[Does left-handedness affect the pattern of cerebral blood flow during cognitive activity?]

In most people the left hemisphere of the brain is dominant for language functions. Because of an increased incidence of atypical language lateralisation in the right hemisphere of left-handed neurological patients, more systematic studies on handedness and cerebral asymmetry of language have been undertaken. The present study is aimed at clarification of the relationship between handedness and language dominance in healthy subjects. Lateralisation was measured directly using functional transcranial Doppler sonography in left-handed subjects. Twenty-six individuals participated in the study. Three kinds of tasks were used, differing in the material involved and in appropriate strategies to be employed by the subjects. Two important parameters of the MCA blood flow were analysed: mean relative increase in the blood flow velocity (MDV) and specific patterns of cognitive task performance (i.e. performance profiles). Our results indicate that the incidence of the right hemisphere dominance for language depends on the degree of handedness, since only in the group of consistent left-handers language was right lateralised. In other left-handers both cerebral hemispheres were functionally equivalent. The measurement of MCA blood flow velocity changes using transcranial Doppler ultrasonography seems to be a simple and non-invasive method of assessing the functioning of the two hemispheres of human brain.