Xi Li

Motor unit acceleration maps and interference mechanomyographic distribution

The study analyses the two-dimensional distribution of surface mechanomyographic (MMG) signal generated by the activation of single motor units located in three transverse positions in the tibialis anterior muscle. In 12 healthy volunteers, surface MMG signals were recorded from the tibialis anterior muscle with a 3 x 4 grid of accelerometers spaced by 20 and 30 mm in the transverse and longitudinal direction. Three intramuscular electromyographic (EMG) signals were recorded with wire electrodes inserted 20-mm apart, between the first and second most proximal accelerometers of each column of the grid. The subject was asked to activate three different motor units (target motor units) in three contractions with visual feedback from each of the three intramuscular recordings (three locations). The MMG signals from the 12 accelerometers were averaged using the intramuscular single motor unit action potentials as trigger in order to obtain surface motor unit acceleration maps (MUAMs). The peak-to-peak value of the averaged MMG depended on motor unit location (P<0.001) and on the transverse position of the accelerometer in the grid (P<0.05). Moreover, MUAM amplitude depended on the interaction between motor unit location and transverse accelerometer position (P<0.05), demonstrating an influence of motor unit location on the generated MUAM. The observed dependency of MUAMs on motor unit location provides a quantitative analysis of the effect of the volume conductor on the recorded surface MMG signal.

High resolution topographical mapping of warm and cold sensitivities.

OBJECTIVE This study aims to explore the thermal sensitivity distribution (topographical mapping) over the glabrous skin of the hand in males and females. METHODS Warm (WT) and cold (CT) thresholds were measured in 25 healthy volunteers (12 females), applying a multi-site test of 23 locations on the volar part of the hand. RESULTS The palm area was more sensitive than the fingers to both warm (P<0.001) and cold (P<0.001) stimuli. On the palm itself, the proximal part was the most sensitive (P<0.05). Heterogeneity was also found to both warm and cold sensibilities within dermatomes (P<0.05) as well as to cold sensitivity across dermatomes (P<0.001). Females were more sensitive than males to both warm (P<0.001) and cold sensations (P<0.001). In addition, painful components were frequently reported as accompanying warm/cold sensations during mild warming/cooling. CONCLUSIONS The thermal sensitivity distribution over the glabrous skin of the hand is highly heterogeneous. SIGNIFICANCE It is appropriate to precisely define testing locations when conducting thermal examinations on the hand.

The importance of stimulus parameters for the experience of the thermal grill illusion.

AIMS This study aimed to investigate the quality of the thermal grill illusion (TGI) and the importance of stimulus parameters (distance between, and number of stimulation bars). MATERIAL AND METHODS Twenty-one different stimuli were applied to a group of 19 healthy subjects on the glabrous skin over the palm and fingers. RESULTS The TGI was found to be painful (19.42% on the palm; 17.98% on the fingers), mechanical (25.24% on the palm; 5.62% on the fingers), emotional (13.59% on the palm; 14.61% on the fingers) or unusual (42.72% on the palm; 61.8% on the fingers) sensations. A total of 89.5% (palm) and 94.4% (fingers) of the subjects reported TGI. Between 45% (fingers) and 50% (palm) of the stimuli elicited TGI. Neither the distance (2 approximately 10 mm) between adjacent warm (40 +/- 1 degrees C) and cold (20 +/- 1 degrees C) bars nor the number of the stimulation bars (2 approximately 6) significantly affected the occurrence of the TGI (N.S.). The average reaction time was 2.4 +/- 0.1 seconds to the TGI sensation. Females showed longer reaction time than males (P <or= 0.001). CONCLUSION The distance and number of stimulation bars were not important to the sensation of TGI, of which the responses varied. These results are useful for future TGI studies with respect to experimental design. The variability of the TGI needs to be considered in future experimental and clinical studies.

293 THE TIME COURSE OF THE THERMAL GRILL ILLUSION

292 A NOVEL METHOD FOR THERMAL AND CHEMICAL STIMULATION OF THE HUMAN OESOPHAGUS I. Larsen *, B. Koch-Henriksen, Sø. Schou Olesen, A. Estrup Olesen, F. Gravesen, Aø. Mohr Drewes. Mech-Sense, Department of Gastroenterology, Aalborg Hospital, Aarhus University Hospital, Aalborg, Denmark; Center for Sensory-Motor Interactions (SMI), Department of Health Science and Technology, Aalborg University, Denmark, Aalborg, Denmark

The time course of the thermal grill illusion: 293

292 A NOVEL METHOD FOR THERMAL AND CHEMICAL STIMULATION OF THE HUMAN OESOPHAGUS I. Larsen *, B. Koch-Henriksen, Sø. Schou Olesen, A. Estrup Olesen, F. Gravesen, Aø. Mohr Drewes. Mech-Sense, Department of Gastroenterology, Aalborg Hospital, Aarhus University Hospital, Aalborg, Denmark; Center for Sensory-Motor Interactions (SMI), Department of Health Science and Technology, Aalborg University, Denmark, Aalborg, Denmark

Poster SessionsPoster Session 1: Anatomy and animal models293 THE TIME COURSE OF THE THERMAL GRILL ILLUSION

292 A NOVEL METHOD FOR THERMAL AND CHEMICAL STIMULATION OF THE HUMAN OESOPHAGUS I. Larsen *, B. Koch-Henriksen, Sø. Schou Olesen, A. Estrup Olesen, F. Gravesen, Aø. Mohr Drewes. Mech-Sense, Department of Gastroenterology, Aalborg Hospital, Aarhus University Hospital, Aalborg, Denmark; Center for Sensory-Motor Interactions (SMI), Department of Health Science and Technology, Aalborg University, Denmark, Aalborg, Denmark