Reliability of EEG Interactions Differs between Measures and Is Specific for Neurological Diseases.

Alterations of interaction (connectivity) of the EEG reflect pathological processes in patients with neurologic disorders. Nevertheless, it is questionable whether these patterns are reliable over time in different measures of interaction and whether this reliability of the measures is the same across different patient populations. In order to address this topic we examined 22 patients with mild cognitive impairment, five patients with subjective cognitive complaints, six patients with right-lateralized temporal lobe epilepsy, seven patients with left lateralized temporal lobe epilepsy, and 20 healthy controls. We calculated 14 measures of interaction from two EEG-recordings separated by 2 weeks. In order to characterize test-retest reliability, we correlated these measures for each group and compared the correlations between measures and between groups. We found that both measures of interaction as well as groups differed from each other in terms of reliability. The strongest correlation coefficients were found for spectrum, coherence, and full frequency directed transfer function (average rho > 0.9). In the delta (2-4 Hz) range, reliability was lower for mild cognitive impairment compared to healthy controls and left lateralized temporal lobe epilepsy. In the beta (13-30 Hz), gamma (31-80 Hz), and high gamma (81-125 Hz) frequency ranges we found decreased reliability in subjective cognitive complaints compared to mild cognitive impairment. In the gamma and high gamma range we found increased reliability in left lateralized temporal lobe epilepsy patients compared to healthy controls. Our results emphasize the importance of documenting reliability of measures of interaction, which may vary considerably between measures, but also between patient populations. We suggest that studies claiming clinical usefulness of measures of interaction should provide information on the reliability of the results. In addition, differences between patient groups in reliability of interactions in the EEG indicate the potential of reliability to serve as a new biomarker for pathological memory decline as well as for epilepsy. While the brain concert of information flow is generally variable, high reliability, and thus, low variability may reflect abnormal firing patterns.

Minimal hepatic encephalopathy: A review.

Minimal hepatic encephalopathy (MHE) is the earliest form of hepatic encephalopathy and can affect up to 80% of patients with liver cirrhosis. By definition, MHE is characterized by cognitive function impairment in the domains of attention, vigilance and integrative function, but obvious clinical manifestation are lacking. MHE has been shown to affect daily functioning, quality of life, driving and overall mortality. The diagnosis can be achieved through neuropsychological testing, recently developed computerized psychometric tests, such as the critical flicker frequency and the inhibitory control tests, as well as neurophysiological procedures. Event related potentials can reveal subtle changes in patients with normal neuropsychological performances. Spectral analysis of electroencephalography (EEG) and quantitative analysis of sleep EEG provide early markers of cerebral dysfunction in cirrhotic patients with MHE. Neuroimaging, in particular MRI, also increasingly reveals diffuse abnormalities in intrinsic brain activity and altered organization of functional connectivity networks. Medical treatment for MHE to date has been focused on reducing serum ammonia levels and includes non-absorbable disaccharides, probiotics or rifaximin. Liver transplantation may not reverse the cognitive deficits associated with MHE. We performed here an updated review on epidemiology, burden and quality of life, neuropsychological testing, neuroimaging, neurophysiology and therapy in subjects with MHE.

Canine degenerative myelopathy: a model of human amyotrophic lateral sclerosis.

Canine degenerative myelopathy (CDM) represents a unique naturally occurring animal model for human amyotrophic lateral sclerosis (ALS) because of similar clinical signs, neuropathologic findings, and involvement of the superoxide dismutase 1 (SOD1) mutation. A definitive diagnosis can only be made postmortem through microscopic detection of axonal degeneration, demyelination and astroglial proliferation, which is more severe in the dorsal columns of the thoracic spinal cord and in the dorsal portion of the lateral funiculus. Interestingly, the muscle acetylcholine receptor complexes are intact in CDM prior to functional impairment, thus suggesting that muscle atrophy in CDM does not result from physical denervation. Moreover, since sensory involvement seems to play an important role in CDM progression, a more careful investigation of the sensory pathology in ALS is also warranted. The importance of SOD1 expression remains unclear, while oxidative stress and denatured ubiquinated proteins appear to play a crucial role in the pathogenesis of CDM. In this updated narrative review we performed a systematic search of the published studies on CDM that may shed light on the pathophysiological mechanisms of human ALS. A better understanding of the factors that determine the disease progression in CDM may be beneficial for the development of effective treatments for ALS.

Effects of theta burst stimulation on referred phantom sensations in patients with spinal cord injury.

To further explore the mechanisms underlying cortical reorganization in patients with phantom sensations after deafferentation, a repetitive transcranial magnetic stimulation study was carried out in two patients with referred phantom sensations (RPS) after incomplete spinal cord injury at the thoracic level. We delivered continuous (inhibitory), intermittent (excitatory), and placebo theta burst stimulation to the contralateral primary motor cortex (M1), primary somatosensory cortex (S1), and secondary somatosensory cortex (S2). Perception of RPS was significantly and transiently disrupted by inhibitory theta burst stimulation applied over S1 and, to a lesser extent, S2. This study supports the hypothesis that RPS depend on remapping in the somatosensory cortex and provides further electrophysiological evidence in vivo that cortical reorganizational processes are critically modulated by GABAergic mechanisms. Enhancement of GABAergic activity may block cortical reorganization, leading to RPS in spinal cord injury patients.

High-frequency oscillations in epilepsy and surgical outcome. A meta-analysis.

High frequency oscillations (HFOs) are estimated as a potential marker for epileptogenicity. Current research strives for valid evidence that these HFOs could aid the delineation of the to-be resected area in patients with refractory epilepsy and improve surgical outcomes. In the present meta-analysis, we evaluated the relation between resection of regions from which HFOs can be detected and outcome after epilepsy surgery. We conducted a systematic review of all studies that related the resection of HFO-generating areas to postsurgical outcome. We related the outcome (seizure freedom) to resection ratio, that is, the ratio between the number of channels on which HFOs were detected and, among these, the number of channels that were inside the resected area. We compared the resection ratio between seizure free and not seizure free patients. In total, 11 studies were included. In 10 studies, ripples (80-200 Hz) were analyzed, and in 7 studies, fast ripples (>200 Hz) were studied. We found comparable differences (dif) and largely overlapping confidence intervals (CI) in resection ratios between outcome groups for ripples (dif = 0.18; CI: 0.10-0.27) and fast ripples (dif = 0.17; CI: 0.01-0.33). Subgroup analysis showed that automated detection (dif = 0.22; CI: 0.03-0.41) was comparable to visual detection (dif = 0.17; CI: 0.08-0.27). Considering frequency of HFOs (dif = 0.24; CI: 0.09-0.38) was related more strongly to outcome than considering each electrode that was showing HFOs (dif = 0.15; CI = 0.03-0.27). The effect sizes found in the meta-analysis are small but significant. Automated detection and application of a detection threshold in order to detect channels with a frequent occurrence of HFOs is important to yield a marker that could be useful in presurgical evaluation. In order to compare studies with different methodological approaches, detailed and standardized reporting is warranted.