SELF-REGULATION OF SLOW CORTICAL POTENTIALS IN EPILEPSY - A RETRIAL WITH ANALYSIS OF INFLUENCING FACTORS

Twenty sessions of biofeedback training were carried out with 12 drug- resistant patients with focal epilepsy who learned to produce either n egative or positive shifts of their slow cortical potentials (SCPs) at vertex. Feedback trials were interspersed with transfer trials in whi ch only a discriminative stimulus (signalizing whether positivity or n egativity was required) was presented, without feedback signal. Patien ts were able to differentiate significantly between the conditions of cortical positivity and cortical negativity, with larger differentiati on scores being obtained in feedback trials than in transfer trials. T he amplitude of positivity generated in the positivity condition incre ased linearly across sessions both in feedback and in transfer trials. The largest negativity was produced in the 5th session; after this, m ore transient negativities were generated, whose amplitude decreased t owards the end of trial. The mean severity of seizures, estimated as t he frequency of seizures weighted by their subjective 'strength', decr eased significantly after training as compared to the pre-training pha se. The data suggest that (1) patients could learn to achieve a state of cortical disfacilitation and (2) with progressed learning, they bec ame less motivated for (or afraid of) producing considerable negative shifts, since extensive negativity may reflect cortical over-excitatio n and therefore be associated with early signs of seizures. The inabil ity of producing cortical negativity is however not necessarily a bad predictor.