MEG's ability to localise accurately weak transient neural sources.
OBJECTIVE
To investigate the accurate localisation of weak, transient, neural sources under conditions of varying difficulty.


METHODS
Multiple dipolar sources placed within a head-shaped phantom at superficial and deep locations were driven separately or simultaneously by a short-lasting current with varied amplitudes. Artificial MEG signals that were very similar to the human High Frequency Oscillations (HFO) were produced. MEG signals of HFO were also recorded from median nerve stimulation. Different inverse techniques were used to localise the phantom dipoles and the human HFO generators.


RESULTS
The human HFO were measured around 200 and 600Hz by using only 120 trials. The 200Hz HFO were localised to BA3b. The superficial phantom's source was localised with an accuracy of 2-3mm by all inverse techniques (120 trials). The 'subcortical' source was localised with an error of approximately 5mm. Localisation of deeper 'thalamic' sources required more trials.


CONCLUSIONS
MEG can detect and localise weak transient activations and the human HFO with an accuracy of a few mm at cortical and subcortical regions even when a small number of trials are used.


CONCLUSIONS
Localizing HFO to specific anatomical structures has high clinical utility, for example in epilepsy, where discrete HFO appears to be generated just before focal epileptic activity.
Papadelis
Christos
C
Laboratory for Human Brain Dynamics, Brain Science Institute (BSI), RIKEN, 2-1 Hirosawa, Wako-shi, Saitama 351-0198, Japan; Laboratory of Functional Neuroimaging, Center for Mind/Brain Sciences (CIMeC), University of Trento, Via delle Regole 101, 38060 Mattarello (TN), Italy. Electronic address: christos.papadelis@unitn.it.
Poghosyan
Vahe
V
Laboratory for Human Brain Dynamics, AAI Scientific Cultural Services Ltd., Office 501, Galaxias Building Block A, 33 Arch. Makarios III Avenue, 1065, Nicosia, Cyprus; Laboratory for Human Brain Dynamics, Brain Science Institute (BSI), RIKEN, 2-1 Hirosawa, Wako-shi, Saitama 351-0198, Japan.
Fenwick
Peter B C
PBC
Laboratory for Human Brain Dynamics, Brain Science Institute (BSI), RIKEN, 2-1 Hirosawa, Wako-shi, Saitama 351-0198, Japan.
Ioannides
Andreas A
AA
Laboratory for Human Brain Dynamics, Brain Science Institute (BSI), RIKEN, 2-1 Hirosawa, Wako-shi, Saitama 351-0198, Japan; Laboratory for Human Brain Dynamics, AAI Scientific Cultural Services Ltd., Office 501, Galaxias Building Block A, 33 Arch. Makarios III Avenue, 1065, Nicosia, Cyprus.
D000328:Adult; D001921:Brain / Q000502:physiology*; D001931:Brain Mapping / Q000379:methods; D006801:Humans; D015225:Magnetoencephalography / Q000379:methods* / Q000592:standards; D008297:Male; D008475:Median Nerve / Q000502:physiology; D004561:Transcutaneous Electric Nerve Stimulation / Q000379:methods / Q000592:standards