Characterizing the Effects of Transcranial Direct Current Stimulation on Frontal Lobe Activity Using Diffuse Correlational Spectroscopy
Evangelia G. Chrysikou1, Wesley Baker2, Lin Wang2, Arjun G. Yodh2, Roy H. Hamilton2; 1University of Kansas, 2University of Pennsylvania
Transcranial direct current stimulation (tDCS) is a cost-effective and noninvasive neuromodulation method involving the application of weak direct currents through electrodes on the scalp. The technique has elicited promising but inconsistent effects across several cognitive neuroscience domains, including memory, language, attention, and executive functions. Our understanding of the mechanisms of tDCS is limited by a critical lack of knowledge about how tDCS influences brain circuits in real time. Here, we address this gap by developing a novel tDCS-integrated diffuse correlational spectroscopy (DCS) probe for the noninvasive, continuous measurement of local cortical cerebral blood flow (CBF) and cerebral metabolic rate of oxygen consumption (CMRO2) during tDCS over lateral prefrontal cortex. We have established a safe and robust protocol for combining DCS hemodynamic monitoring with administration of tDCS and examined the protocol in healthy adult subjects. To evaluate the steady-state effect of tDCS on cerebral hemodynamics, we computed the average CBF, StO2, and HbT changes across the final 5 minutes of tDCS administration. On average, although tDCS significantly increased CBF and HbT, there was no significant change in StO2. The constant StO2 rate indicates that the oxygen extraction fraction from the blood to the cerebral tissue also remains constant. Therefore, our results are consistent with the hypothesis that tDCS increases the cerebral metabolic rate of oxygen (CMRO2). Our method provides a novel way of examining how complex neural circuits interact in space and time in response to tDCS that can optimize the use of tDCS for further research and clinical applications.
Topic Area: METHODS: Other