Comparison of Measures of Plasticity
Condition: Depression; Healthy
MeSH terms: Depression
Study type: Interventional

Summary: 
      Neuroplasticity refers to the ability of the nerve cells to modify their structure or
      function in response to injury or insult, or other environmental stimuli, with these changes
      outlasting the period of exposure. Plasticity may be observed as short term or long term
      changes. In humans, neuroplasticity can be readily assessed in the motor cortex, as
      excitability changes are demonstrated in the degree to which peripheral muscles are
      activated, seen through changes in motor-evoked potentials (MEPs). In this study, a number of
      approaches to assessing neuroplasticity will be evaluated: Paired-associative stimulation
      (PAS), Theta Burst Stimulation (TBS), which is a form of transcranial magnetic stimulation
      (TMS) and protocols that combine these two. In addition, participants will complete a
      computerised 'rotor pursuit task' designed to provide a measure of motor learning.

      The investigators aim to find the most efficacious (defined by greatest number of responders
      and effect size as seen in an increase in MEP amplitude) brain stimulation protocol. The
      investigators will expose the same participants to four excitatory conditioning stimulation
      paradigms, with each session separated by at least a week.

      Our hypotheses include:

      The four conditioning stimulation protocols should increase motor cortical excitability, the
      investigators therefore expect there to be a significant increase in participant MEPs, with a
      positive correlation in the increase ofMEP amplitude of the protocols. The investigators do
      however expect that due to the principles of homeostatic metaplasticity, that the protocols
      preceded by cTBS will show greater MEP change, due to the lowering of the threshold for LTP
      plasticity induction. In addition, the investigators expect that an increase in the motor
      learning manifest by the rotor pursuit task and for there to be a correlation in participants
      between the increase in MEP amplitude and the improvement in time on target (TOT) shown in
      the motor learning task (MLT).
    


Intervention name(s): cTBS-PAS25; cTBS-iTBS; PAS25; iTBS
Intervention type(s): Procedure; Procedure; Procedure; Procedure
Intervention description(s): 40 seconds of continuous Theta-burst stimulation, followed by PAS25 which refers to the intervention 'paired-associative stimulation' with peripheral ulnar nerve stimulation followed by TMS to the motor cortex 25 ms after; 40 seconds of continuous Theta-burst stimulation, followed by 190 seconds of intermittent Theta-burst stimulation; PAS25 refers to the intervention 'paired-associative stimulation' with peripheral ulnar nerve stimulation followed by TMS to the motor cortex 25 ms after.; 190 seconds of intermittent theta-burst stimulation
Other intervention name(s): Magstim,; Digitimer; Magstim; Digitimer; Magstim
Allocation: Randomized
Intervention model: Crossover Assignment
Masking: None (Open Label)
Primary purpose: Diagnostic
Keywords: paired associative stimulation; theta burst stimulation; transcranial magnetic stimulation; neuroplasticity; healthy controls