Viganò A, et al. - Researchers sought neurophysiological factors that correlate with greater occipital nerve block (GON-B) effects in chronic migraine (CM) by evaluating 17 CM women, 12 of whom have medication overuse headache (MOH), and 19 healthy volunteers. Findings support the efficacy of GON-B treatment of CM, with or without MOH. The pre-treatment intensity dependence of auditory evoked potentials (IDAP) increase is compatible with a weak central serotonergic tone, which is strengthened after GON-B, suggesting that serotonergic mechanisms may play a role in CM and its reversion to episodic migraine. As there was a correlation between the degree of post-treatment IDAP decrease and clinical improvement, IDAP could have potential utility as an early predictor of GON-B efficacy.