Functional neuroimaging: Enhanced understanding of migraine pathophysiology

Research into migraine pathophysiology has been hampered by the episodic na ture and unpredictable onset of migraine attacks. Recently, newer imaging t echniques have been providing noninvasive methods of studying metabolism an d hemodynamics in the brains of migraineurs during and between acute attack s. Xe-133 blood flow techniques, transcranial Doppler, and SPECT have all b een employed to investigate hemodynamic changes during migraine aura. PET h as been useful in the study of migraine without aura, with findings of incr eased blood flow related to pain in cortical areas and in the medial brains tem. Currently, three functional MRI imaging techniques are being used in m igraine research. Diffusion-weighted imaging has shown normal findings in m easures of the ability of neurons to maintain osmotic gradients. Studies us ing perfusion-weighted imaging have shown alterations in relative cerebral blood flow (CBF), relative cerebral blood volume, and mean transit time dur ing migraine visual aura. The blood oxygen level-dependent technique can su pply information related to neuronal activation during acute migraine aura. MRS has been used with mixed success to look for evidence of abnormal ener gy 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 p atients to develop aura symptoms. Despite conflicting findings, migraine wi th visual aura appears to be generally associated with transient decreases in regional CBF.