Steep early negative slopes can be demonstrated in pre-movement bereitschaftspotential

Objectives: The study presents data suggesting that the classic bereitschaf tspotential hides in its early component (BPI) steep increases of negativit y which precede the movement at-varying intervals in repeated trials. Methods: In 12 volunteers, surface EEG from Fz, Cz, C3, C4, and Pz electrod es and EMG from the flexor digitorum communis were. recorded during self-pa ced wrist flexions. Two hundred trials were collected from each subject. Th e single trials were grouped for averaging in two different ways. In the fi rst one, single trials for each subject were used to create individual aver ages. In the second, all single trials were divided into groups according t o the point in time of small steep negative shift from the baseline detecte d on sweeps before the movement and time group averages were created. The i dentification of small shifts was based on the comparison of calculated mea n amplitudes in the first and the second half of the I s time window moved along the time axis. Results: The small negative shifts were identified in 97.2% of analyzed rec ords. In each subject, their position on the time axis varied considerably. Individual averages exhibited the characteristics of classical readiness p otential, i.e. slow early component, steep late component, laterality over motor cortices. On the other hand, all time group averages (26) displayed a n early steep negative shift followed by plateau which, about 0.5 s be fore the movement, gave rise to the second, late steep negative shift. The slop e values calculated in the definite segments of averaged curves were used a s a measure of the amplitude of these shifts over various brain areas. MANO VA showed a significant effect of the electrode position both in the case o f early slopes (F(4, 115) = 9.7; P < 0.000) and in the case of late slopes (F(4,115) = 22.5; P < 0.000). In both cases, the largest value was demonstr ated under Cz electrode. In contrast to the late slopes, the values of earl y slopes did not exhibit laterality and suggested greater importance of pre -frontal regions in their formation. Conclusion: We have suggested that the formation of steep early negative sh ifts from the baseline in time group averages was due to synchronization of a mental process which, under classical averaging procedure, was dispersed uniformly throughout the pre-movement period. <(c)> 2001 Elsevier Science Ireland Ltd. All rights reserved.