Differential Activation of Visual Areas V1 and V5 by Pattern Reversal Stimulation – An MEG Study

We have studied the differential activation of visual areas V1 and V5 during early visual information processing in eight healthy subjects in a full-field pattern reversal task (black and white checkerboard). Magnetic fields were registered with a whole-head magnetometer system (Magnes 2500 WH, 4D-Neuroimaging) with 148 SQUIDS and averaged relative to stimulus onset. The underlying current source density was determined by means of the magnetic field tomography [1]. Brain areas displaying stimulus-locked responses were anatomically identified with anatomical probability maps [2]. Our approach revealed that V1 and V5 generate pronounced stimulus-locked responses. The time courses of the V1 and the V5 responses displayed a pattern which was consistent over all subjects: The averaged response in V1 was maximal at 109 ms (standard deviation=10 ms), whereas the maximum of the averaged response of V5 appeared at 168 ms after stimulus onset (standard deviation=11 ms). Our findings contribute to assess the functional role of the different parallel pathways activating V5. References: [1] Ioannides AA, Bolton JPR et al. Continuous probabilistic solutions to the biomagnetic inverse problem. Inverse Problems 1999; 6: 523–542. [2] Amunts K, Malikovic A et al. Brodmann's area 17 and 18 brought into stereotaxic space – Where and how variable? NeuroImage 2000; 11: 66–84.