Motor-related cortical dynamics to intact movements in tetraplegics as revealed by high-resolution EEG.

We explored the cortical dynamics during movements of an unaffected body part in tetraplegic subjects with chronic spinal cord injury (SCI). The aims were to find out whether the intact movements were associated with a physiological time-varying pattern of activity in the motor-related cortical areas and whether the primary motor area (MI) activation followed a somatotopic distribution. Event-related potentials to self-initiated lip movements were analyzed by means of cortical source imaging of EEG recorded from seven tetraplegic subjects and seven control subjects. Regions of interest (ROIs) were selected on individual MRI and the time-varying electrophysiologic activity (cortical current density, CCD) was estimated on these ROIs and subjected to across-subject analysis. A significant, bilateral movement-related pattern of MI activation was detected during motor task execution in SCI patients as well as in controls. The site of local maxima activation displayed a symmetrical discrete distribution within MI, consistently with a putative somatotopic lip representation, in all the subjects. The supplementary motor area proper (SMAp) was always coactivated with MI and coactivation was characterized by a time course with typical premotion and motion phases over both motor areas. A clear-cut temporal delay between the SMAp and MI activation did not occur either in SCI patients or in controls. These findings obtained with noninvasive neuroelectrical source imaging document that in chronic SCI subjects "executive" motor areas are engaged with a preserved temporal and spatial pattern during preparation and execution of intact movements.

Cortical connectivity patterns during imagination of limb movements in normal subjects and in a spinal cord injured patient.

The problem of the definition and evaluation of brain connectivity has become a central one in neuroscience during the latest years, as a way to understand the organization and interaction of cortical areas during the execution of cognitive or motor tasks. In this paper we propose the use of the DTF method on cortical signals estimated from high resolution EEG recordings. An application of the proposed technique to the estimation of cortical connectivity pattern in normal subjects and in one spinal cord injured patient is also provided.

Hypermethods for EEG hyperscanning.

Until now, in EEG studies the activity of the brain during simple or complex tasks have been recorded in a single subject. Often, during such EEG recordings, subjects interacts with the external devices or the researchers in order to reproduce conditions similar to the those usually occurring in the real-life. However, in order to study the concurrent activity in subjects interacting in cooperation or competition activities, the issue of the simultaneous recording of their brain activity became mandatory. The simultaneous recording of hemodynamic or neuroelectric activity of the brain is called "hyperscanning". We would like present results obtained by EEG hyperscannings performed on a group of subjects engaged in cooperative games. The EEG hyperscannings have been performed with the simultaneous use of high resolution EEG devices on groups of three and four subjects while they were playing cooperative games. The analysis of such data have been conducted with analysis method that taken into account the particular nature of the data simultaneously gathered from different subjects. We called these methods hypermethods. In particular, we estimate the concurrent activity in multiple brains of the group and we depicted the causal connections between regions of different brains (hyperconnectivity). The resulting causality patterns will link certain areas of the brain of a subject to the waveforms obtained from the other brain areas of another subject of the same group. Results obtained in a study of several groups recorded by the hyperscanning reveals causal links between prefrontal areas of the different subjects when they are performing cooperative games in different frequency bands. Hypermethods for hyperscanning will open a different area for the study of neuroscience, in which the activity of multiple brains during social cooperation could be investigated. In such area the importance of EEG will be relevant due to its temporal and spatial resolution now obtainable w- ith the high resolution EEG techniques.

Neural basis for the brain responses to the marketing messages: an high resolution EEG study.

We investigated the behaviour of the brain during the visualization of commercial videos by tracking the cortical activity and the functional connectivity changes in normal subjects. High resolution EEG recordings were performed in a group of healthy subjects, and the cortical activity during the visualization of standard commercial spots and emotional spots (no profit companies) was estimated by using the solution of the linear inverse problem with the use of realistic head models. The cortical activity was evaluated in several regions of interest (ROIs) coincident with the Brodmann areas. The pattern of cortical connectivity was obtained by using the partial directed coherence (PDC) and investigated in the time and frequency domains, in the principal four frequency bands, namely the theta (4-7 Hz), the alpha (8-12 Hz), the beta (13-30 Hz) and the gamma (above 30 Hz). Results suggest a time-varying engagement of the orbitofrontal circuits that is thought to be involved in the reward value of the stimuli.

Removal of ocular artifacts for high resolution EEG studies: a simulation study.

Eye movements and blinks may produce unusual voltage changes that propagates from the eyeball through the head as volume conductor up to the scalp electrodes, generating severe electroencephalographic artifacts. Several methods are now available to correct the distortion induced by these events on the EEG, having different advantages and drawbacks. The main focus of this work is to quantify the performance of the removal of EOG artifact due to the application of the independent component analysis (ICA) methodology. The precise quantification of the effects of artifact removal by ICA is possible by using a simulation setup, with a realistic head model, that it is able to mimic the occurrence of an eye blink. The electrical activity generated by the simulated eyeblink were propagated through the realistic head model and superimposed to a clean segment of EEG. Then, artifact removal was performed by using the ICA approach. Ocular artifact removal was evaluated in different operative conditions, characterized by different signal to noise ratio and number of electrodes. The error measures used were the relative error and the correlation coefficient between the clear, original EEG segment and those obtained after the application of the ICA procedure.