Using electrocorticography (ECoG), we probed the neurocognitive substrates of mentalizing at the level of neuronal populations. We found that mentalizing about the self and others recruited near-identical cortical sites (Fig. 5a, b) in a common spatiotemporal sequence (Figs. 5 c and 6). Within our ROIs, activations began in visual cortex, followed by temporoparietal DMN regions (TPJ, ATL, and PMC), and lastly in mPFC regions (amPFC, dmPFC, and vmPFC; Fig. 3e, f). Critically, regions with later activations exhibited greater functional specialization for mentalizing as measured by three metrics: functional specificity for mentalizing versus arithmetic (Figs. 3 c, d and 4b), self/other differentiation in activation timing (Fig. 5c, d), and temporal associations with behavioral responses (Fig. 4D and Table 1). Taken together, these results reveal a common neurocognitive sequence^28,29,30,31 for self-and other-mentalizing, beginning in visual cortex (low specialization), ascending through temporoparietal DMN areas (intermediate specialization), then reaching its apex in mPFC regions (high specialization).

Our results are consistent with gradient-based models of brain function, which posit that concrete sensorimotor processing in unimodal regions (e.g., visual cortex) gradually yields to increasingly abstract and inferential processing in ‘high-level’ transmodal regions like mPFC^41,42. We found that the strength of self/other differences in activation timing increased along a gradient from visual cortex to mPFC. Specifically, other-mentalizing evoked slower (Fig. 5c) and lengthier (Fig. 5d) activations than self-mentalizing throughout successive DMN ROIs. These self/other functional differences corresponded with self/other differences in RT_Behav (Supplementary Fig. 4), although the two were often dissociable (Table 1). Thus, perhaps because we know ourselves better than others, other-mentalizing may require lengthier processing at more abstract and inferential levels of representation, ultimately resulting in slower behavioral responses.

What might our results imply about extant fMRI findings? Hundreds of fMRI studies consistently suggest that: TPJ and dmPFC are most crucial for mentalizing^{6,8,11,12,43,44,45,46}, and dmPFC is selective for thinking about others over oneself ^32,33,34,35. However, when examined with ECoG, we found that both pieces of received wisdom are not what they seem. Below, we discuss both issues before moving onto our peculiar vmPFC results, and then conclude with systems-level discussion.

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Researchers from École Polytechnique Fédérale de Lausanne (EPFL) have discovered that vanadium dioxide (VO2) is capable of “remembering” the entire history of previous external stimuli.

Vanadium dioxide marks the first material EPFL researchers have discovered that identified as possessing this property.

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EPFL researchers have discovered that Vanadium Dioxide (VO₂), a compound used in electronics, is capable of “remembering” the entire history of previous external stimuli. This is the first material to be identified as possessing this property, although there could be others.

Mohammad Samizadeh Nikoo, a Ph.D. student at EPFL’s Power and Wide-band-gap Electronics Research Laboratory (POWERlab), made a chance discovery during his research on phase transitions in Vanadium Dioxide (VO₂). VO₂ has an insulating phase when relaxed at room temperature, and undergoes a steep insulator-to-metal transition at 68 °C, where its lattice structure changes. Classically, VO₂ exhibits a volatile memory: “the material reverts back to the insulating state right after removing the excitation” says Samizadeh Nikoo. For his thesis, he set out to discover how long it takes for VO₂ to transition from one state to another. But his research led him down a different path: after taking hundreds of measurements, he observed a memory effect in the material’s structure.