Aftereffects and Reliability of Two Homeostatic Plasticity Induction Protocols
Condition: Healthy
Study type: Interventional

Summary: 
      People suffering from chronic pain exhibit changes in the way the central nervous system
      processes pain. Some of the changes in the central nervous system are associated with how the
      brain adapts to the process of different stimuli. There are several physiological mechanisms
      that regulates how the brain adapts to changes and one of these mechanisms is called
      homeostatic plasticity (or equilibrium plasticity ). In healthy participants homeostatic
      plasticity mechanisms have been tested and considered normal, whereas in patients with
      chronic conditions, such as low back pain, this mechanism was shown to be dysfunctional.
      However, it is unknown when this difference in the pain system develops. It is possible that
      homeostatic mechanism becomes impaired over a period of time. Current studies have
      investigate a cohort of patients and there is a lack of longitudinal designs. In order to
      investigate the long-term effects of pain on homeostatic plasticity mechanisms it is
      important to first investigate the reliability of the methods. This study will investigate
      the reliability of two protocols of homeostatic plasticity induction.
    

Detailed description: 
      The aim of this study is to investigate the corticomotor excitability changes provoked by two
      homeostatic plasticity induction protocols, specifically the duration and the test-retest
      reliability of such corticomotor excitability changes.

      A within-subject repeated-measures design will be used to evaluate the aftereffects and the
      reliability of two homeostatic plasticity induction protocols using cathodal transcranial
      direct current stimulation (tDCS) (experiment 1) and anodal tDCS (experiment 2). Each
      participant will take part in two experimental sessions during which homeostatic plasticity
      and corticomotor excitability will be induced and measured in the left primary motor cortex.

      A sample size calculation was conducted using α of 0.05, β of 0.80 and effect size of 0.48
      based on motor evoked potential (MEP) analysis of previous studies (Thapa, Schabrun, 2018,
      Thapa et al., 2018) resulting in a target of 13 participants. To account for differences in
      study designs and for the possibility of participant withdrawal/dropout, the investigators
      set target recruitment at 15 participants for each experiment.

      Each participant will attend two identical experimental sessions on the same time in two
      consecutive days. During the experiment, participants will be seated comfortably with hands
      and arms at rest. First, the electromyography electrodes will be placed at the right hand
      muscle to be used for assessing the corticomotor excitability by recordings of motor evoked
      potentials by transcranial magnetic stimulation (TMS) on the left primary motor cortex. Then,
      the neoprene cap for tDCS on the left primary motor cortex will be mounted. The optimal scalp
      position (hot spot) for TMS stimulation will be identified and marked with a pen on the cap
      for standardisation. The corticomotor excitability in response to the homeostatic plasticity
      protocol (cathodal tDCS in experiment 1 or anodal tDCS in experiment 2) will be measured
      before and immediately post paradigm (time point 0-min), and then every 10 minutes for 70
      minutes.

      Homeostatic plasticity will be induced in the left primary motor cortex using tDCS applied
      for 7 minutes followed by an interval of 3 minutes and another block of 5 minutes of
      stimulation (Thapa, Schabrun, 2018, Thapa et al., 2018). A constant current of 1mA will be
      transmitted through the tDCS system (Starstim, Neuroelectrics, Barcelona, Spain), using two
      3.14 cm2 Ag/AgCl gelled electrodes placed into holes of a neoprene cap corresponding to the
      international 10/10 EEG system, placed on participants head with the central Cz position
      aligned to the vertex of the head. In experiment 1 the cathode will be placed at C3 and
      return electrode placed at Fp2. In experiment 2 the anode will be placed at C3 and return
      electrode placed at Fp2.

      Data distribution will be assessed using the Shapiro-Wilk test. A repeated measures analysis
      of variance (ANOVA) will be conducted on mean MEPs with factors Session (Day1 and Day2) and
      Time (baseline, 0 min, 10 min, 20 min, 30 min, 40 min, 50 min, 60 min, 70 min). A
      Greenhouse-Geisser correction will be used if Mauchly's test shows that sphericity cannot be
      assumed. Adjustments will be made for multiple post-hoc comparisons using the Bonferroni
      correction. Results will be interpreted according to the level of statistical significance
      p≤0.05 and effect size reported as partial eta squared.
    

Intervention name(s): Homeostatic plasticity induction using transcranial direct current stimulation
Intervention type(s): Other
Intervention description(s): Homeostatic plasticity will be induced in the left primary motor cortex using tDCS applied for 7 minutes followed by an interval of 3 minutes and another block of 5 minutes of stimulation
Intervention model: Single Group Assignment
Masking: None (Open Label)
Primary purpose: Basic Science