Determination of convulsive threshold by photo-pharmacologic stimulation: A study of technique and reliability

1. 1. A study of the technique and reliability of the photo-pharmacologic determination of convulsive threshold was made on 27 subjects. Observations of EEG change and myoclonic reaction were made on repeated occasions using both hexazole and Metrazol. In a final activation each subject received a generalized convulsive seizure. 2. 2. A standard method for photo-pharmacologic activation is described which yields a reliable determination of myoclonic threshold. 3. 3. An either-or, multiple-sign end-point was developed in which the appearance of spike and wave, or rhythmic polyspikes in the EEG or myoclonus extending beyond the face correlated .7 with the threshold for a generalized convulsion. Slow activity, sharp waves, high voltage fast activity or random spikes in the EEG, and myoclonus limited to the face were found to have low correlation with the threshold for a generalized convulsion. 4. 4. Hexazole was found preferable to Metrazol for activation studies. 5. 5. No invariant progressive increase in photic driving, occurrence of harmonics or other EEG change was found to precede or accompany the myoclonic reaction.