Hemodynamic Changes in Cortical Sensorimotor Systems Following Hand and Orofacial Motor Tasks and Pulsed Cutaneous Stimulation

The integrity of the cerebral cortex can be assessed by measuring its responsiveness to repetitive sensory stimulation and voluntary motor activity. This neurophysiologic feature is called neural adaptation, and is thought to enhance learning and detection of environmental stimuli. The adaptation of hemodynamic responses to motor and sensory experiences in hand and face are of particular interest—as these are structures used in human communication—and proper delivery of oxy-hemoglobin to primary motor (M1) and somatosensory (S1) cortices is essential for functional cortical activation. The objective of this study was to examine the hemodynamic differences between hand and face cortical representations during motor and passive somatosensory conditions, as measured with functional near-infrared spectroscopy (fNIRS). The study design included 22 neurotypical adults, ages 19-30, and 11 neurotypical children, ages 6-13. Anatomical MRI localized each individual’s M1 and S1. fNIRS determined relative levels of oxy- and deoxy-hemoglobin during the stimulus conditions. Motor tasks consisted of repetitive squeezing on a grip force strain gage, and repetition of bilabial compressions on a lip force strain gage. Somatosensory stimulation with a Galileo™ tactile stimulus stimulator occurred through pneumatic TAC-Cells placed on the glabrous right hand and lower face near right oral angle. Results from healthy participants (N=22 adults, mean age 23.16 ± 1.76; N=11 children, mean age 10.05 ± 2.76) revealed significant oxygenation differences across stimulus conditions in respective cortical regions. Overall, children exhibited greater mean cortical oxygen concentration levels and more variability than adults, with adults displaying more typical patterns of neural activation following each stimulus condition. The precise delivery of natural, pneumatic stimulation as well as functionally relevant and measurable motor tasks, allowed for a novel examination of hemodynamic changes in somatosensory and motor cortices using fNIRS technology. These data present a picture of normal physiologic connectivity and function across a wide range of ages, which provides a broader view of how the healthy cerebral cortex operates in terms of neuronal responses to specific types of stimuli, neurovascular coupling, and cerebral oxygenation. Advisor: Steven M. Barlo