"Cognitive activity" monitored by non-invasive measurement of cerebral blood flow velocity and its application to the investigation of cerebral dominance.

We have developed a method of non-invasively detecting language lateralisation by measuring the increase in middle cerebral artery blood flow velocity occurring during a word association task, using transcranial Doppler ultrasonography. All exclusively right handed subjects (N = 12) showed a relative increase in left sided flow velocity during the task; mean rise was 4.04% on the left, and -0.03% on the right (p < 0.002). Left handed subjects (N = 6) showed a mixed pattern with three showing much greater increases (> 5%) in left, compared with right, hemisphere flow velocity, and three showing only small differences between left and right sides, possibly reflecting bilateral language representation. This technique offers potential not only in studying patterns of cerebral dominance, but also in studying cognitive responses to other stimuli.