Phasic and repetitive self-touch differ in hemodynamic response in the prefrontal cortex-An fNIRS study

Abstract

Introduction: Each individual touches the own body several 100 times a day. While some researchers propose a self-regulatory function of self-touch, others report that self-touching increases nervousness. This controversy appears to be caused by the fact that researchers did not define the kind of self-touch they examined and actually, referred to different types of self-touch. Thus, kinematically defining different types of self-touch, such as phasic (discrete), repetitive, and irregular, and exploring the neural correlates of the different types will provide insight into the neuropsychological function of self-touching behavior.

Methods: To this aim, we assessed hemodynamic responses in prefrontal brain areas using functional near-infrared spectroscopy (fNIRS) and behavioral responses with NEUROGES®. Fifty-two participants were recorded during three specific kinematically types of self-touch (phasic, irregular, repetitive) that were to be performed on command. The recently developed toolbox Satori was used for the visualization of neuronal processes.

Results: Behaviorally, the participants did not perform irregular self-touch reliably. Neurally, the comparison of phasic, irregular and repetitive self-touch revealed different activation patterns. Repetitive self-touch is associated with stronger hemodynamic responses in the left Orbitofrontal Cortex and the Dorsolateral Prefrontal Cortex than phasic self-touch.

Discussion: These brain areas have been reported to be associated with self-regulatory processes. Furthermore, irregular self-touch appears to be primarily generated by implicit neural control. Thus, by distinguishing kinematically different types of self-touch, our findings shed light on the controverse discussion on the neuropsychological function of self-touch.

Keywords: functional near-infrared spectroscopy; left dorsolateral prefrontal cortex; left orbitofrontal cortex; prefrontal activity; self-touch.

Figure 1

Study design and experimental setup.

Figure 2

Optode placement according to the 10–20 system above the prefrontal cortex of the left and right hemispheres.

Figure 3

Brain activation (oxygenated hemoglobin) for the analysis of repetitive vs. phasic and irregular vs. phasic self-touch conditions for each single channel in the prefrontal cortex (red represents contrast: the darker the red, the greater the contrast described).

Figure 4

Group means and individual scores for oxygenated hemoglobin of the irregular, phasic, and repetitive conditions in channels 11, 13, 5, and 6. There were no significant effects for beta weights of Δdeoxy-Hb. *p < 0.05; **p < 0.01; ***p < 0.001.