Brain responses to frequency changes due to vibratory stimulation of human fingertips: An fMRI study

Neural correlates of tactile hardness intensity perception during active grasping

While tactile sensation plays an essential role in interactions with the surroundings, relatively little is known about the neural processes involved in the perception of tactile information. In particular, it remains unclear how different intensities of tactile hardness are represented in the human brain during object manipulation. This study aims to investigate neural responses to various levels of tactile hardness using functional magnetic resonance imaging while people grasp objects to perceive hardness intensity. We used four items with different hardness levels but otherwise identical in shape and texture. A total of Twenty-five healthy volunteers participated in this study. Before scanning, participants performed a behavioral task in which they received a pair of stimuli and they were to report the perceived difference of hardness between them. During scanning, without any visual information, they were randomly given one of the four objects and asked to grasp it. We found significant blood oxygen-level-dependent (BOLD) responses in the posterior insula in the right hemisphere (rpIns) and the right posterior lobe of the cerebellum (rpCerebellum), which parametrically tracked hardness intensity. These responses were supported by BOLD signal changes in the rpCerebellum and rpIns correlating with tactile hardness intensity. Multidimensional scaling analysis showed similar representations of hardness intensity among physical, perceptual, and neural information. Our findings demonstrate the engagement of the rpCerebellum and rpIns in perceiving tactile hardness intensity during active object manipulation.

Brain responses to high frequencies (270 Hz-480 Hz) changes due to vibratory stimulation of human fingertips: An fMRI study

This fMRI study investigated the effects of vibratory stimulation on somatosensory areas during high-frequencies stimulation using a piezoelectric finger stimulation system during an fMRI scan. Twelve healthy right-handed subjects were stimulated at 270 Hz-480 Hz and the fMRI dataset was analysed to generate the activated regions due to the high-frequencies stimulation. The activated regions were identified and thresholded at Puncorrected<0.001 for multiple comparisons. The average effect of frequencies revealed significant activation in the left thalamus, right inferior parietal gyrus, right medial frontal gyrus, and right precuneus whereas the main effect of frequencies revealed significant activation in the left thalamus. The positive effect of frequencies displayed significant activation in the left pallidum, right amygdala, right superior temporal gyrus, right medial temporal gyrus. The vibratory stimulation at a frequency of 330 Hz and 360 Hz (330 Hz<360 Hz) revealed a significant difference in the left thalamus. Findings indicated the role of the secondary somatosensory areas processing and transporting sensory information to perform the perceptual and cognitive function.