Delineating the heartbeat-evoked potential from cardiac artefact
Introduction The heartbeat-evoked potential (HEP) is widely interpreted as an EEG/MEG marker of cortical processing of cardiac afferent signals. It is superimposed on electrical and mechanical signals generated by the heartbeat. Because the neural response and cardiac artefact share the same trigger, conventional averaging and blind-source correction lack an observable cardiac-only reference. Methods We used clinically acquired EEGs with isoelectric-appearing cerebral activity and preserved cardiac activity as a negative control for non-neural heartbeat-locked scalp signal. Thirty-nine isoelectric participants were compared with 118 heart-rate-matched participants whose clinical EEGs were reported as normal. Participant-level heartbeat averages were analysed using covariate-adjusted spatiotemporal permutation tests. We characterised interindividual cardiac-artefact morphology and tested the primary group contrast across average-reference, surface-Laplacian and cardiac-artefact-directed ICA analyses, with pseudotrial correction for heartbeat-independent EEG activity. Results Cardiac-artefact morphology varied markedly across isoelectric participants and was predominantly posterior or posterolateral. In the prespecified primary analysis, controls showed a negative frontocentral cluster persisted at 90-365 ms, p=.016, and a posterior cluster at 145-310 ms, p=.03. The topography of the first cluster aligns with the spatiotemporal characteristics of the early window of the HEP as identified in the literature. This cluster was negative in polarity at the scalp. This suggests positive voltage changes in the early HEP are in fact reductions in HEP activity. Exploratory analyses explored the effects of montage, and artefact correction with independent component analysis to remove CA. There was no significant group difference in ECG. Conclusion These findings provide an important first empirical scalp-level dissociation of the early HEP from CA using an inversion-of-ground-truth approach. A robustly observed cluster of difference, consistent with the early HEP, suggests that this part of the HEP is a distinct, frontocentral, negative cortical response.