) occurring between 2s after the onset of the imagination, to -‐0.4 seconds before the end of the imagination period (Fig. 1B)
Summary
The ability to imagine is one of the most intriguing mental activities (Schacter et al, 2007; Suddendorf et al, 2009). It implies the ability to create mental scenes in the absence of any sensory input. How can the brain tag the protagonist of an imaginary scene as being oneself or someone else? Since imagination is developed internally, no external/sensory stimuli nor motor feedback can help disentangle self from other. There is considerable anatomical overlap between the brain regions activated when imagining oneself and those recruited when imagining someone else (Decety and Grèzes, 2006). An additional neural mechanism is required in those regions to account for the biological bases of the self-‐other distinction. It was proposed that the neural monitoring of internal bodily signals, such as heartbeats, would serve as a marker of the self (Park and Tallon-‐Baudry, 2014; Tallon-‐Baudry et al, 2017)
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