Functional neuroimaging: Enhanced understanding of migraine pathophysiology

Research into migraine pathophysiology has been hampered by the episodic nature and unpredictable onset of migraine attacks. Recently, newer imaging techniques have been providing noninvasive methods of studying metabolism and hemodynamics in the brains of migraineurs during and between acute attacks. ¹³³Xe blood flow techniques, transcranial Doppler, and SPECT have all been employed to investigate hemodynamic changes during migraine aura. PET has been useful in the study of migraine without aura, with findings of increased blood flow related to pain in cortical areas and in the medial brainstem. Currently, three functional MRI imaging techniques are being used in migraine research. Diffusion-weighted imaging has shown normal findings in measures of the ability of neurons to maintain osmotic gradients. Studies using perfusion-weighted imaging have shown alterations in relative cerebral blood flow (CBF), relative cerebral blood volume, and mean transit time during migraine visual aura. The blood oxygen level-dependent technique can supply information related to neuronal activation during acute migraine aura. MRS has been used with mixed success to look for evidence of abnormal energy metabolism in the brains of migraineurs. Magnetoencephalography studies support the presence of a spreading depression-like phenomenon in migraine with aura. Two groups have used transcranial magnetic stimulation to assess whether neurons in the occipital cortex are hyperexcitable, predisposing patients to develop aura symptoms. Despite conflicting findings, migraine with visual aura appears to be generally associated with transient decreases in regional CBF.