Movement-related potentials in the basal ganglia: a SEEG readiness potential study

Objectives: The brain potentials preceding and accompanying self-paced acra l limb movements (Bereitschaftspotential/readiness potential (RP) paradigm) were studied in 12 patients. Methods: Intracranial electrodes were implanted in order to explore intract able epilepsy. The electrodes were introduced into sites corresponding to t he electroclinical characteristics of each patient's epileptic seizures. In 7 patients, several depth electrodes were implanted orthogonally, in the t emporal, fronto-orbital and prefrontal cortex. In 4 patients, subdural stri p electrodes were used for the exploration of the fronto-temporal convexity . There were no RPs recorded in these areas. No contacts were placed in the central region known to generate cortical RP. In all the patients. one or two diagonal electrodes passed through or touched the basal ganglia to reac h the amygdala and the hippocampus, The putamen was explored in I I patient s (in 3 of them bilaterally), the caudate head was explored in two patients , and the pallidum was explored in two patients. Results: RP with a clear amplitude gradient was present in all explored str uctures. however a phase reversal was never observed. RP was observed in th e caudate in all recordings. and in the pallidum in one patient. It was rec orded in the putamen in 8 out of the I I explored patients. RPs were displa yed contralaterally to the movement 9 times in 13 explorations, and ipsilat erally 4 times in 9 explorations. The shape of RP resembled the RP shape in the cortex and on the scalp. Movement accompanying potentials (MAPs) were also present in all 3 explored structures. The electrophysiological charact eristics of MAP differed from RP, indicating separate generators. In the ba sal ganglia, RPs preceded the onset of movement by 500-1500 ms. at an avera ge of 1080 (+/- 330) ms. It seems that the RP in the basal ganglia starts s lightly later than the RP in the motor cortices. That should be definitely demonstrated in patients with simultaneous recordings from cortical and sub cortical structures. RP and MAP were displayed synchronously in the cortex and in the basal ganglia during most of the premovement period, as well as during the execution of movement. RP generators were reported by several au thors in other deeply located structures, i.e. in the thalamus and in the b rain-stem. Conclusions: Based on all these recordings, we presume that the RPs recorde d on the scalp are generated simultaneously in several cortical as well as subcortical structures. (C) 2001 Published by Elsevier Science Ireland Ltd.