CEREBRAL-ACTIVITY DURING VISUAL-STIMULATION - A POSITRON EMISSION TOMOGRAPHY AND FUNCTIONAL MAGNETIC-RESONANCE-IMAGING STUDY

Stimulation of cerebral areas induces a regional increase in blood flo w and metabolism. Positron emission tomography (PET) is an established procedure to localize cerebral regions of enhanced activity. Exposure to a radioactive indicator and limited spatial and temporal resolutio n are disadvantages of this method as compared with other imaging tech niques, but anatomical orientation can be improved by matching PET ima ges with high-resolution magnetic resonance imaging (MRI) scans. Recen tly, functional MRI (fMRI) has arisen as an alternative method. This p rocedure presumably detects changes in the paramagnetic properties of hemoglobin, depending on its oxygenation state, as well as an increase d regional blood flow in activated cerebral areas. These structures ca n be visualized using sensitive scanning techniques and appear with br ight signal intensities. Visual stimulation was performed with the hel p of a high-resolution color VDU for PET registration and of an LCD vi deo projector for fMRI (1.5 T). Hemifield stimulation as well as subtr action between images of flickering and stable random dot stimuli show ed a preferential activation of the primary visual cortex. In addition , the first MRI results obtained during stimulation with moving gratin gs are demonstrated; hereby, preferentially extrastriate regions presu mably responsible for motion detection were activated.