In the migraine brain, pathological activity seems to nucleate in a few hot spots and then travel the convoluted cortical surface like something finding its way through a labyrinth. If that is true, a one-size-fits-all stimulator is the wrong device.
Non-invasive neuromodulation — stimulating the brain through the skull with magnetic pulses or through the skin with small currents — is one of the more promising ways to treat migraine without drugs. But the devices are still used bluntly: a fixed protocol, applied the same way to everyone. I have long argued that this is the wrong default, and that computer models can tell us why.
Hot spots and labyrinths
Using computer models and numerical simulations of cortical spreading depression — the wave that underlies the migraine aura — we can watch where pathological activity is likely to begin and where it goes. Two features stand out. First, the wave does not start just anywhere: it tends to nucleate in hot spots, particular places where the cortical geometry makes ignition easy. Second, once started, it does not spread as a tidy expanding circle. The human cortex is deeply folded, and the wave threads through that convoluted surface like a traveller in a labyrinth, its path shaped by the individual anatomy of that brain.
Both the hot spots and the labyrinth are personal. They depend on the fine geometry of a given cortex — which means the ideal place, and moment, to intervene is personal too.
Transient patterns and phase-dependent stimulation
There is a second lever. The simulated patterns of spreading depression fall into two families: continuous wave fronts and discontinuous (broken) ones. These can be told apart by their size and duration, and the rarer, broken kind matches patterns seen with fMRI in migraine with aura. Because these transient patterns have a characterisable life cycle, they open the door to phase-dependent stimulation: timing a pulse to the state the wave is in, rather than firing on a fixed clock.
Put the two ideas together — a personalised map of hot spots and labyrinthine paths, plus stimulation timed to the wave’s phase — and you get the outline of a genuinely rational design for neuromodulation. This is what the field now calls electroceuticals: treatments defined not by a molecule but by a control strategy. Getting them right is, at heart, a problem of physics and control theory.
References
- Dahlem MA, Schmidt B, Bojak I, Boie S, Kneer F, Hadjikhani N, Kurths J. Hot spots and labyrinths: why neuromodulation devices for episodic migraine should be personalized. PeerJ PrePrints 2:e515 (2014).
- Dahlem MA, Isele T. Transient localized wave patterns and their application to migraine. Journal of Mathematical Neuroscience 3:7 (2013).
A full publication list is on Google Scholar ↗. For the bigger picture on physics and headache, see Physics to treat migraines.