Brain Research, 159 (1978) 473-476 © Elsevier/North-Holland Biomedical Press

473

An electrical sign of participation of the mesial 'supplementary' motor cortex in human voluntary finger movement

L1DDER DEECKE and HANS HELMUT KORNHUBER Abteilung Neurologie, Universitiit Ulm, D-79 Ulm (G.F.R.)

(Accepted September 7th, 1978)

The vertex maximum of the readiness potential (Bereitschaftspotential, BP 1,3,5,6) has previously been explained by volume conduction xl. It was argued that a vertex electrode collects activity from both motor cortices. In bilateral parkinsonism, however, we see a bilateral abolition of the precentral Bereitschaftspotential, whereas over other cortical areas (mid- and lateral parietal or vertex) it is not significantly reduced2, 4. Experiments were carried out in 10 patients with bilateral parkinsonism selected for pronounced akinesia but minimal tremor, and in 10 age-matched healthy control subjects. Movements consisted of quick voluntary volar flexions of the index finger by pulling th,e trigger of a pistol. Subjects fixed their gaze on a given spot and avoided eye blinking Or other artefacts. Trials contaminated by such artefacts were rejected as judged by EOG and EEG records as well as direct observation of the subject. A total of 400-500 such clean movements were averaged per experiment. Recordings with long time constant were obtained from left and right precentral, vertex, left, mid-, and right parietal electrodes referred to linked ears. The right and left precentral electrodes were placed to overly the hand area of the precentral gyrus as described previously~, 3, the mid-precentral ~ vertex electrode was placed at Cz according to the 10/20 method s, i.e. 50 ~ the nasion-inion circumference, a position which is 2.5 cm anterior to the Rolandic fissure. The left, mid-, and right parietal electrodes corresponded to P3, Pz and P4 of the 10/20 system. Movement onset was determined by the EMG. Eight of the 10 patients received L-DOPA treatment. A typical example of the cerebral potentials preceding voluntary finger movement in a patient with bilateral parkinsonism is shown in Fig. 1. The slowly increasing negativity called the Bereitschaftspotential is well-pronounced in the midprecentral = vertex lead ( - - I 1.5 #V) and to a lesser degree also in the parietal leads. However, it is absent in the lateral precentral leads overlying the hand area of the M! motor cortex. A similar BP distribution results when averaging over all patients. The results are shown in Table I, where they are compared to those of age-matched healthy control subjects. An abolition or rather slight positivity of the precentral BP was seen

474

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Fig. 1. Cerebral potentials preceding voluntary fingermovement in a patient with bilateral parkinsonism. Averages of 453 left index finger flexions recorded in contralateral and ipsilateral precentral and parietal leads and the vertex, referred to linked ear lobes. Maximal Bereitschaftspotential at thevertex, marked negativity also over parietal areas, but virtually no potential in contralateral or ipsilateral precentral leads overlying the hand representation of the MI motor cortex. Thus, the vertex maximum cannot be the result of potential pick-up from both MI cortices but must have its own potential generator, which probably is the mesiat supplementary motor cortex. TABLE I

Bereitschaftspotential amplitude 150 msec prior to movement onset Recording

con prec ips prec vertex mid-par

Parkinsonian patients (n = 10)

Age-matched normal controls (n = 10)

~ ( # V)

SD

SE

~

SD

SE

+0.47 +0.49 -4).18 --0.01

2.18 1.47 3.94 2.39

0.69 0.46 1.24 0.76

--1.26 ---0.75 ---0.82 ---0.79

1.93 1.75 1.98 2.51

0.61 1.72 0.63 0.80

Significance

P P P P

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