Disruption of the Posterior Medial Network during the Acute Stage of Transient Global Amnesia: A Preliminary Study

Acute perturbation of the corticohippocampal circuitry is a primary pathophysiological mechanism underlying transient global amnesia (TGA). With regard to memory, 2 distinct corticohippocampal circuitries potentially exist: the anterior temporal network and the posterior medial network. We used electroencephalography (EEG) spectral analysis to determine which network is disrupted during the acute stage of TGA. Patients with TGA who visited Seoul National University Bundang Hospital within 24 hours after symptom onset were retrospectively identified. Twenty patients underwent EEG twice, once in the acute stage (<24 hours after symptom onset) and once in the resolved stage (>2 months after symptom onset). A fast Fourier transform was applied to compute the spectral power of the 6 frequency bands: delta, theta, alpha, beta 1, beta 2, and gamma. We assumed that the frontocentral and temporal regions belonged to the anterior temporal network, whereas the parieto-occipital regions belonged to the posterior medial network. A paired Student's t test was used to evaluate the difference in the regional spectral powers in each frequency band between the acute and resolved TGA stages. Compared with the resolved stage, relative theta power in the left parieto-occipital region was increased and relative alpha power in the right parieto-occipital region was reduced during the acute stage of TGA, with a statistical significance of P<.05 (uncorrected). The cortical regions that belonged to the posterior medial network showed alterations of neuronal activity, which reflects disruption of the posterior medial network during the acute stage of TGA.