Figure 2.

Imploding/ocular pain might be a consequence of the trigemino-autonomic reflex activation: a hypothesis.

Notes: In 1/3 of migraineurs, an overactivation of the TN – causing a more strictly unilateral and severe headache located along the areas of cutaneous distribution of the ophthalmic branch (1) – induces both central sensitization (allodynia and photophobia) and the activation of the efferent arm of the trigeminal-autonomic reflex (2). Activated preganglionic parasympathetic fibers originating in the SSN exit the brainstem via the seventh cranial nerve (VII), traverse the GG and synapse in the SPG with postsynaptic neurons innervating cranial and conjunctival vessels, lacrimal glands and nasal mucosa, triggering UAs (ocular/periocular vasodilation and edema, lacrimation and rhinorrhea) (3). UAs would activate extracranial nociceptors (4), being responsible for imploding/periocular pain characteristics, and would in turn amplify trigeminal afferent firing (5), further perpetuating the vicious cycle.

Abbreviations: TN, trigeminal nerve; SSN, superior salivatory nucleus; GG, geniculate ganglion; SPG, sphenopalatine; UAs, unilateral autonomic symptom; TCC, trigeminocervical complex; TG, trigeminal ganglion.