Que manque-t-il à la rTMS pour devenir une thérapie ?

Repetitive trans-cranial magnetic stimulation (rTMS) can modulate cortical excitability. Consequently, it appears appealing for the treatment of some affections such as depression or hallucinations. There is already some proof that the concept is valid, but rTMS is slow in progressing in the therapeutic field as a true armamentum. Indeed its effects are of short duration and even inconstant from one patient to the next. These drawbacks depend on certain factors that we will discuss. Until now, there has been inadequate control of the stimulation site. It is possible that this site could vary on an individual basis. It seems logical to propose the use of functional imaging for such a purpose, but its use should be adapted to the symptom. Even after localizing the site, the coil has to be placed accurately. This could be facilitated by a neuronavigator. Stimulation protocols are currently defined by three parameters: the frequency modulating the cortical action either as a stimulation (>5 Hz) or an inhibition (<1 Hz), the intensity and the number of stimuli influencing, notably, the amplitude and duration of the effect. Unfortunately, the effect is inconstant in a given patient and paradoxical reactions have been observed in more than 15% of normal individuals. Improved reliability and amplification of the effect rely on the better control of other parameters: pattern of stimulation, pre and post-conditioning, state of the cortex during stimulation, associated medications, endogenous idiosyncratic factors and related pathology. We will review the current physiological literature to discuss the possible options that would constitute a rational basis for setting up more efficient protocols.