[Slow brain potentials in writing: the correlation between writing hand and speech dominance in right-handed humans].

1. Slow cerebral potential shifts were recorded from the scalp over both cerebral hemispheres by retrograde summation while 23 right-handers were writing. Averaging included writing errors, but eliminated eye movements and other artifacts. Repeated writing of the same word or sentence was compared to writing different dictated words, to drawings, and to other control experiments. 2. Surface negative readiness potentials (Bereitschaftspotential) appeared about 1 s before writing, which was similar to those preceding other voluntary movements. 3. During writing, the writing potentials in different cortical regions began with a negative increase of the Bereitschaftspotential, usually followed by a plateau or positive waves. One or several biphasic potentials persisted for another 2 s after writing had ceased. 4. The writing potentials had rather constant forms in the same individual, but showed large interindividual variations of form and polarity. The largest initial negativity (with both ear lobes serving as reference) occurred at the vertex and the left motor region contralateral to the writing hand. 5. The left hemispheric preponderance of writing potentials, maximal at the precentral region contralateral to the writing hand, was less marked when writing with the left hand. An interaction of the writing hand and language dominance is assumed. 6. Writing the same word or short sentence repeatedly caused potentials of larger amplitude than the preceding readiness potentials. Writing dictated words or drawing figures after verbal stimuli that require language processing caused larger potentials in the left hemisphere than did repeated word writing. 7. The fact that negative potentials with larger left hemispheric amplitudes appear after verbal stimuli may indicate that language information is processed in the speech-dominant hemisphere before and during writing or drawing. 8. By variously combining bipolar leads, the lateral differences of the potential fields can be more clearly distinguished than by using only unipolar leads with ear reference.