ABSTRACT
BACKGROUND:
Electromagnetic forces in
transcranial magnetic stimulation (TMS) coils generate a loud clicking
sound that produces confounding auditory activation and is potentially hazardous to
hearing. To reduce this
noise while maintaining stimulation
efficiency similar to conventional TMS coils, we previously developed a quiet TMS double containment coil (qTMS-DCC).
OBJECTIVE:
To compare the stimulation strength, perceived loudness, and
EEG response between qTMS-DCC and a commercial TMS coil.
METHODS:
Nine
healthy volunteers participated in a within-subject study design. The resting motor thresholds (RMTs) for qTMS-DCC and MagVenture Cool-B65 were measured.
Psychoacoustic titration matched the Cool-B65 loudness to qTMS-DCC pulsed at 80, 100, and 120% RMT.
Event-related potentials (ERPs) were recorded for both coils. The
psychoacoustic titration and ERPs were acquired with the coils both on and 6 cm off the
scalp, the latter isolating the effects of airborne
auditory stimulation from body
sound and electromagnetic stimulation. The ERP comparisons focused on a centro-frontal region that encompassed peak responses in the global signal.
RESULTS:
RMT did not differ significantly between the coils, with or without the
EEG cap on the
head. qTMS-DCC was perceived to be substantially quieter than Cool-B65. For example, qTMS-DCC at 100% coil-specific RMT sounded like Cool-B65 at 34% RMT. The general ERP waveform and
topography were
similar between the two coils, as were early-latency components, indicating comparable electromagnetic
brain stimulation in the on-
scalp condition. qTMS-DCC had a significantly smaller P180 component in both on-
scalp and off-
scalp conditions, supporting reduced auditory activation.
CONCLUSIONS:
The stimulation
efficiency of qTMS-DCC matched Cool-B65, while having substantially lower perceived loudness and auditory-
evoked potentials. Highlights qTMS coil is subjectively and objectively quieter than conventional Cool-B65 coilqTMS coil at 100% motor threshold was as loud as Cool-B65 at 34% motor thresholdAttenuated coil
noise reduced auditory N100 and P180 evoked response componentsqTMS coil enables reduction of auditory activation without masking.