Hemodynamic and EEG Time-Courses During Unilateral Hand Movement in Patients with Cortical Myoclonus. An EEG-fMRI and EEG-TD-fNIRS Study.

Multimodal human brain mapping has been proposed as an integrated approach capable of improving the recognition of the cortical correlates of specific neurological functions. We used simultaneous EEG-fMRI (functional magnetic resonance imaging) and EEG-TD-fNIRS (time domain functional near-infrared spectroscopy) recordings to compare different hemodynamic methods with changes in EEG in ten patients with progressive myoclonic epilepsy and 12 healthy controls. We evaluated O2Hb, HHb and Blood oxygen level-dependent (BOLD) changes and event-related desynchronization/synchronization (ERD/ERS) in the α and ß bands of all of the subjects while they performed a simple motor task. The general linear model was used to obtain comparable fMRI and TD-fNIRS activation maps. We also analyzed cortical thickness in order to evaluate any structural changes. In the patients, the TD-NIRS and fMRI data significantly correlated and showed a significant lessening of the increase in O2Hb and the decrease in BOLD. The post-movement ß rebound was minimal or absent in patients. Cortical thickness was moderately reduced in the motor area of the patients and correlated with the reduction in the hemodynamic signals. The fMRI and TD-NIRS results were consistent, significantly correlated and showed smaller hemodynamic changes in the patients. This finding may be partially attributable to mild cortical thickening. However, cortical hyperexcitability, which is known to generate myoclonic jerks and probably accounts for the lack of EEG ß-ERS, did not reflect any increased energy requirement. We hypothesize that this is due to a loss of inhibitory neuronal components that typically fire at high frequencies.

From neurovascular coupling to neurovascular cascade: a study on neural, autonomic and vascular transients in attention.

Mental processes bring about neural, vascular and autonomic changes in the brain cortex. Due to the different nature of these modifications, their onsets show no synchrony and time dynamics is often strongly dissimilar. After acquiring data from a group of 16 subjects, we estimated temporal correlation between task and signals in order to assess possible influences induced by an attentive task on electroencephalographic (EEG), heart rate variability (HRV), oxy- and deoxy-haemoglobin concentration signals. We also investigated correlations and time delays between couples of different biological signals. This allowed for the isolation of a subgroup of subjects showing similar tracks. Cardiac frequency and deoxy-haemoglobin signals displayed a strong positive correlation with the task design, while EEG alpha rhythm and oxygenation showed a negative correlation. Neural electrical response was nearly instantaneous with respect to the task progression, and autonomic response showed a mean delay of about 15 s and a slower hemodynamic response (mean delay above 20 s) was finally induced. Globally, the task elicited a cascade of responses, in which delays can be quantified.

Study of neurovascular and autonomic response in a divided attention test by means of EEG, ECG and NIRS signals.

We evaluated neurovascular and autonomic response to a Divided Attention task within a group of 16 healthy subjects, by means of Electroencephalography, Electrocardiography, functional Near Infrared Spectroscopy techniques, acquired simultaneously. We exctracted Alpha (8-13,5 Hz) and Beta (13,5-30 Hz) power rhythms with a spectral autoregressive residual model, and inter-beat-interval (RR series) and separated superficial (extracortical) and depth NIRS contribution. Cross Correlation Function at different time lags was then calculated between each signal and the task, modeled as a square wave and among couples of signals, in order to evaluate the sequence of activation of the different physiological districts involved and the common information shared. Results showed the presence of a cascade of responses and a strong influence by the block task on each signal, representative of the neurovascular coupling elicited by the cognitive cerebral activation.