Event-related potentials and deep grey matter atrophy in multiple sclerosis: Exploring the possible associations with cognition.

BACKGROUND: Event-related potentials (ERPs) have been proposed as a neurophysiological biomarker to capture cognitive dysfunction in multiple sclerosis (MS). Few studies have evaluated the relationships between ERPs and brain atrophy as known marker of structural brain damage related to cognitive impairment (CI). OBJECTIVES: To explore the relationships of brain atrophy, including of the cortex and deep grey matter, with ERP abnormalities and cognitive function, as defined using the Brief Repeatable Battery of Neuropsychological Tests (BRBN). RESULTS: Seventy-eight patients with relapsing-remitting MS were enroled, of which 38 (48.7%) had CI. Independent t-test comparisons of the ERP parameters found a significant difference in P300 wave latency, with a latency of 343.7 ± 32.6 ms in the CI group vs. 320.3 ± 16.5 ms in the cognitively preserved (CP) group (p = 0.001). Significant differences in the MRI measurements, including the cortex (p = 0.02) and deep grey matter structures [thalamus (p = 0.001), amygdala (p = 0.030), and nucleus accumbens (p = 0.004)) were observed, with lower measurements in the CI group. Regression models were also performed to explore the impact of brain volumes on ERP parameters. This showed a relationship between P300 latency and the lower amygdala (p = 0.02) and hippocampus (p = 0.03) volumes, while the amplitude of the P300 was significantly associated with a lower cortex volume (p = 0.01). CONCLUSION: Cortex volume emerged as the most significant predictor of the P300 amplitude. The amygdala and hippocampal volumes were found to influence P300 latency, highlighting the role of deep grey matter atrophy in ERPs for the first time. The combination of structural MRI and neurophysiological techniques, sensitive to diverse aspects of MS pathology, could improve the understanding of CI in MS and its neurodegenerative and inflammatory substrate.

Interactions between different EEG frequency bands and their effect on alpha-fMRI correlations.

In EEG/fMRI correlation studies it is common to consider the fMRI BOLD as filtered version of the EEG alpha power. Here the question is addressed whether other EEG frequency components may affect the correlation between alpha and BOLD. This was done comparing the statistical parametric maps (SPMs) of three different filter models wherein either the free or the standard hemodynamic response functions (HRF) were used in combination with the full spectral bandwidth of the EEG. EEG and fMRI were co-registered in a 30 min resting state condition in 15 healthy young subjects. Power variations in the delta, theta, alpha, beta and gamma bands were extracted from the EEG and used as regressors in a general linear model. Statistical parametric maps (SPMs) were computed using three different filter models, wherein either the free or the standard hemodynamic response functions (HRF) were used in combination with the full spectral bandwidth of the EEG. Results show that the SPMs of different EEG frequency bands, when significant, are very similar to that of the alpha rhythm. This is true in particular for the beta band, despite the fact that the alpha harmonics were discarded. It is shown that inclusion of EEG frequency bands as confounder in the fMRI-alpha correlation model has a large effect on the resulting SPM, in particular when for each frequency band the HRF is extracted from the data. We conclude that power fluctuations of different EEG frequency bands are mutually highly correlated, and that a multi frequency model is required to extract the SPM of the frequency of interest from EEG/fMRI data. When no constraints are put on the shapes of the HRFs of the nuisance frequencies, the correlation model looses so much statistical power that no correlations can be detected.

Changes in autonomic and EEG patterns induced by hypnotic imagination of aversive stimuli in man.

Autonomic and electroencephalographic (EEG) responses to aversive stimuli presented by means of hypnotic suggestion have been studied in man.Healthy volunteers with simple phobia were screened for susceptibility to hypnosis. The experimental paradigm included periods of rest during which the hypnotized subjects were asked to produce an emotionally neutral mental image and periods of emotional activation in which they were asked to image a phobic object. Heart rate (HR), respiratory frequency (RF) and EEG were processed to obtain the HR-related indexes of sympatho-vagal balance and the EEG spectral components. The results showed a significant increase in HR and RF with a shift of the sympatho-vagal indexes towards a sympathetic predominance during the hypnotic emotional activation. EEG activity showed a significant increase in the gamma band with a left fronto-central prevalence. There was also a less pronounced increase in the beta band. In conclusion, by means of hypnosis, autonomic and behavioral responses to fear-like stimuli can be induced in man in a reproducible and controlled manner. Such a paradigm could be applied in human neuroimaging studies to identify central nervous structures that modulate stress and fear-related reactions.