Biomagnetic methodologies for the noninvasive investigations of the human brain (Magnobrain)

Magnetoencephalography (MEG) non-invasively infers the distribution of electric currents in the brain by measuring the magnetic fields they induce. Its superb spatial and temporal resolution provides a solid basis for the `functional imaging¿ of the brain provided it is integrated with other brain imaging techniques. MAGNOBRAIN is an applied research project that developed tools to integrate MEG with MRI and EEG. These include: (1) software for MEG oriented MRI feature extraction; (2) the Brain Data Base (BDB) which is a reference library of information on the brain used for more realistic and biologically meaningful functional localisations through MEG and EEG; and (3) a database of normative data (age and sex matched) for the interpretation of MEG. It is expected that these tools will evolve into a medical informatics environment that will aid the planning of neurosurgical operations as well as contribute to the exploration of mental function including the study of perception and cognition

Transition to seizure in photosensitive epilepsy

Photosensitive epilepsy (PSE) offers a highly reproducible model to investigate whether changes in neuronal activity preceding the transition to an epileptic photoparoxysmal response (PPR) may be detected. We investigated this possibility in patients with idiopathic PSE using MEG, as well as normal controls and non-photosensitive epileptic patients of the same age group. Spectral analysis of the MEG signals recorded during intermittent light stimulation revealed relevant information in the phase spectrum. To quantify this effect, we introduced a second order response feature of the stimulus-triggered visual response preceding the PPR: the phase clustering index, which measures how close the phases of successive periods are grouped for each frequency component for all periods of the stimuli applied. We found that an enhancement of phase synchrony in the gamma-band (30-120 Hz), harmonically related to the frequency of stimulation, preceded the stimulation trials that evolved into PPRs, and differed significantly from that encountered in trials not followed by PPR or in control subjects. Thus this index can be considered a valuable index of the pro-ictal transition to seizures in photosensitive epilepsy