Abstract Functional seizures (FS) are common, but distinguishing FS from epileptic seizures (ES) can be challenging, and the pathophysiology is not well-understood. The heartbeat evoked potential (HEP) reflects the central processing of cardiac signals and bodily attention. Our group previously demonstrated HEP differences between FS and ES. Here, we sought to replicate these HEP findings in an independent retrospective sample and observe effects of semiology. Because we lacked symptom reporting at the time of a seizure, in the second part of the study we examined whether HEP modulation was associated with real-time bodily symptom reporting in a second retrospective sample of individuals with functional or vasovagal syncope where symptom data was available. In the first part, we identified FS (n=57) or ES (n=31) from video telemetry with electroencephalography (vEEG) recordings of patients referred for assessment of their events. We categorised FS and ES into “motile” or “non-motile” according to semiology with predominantly positive motor features, or with subjective sensory or negative motor features, respectively. HEP amplitude was calculated by averaging EEG segments time-locked to ECG R-waves, correcting for pre-R wave baseline, to quantify the average voltage between 0.455 and 0.595 seconds after the R wave. We compared HEP amplitude at baseline, preictal and postictal periods between FS and ES of equivalent semiology. In the second part, we measured HEP amplitude in functional syncope or vasovagal syncope (30 participants per group), from EEG recorded during head-up tilt procedure. We compared the HEP amplitude around the time of symptom reporting to its baseline value. HEP amplitude distinguished FS from ES with matched semiology: In non-motile FS, HEP become more positive at the scalp from the interictal to preictal period, whereas in motile FS, the HEP became less positive at the scalp. ES were not associated with significant changes in HEP. In functional syncope, a more positive HEP amplitude was associated with reported bodily symptoms, but not for psychological or emotional symptoms. In vasovagal syncope, a less positive HEP was associated with bodily symptoms. These findings indicate that FS semiology may relate to patterns of bodily attention, as reflected by HEP amplitude change. Non-motile FS were preceded by increased HEP amplitude, and the opposite was seen in motile FS. The increased HEP amplitude associated with bodily symptom reporting in functional syncope supports a role for the HEP in tracking interoception and bodily attention. HEP may therefore help us understand interoceptive mechanisms underlying FS.
Kandasamy et al. (Thu,) studied this question.