Analysis of cerebral responses to flicker in patients complaining of episodic headache

Abstract

1. 1. Frequency analyses of electroencephalograms from 50 subjects with no clinical complaint of headache and 113 suffering from episodic headache provide statistically significant evidence of a specific response spectrum to stimulation by flickering light in patients complaining of severe episodic headaches with associated nausea, vomiting and visual disturbances, or paraesthesia. 2. 2. Two main types of fundamental frequency response curves were obtained: ◦ ( a) the “N” type in subjects without headache, with a peak in the alpha band and declining rapidly with increase of stimulus frequency above 14 f/sec.; ◦ ( b) the “H” type in patiens complaining of headache, with a flat top showing a response maintained up to or above 20 f/sec. 3. 3. A third type of frequency response curve was observed in a few patients in the control group; this showed a peak in the alpha band, a trough at about 14 f/sec. and a second peak at about 18 f/sec. 4. 4. The three types of curve can be differentiated by direct comparison of the abundance of response at 18 f/sec. with that at the peak, and of the abundance at the trough to that at 18 f/sec. 5. 5. Statistical analysis of the results showed that the odds against the association between the “H” type of frequency response curve and clinical complaint of headache being fortuitous are greater than a million to one. 6. 6. The examination can be performed in approximately 2 min. with the aid of a frequency analyser and stroboscope and provides a useful method for the investigation of patients complaining of headaches, particularly those considered to be suffering from migraine. 7. 7. No significant alteration in the flicker response curve has been observed during a headache attack and the conventional forms of medication have no apparent effect on the response, even when symptomatic relief is obtained. 8. 8. Blocking the cervical sympathetic chain with procaine was followed by conversion of the “H” type to the normal curve for a few hours in the two cases tried, and both obtained symptomatic relief. 9. 9. The spatial distribution of the cerebral mechanisms involved in the flicker response is being studied, together with the effect of postural change in order to test the hypothesis that the clinical and electro-cerebral features are both the result of disturbance in the cardio-vascular barostatic mechanisms.