Cortical control of optokinetic nystagmus in humans: a positron emission tomography study

Positron emission tomography (PET) was used to address the issue of physiol ogical changes in the cerebral cortex associated to optokinetic nystagmus ( OKN) in humans. We studied regional cerebral blood flow in eight volunteers during reflexive induction of OKN by a pattern of dots moving unidirection ally (toward the left side). We used two control conditions, with subjects passively viewing either stationary or incoherently moving dots. This parad igm was designed in order to differentiate the OKN-related activations from blood flow changes related to visual motion. When compared with the statio nary condition, OKN activated a set of occipital areas known to be sensitiv e to visual motion. Bilateral activation was found in the striate cortex (V 1) and the parietooccipital fissure, while area V5, the intraparietal sulcu s, and the pulvinar were activated only in the left hemisphere. When compar ed with incoherent motion, OKN activated the V1 and the parieto-occipital f issure bilaterally and the right lingual gyrus, while a signal decrease was observed in the V5 region in both hemispheres. No significant signal chang es were found in areas implicated in saccades or in processing vestibular i nformation. These results indicate that processing of OKN-related informati on is associated with neural activity in a specific set of visual motion ar eas and suggest that this network can be asymmetrically activated by a stri ctly unidirectional stimulation. Results are also discussed in terms of the specific kinds of OKN-related information processing subserved by each are a in this network.