Transient Global Amnesia Deteriorates the Network Efficiency of the Theta Band

Abstract

Acute perturbation of the hippocampus, one of the connector hubs in the brain, is a key step in the pathophysiological cascade of transient global amnesia (TGA). We tested the hypothesis that network efficiency, meaning the efficiency of information exchange over a network, is impaired during the acute stage of TGA. Graph theoretical analysis was applied to resting-state EEG data collected from 21 patients with TGA. The EEG data were obtained twice, once during the acute stage (< 24 hours after symptom onset) and once during the resolved stage (> 2 months after symptom onset) of TGA. Characteristic path lengths and clustering coefficients of functional networks constructed using phase-locking values were computed and normalized as a function of the degree in the delta, theta, alpha, beta 1, beta 2 and gamma frequency bands of the EEG. We investigated whether the normalized characteristic path length (nCPL) and normalized clustering coefficients (nCC) differed significantly between the acute and resolved stages of TGA at each frequency band using the Wilcoxon signed-rank test. For networks where the nCPL or nCC differed significantly between the two stages, we also evaluated changes in the connections of the brain networks. During the acute stage of TGA, the nCPL of the theta band networks with mean degrees of 8, 8.5, 9 and 9.5 significantly increased (P < 0.05). During the acute stage, the lost edges for these networks were mostly found between the anterior (frontal and anterior temporal) and posterior (parieto-occipital and posterior temporal) brain regions, whereas newly developed edges were primarily found between the left and right frontotemporal regions. The nCC of the theta band with a mean degree of 5.5 significantly decreased during the acute stage (P < 0.05). Our results indicate that TGA deteriorates the network efficiency of the theta frequency band. This effect might be related to the desynchronization between the anterior and posterior brain areas.

Abnormal EEG Power Spectra in Acute Transient Global Amnesia: A Quantitative EEG Study

“…Investigating the qEEG differences between patients with acute TGA and control subjects is still an underdeveloped research area. 14 Therefore, the main aim of the present study was to extend these previous findings by exploring EEG power spectra differences between patients with acute TGA and healthy controls using the exact low-resolution brain electromagnetic tomography software (eLORETA), a validated tool for localizing the electric activity in the brain based on multichannel surface EEG recordings. 22…”

“…Electroencephalographic (EEG) measurements are commonly used in both clinical and research setting with TGA patients, 14 because they are suitable to investigate the objective state during transitory memory alterations. 15 Although a considerable percentage of patients with TGA have EEG abnormalities (eg, epileptiform discharges, spikes or sharp waves) in resting wake 16 and sleep, 17 most of them are supposed to be of scarce pathological significance or related to some other underlying condition.…”

Is Transient Global Amnesia a Network Disease?

“…These studies have suggested that many neurologic diseases could be produced by the dysfunction of a brain network. However, few studies have investigated alterations of a brain network using graph theory in patients with TGA [15,16].…”

Power Spectral Differences between Transient Epileptic and Global Amnesia: An eLORETA Quantitative EEG Study

“…We can infer that these differences are generated by background activity and not by ictal/interictal activity, since epileptic discharges were manually removed from the EEGs of TEA patients. The EEGs of TGA patients were assumed to be comparable to that of healthy subjects since symptoms were fully regressed at the time of recording [40], and no particular findings were reported in the EEG's referral.…”