[Reappearance and recovery of alpha rhythm after eye opening]

To obtain more informations from routine EEG recording, we studied changes in alpha rhythm after eye opening that had been almost disregarded hitherto. The study was carried out on 26 normal controls and 137 patients with four categories of diseases including 52 patients with psychiatric diseases, 8 with trifling neurological symptoms, 68 with defined organic brain diseases, and 9 with headache without defined organic cause. Following routine EEG recording, each subject was asked to keep their eyes opened for three minutes. The major changes in alpha rhythm after eye opening were composed of two patterns; "reappearance" and "recovery". The reappearance was defined as appearance of 5 or more alpha waves in series; and the recovery, as the amount and amplitude of the alpha rhythm became equal to those of the back ground alpha-rhythm which was seen while their eyes were kept closed. The reappearance was noticed in 84.6% of normal controls and in 89.1% of all patients. In patients with organic brain diseases, the reappearance was seen in 88.2%, while it was in 68.6% of the patients without organic brain disease. The recovery was noticed in 34.3% of all patients (p less than 0.01), while it was only in 15.4% of normal controls. The incidence of the recovery in the patients with organic brain diseases was 41.2%, the value of which was significantly higher than that of the rest of patients (28.8%, 15 out of 52 patients, p less than 0.05). These patients with the recovery tended to show slower frequency and higher amplitude in the back ground alpha-rhythm than the patients without recovery.