SHORT-TERM SYNAPTIC PLASTICITY IN MIGRAINE MOTOR CORTEX: EVIDENCE BY PRECONDITIONING OF HIGH-FREQUENCY REPETITIVE TRANSCRANIAL MAGNETIC STIMULATION (rTMS) WITH TRANSCRANIAL DIRECT CURRENT STIMULATION (tDCS)

Background: Brief 5Hz repetitive transcranial magnetic
stimulation (rTMS) trains at 120% of the resting- motorthreshold
(RMT) intensity determine in healthy subjects a
potentiation of motor evoked potentials (MEPs), likely due
to short-term presynaptic plasticity facilitation. We recently
showed paradoxical intensity-dependent MEP changes to
5Hz rTMS in migraine with MEP facilitation at 110% and
inhibition at 130% RMT. This provides evidence of both
hyper-responsivity and self-limiting hyperexcitability
capacity in migraine, likely due to earlier activation of
inhibitory homeostatic plasticity mechanisms. To explore
this, we applied in migraineurs cathodal transcranial Direct
Current Stimulation (tDCS) to reduce motor-cortical
excitability and subsequently reassess motor-cortical
response to 5Hz rTMS trains at 130% RMT- intensity.
Methods: 10 migraine with aura patients received 5Hz
rTMS of motor cortex at 130% RMT intensity (10 pulses),
recording MEP from contralateral abductor pollicis brevis
(APB). This protocol was preconditioned by cathodal tDCS
(10 min, 1mA intensity). Sham cathodal tDCS was used as
control.
Results: As expected MEP amplitude decreased significantly
during trains of 5Hz before tDCS preconditioning or
with sham tDCS. Conversely, after inhibitory preconditioning
with cathodal tDCS, 5Hz rTMS trains determined a
reduction in the first MEP size and a trend toward MEP
facilation during the trains.
Conclusions: Inhibitory cathodal tDCS preconditioning is
able to normalize the response of migraine motor-cortex to
rTMS trains at 130% of RMT. This supports the hypothesis
that in migraine motor cortex the mechanisms of short-term
presynaptic plasticity evaluated by 5Hz rTMS trains could
be affected intericatally by an abnormal increased cortical
excitability level.