Objective:

In this study we used Sound-Induced Flash Illusions (SIFI) to explore the role of changes of cortical
excitability in precipitation/resolution of migraine attacks across the migraine cycle.

Background:

In a previous study using transcranial magnetic stimulation, we found paradoxical inhibitory
responses in the ictal phase, where an increased response due to cortical hyperexcitability was
expected. In 2015, we adopted a different approach based on SIFI. Here, subjects are presented
with auditory (0, 1, 2, 3, or 4 beeps) and visual stimuli (1, 2, 3, or 4 flashes) and must report the
number of flashes seen. As beeps occur a few milliseconds before flashes, flash perception is
influenced by beeps: when two or more beeps accompany one flash, subjects report two flashes
(fission illusions). Such illusions depend on visual-cortical excitability (increased excitability
reduces illusions). Using SIFI, we obtained clear, linear responses in migraine, supporting the
hypothesis of cortical hyperexcitability.

Design/Methods:

One hundred migraine without aura patients (26 interictal, 24 preictal, 25 ictal, and 25 postictal)
and 25 sex- and age-matched healthy controls underwent the SIFI induction procedure. The
protocol was performed in similar conditions for each subject using identical equipment.
Responses were recorded, and the mean number of perceived flashes was compared among
groups.

Results:

Cortical excitability was increased in the interictal phase in migraineurs compared to controls (<.001). Moreover, we found a progressive significant rise from interictal to preictal (<.01 vs.
interictal and ictal) and ictal (<.001 vs. interictal and <.05 vs. preictal), followed by a decline
through postictal (<.01 vs. ictal and interictal) back to the interictal state.

Conclusions:

The higher level of excitability in the interictal phase with respect to healthy control could represent
a predisposition to migraine attacks, while further excitability increase and deacrease could be at
the basis respectively of precipitation/resolution of migraine attacks.