Migraine sufferers’ brains respond differently to visual stimulation

A new study has demonstrated that the brains of people who experience migraines and other types of headaches cannot modulate visual stimulation in the same way a person without these conditions can.

Daniele Piscitelli, assistant professor of kinesiology in the College of Agriculture, Health and Natural Resources (CAHNR), published these findings in Restorative Neurology and Neuroscience.

Piscitelli had been collaborating with colleagues in Brazil to study changes in the cortical activity and neuroplasticity in the brains of individuals with stroke. In the course of their work, they found that other researchers had been using the same kinds of measurements to study migraines.

This led Piscitelli and his collaborators to wonder if their work could improve understanding of what causes migraines.

Piscitelli was co-responsible for the study design and data analysis. The study was conducted in the laboratory of Kátia Monte-Silva, Ph.D., at the Laboratório de Neurociência Aplicada, Universidade Federal de Pernambuco, Recife, Brazil.

They recruited three populations of participants: people who experience migraines, people who regularly experience other kinds of headaches, and a “healthy” population that did not have migraines nor other headaches in the past month.

They took measurements of cortical excitability in each of the groups. Cortical excitability is a measure of brain activity, essentially how much a person’s brain responds to stimuli. Previous research had demonstrated that people who experience migraines have higher cortical excitability. This means their neurons have a lower threshold for excitability than the healthy population, leading their brains to become overstimulated more easily.

The researchers here were interested specifically in two areas of the cerebral cortex – the visual cortex, which processes visual information, and the motor cortex – which controls voluntary movement.

“We were interested in seeing the cortical excitability, specifically the motor cortex excitability and the visual cortex excitability in a window that was one day after or before the [migraine or headache] attack,” Piscitelli says.

To evaluate motor cortex excitability, the researchers the researchers applied single-pulse transcranial magnetic stimulation (TMS) over the motor cortex and recorded the resulting muscle activity using electromyography (EMG) from the hand muscles. To measure excitability in the visual cortex they asked participants when they saw light (phosphenes) in their visual field when TMS was applied over the occipital cortex.

“Both of these are measures that are broadly used to measure the cortical excitability that give us an indirect information about the threshold of the neurons,” Piscitelli says.

In these preliminary measurements, there were no significant differences between the three groups.

The next part of the study involved participants looking at a black and white checkerboard that alternated colors with one eye covered at a time (i.e., pattern-reversal visual stimulation). The researchers then took the same visual and motor cortex excitability measurements after this stimulation.

This time, the researchers saw significant differences between the groups.

Both those who experience migraines and other headaches had increased levels of visual cortex excitability compared to the healthy control group.

“Healthy subjects were able to modulate cortical excitability following the stimulation while people with migraines and other types of headaches had an increase in the cortical excitability,” Piscitelli says.

There were no differences in motor cortex excitability.

The fact that both people with migraines and other headaches responded in the same way to the stimulation indicates that both conditions share a neurological basis.

These results also indicate that existing medications that reduce visual cortex excitability, like those used to treat epileptic seizures, could be useful for this population as well.

Given this, one of the next steps of this research will be conducting a study with people who experience seizures to determine if they have similar cortical excitability.

“How the brain organizes information is the key to pathophysiology and is probably the key to treat the patients,” Piscitelli says.