Mechanosensitivity and Neural Adaptation in Human Somatosensory System

Magnetoencephalography (MEG) was utilized to characterize the adaptation in the somatosensory cortical network due to repeated cutaneous tactile stimulation applied unilaterally on the face and hand using a custom-built pneumatic stimulator called the TAC-Cell. Face stimulation invoked neuromagnetic responses reflecting cortical activity in the contralateral primary somatosensory cortex (SI), while hand stimulation resulted in robust contralateral SI and posterior parietal cortex (PPC) activation. There was also activity observed in regions of the secondary somatosensory cortical areas (SII), although with a reduced amplitude and higher variability across subjects. There was a significant difference in adaptation rates between SI, and higher-order sensory cortices like the PPC for hand stimulation. Adaptation was also significantly dependent on the stimulus frequency and pulse index number within the stimulus train for both hand and face stimulation. The latency of the peak responses was significantly dependent on stimulus site and response component (SI, PPC). The difference in the latency of peak SI and PPC responses can be reflective of a hierarchical serial-processing network in the somatosensory cortex. Age- and sex-related changes of vibrotactile sensitivity in the orofacial and hand skin surfaces of healthy adults was demonstrated using an established psychophysical protocol. Vibrotactile threshold sensitivity increased as a function of age for finger stimulation, but remained unaltered for the face. Increase in the finger threshold sensitivity is due to age-related changes in the number and morphology of Pacinian corpuscles (absent in the face). Vibrotactile threshold sensitivity is significantly dependent on stimulation site, stimulus frequency, and sex of the participant. These differences are presumably due to dissimilarities in the type and density of mechanoreceptors present in the face and hand. A novel-method was developed to couple the use of fiber-optic displacement sensors with the pneumatic stimulator built in our laboratory called the TAC-Cell. This displacement sensor which is commonly used in industrial applications was successfully utilized to characterize the skin response to TAC-Cell stimulation. Skin displacement was significantly dependent on input stimulus amplitudes and varied as a function of the participants' sex. Power spectrum analysis and rise-fall time measurement of the skin-displacement showed that the TAC-Cell stimulus consists of a spectrally rich, high velocity signal that is capable of evoking a cortical response due to stimulation of the medial-lemniscus and trigeminal pathways

Frequency Modulation and Spatiotemporal Stability of the sCPG in Preterm Infants with RDS

This is the published version, also available here: http://dx.doi.org/10.1155/2012/581538.The nonnutritive suck (NNS) is an observable and accessible motor behavior which is often used to make inference about brain development and pre-feeding skill in preterm and term infants. The purpose of this study was to model NNS burst compression pressure dynamics in the frequency and time domain among two groups of preterm infants, including those with respiratory distress syndrome (RDS, N=15) and 17 healthy controls. Digitized samples of NNS compression pressure waveforms recorded at a 1-week interval were collected 15 minutes prior to a scheduled feed. Regression analysis and ANOVA revealed that healthy preterm infants produced longer NNS bursts and the mean burst initiation cycle frequencies were higher when compared to the RDS group. Moreover, the initial 5 cycles of the NNS burst manifest a frequency modulated (FM) segment which is a significant feature of the suck central pattern generator (sCPG), and differentially expressed in healthy and RDS infants. The NNS burst structure revealed significantly lower spatiotemporal index values for control versus RDS preterm infants during FM, and provides additional information on the microstructure of the sCPG which may be used to gauge the developmental status and progression of oromotor control systems among these fragile infants

Cutaneous stimulation of the digits and lips evokes responses with different adaptation patterns in primary somatosensory cortex

Neuromagnetic evoked fields were recorded to compare the adaptation of the primary somatosensory cortex (SI) response to tactile stimuli delivered to the glabrous skin at the fingertips of the first three digits (condition 1) and between midline upper and lower lips (condition 2). The stimulation paradigm allowed to characterize the response adaptation in the presence of functional integration of tactile stimuli from adjacent skin areas in each condition. At each stimulation site, cutaneous stimuli (50 ms duration) were delivered in three runs, using trains of 6 pulses with regular stimulus onset asynchrony (SOA). The pulses were separated by SOAs of 500 ms, 250 ms or 125 ms in each run, respectively, while the inter-train interval was fixed (5 s) across runs. The evoked activity in SI (contralateral to the stimulated hand, and bilaterally for lips stimulation) was characterized from the best-fit dipoles of the response component peaking around 70 ms for the hand stimulation, and 8 ms earlier (on average) for the lips stimulation. The SOA-dependent long-term adaptation effects were assessed from the change in the amplitude of the responses to the first stimulus in each train. The short-term adaptation was characterized by the lifetime of an exponentially saturating model function fitted to the set of suppression ratios of the second relative to the first SI response in each train. Our results indicate: 1) the presence of a rate-dependent long-term adaptation effect induced only by the tactile stimulation of the digits; and 2) shorter recovery lifetimes for the digits compared with the lips stimulation