The Effect of Repetitive Transcranial Magnetic Stimulation on Brain Activity in Healthy Human Volunteers (ERP)

• The primary outcome measure will be global mean field amplitude (GMFA) before and after treatment with true or sham rTMS using a range of stimulus train durations and several stimulation sites. [ Time Frame: The GMFA will be measured for 1 minutes after each rTMS train is delivered. ] [ Designated as safety issue: No ]
  

• Secondary outcome measures will include magnetically evoked response potentials in the multi-channel recorded EEG signals. [ Time Frame: The L/R APR will be measured for 1 minute after each TMS train is delivered. ] [ Designated as safety issue: No ]

  The magnetically evoked response potentials will be measured over the first 500 milliseconds after each TMS pulse.

  We will also determine weather rTMS can produce measurable changes in left/right alpha power ratio (L/R APR). The L/R APR will be measured for 1 minute after each TMS train is delivered.

  
  

A previously recorded MRI will be loaded into Brainsight, a stereotactic neuronavigation system specifically designed to be used with rTMS, and the scalp surface site overlying the centre of Brodmann area 46 in the dorsolateral prefrontal cortex (DLPFC) of both the left and right hemisphere will be identified and marked on a spandex swim cap placed on the subjects head over 31 EEG electrodes (notched to prevent eddy currents) placed at international 10-20 locations . Three trains of true 10 Hz (110% motor threshold (MT)] rTMS (one train each with duration=2,4, and 8 seconds) and 6 similar trains of sham rTMS (3 of active sham and 3 of inactive sham) will be delivered to the left hemisphere in Brodmann area 46 in random order. Eyes-closed QEEG power will be recorded across all leads over 10 second "blocks" for 1 minute after each 10 Hz stimulus to determine the distribution and time course of any changes in electrical potential and QEEG spectrum. The subjects will be asked to rate their mood and anxiety by placing a mark along 100 mm long Visual Analogue Scales for depression and anxiety after each stimulus train. We will also measure ERPs after 1 Hz stimulation to the right DLPFC (centre of Brodmann area 46). We will administer three 60-second trains of true 1 Hz rTMS (at 90%, 100% and 110% motor threshold), and six 60-second trains of sham rTMS (3 of "active" sham and 3 of "inactive" sham) with device intensity setting of 10 %, 30% and 50% motor threshold and coil tilted at 90 degrees away form the head. Part 2 (location testing): Twenty four to 48 hours later, the swim hat will be placed on the subject's head and the neuroanatomical landmarks reconfirmed using Brainsight. One true train and 1 inactive sham train of 10 Hz rTMS (10 Hz, 110% MT) will be delivered in random order to Brodmann area 46 and two other sites (in Brodmann areas 9 and 10). The rTMS train duration will be 8 seconds. The subjects will be asked to rate their mood and anxiety by placing a mark along 100 mm long Visual Analogue Scales for depression and anxiety after each stimulus train. The same procedure will be done over the right hemisphere using 1 Hz stimulation set at 110% motor threshold. True rTMS pulses at 1 Hz, or inactive sham rTMS pulses will be delivered in 60 second trains to the 3 sites as described above, but marked over the right DLPFC. QEEG activity will be recorded for 1 minute after each stimulus train. The subjects will be asked to rate their mood and anxiety by placing a mark along 100 mm long Visual Analogue Scales for depression and anxiety after each stimulus train. Diffusion Tensor Imaging: The 15 healthy subjects (18-65 years old) will also undergo diffusion tensor imaging (DTI) along with the MRI, which will add approximately 10 minutes to the MRI procedure. Following a routine brain imaging protocol whole brain DTI measurements will be conducted in each subject using a single shot spin echo EPI diffusion tensor imaging sequence.