Altered sense of self during seizures in the posteromedial cortex

Abstract

The posteromedial cortex (PMC) is known to be a core node of the default mode network. Given its anatomical location and blood supply pattern, the effects of targeted disruption of this part of the brain are largely unknown. Here, we report a rare case of a patient (S19_137) with confirmed seizures originating within the PMC. Intracranial recordings confirmed the onset of seizures in the right dorsal posterior cingulate cortex, adjacent to the marginal sulcus, likely corresponding to Brodmann area 31. Upon the onset of seizures, the patient reported a reproducible sense of self-dissociation—a condition he described as a distorted awareness of the position of his body in space and feeling as if he had temporarily become an outside observer to his own thoughts, his “me” having become a separate entity that was listening to different parts of his brain speak to each other. Importantly, 50-Hz electrical stimulation of the seizure zone and a homotopical region within the contralateral PMC induced a subjectively similar state, reproducibly. We supplement our clinical findings with the definition of the patient’s network anatomy at sites of interest using cortico-cortical–evoked potentials, experimental and resting-state electrophysiological connectivity, and individual-level functional imaging. This rare case of patient S19_137 highlights the potential causal importance of the PMC for integrating self-referential information and provides clues for future mechanistic studies of self-dissociation in neuropsychiatric populations.

Targeting Affective Mood Disorders With Ketamine to Prevent Chronic Postsurgical Pain

“…When thinking about the relevance of these observations vis-à-vis the relationship between subjective effects induced by a single dose of ketamine and treatment response ( 108 , 123 , 128 ), it is important to remember that the ketamine concentrations here are comparable to those achieved in subjects with major depressive illness ( Table 2 ). The subjective experiences reported here are not dissimilar to the dissociated state reported during pre-seizure auras and in response to electrical stimulation of the PMC in the patient with epilepsy ( 128 , 134 ), and emphasize the commonality and potential relevance of the experience to symptomatic relief in patients with depression.…”

“…The relationship between the retrosplenial slow-wave rhythm and the behavioral dissociation observed in mice was also examined in a human patient with epilepsy using brain-wide intracranial electrodes that enabled intracranial electroencephalography/stereoelectroencephalography for both diagnostic recording and focal stimulation ( 128 , 134 ). During pre-seizure auras, a distinct slow-wave (3.4 Hz) patten of activity was observed in the PMC bilaterally.…”

Loneliness is linked to specific subregional alterations in hippocampus-default network covariation

“…The concomitant structural divergences of HC and DN subregions in lonely individuals may in part be explained by the varieties of internally directed cognition that have been consistently associated with each neural system—such as episodic memory processing, sense of self, and prospective cognition ( 21 , 75 – 77 ). Especially midline structures of the DN such as the vmPFC ( 78 ), posteromedial cortex ( 79 , 80 ), and the RSC ( 75 ) have been found to serve these types of neural processes. In line with this notion, the fornix—known to be a direct mediator between the HC and midline DN subregions—has been found to be the white matter structure that is most strongly linked to loneliness profiles ( 29 ).…”

The Temporal Lobe as a Symptomatogenic Zone in Medial Parietal Lobe Epilepsy

“…Moreover, tractography data and post-mortem analysis have shown extensive projections from the posterior precuneus to the MTL, specifically, the anterior para-hippocampal gyrus ( 16 ). Seizures originating from the precuneus may be clinically silent or potentially cause some alteration of awareness ( 19 , 20 ). When clinically silent, they may be mistaken as temporal onset seizures because the scalp-recorded ictal discharge and seizure semiology may be indistinguishable from TLE.…”