Effects of Transcranial Direct Current Stimulation on Baseline and Slope of Prefrontal Cortex Hemodynamics During a Spatial Working Memory Task

Ryan McKendrick; Brian Falcone; Melissa Scheldrup; Hasan Ayaz

doi:10.3389/fnhum.2020.00064

Effects of Transcranial Direct Current Stimulation on Baseline and Slope of Prefrontal Cortex Hemodynamics During a Spatial Working Memory Task

Front Hum Neurosci. 2020 Apr 9:14:64. doi: 10.3389/fnhum.2020.00064. eCollection 2020.

Authors

Ryan McKendrick¹, Brian Falcone¹, Melissa Scheldrup², Hasan Ayaz^{3

4

5

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Affiliations

¹ Northrop Grumman Company, Mission Systems, Falls Church, VA, United States.
² Department of Psychology, George Mason University, Fairfax, VA, United States.
³ School of Biomedical Engineering, Science and Health Systems, Drexel University, Philadelphia, PA, United States.
⁴ Department of Psychology, College of Arts and Sciences, Drexel University, Philadelphia, PA, United States.
⁵ Department of Family and Community Health, University of Pennsylvania, Philadelphia, PA, United States.
⁶ Center for Injury Research and Prevention, Children's Hospital of Philadelphia, Philadelphia, PA, United States.

Abstract

Background: Transcranial direct current stimulation (tDCS) has been shown to be an inexpensive, safe, and effective way of augmenting a variety of cognitive abilities. Relatively recent advances in neuroimaging technology have provided the ability to measure brain activity concurrently during active brain stimulation rather than after stimulation. The effects on brain activity elicited by tDCS during active tDCS reported by initial studies have been somewhat conflicted and seemingly dependent on whether a behavioral improvement was observed. Objective: The current study set out to address questions regarding behavioral change, within and between-participant designs as well as differentiating the effects on hemodynamic amplitude and baseline during active tDCS stimulation. Methods: We tested the effects of transcranial direct current stimulation (tDCS) on anterior hemodynamics in prefrontal cortex during performance on a spatial memory task. Prefrontal cortex activity was measured with functional near infrared spectroscopy (fNIRS), a wearable and portable neuroimaging technique that utilizes near infrared light to measure cortical oxygenated and deoxygenated hemoglobin changes non-invasively. There were two groups, one group (n = 10) received only sham stimulation and the other group (n = 11) received sham followed by anodal stimulation to right ventral lateral prefrontal cortex. Results: Analyses revealed an increase in spatial memory performance following tDCS stimulation. This augmented performance was accompanied by changes to oxygenation (HbO-HbR) at the onset of the hemodynamic response in bilateral dorsolateral prefrontal cortex and left ventral medial prefrontal cortex. In these regions we also observed that stimulation improved neural processing efficiency, by reducing oxygenation and increasing performance from block to block. During and following tDCS stimulation, it was also observed that in bilateral dorsolateral prefrontal cortex the relationship between performance and oxygenation inverted, from a negative relationship to a positive relationship. Conclusion: The results suggest that tDCS is predominately a mechanism for changing neurons propensity for activity as opposed to their strength of activity. tDCS not only alters the efficiency of task relevant processing, but also the nature in which hemodynamic resources are used during augmented task performance.

Keywords: fNIRS; mixed models; neural efficiency; tDCS; working memory.