Paired associative stimulation of the auditory system: a proof-of-principle study.

Paired associative stimulation (PAS) consisting of repeated
application of transcranial magnetic stimulation (TMS) pulses and
contingent exteroceptive stimuli has been shown to induce
neuroplastic effects in the motor and somatosensory system. The
objective was to investigate whether the auditory system can be
modulated by PAS. Acoustic stimuli (4 kHz) were paired with TMS of
the auditory cortex with intervals of either 45 ms (PAS(45 ms)) or
10 ms (PAS(10 ms)). Two-hundred paired stimuli were applied at 0.1
Hz and effects were compared with low frequency repetitive TMS
(rTMS) at 0.1 Hz (200 stimuli) and 1 Hz (1000 stimuli) in eleven
healthy students. Auditory cortex excitability was measured before
and after the interventions by long latency auditory evoked
potentials (AEPs) for the tone (4 kHz) used in the pairing, and a
control tone (1 kHz) in a within subjects design. Amplitudes of the
N1-P2 complex were reduced for the 4 kHz tone after both PAS(45 ms)
and PAS(10 ms), but not after the 0.1 Hz and 1 Hz rTMS protocols
with more pronounced effects for PAS(45 ms). Similar, but less
pronounced effects were observed for the 1 kHz control tone. These
findings indicate that paired associative stimulation may induce
tonotopically specific and also tone unspecific human auditory
cortex plasticity.