Blood oxygenation changes resulting from suprathreshold transcranial magnetic stimulation

Area of Science:

• Neuroscience
• Biomedical Engineering
• Physiology

Background:

• Transcranial magnetic stimulation (TMS) is a non-invasive brain stimulation technique.
• Hemodynamic responses to TMS at the motor cortex are well-documented using near-infrared spectroscopy (NIRS).
• The impact of TMS on prefrontal cortex hemodynamics, particularly oxy-hemoglobin (HbO) levels, requires further investigation.

Purpose of the Study:

• To examine the effect of varying transcranial magnetic stimulation (TMS) intensities on oxy-hemoglobin (HbO) levels in the prefrontal cortex.
• To determine if subthreshold and suprathreshold TMS, relative to resting motor threshold (rMT), elicit significant hemodynamic changes.
• To provide insights into optimal TMS parameters for non-motor cortex stimulation.

Main Methods:

• Applied subthreshold (90% rMT) and suprathreshold (110% and 130% rMT) transcranial magnetic stimulation (TMS) to the prefrontal cortex.
• Utilized near-infrared spectroscopy (NIRS) to measure changes in oxy-hemoglobin (HbO) concentration.
• Analyzed hemodynamic responses in relation to different TMS intensities.

Main Results:

• No significant changes in HbO were observed following 90% and 110% rMT TMS.
• A significant decrease in HbO was detected after 130% rMT TMS.
• The maximal HbO drop occurred approximately 8 seconds post-TMS.

Conclusions:

• Higher intensity TMS (130% rMT) induces a significant hemodynamic response, specifically a decrease in HbO, in the prefrontal cortex.
• Lower intensity TMS (90% and 110% rMT) did not produce significant hemodynamic changes in this region.
• These findings highlight the importance of selecting appropriate TMS intensities for effective and safe stimulation of non-motor cortical areas.