ReXexive saccades are driven by visual stimulation whereas voluntary saccades require volitional control. Behavioral and lesional studies suggest that there are two separate mechanisms involved in the generation of these two types of saccades. This study investigated diVerences in cerebral and cerebellar activation between reXexive and self-paced voluntary saccadic eye movements using functional magnetic resonance imaging. In two experiments (whole brain and cerebellum) using the same paradigm, diVerences in brain activations induced by reXexive and self-paced voluntary saccades were assessed. Direct comparison of the activation patterns showed that the frontal eye Welds, parietal eye Weld, the motion-sensitive area (MT/ V5), the precuneus (V6), and the angular and the cingulate gyri were more activated in reXexive saccades than in voluntary saccades. No signiWcant diVerence in activation was found in the cerebellum. Our results suggest that the alleged separate mechanisms for saccadic control of reXexive and self-paced voluntary are mainly observed in cerebral rather than cerebellar areas.

The measurement of airway responsiveness in preschool children is hampered by the fact that most tests of airway caliber are difficult to carry out at a young age. Patient cooperation is only needed to a limited extent when transcutaneous oxygen tension (PtcO2) is used as an indicator of airway obstruction following bronchial provocation. In 51 children, aged 6-14 years with asthma we have measured PtcO2 and forced expiratory volume in 1 second (FEV1) concurrently after bronchial provocation, using increasing doses of methacholine administered with a De Villbiss 646 nebulizer and a French-Rosenthal dosimeter. The shapes of the dose-response curves to PtcO2 and FEV1 show a close similarity. After methacholine challenge, the decrease in PtcO2 correlates highly with the decrease in FEV1. We conclude that in children a 20% decrease in PtcO2 can be used as a sensitive indicator of airway narrowing after methacholine challenge.