Two types of ictal phase-amplitude couplings in epilepsy patients revealed by spectral harmonicity of intracerebral EEG recordings

DELLAVALE, DAMIÁN; URDAPILLETA, EUGENIO; CÁMPORA, NURIA; VELARDE, OSVALDO MATÍAS; KOCHEN, SILVIA; MATO, GERMÁN

CLINICAL NEUROPHYSIOLOGY

ELSEVIER IRELAND LTD

Año: 2020 vol. 131 p. 1866 - 1885

1388-2457

Objective: Spectral harmonicity of the ictal activity was analyzed regardingtwo clinically relevant aspects, (1) as a confounding factor producing `spurious'phase-amplitude couplings (PAC) which may lead to wrong conclusions aboutthe underlying ictal mechanisms, and (2) its role in how good PAC is in correspondenceto the seizure onset zone (SOZ) classication performed by theepileptologists.Methods: PAC patterns observed in intracerebral electroencephalography (iEEG)recordings were retrospectively studied during seizures of seven patients withpharmacoresistant focal epilepsy. The time locked index (TLI) measure wasintroduced to quantify the degree of harmonicity between frequency bands associatedto the emergence of PAC during epileptic seizures.Results: (1) Harmonic and non harmonic PAC patterns coexist during theseizure dynamics in iEEG recordings with macroelectrodes. (2) Harmonic PACpatterns are an emergent property of the periodic non sinusoidal waveform constitutingthe epileptiform activity. (3) The TLI metric allows to distinguish thenon harmonic PAC pattern, which has been previously associated with the ictalcore through the paroxysmal depolarizing shifts mechanism of seizure propagation.Conclusions: Our results suggest that the spectral harmonicity of the ictal activityplays a relevant role in the visual analysis of the iEEG recordings performedby the epileptologists to dene the SOZ, and that it should be considered forthe proper interpretation of ictal mechanisms.