4 mA tDCS, Estrogen, and Leg Muscle Fatigability
Condition: Healthy
Study type: Interventional

Summary: 
      The majority of transcranial direct current stimulation (tDCS) studies have failed to
      consider sex as a modulating factor. This neglect may partly account for the high
      inter-subject variability bemoaned by many tDCS investigators (e.g., approximately 50% of
      participants do not respond to tDCS) and has certainly delayed progress in the field.
      Therefore, research into how sex influences stimulation-related outcomes is vital to fully
      understand the underlying mechanisms of tDCS, which has shown great inconsistency.

      Because of the menstrual cycle, the hormonal levels of women fluctuate considerably more than
      in men. Importantly, these hormonal variations might impact the efficacy of neuromodulatory
      tools, like tDCS. It is suggested that estrogen, which is high in the second follicular
      phase, reinforces excitatory mechanisms in the motor cortex. However, because anodal tDCS
      enhances cortical excitation there is also a possibility of excessive excitability. For
      instance, anodal tDCS may lead to overexcitation and non-optimal performance when it is
      applied in the second follicular phase of the menstrual cycle. Currently, there is a lack of
      knowledge on how the phases of the menstrual cycle affect tDCS performance outcomes in
      healthy young women because no studies have examined if and how the phases of the menstrual
      cycle alter tDCS efficacy.

      This study is critical for determining the optimal time to administer anodal tDCS, and the
      ideal intensity for that administration, to achieve the most beneficial results. Furthermore,
      this investigation will emphasize the need for future tDCS studies to test women during the
      same menstrual cycle phase.
    

Detailed description: 
      The majority of transcranial direct current stimulation (tDCS) studies have failed to
      consider sex as a modulating factor. This neglect may partly account for the high
      inter-subject variability bemoaned by many tDCS investigators (e.g., approximately 50% of
      participants do not respond to tDCS) and has certainly delayed progress in the field.
      Therefore, research into how sex influences stimulation-related outcomes is vital to fully
      understand the underlying mechanisms of tDCS, which has shown great inconsistency.

      Because of the menstrual cycle, the hormonal levels of women fluctuate considerably more than
      in men. There are two main phases of the menstrual cycle: 1) the follicular phase,
      characterized by low levels of estradiol and progesterone (first follicular phase, days 1-7)
      followed by increased levels of estradiol and low levels of progesterone (second follicular
      phase, days 7-14); and 2) the luteal phase (days 14-28), characterized by moderate estradiol
      and high progesterone levels. Importantly, these hormonal variations might impact the
      efficacy of neuromodulatory tools, like tDCS.

      It is suggested that estrogen, which is high in the second follicular phase, reinforces
      excitatory mechanisms in the motor cortex. Thus, it appears that higher levels of estradiol
      increase cortical excitability. However, because anodal tDCS enhances cortical excitation
      there is also a possibility of excessive excitability. For instance, anodal tDCS may lead to
      overexcitation and nonoptimal performance when it is applied in the second follicular phase
      of the menstrual cycle. Currently, there is a lack of knowledge on how the phases of the
      menstrual cycle affect tDCS performance outcomes in healthy young women because no studies
      have examined if and how the phases of the menstrual cycle alter tDCS efficacy.

      This research will be significant because the changing hormone levels during the different
      phases of menstruation in women is an especially important factor for minimizing response
      variability from tDCS. Thus, this study is critical for determining the optimal time to
      administer anodal tDCS, and the ideal intensity for that administration, to achieve the most
      beneficial results. Furthermore, this investigation will emphasize the need for future tDCS
      studies to test women during the same menstrual cycle phase.
    

Intervention name(s): Sham transcranial direct current stimulation 4 mA; Transcranial direct current stimulation 4 mA
Intervention type(s): Device; Device
Intervention description(s): Uses weak electrical current (4 mA intensity) at the beginning and the end of a given stimulation period to control for potential placebo-like effects or participant expectation bias.; Uses weak electrical current (4 mA intensity) to either increase or decrease brain excitability and improve functional or cognitive outcomes.
Other intervention name(s): Sham tDCS 2 mA; tDCS 4 mA
Intervention model: Single Group Assignment
Masking: None (Open Label)
Primary purpose: Treatment
Keywords: transcranial direct current stimulation; muscle fatigue; brain stimulation