cTMS the next innovation in TMS

Some interesting developments from the recent Brain Stimulation 2015 conference in Singapore in the field of controllable TMS (cTMS) the next true innovation in TMS. cTMS is a new device that gives the user the ability to define:

  • near rectangular electric field pulses;
  • mono/bi/multi-phasic;
  • controllable pulse width;
  • controllable directionality;
  • lower energy use and coil heating;
  • magnetic stimulation pulses within a single device.

The following is a poster presented at Brain Stimulation 2015:

Effects of transcranial magnetic stimulation coil orientation and pulse width on short-latency afferent inhibition.

Ricci Hannaha, Kevin D’Ostilioa,b, Stefan Goetzc,d, Matteo Cioccaa,e, Raffaella Chieffoa,f, Jui-Cheng A. Chena,g,h, Angel V. Peterchevc, John C. Rothwella

  1. UCL Institute of Neurology, UK
  2. University of Liege, Belgium
  3. Duke University, USA
  4. Technical University Munich, Germany
  5. University of Milan, Italy
  6. Scientific Institute Hospital San Raffaele, Italy
  7. China Medical University Hospital, Taiwan
  8. China Medical University, Taiwan

We used a controllable pulse parameter transcranial magnetic stimulation (cTMS) device to assess whether adjusting pulse width and coil orientation would allow more selective stimulation of different neuronal populations.

Young healthy subjects participated in experiments involving single pulse stimulation over the hand motor area elicited by a cTMS device connected to a figure-of-eight coil. Experiment 1 (n=10) evaluated the effect of coil orientation (posterior-anterior, PA; anterior-posterior, AP) and pulse width (30, 60 and 120 µs) on the strength-duration curve, the input-output (IO) curve and the latency of the motor evoked potentials (MEPs) in the first dorsal interosseous muscle. Experiment 2 (n=12) evaluated the effect of coil orientations (PA, AP) and pulse width (30 and 120 ms) on short-latency afferent inhibition (SAI), tested with electrical median nerve stimulation at the wrist prior to TMS (inter-stimulus intervals: N20 latency +2 and +4 ms). All tests were completed during background contraction (~10% maximum).

The mean strength-duration time constants were shorter for PA than AP directed currents when estimated using motor threshold data (231 vs. 294 µs; t-test, p = 0.008) and IO data (252 vs. 296 µs; t-test, p < 0.001). ANOVA revealed an interaction of pulse width and orientation on MEP latencies (p=0.001), due mainly to the increase in latencies with short duration AP stimuli. A similar pulse width and orientation interaction was observed for SAI (p=0.011), resulting from the stronger inhibition with AP stimuli of short duration.

PA and AP oriented pulses appear to activate neural populations with different time constants. The AP-sensitive neural populations that elicit the longest latency MEPs are more readily stimulated by short than by long duration pulses, and appear more sensitive to SAI. Manipulating pulse width may improve the selectivity of AP stimulation.

cTMS Poster