Slow cortical potentials indicate a state of excitation or inhibition of large cortical neuron pools. Negative slow brain potentials of several seconds duration indicate depolarization of the underlying cortical network, positivity reflects reduction of fascilitation. In several papers biofeedback of slow cortical potentials in normal populations where described (Birbaumer et al 1990, Physiological Reviews) which showed that self-produced negativity improves those behavioral and cognitive activities which utilize mobilization of cortical networks. Response speed, vigilance and concentration is increased during negativity, positivity reduces mobilization.
Cholinergic inflow to the cortical mantle seems to be responsible for negativity, while positivity depends on the activation of GABAergic inhibitory synapses. Measurement of brain blood flow with functional MRI during biofeedback of slow cortical potentials (Birbaumer et al, in press) demonstrates that during self-produced negativity prefrontal thalamic and parietal structures are activated while during self-induced positivity those structures are inhibited. Therefore it can be concluded that self-regulation of slow cortical potentials involves excitation and inhibition of attentional systems in cortical and subcortical structures.
Biofeedback of slow cortical potentials was first applied to the treatment of epilepsy, particular temporal lobe epilepsy (Rockstroh et al 1989).
Several controlled studies have shown that training of positivity for more than 40 sessions improves seizure frequency and neuropsychological functions in temporal lobe epilepsy: three studies with 60 patients have demonstrated that after extended training of positivity one third of patients is seizure-free, one third shows significant improvement and one third does not respond. All patients were drug-refractory epileptic patients with more than one seizure a week. These studies will be reviewed and new data will be added.
Another successful application of slow brain potential biofeedback is a brain-computer-interface communication system for locked-in patients.
Locked-in-patients have no means to communicate because all muscles including face muscles are paralyzed. Most of the patients in our studies are patients with amyotrophic lateral sklerosis, a neurological disease which leads to complete motor paralysis while all sensory systems remain intact. Patients are artificially ventilated and have to be fed artificially. These patients learn to produce cortical negativity and positivity at different locations of the brain and use this brain response to select in a special computer program verbal communication subprograms by which a more or less fluent verbal communication through the brain with the help of the computer becomes possible. Video demonstrations and results of these studies will be presented at the conference. A new successful application of slow brain potential biofeedback is the training of left temporal negativity in aphasic patients. Already after 5 training sessions improvement in expression and processing of words can be shown.
