Functional neuroimaging in migraine: usefulness for the clinical neurologist

A state-of-the-art review of functional magnetic resonance imaging technique integrated with advanced statistical modeling and machine learning for primary headache diagnosis

Primary headache is a very common and burdensome functional headache worldwide, which can be classified as migraine, tension-type headache (TTH), trigeminal autonomic cephalalgia (TAC), and other primary headaches. Managing and treating these different categories require distinct approaches, and accurate diagnosis is crucial. Functional magnetic resonance imaging (fMRI) has become a research hotspot to explore primary headache. By examining the interrelationships between activated brain regions and improving temporal and spatial resolution, fMRI can distinguish between primary headaches and their subtypes. Currently the most commonly used is the cortical brain mapping technique, which is based on blood oxygen level-dependent functional magnetic resonance imaging (BOLD-fMRI). This review sheds light on the state-of-the-art advancements in data analysis based on fMRI technology for primary headaches along with their subtypes. It encompasses not only the conventional analysis methodologies employed to unravel pathophysiological mechanisms, but also deep-learning approaches that integrate these techniques with advanced statistical modeling and machine learning. The aim is to highlight cutting-edge fMRI technologies and provide new insights into the diagnosis of primary headaches.

Physiopathology of Migraine: What Have We Learned from Functional Imaging?

PURPOSE OF REVIEW

This review aims to provide an overview of the most recent and significant functional neuroimaging studies which have clarified the complex mechanisms underlying migraine pathophysiology.

RECENT FINDINGS

The recent data allow us to overcome the concept of a migraine generator suggesting that functional networks abnormalities may lead to changes in different brain area activities and consequent reduced migraine thresholds susceptibility, likely associated with higher migraine severity and burden. Although functional magnetic resonance imaging studies have allowed recognition of several migraine mechanisms, its pathophysiology is not completely understood and is still a matter of research. Nevertheless, in recent years, functional magnetic resonance imaging studies have allowed us to implement our knowledge of migraine pathophysiology. The pivotal role of both the brainstem and the hippocampus in the first phase of a migraine attack, the involvement of limbic pathway in the constitution of a migrainous pain network, the disrupted functional connectivity in cognitive brain networks, as well as the abnormal function of the visual network in patients with migraine with aura are the main milestones in migraine imaging achieved through functional imaging advances. We believe that further studies based on combined functional and structural techniques and the investigation of the different phases of migraine cycle may represent an efficient methodological approach for comprehensively looking into the migrainous brain secrets.

Interictal abnormal fMRI activation of visual areas during a motor task cued by visual stimuli in migraine

Objective

To assess changes in blood-oxygen-level-dependent activity after light deprivation compared to regular light exposure in subjects with migraine in the interictal state and in controls.

Methods

Ten subjects with migraine and ten controls participated in two sessions of functional magnetic resonance imaging. In each session, they performed a finger-tapping task with the right hand, cued by visual stimuli. They were scanned before and after 30 minutes of light deprivation or light exposure. In subjects with migraine, functional magnetic resonance imaging was performed interictally. Analysis of variance was made with the factors time (before or after), session (light deprivation or exposure), and group (migraine or control).

Results

There were significant “group” effects in a cluster in the bilateral cuneus encompassing the superior border of the calcarine sulcus and extrastriate cortex. There were no significant effects of “time”, “session”, or interactions between these factors.

Conclusion

The main result of this study is consistent with aberrant interictal processing of visual information in migraine. Light deprivation did not modulate functional magnetic resonance imaging activity in subjects with or without migraine.

Relevance of functional neuroimaging studies for understanding migraine mechanisms

Advances in imaging have provided further insights into the complex migraine pathophysiology. Functional neuroimaging by means of PET and functional MRI studies have addressed crucial migraine-related issues, improving our understanding of the circuitry that may be involved in the generation, maintenance and recurrence of pain symptoms in migraine. In the last few years, a growing body of imaging literature has also explored pathophysiology of associated migraine symptoms. Of great interest will be the use of advanced imaging techniques to elucidate neural correlates of migraine prodromal, in order to identify clinical subgroups of migrainous subjects. However, the interpretation of the biological significance of these various functional changes could remain incomplete without a combination of expanding genomic information about neurochemical pathways and genetic polymorphisms linked to specific migraine subtypes. Hopefully, a more detailed picture of the migraine neurobiology will emerge from future neuroimaging studies, which may eventually lead to better and more rational treatments.