The anterior-posterior gradient of the fusiform gyrus modulates the transition between mnemonic and perceptual features during reminiscences

Our cognition can be oriented either towards the external environment, as in perception, or towards our own self and its memories. However, the perception-memory continuum underlying the construction of memories remains unclear. Addressing this gap in our knowledge is the goal of our study; for that we uniquely investigate a rare mental phenomenon, namely internally- and externally-oriented reminiscences as manifest in memories and experiential hallucinations. To probe the causality of precisely located areas in eliciting and structuring such perceptual-mnemonic interactions, we studied a large sample of 335 patients with electrodes implanted across nearly the entire cortical surface, combining intracranial electrical stimulation (iES) and electrophysiological causal connectivity. We demonstrate that the likelihood of internally-oriented reminiscences was significantly higher during stimulation of the anterior fusiform gyrus. Conversely, externally-oriented hallucinations were far more likely to occur upon stimulation of the posterior fusiform gyrus. The probability of connections from regions outside the fusiform gyrus that displayed internally-oriented reminiscences to the fusiform gyrus decreased along the anterior-posterior axis. This suggests that an anterior-posterior gradient within the fusiform gyrus mediates an analogous external-internal perceptual-mnemonic continuum.