The Gamma Knife can destroy a small region of the brain – as a therapy. | Gamma Knife ICON, Elekta Instruments, AB, Sweden

A patient with essential tremor has difficulty writing and grasping objects: voluntary gestures are disturbed by physical shaking. One therapeutic option is Gamma Knife radiosurgery, which involves high-energy gamma rays penetrating into an area deep in the brain, located in the motor thalamus.

Half of patients respond well to this treatment and actually see their tremor halved. But the process is not yet well understood. Researchers have so far only provided an initial response having studied the brains of cured patients.

“We compared grey matter density in 38 patients before and after surgery using structural MRI”, explains Constantin Tuleasca of the CHUV’s Gamma Knife Center in Lausanne and the main author of the study, conducted with EPFL and Marseille’s Centre Hospitalier de la Timone (France). “We found a correlation between stopping the tremor and altering another cortical area involved in vision”, he says.

This link was subsequently confirmed. Tuleasca predicted the efficacy of treatment in an additional 52 patients based on an image analysis of this visual area. “The answer was even better because the grey matter density in this area was high before the intervention”, he says. The role of the area remains to be determined, as it is not affected during radiosurgery. Experiments are under way with another MRI technique to assess the correlation between thalamus activity and visual-cortex activity. “We can then decide whether we should also target the visual cortex”, says Tuleasca. “Not for the purpose of harming it, but to modulate activity and improve the outcome of the treatment”.

Aurélie Coulon