Gamma activation spread reflects disease activity in amyotrophic lateral sclerosis

A non-invasive measure of cerebral motor system dysfunction would be valuable as a biomarker in amyotrophic lateral sclerosis (ALS). Task-based magnetoencephalography (tMEG) measures the magnetic fields generated by cortical neuronal oscillatory activity during task performance. Gamma activations are periods of high-power and high-frequency cortical oscillations integral to motor control.

tMEG was undertaken during 60 bilateral isometric hand grip exercises in ALS (n = 42) and compared with healthy controls (HC, n = 33). Gamma activation spread (GAS) was estimated by calculating the number of activated regions during each 100 ms time-bin and compared statistically between groups. Gamma activation patterns were visualised by plotting each participant's brain activity separately as a 2-dimensional video.

There was no difference in grip strength between groups. GAS was greatly increased in the ALS group compared to HC (p < 0.001) and correlated positively with rate of ALSFRS-R progression (t = 1.35, p = 0.023) and a fine motor sub-score (t = -1.18, p = 0.047).

ALS was associated with a marked increase in regional spread of gamma frequency activation, greater in those with higher disease progression rates.

The regional spread of gamma activity may reflect disease activity in ALS, with potential application as an experimental medicine readout.