Habituation of orienting reaction in therapy-resistant partial epilepsy.

A polygraphic study on resistance to habituation of the somatic, autonomic and EEG components of the orienting reaction elicited by a repetitive auditory stimulus was performed in 66 epileptics with therapy-resistant partial seizures (TRPS) and in 135 matched subjects in two control groups. The study showed a significantly higher resistance to habituation of the orienting reaction in epileptics with TRPS vs. the normal subjects of the control group I. A significantly higher resistance to habituation was also noted vs. the epileptics with therapy-controlled partial seizures of control group II. The correlational analysis of data showed that the severity of these habituation disturbances in epileptics with TRPS depended on the patients' age, type of electroclinical seizures, pretrial seizure frequency, type of resting EEG, administered treatment (no. of administered antiepileptic drugs/patient), daily dose, as well as on the serum level of these drugs. The multivariate regression analysis showed that the most significant predictive variables for the habituation disturbances were the pretrial seizure frequency, type of electroclinical seizures, daily dose of administered antiepileptic drugs and their serum level. The data also evidenced that the antiepileptic treatment improves the interictal habituation disturbances, the effect being more marked as the treatment was more sustained. The above-mentioned habituation changes in epileptics with TRPS should be ascribed to some disturbances in nervous excitability.