Altered Resting-State Cortical EEG Oscillations in Patients With Severe Asymptomatic Carotid Stenosis

Resting State Electrophysiological Cortical Activity: A Brain Signature Candidate for Patients with Migraine

PURPOSE OF REVIEW

Studies on event-related evoked potentials have indicated that altered cortical processing of sensory stimuli is associated with migraine. However, the results depend on the experimental method and patients. Electrophysiology of resting state cortical activity has revealed compelling results regarding the pathophysiology of migraine. This review summarized the available information related to patients with episodic and chronic migraine to determine whether certain features can be used as signatures for migraine.

RECENT FINDINGS

A recent study examined differences in resting state functional connectivity among the pain-related regions and revealed that beta connectivity was attenuated in migraine and that altered connectivity in the anterior cingulate cortex was linked to migraine chronification. These findings suggested that chronification leads to neuroplasticity in the pain areas of higher-level processing rather than in areas involved in basic sensory discrimination (i.e., primary and secondary somatosensory areas). Another study discovered that the betweenness centrality of delta band in right precuneus was significantly lower in those with longer history of migraine. Electroencephalogram may also predict the treatment outcomes in patients with chronic migraine that those with lower pre-treatment occipital alpha power tend to show greater reduction in headache frequency. Studies on resting state activity have yielded convincing findings regarding aberrant oscillatory power and functional connectivity in relation to migraine, thus contributing to identifying brain signatures for migraine. The role of such assessment in precision medicine should be further investigated.

Normalization of reduced functional connectivity after revascularization of asymptomatic carotid stenosis

Internal carotid artery stenosis is a risk factor for ischemic stroke. Even in the absence of visible structural brain changes, patients with asymptomatic stenosis are prone to cognitive impairment. On a neuronal level, it was suggested that stenosis may lead to disturbed functional brain connectivity. If so, carotid revascularization should have an effect on hypothesized brain network disturbances. We studied functional connectivity in a motor network by resting-state electroencephalography in 12 patients with high grade asymptomatic carotid stenosis before and after interventional or surgical revascularization as compared to 23 controls. In patients with stenosis, functional connectivity of neural oscillations was significantly decreased prior and improved returning to normal connectivity after revascularization. In a subgroup of patients, also studied by contrast perfusion magnetic resonance imaging, reduced connectivity was associated with decreased regional brain perfusion reflected by increased mean transit time in the middle cerebral artery borderzone. Cognitive testing revealed only minor differences between patients and controls. In summary, we identified oscillatory connectivity changes in patients with asymptomatic carotid stenosis correlating with regional hypoperfusion, which both normalized after revascularization. Hence, electrophysiological changes might be a reversible precursor preceding macroscopic structural brain damage and behavioral impairment in patients with asymptomatic carotid stenosis.

Altered Neuronal Activity Topography Markers in the Elderly with Increased Atherosclerosis

Background: Previously, we reported on vascular cognitive impairment (VCI) templates, consisting of patients with VCI associated with carotid stenosis (>60%) using a quantitative electroencephalographic (EEG) technique called neuronal activity topography (NAT). Here using the VCI templates, we investigated the hypothesis that internal carotid artery-intima-media thickness (ICA-IMT) is associated with EEG spectrum intensity (sNAT) and spectrum steepness (vNAT). Methods: A total of 221 community-dwelling elderly subjects were recruited. Four groups were classified according to quartiles of ICA-IMT as assessed by ultrasonography: control group A, normal (≤0.9 mm); group B, mild atherosclerosis (1-1.1 mm); group C, moderate atherosclerosis (1.2-1.8 mm); and group D, severe atherosclerosis (≥1.9 mm). EEG markers of power ratio index (PRI), and the binary likelihood of being in the VCI group vs. the that of being in control group A (sL _x:VCI-A , vL _x:VCI-A ) were assessed, respectively. Differences in mean total scores for PRI, sL _x:VCI-A , vL _x:VCI-A , between control group A and the other groups were compared using Dunnett's test, respectively. Results: The mean total scores of the PRI were 3.25, 3.00, 2.77, and 2.26 for groups A, B, C, and D, respectively. There was a significant decrease in the PRI in group D compared with group A (P = 0.0066). The mean total scores of the sL _x:VCI-A were -0.14, -0.11, -0.1, and -0.03 for groups A, B, C, and D, respectively. The sL _x:VCI-A in group D was significantly higher compared to that in group A (P < 0.0001). The mean total scores of the vL _x:VCI-A were -0.04,-0.01, 0.01, and 0.06 for group A, B, C, and D, respectively. The vL _x:VCI-A in group D and group C was significantly higher compared to that in group A, respectively (P < 0.0001, P = 0.02). Conclusion: Community-dwelling elderly subjects in the increased carotid atherosclerosis of ICA-IMT (≥1.9 mm) were at greatest risk of an EEG change as assessed by NAT.