Multifocal visual functional magnetic resonance imaging

S. Vanni and L. Henriksson

Collaborator: A. James, Centre for Vision Sciences, Australian National University, Canberra, Australia.

We have applied multifocal stimulation technique, recently developed for electroretinograms and visual evoked potential measurements, to functional magnetic resonance imaging (fMRI). In collaboration with mathematician Andrew James (Australian National University, Canberra, Australia) different kinds of visual stimuli and imaging parameters were tested. Eventually, with multifocal stimulus cortical responses to 60 local visual field stimuli were measured in parallel. In the unfolded cortex, representations of the 60 visual field regions could be distinguished. This method allows a new way of retinotopic mapping of human visual cortex, and estimation of local anisotropy of visual field representation in single individuals. In future, it will be used as a powerful constraint of inverse solutions in magnetoencephalography to study quantitatively the timing and magnitude of retinotopic visual processes. In addition, multifocal fMRI allows robust localization of primary visual cortex, which could be applied as preoperative mapping for neurosurgery patients.