Cortical pain processing in migraine
Among painful disorders, migraine is distinguishable by its chronic pathology and episodic clinical manifestation. Only a small percentage of patients with migraine progress to a chronic form of migraine. Both peripheral and central portions of the trigeminal system are involved in the pathophysiology of migraine pain, as they are involved in the processes of peripheral and central sensitization, alongside various subcortical and cortical brain structures. This review focuses on clinical, neurophysiological, and neuroimaging data underscoring cortical pain processing in migraine. Data obtained from quantitative sensory testings are inconclusive and support the involvement of the peripheral portion of the trigeminovascular system as indirect evidence of peripheral sensitization, solely during the headache phase. The assessment of subjective pain intensity in response to several painful modalities has not been conclusive for the clear state of central sensitization in between migraine attacks but for the subclinical allodynia state that defines the boundary between behavioural responses and an irritable nervous state. Modulation of the brainstem and midbrain pain pathways, in conjunction with the thalamic and thalamocortical pathways, may be critical for the initiation and maintenance of migraine attacks. Several studies using different neuroimaging techniques have demonstrated that brains experiencing migraine undergo plastic changes in both microstructure and macrostructure and in the functioning of cortical networks, which may manifest early in the life of a patient with migraine. Further studies are required to understand how specific these results are to migraine relative to other painful disorders.