Assessing the Effects of Hormones on Noninvasive Transcranial Stimulation

Carnegie Mellon University

Summary

This study is investigating how two types of non-invasive brain stimulation, transcranial electrical stimulation (TES) and transcranial magnetic stimulation (TMS), affect brain activity, and whether combining them produces stronger or more consistent effects than either one used alone. The motivation for this comes from the observation that TMS, which is FDA-approved for treating depression, tends to work less well in postmenopausal women because lower estrogen levels reduce the brain's ability to respond to stimulation. The research team believes that pairing TMS with TES, which targets a different set of brain cells, may be able to overcome this hormonal barrier and make stimulation more effective. Participants will come into the lab for up to 24 visits over 8 months, beginning with an initial visit to establish the right stimulation settings, followed by a series of stimulation sessions in which brain activity is measured before and after receiving either TES, TMS, or both together. For female participants, sessions will be scheduled at specific points in the menstrual cycle to capture the natural monthly rise and fall of estrogen, while male participants will be scheduled on a comparable fixed interval as a comparison group. The insights gained from this study could directly inform the development of better, more reliable brain stimulation treatments for women with depression.

Description

TMS is well understood to have variable effects depending on hormonal levels such as estrogen, progesterone, testosterone, and thyroid hormone. A leading theory for this variability is that these hormones, particularly estrogen, exert neuroprotective effects on NMDA receptors in the brain. These NMDA receptors are ligand/voltage gated ion channels present in neurons in the cortex. Conventional TMS produces electric fields parallel to the skull surface and is therefore more likely to excite Layer 2/3 (L2/3) pyramidal neurons. Under normal circumstances, these neurons excite downstream projectio…

Interventions

Device

Transcranial Electrical Stimulation

SharpFocus transcranial electrical stimulation (TES) uses a multichannel stimulator connected to a scalp electrode to deliver precisely timed, intensity-modulated electrical pulses. By varying the timing, amplitude, and location of these pulses, the system achieves focal stimulation of targeted cortical regions. Investigators will use Digitimer DS8R and/or Digitimer DS5 current stimulators to apply all current stimuli. These stimulators are CE certified and are intended for use in human research applications. The stimulator safely delivers brief duration (50-2000µs) current pulses for transcranial electrical stimulation and activation of nerves and muscles via surface electrodes. The current output of the DS8R is adjustable over the range 0mA to 1000mA, with a compliance voltage of up to 400V and an energy limit of 300mJ.

Device

Transcranial Magnetic Stimulation

Transcranial magnetic stimulation (TMS) uses an electromagnetic coil placed over the scalp to deliver precisely timed magnetic pulses that induce electric fields in targeted cortical regions. By varying the frequency, intensity, and coil position, the system achieves non-invasive stimulation of specific brain areas. Investigators will use the DuoMag XT-100 rTMS system manufactured by DEYMED Diagnostic. The device is a CE-certified Class IIa medical device intended for use in human research and clinical applications. The DuoMag XT-100 delivers both monophasic and biphasic pulses with a total pulse duration of 290 µs and a maximum discharge energy of 265 J, capable of stimulating at 100% intensity at 22 Hz and up to 100 Hz at less than 50% intensity.

Device

TES + TMS

The combined TMS+TES intervention delivers concurrent transcranial magnetic and electrical stimulation using the DuoMag XT-100 rTMS system and the Digitimer DS8R/DS5 current stimulators simultaneously. The DuoMag XT-100 is a CE-certified Class IIa device manufactured by DEYMED Diagnostic, delivering monophasic and biphasic pulses with a 290 µs pulse duration and 265 J maximum discharge energy, capable of 100% intensity at 22 Hz and up to 100 Hz at less than 50% intensity. The Digitimer DS8R/DS5 are CE-certified stimulators delivering brief duration (50-2000 µs) current pulses via surface electrodes, with current output adjustable from 0mA to 1000mA, compliance voltage up to 400V, and energy limit of 300mJ. Standard adhesive electrodes are replaced with Soterix Sintered Ag/AgCl ring electrodes featuring radial slits to impede induced eddy currents. Magnetic pulses are delivered via the DuoMag 70BF liquid-cooled butterfly coil. Pulses are interleaved with a 1-3 ms latency.

Assessing the Effects of Hormones on Noninvasive Transcranial Stimulation

Summary

Description

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Interventions

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