engleski

Early human vision as revealed by MEG

Neuromagnetic measurements combined with spatio-temporal modeling strategies allow a noninvasive identification and real time tracking of cortical pathways. We used simple difference of Gaussians (DOG) and target stimuli as well as complex face stimuli to examine early neurodynamics of the human visual cortex. The use of spatio-temporal models assuming focal cortical activations revealed retinotopic organization of striate and extrastriate regions (Aine et al., 1996, Supek et al. 1999). Primary visual cortex was reactivated at 160 ms post-stimulus in a selective spatial visual attention study (Aine at al., 1995) as a first evidence of a feedback mechanism demonstrating a unique insight into the cognitive neurodynamics. Our most recent results suggest important role of the occipital cortex in face selective processing already at 100 ms post-stimulus where we demonstrated dissociation of face and object processing (Susac et al, 2008 in press). These empirical results together with a range of numerical simulation studies indicate that a millisecond temporal resolution of MEG not only allows estimation of both location and cortical source dynamics but improved source discrimination as well, in particular for asynchronous activations, which contributed to a unique insight into early vision not available by hemodynamic and metabolic measures.

MEG; human visual system; functional and retinotopi organization; early cognition

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