Dynamical Cortical Activations Associated with Saccade Execution: A Normalized Integrative fMRI-MEG Study

Vol. 1 (2012) p. 27-35

To validate the performance of a newly developed normalized integrative functional magnetic resonance imaging-magnetoencephalography (fMRI-MEG) method and identify the temporal and spatial characteristics of multiple cortical activations preceding and following saccade execution, we used the fMRI-MEG method to measure and compare neuronal activities while subjects performed both a visually-guided saccade and an apparent motion perception task. Eight healthy subjects participated in the experiments. In the normalized integrative fMRI-MEG method, time-varying dipole moments of activated regions were reconstructed from measured MEGs. Sets of activated regions were determined from statistically analyzed fMRI data and were used as spatial constraints for the integrative fMRI-MEG method. Dynamic recurrent neural activities prior to saccade onset were successfully detected in multiple cortical areas including the V1/V2, V2/V3, frontal eye field (FEF), human middle temporal area (hMT), human medial superior temporal area (hMST), intraparietal sulcus (IPS) and ventral intraparietal area (VIP). These activities lasted for the whole duration of saccade and also showed double-peak responses ; before saccade onset and at saccade termination. These results demonstrated that our proposed normalized integrative fMRI-MEG method is able to reconstruct reasonable time courses of cortical activations commonly occurring in humans. In addition, these results suggest that the double-peak activities observed during saccade execution may be derived from the activities of saccade and fixation neurons. Moreover, repetitive activities in the V1/V2, V2/V3, MT, and MST indicate a possibility of feedforward process triggering discharge of FEF neurons.