In most people the left hemisphere of the brain is dominant for language. Because of the increased incidence of atypical right-hemispheric language in left-handed neurological patients, a systematic association between handedness and dominance has long been suspected. To clarify the relationship between handedness and language dominance in healthy subjects, we measured lateralization directly by functional transcranial Doppler sonography in 326 healthy individuals using a word-generation task. The incidence of right-hemisphere language dominance was found to increase linearly with the degree of left-handedness, from 4% in strong right-handers (handedness = 100) to 15% in ambidextrous individuals and 27% in strong left-handers (handedness = -100). The relationship could be approximated by the formula: f1.gif" BORDER="0">. These results clearly demonstrate that the relationship between handedness and language dominance is not an artefact of cerebral pathology but a natural phenomenon.

Our knowledge about the variability of cerebral language lateralization is derived from studies of patients with brain lesions and thus possible secondary reorganization of cerebral functions. In healthy right-handed subjects 'atypical', i.e. right hemisphere language dominance, has generally been assumed to be exceedingly rare. To test this assumption we measured language lateralization in 188 healthy subjects with moderate and strong right-handedness (59% females) by a new non-invasive, quantitative technique previously validated by direct comparison with the intracarotid amobarbital procedure. During a word generation task the averaged hemispheric perfusion differences within the territories of the middle cerebral arteries were determined. (i) The natural distribution of language lateralization was found to occur along a bimodal continuum. (ii) Lateralization was equivalent in men and women. (iii) Right hemisphere dominance was found in 7.5% of subjects. These findings indicate that atypical language dominance in healthy right-handed subjects of either sex is considerably more common than previously suspected.

Background and Purpose-Functional transcranial Doppler ultrasonography (fTCD) can assess event-related changes in cerebral blood flow velocities and, by comparison between sides, can provide a measure of hemispheric perfusional lateralization. It is easily applicable, insensitive to movement artifacts, and can be used in patients with less than perfect cooperation. In the present study we investigated the validity of fTCD in determining the hemispheric dominance for language by direct comparison of fTCD with intracarotid amobarbital anesthesia (Wada test). Methods-fTCD and the Wada test were performed in 19 patients evaluated for epilepsy surgery. By the Wada test, 13 patients were classified as left-hemisphere dominant and 6 as right-hemisphere dominant for language. fTCD was based on the continuous bilateral measurements of blood flow velocities in the middle cerebral arteries and event-related averaging during a cued word generation task previously shown to activate lateralized language areas in normal adults. Results-In 4 patients fTCD assessment was not possible because of lack of an acoustic temporal bone window. In the remaining 15 candidates, determination of language dominance was concordant with the Wada test in every case. Moreover, the correlation of the lateralization measures from both procedures was highly significant (rϭ.92, PϽ.0001). Conclusions-This strong correlation validates fTCD as a noninvasive and practical tool for the determination of language lateralization that can be applied for clinical and investigative purposes. (Stroke. 1998;29:82-86.)

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Depending on individual lesion location and extent, reorganization of the human motor system has been observed with a high interindividual variability. In addition, variability of forces exerted, of motor effort, and of movement strategies complicates the interpretation of functional imaging studies. We hypothesize that a general pattern of reorganization can be identified if a homogeneous patient population is chosen and experimental conditions are controlled. Patients with amyotrophic lateral sclerosis (ALS) and healthy volunteers were trained to perform a simple finger flexion task with 10% of each individual's maximum grip force with constant movement amplitude and frequency. The activation pattern in ALS patients was distinctly different to that in healthy controls: In ALS patients, motor cortex activation was located more anteriorly, encompassing the premotor gyrus. The cluster volume within the supplementary motor area (SMA) was higher and shifted toward the pre-SMA. Contralateral inferior area 6 and bilateral parietal area 40 revealed higher cluster volumes. Our results demonstrate a general pattern of functional changes after motor neuron degeneration. They support the concept of a structurally parallel and functionally specialized organization of voluntary motor control. Degeneration of the first and second motor neurons leads to enhanced recruitment of motor areas usually involved in initiation and planning of movement. Partial compensation between functionally related motor areas seems to be a strategy to optimize performance if the most efficient pathway is unavailable.

Language is considered a function of either the left or, in exceptional cases, the right side of the brain. Functional imaging studies show, however, that in the general population a graded continuum from left hemispheric to right hemispheric language lateralization exists. To determine the functional relevance of lateralization differences, we suppressed language regions using transcranial magnetic stimulation (TMS) in healthy human subjects who differed in lateralization of language-related brain activation. Language disruption correlated with both the degree and side of lateralization. Subjects with weak lateralization (more bilaterality) were less affected by either left- or right-side TMS than were subjects with strong lateralization to one hemisphere. Thus in some people, language processing seems to be distributed evenly between the hemispheres, allowing for ready compensation after a unilateral lesion.

Background and Purpose-Since functional transcranial Doppler ultrasonography (fTCD) allows convenient and fully automated quantification of language lateralization, it seems ideal for longitudinal studies of perfusion changes during deterioration as well as recovery of language functions. However, during serial examinations, the technical, stochastic, and physiological variabilities of cerebral blood flow velocities (CBFV) have to be considered. Therefore, before fTCD is accepted as a tool for evaluation of changes in lateralization in the diseased state, its reliability in healthy subjects needs to be determined. Methods-We performed fTCD during a word generation task based on a previously validated technique with automated calculation of the averaged CBFV differences in the middle cerebral arteries providing an index of lateralization (LI). Results-(1)The accuracy of the LI as assessed by the confidence interval was better than 1% of the mean hemispheric difference. (2)