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Summary: The aim of this study was to investigate side-to side differences of simultaneously measured middle cerebral artery (MCA) blood flow velocities during various hemisphere specific tasks, Using a transcranial Doppler device, flow ve locity changes of 24 healthy, right-handed subjects were moni tored simultaneously in the left and right MCA during different hemisphere-specific tasks. Mean flow velocity (MFY) curves were averaged for each individual subject and task. Simulta neously, heart rate, blood pressure and end-tidal carbon dioxide (C02) were measured in a subgroup of six subjects. When compared with the resting state, all stimuli produced significant (p < 0.001) bilatocal MFY increases, ranging from 2.5-9.2%. A lateralization of MFY increases with a significantly (p < 0.001) more pronounced increase in MFY in the hemisphere contra lateral to the performing hand was observed both during simple sequential finger movements and a complex spatial task. Dur ing the complex spatial task, consistently higher MFY increases were observed in the right MCA (p < 0.00 I), regardless of the side of task performance. Recognition of pictorial material pre-A close coupling of neuronal activIty and regional cerebral blood flow (rCBF) has been shown by several authors. Neuronal activity is tightly coupled to local changes in rCBF (Woolsey and Rovainen, 1991). The first to report a direct connection between brain activity and rCBF was Fulton in 1928. He described an increased blood flow murmur over a patient's occipital angioma while the patient was reading. Today, a variety of tracer techniques are available for in vivo rCBF measurements, including Xenon-133 inhalation or injection techniques, single photon emission computed tomography and posReceived January 25, 1996; final revision received August 10, 1996; accepted December 10, 1996. itron emission tomography. These methods have been used to evaluate changes in rCBF during different func tional activities such as visual stimulation, speech, read ing, and cognitive tasks (Risberg and Ingvar,

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