Intensity-Dependent Effects of Low-Frequency Subthreshold rTMS on Primary Motor Cortex Excitability and Interhemispheric Inhibition in Elderly Participants: A Randomized Trial.
Miles Wischnewski, Lauren Edwards, Kate P Revill and 3 others
PMID 39462433WHAT IT FOUND
Two doses of low-frequency rTMS to the motor cortex did not clearly change cortical responses to stimulation in 20 healthy older adults.
Post hoc tests hinted 90% of resting threshold raised responses and 80% lowered them, but neither differed from sham.
Key findings
01In the main analysis, the slope and midpoint of the stimulus-response curve showed no significant main effects or interactions, and the main analysis of the curve's maximum response found no significant interaction with the intervention.
02Post hoc tests suggested that 90% of resting motor threshold increased the maximum muscle response in the stimulated left motor cortex and the curve's slope in the right motor cortex, while 80% had no effect; the authors state that a type I error cannot be excluded.
03The two intensities had opposite effects on inhibition between the two motor cortices, with 90% strengthening it and 80% weakening it, but neither differed significantly from sham.
STILL TO COME
How it was doneWhat they foundWhat it means for PTs
Read the rest of this summary
You get three full summaries a month, free, and we do not ask for a card. Search, the TL;DRs and your library stay unlimited either way.
What it does not show
The study is small: 20 people, and the sample size was worked out for the comparison in the larger stroke study this was nested in, not for this set of measurements, so it was not powered to detect these effects. The increase in excitability after 90% intensity came from post hoc testing after the main analysis found no significant interaction. The authors say a type I error cannot be excluded and the results should be read as tentative. There was no correction for multiple comparisons, and many comparisons were run. The two intensities differed from each other but neither differed from sham on the curve measures or on inhibition between the hemispheres, so these are not demonstrated effects of rTMS. Participants were blinded to the condition, but blinding was never checked afterwards, so it is possible some could tell which session was which. Only 10 pulses were given at each intensity. The authors note that more pulses would reduce variability but the sessions already lasted about four hours. Everyone was healthy, right-handed, aged 50 to 80, free of neurological disorders and able to produce a measurable muscle response; nothing here speaks to patients with stroke or other neurological impairment. Caffeine was controlled only immediately before and during the experiment, not in general.
Declared interests
The authors declare they have no conflict of interest, and no other funding statement appears in the text supplied; the article's publication record lists US government public health service research support. The study is described as part of a larger prospective longitudinal study of patients with stroke.
The easy way to misread this
Do not read this as showing that rTMS reliably changes brain excitability in a predictable direction. The pre-specified main analysis found no significant effect, the increase after 90% intensity came from post hoc testing that the authors themselves call tentative, and none of the differences reached significance against sham. These were 20 healthy older adults, not patients, so nothing here says rTMS helps anyone recover.
Summarised by AI from the full paper, without a clinician reviewing it. Check it against the source before it changes what you do. Read it on PubMed →