Pressure stimulation of the jaw and cortical blood flow signatures

Little is known regarding the relationship between subjective experience and cortical activationcaused by a given pressure stimulus. Therefore, this study had three aims: First, to investigatethe relationship between pressure stimulation and perceptual intensity. Second, to examinewhether functional near-infrared spectroscopy (fNIRS) can capture the cortical response fromapplying pressure to the jaw. Third, to investigate whether pressure-elicited cortical activationin the primary somatosensory cortex (S1) and middle temporal gyrus (MTG) follows a pressurelevel-dependent increase. Eighteen participants (11 women, 6 men and 1 non-binary. Mean age= 24.3, SD = 3.4) were recruited for an experiment that consisted of rating 80 stimuli (40pressure stimuli applied to the right jaw, and 40 olfactory stimuli not reported here) using aBorg CR100 scale, while measuring their cortical response with a NIRSport2 fNIRS setup. Thepressure stimuli were presented ten times each in a semi-randomized order, consisting of abaseline pressure level (0 kPa) and three pressure levels (P1 = 33.91 kPa; P2 = 56.91 kPa; P3= 200 kPa). The behavioral data revealed a positive correlation between pressure levels andintensity ratings. The fNIRS data were revealed to successfully capture the cortical responseelicited by applying the pressure stimulus, which was found in S1 and MTG. An exploratoryanalysis revealed ipsilateral MTG activation to increase as pressure levels increased, butunexpectedly, S1 activity decreased. As the unexpected results are likely due to confoundingfactors (e.g., head tilting), future research should investigate the relationship between corticalactivation and pressure level further.