For migraine sufferers everywhere, one of the worst symptoms that accompanies their migraine attacks are extreme sensitivity to light or sound. The reason for this sensitivity has remained a bit of a mystery, but now recent research is shedding light on a likely cause.
Altered Sensory Processing
Research has established a connection between light and sound sensitivity in migraine patients due to a heightened connection between their primary sensory cortices, also known as the anterior insula (AI), and the pons (part of the brainstem).
This heightened connectivity in the sensory region involves the cognitive networks that process sensory information and that make specific stimuli stand out to our attention. During a migraine, this altered system of sensory processing causes different stimuli to become bothersome or painfully obvious.
According to lead author of the study Amy R. Tso, MD, headache fellow, Department of Neurology, University of California, San Francisco, “For some it might be lights and sounds, but for others it’s smells or even light touch or motion.”
Sensory Overload
It was because of the increased awareness of some sensory stimuli that Dr. Tso and her colleagues hypothesized that migraine sufferers could have a highly sensitized salience network. This network involves the processing of relevant external and internal stimuli, as well as networks for visual and auditory function. Researchers also believed the dorsal pons might be involved because of its history for activating pain during migraine attacks.
The study looked at 15 patients with migraine without aura, all between the ages of 21 and 52, who suffered from sound and light sensitivity during attacks. There was also a control group of 15 healthy individuals of the same age group and gender.
Researchers used functional MRI (fMRI) to study brain regions responsible for processing auditory and visual stimuli. Findings showed that migraineurs had increased connectivity between auditory and visual cortices and the right dorsal AI (dAI) as well. This latter region is involved in coordinating responses involving salient external and internal stimuli.
“Increased dAI-to-sensory cortex connectivity could provide a neuroanatomical framework for understanding why visual and auditory stimuli not noxious to controls can become unpleasant to migraineurs and evoke escape responses,” wrote researchers.
Continued Sensitivity Between Attacks
The study revealed that the dorsal pons, which is a brain region that is active during migraine attacks, had increased connection with bilateral AI in migraineurs. The right ventral AI had increased connectivity to the left ventral AI too. Researchers noted that the ventral AI is activated during pain and may be part of the process of representing emotional salience in all domains of stimuli.
Because the study was conducted outside of a three-day window before or after migraine attacks, head researcher Dr. Tso explained, “It appears that this network change that we think underlies patients’ sensitivity still persists between attacks when patients themselves wouldn’t even feel like they are more sensitive to lights and sounds.”
-The Alternative Daily
Sources:
http://www.neurologyadvisor.com/sensory-symptoms-migraine-brain-connectivity/article/404814
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4038337
http://www.neurology.org/content/84/10/1043.abstract?sid=3b9544cd-e114-4643-a87c-187df006de01
