Repetitive Transcranial Magnetic Stimulation (rTMS) and P50 Evoked Potential Component
Condition: Depression; Schizophrenia
MeSH terms: Schizophrenia
Study type: Interventional
Phase: Phase 2

Summary: 
      The repetitive transcranial magnetic stimulation (rTMS) is a recent technique that has
      demonstrated its efficiency in both depression and schizophrenia. However if its efficiency
      has been recognized by the scientific community and the clinicians, its action on neurons and
      cerebral networks remains debated.

      In the motor regions, the different rTMS studies generally use frequencies of stimulation of
      1 to 40 Hz with differential effects; the low frequencies being associated with an inhibitory
      effect whereas highest frequencies have rather some facilitator effects as attested by the
      motor responses. What is valid for the motor system is not however necessarily applicable to
      other cerebral regions that have different neuronal organizations. If it is easy to observe
      these opposite effects of rTMS on the motor system (presence or absence of movements), these
      potential effects on more integrated cortex involved in high level functions have not been
      proved.

      One of the possibilities to interpret the effects of the rTMS in no-motor cerebral regions
      would be to study the modifications of the EEG before and after rTMS and to see if a
      differential effect of the high and low frequencies of stimulation exists. Up to now, the
      studies having coupled these two techniques have observed modifications of the brain electric
      activity only during some seconds to minutes after rTMS, what appears in contrast with the
      clinical effects observed after a long delay (several days).

      The contribution of our research resides in the use of the paradigm of suppression of P50
      evoked potential component before and after rTMS tested with low and high frequencies of
      stimulation. This paradigm consists in two identical auditory stimuli presented at a very
      short interval (generally 500 milliseconds), the second sound generating a P50 wave of weaker
      amplitude than the first or being completely abolished in healthy subjects. However, this
      effect that has been well studied could result from an inhibitory action due to the gabaergic
      interneurons on the pyramidal neurons of the cortex. Thus, the investigators hypothesize that
      high frequency rTMS would have a facilitator effect on temporal lobe and so would induce no
      suppression of the P50 after-rTMS whereas low frequency rTMS would induce an inhibitory
      effect marked by a greater suppression of the P50.

      Methods: 30 healthy subjects (of which 16 women) will be included after written consent. They
      will receive after randomization 2 sessions of rTMS in cross over at 1Hz and 20Hz at 30 days
      interval. An EEG and a P50 evoked potential will be done before and after rTMS. The site of
      stimulation will be determined by neuronavigation and will correspond to the maximal
      activation cluster generated by a language task during functional magnetic resonance imaging.
      The main judgment criterion is the S2/S1 ratio of the P50. The potential secondary effects
      will be evaluated (UKU adapted). The secondary criteria are the comparisons before and after
      rTMS of EEG spectrums in the alpha, beta and gamma bands.
    


Intervention name(s): high-frequency of repetitive transcranial magnetic stimulation (rTMS); low frequency of repetitive transcranial magnetic stimulation (rTMS)
Intervention type(s): Procedure; Procedure
Intervention description(s): frequency of stimulation of 20 Hz; frequency of stimulation of 1 Hz
Allocation: Randomized
Intervention model: Crossover Assignment
Masking: None (Open Label)
Primary purpose: Basic Science
Keywords: rTMS; P50; inhibitory; facilitatory; physiological process; brain changes