Neural effects of continuous theta-burst stimulation in macaque parietal neurons

Theta-burst transcranial magnetic stimulation (TBS) has become a standard
non-invasive technique to induce offline changes in cortical excitability
in human volunteers. Yet, TBS suffers from a high variability across
subjects. A better knowledge about how TBS affects neural activity in vivo
could uncover its mechanisms of action and ultimately allow its mainstream
use in basic science and clinical applications. To address this issue, we
applied continuous TBS (cTBS, 300 pulses) in awake behaving rhesus monkeys
and quantified its after-effects on neuronal activity. Overall, we
observed a pronounced, long-lasting and highly reproducible reduction in
neuronal excitability after cTBS in individual parietal neurons, with some
neurons also exhibiting periods of hyperexcitability during the recovery
phase. These results provide the first experimental evidence of the
effects of cTBS on single neurons in awake behaving monkeys, shedding new
light on the reasons underlying cTBS variability.