Compressibility of High-Density EEG Signals in Stroke Patients

Abstract

Stroke is a critical event that causes the disruption of neural connections. There is increasing evidence that the brain tries to reorganize itself and to replace the damaged circuits, by establishing compensatory pathways. Intra- and extra-cellular currents are involved in the communication between neurons and the macroscopic effects of such currents can be detected at the scalp through electroencephalographic (EEG) sensors. EEG can be used to study the lesions in the brain indirectly, by studying their effects on the brain electrical activity. The primary goal of the present work was to investigate possible asymmetries in the activity of the two hemispheres, in the case one of them is affected by a lesion due to stroke. In particular, the compressibility of High-Density-EEG (HD-EEG) recorded at the two hemispheres was investigated since the presence of the lesion is expected to impact on the regularity of EEG signals. The secondary objective was to evaluate if standard low density EEG is able to provide such information. Eighteen patients with unilateral stroke were recruited and underwent HD-EEG recording. Each EEG signal was compressively sensed, using Block Sparse Bayesian Learning, at increasing compression rate. The two hemispheres showed significant differences in the compressibility of EEG. Signals acquired at the electrode locations of the affected hemisphere showed a better reconstruction quality, quantified by the Structural SIMilarity index (SSIM), than the EEG signals recorded at the healthy hemisphere (p < 0.05), for each compression rate value. The presence of the lesion seems to induce an increased regularity in the electrical activity of the brain, thus an increased compressibility.

Cortical Reorganization after Rehabilitation in a Patient with Conduction Aphasia Using High-Density EEG

“…In our case, we used a neurophysiologic method, such as HD-EEG, to obtain objective data and provide evidence of the importance and effectiveness of an intensive rehabilitative training in an aphasic patient. In fact, a study conducted on stroke patients with HD-EEG demonstrated that, with respect to standard EEG, high-density EEG could describe the asymmetric electrical signals of the brain activity in stroke patients [18]. Results showed that, during the repetition, reading and writing tasks, the left parieto-temporo-frontal areas are more activated at T1 respect to baseline evaluation.…”

High-Density EEG Signal Processing Based on Active-Source Reconstruction for Brain Network Analysis in Alzheimer’s Disease

“…From a neurological point of view, brain connections are weakened or completely lost because of the death of neurons. EEG is a powerful tool to explore brain functioning and detect any alterations in the presence of pathological conditions [43][44][45][46]. Recently, graph theory has widely been employed to quantify the brain functional connectivity; it has also been proved that brain networks are characterized by small-world architecture.…”

Findings about LORETA Applied to High-Density EEG—A Review

“…After some modifications it became the standard of the American Clinical Neurophysiology Society and the International Federation of Clinical Neurophysiology. Later, the results of several studies showed that the interelectrode distance should be between 1 cm and 3 cm, which implies the use of at least 100 electrodes [14][15][16][17][18][19]. Therefore, a farther extension of the 10-10 system was introduced, the so-called 10-5 system, which consists of 345 electrode locations [20] (Figure 2b).…”