Cuff-type pneumatic stimulator for studying somatosensory evoked responses with fMRI.

For quantitative somatosensory testing in the clinical environment a microprocessor controlled MR-compatible stimulation device was developed. A main feature of this device is the use of an inflatable cuff allowing the application of defined test pressures (0-1000 mbar) to the skin surface. The cuff is pressurized by a piezoelectric proportional valve with embedded closed loop controller. The distortion of the pressure pulses, introduced by the tube between valve and cuff (tube lengths of 2 and 6 m), was evaluated. Two kinds of stimulation patterns were implemented by the microprocessor: constant frequency stimulation (selectable between 1 and 20 Hz) and stimulation with stepwise changing frequencies according to a pseudorandom sequence. Imaging tests (n=8, index finger) showed more robust responses in S1 (contralateral) and S2 (bilaterally) if evoked by the random sequence. Both, the technical tests and the imaging results, demonstrate that this new stimulation system is well suited to set a standard for somatosensory stimulation in individual longitudinal studies or multicenter comparisons.

Personal noise ranking of road traffic: subjective estimation versus physiological parameters under laboratory conditions.

OBJECTIVE: To evaluate the subjective estimation of noise-induced discomfort and its correlation to psychoacoustic and physiological parameters under laboratory conditions. To establish an effective description of sound qualities of road traffic noise, supplementing the current standards and calculation specifications. METHODS: Pass-by vehicle noise samples were binaurally recorded with a dummy head measurement system, and synthetically composed to six vehicle ensembles considering different road beds, varying speed profiles and noise barriers. Fifty-one persons were selected and tested under laboratory conditions. Study participants were exposed to defined acoustic stimuli, alternating with neutral phases lacking acoustic content in a listening room. Concomitant recording of electrocardiogram (ECG) and respiratory rate was performed. Subjective estimation of noise-induced discomfort of assigned vehicle ensembles was rated on a personal ranking scale (PRS) by the study subjects. Subjective ratings were combined with objective psychoacoustic parameters by multiple regression analysis. RESULTS: Heart rate was increased during all noise exposure phases compared to neutral phases; the increase of heart rate differed among vehicle ensembles and was statistically significant in two cases (p<0.01). Respiratory rate remained unaffected. Personal rankings also differed among vehicle ensembles and correlated well with objective psychoacoustic parameters (p<0.0001); e.g., loudness combined with roughness describes the correlation with subjective estimation of noise-induced discomfort better than the A-weighted sound level. Vehicle ensembles rated more unpleasant caused higher increases in heart rate as well (p<0.0001). CONCLUSIONS: The sound quality of road traffic noise as it is described by various psychoacoustic parameters not only determines the subjective estimation of noise-induced discomfort but in addition affects physiological parameters like heart rate. This should be considered for future perspectives in road- and traffic planning and therefore may serve construction engineers as well as traffic planner as a supplemental tool.

Contact force- and amplitude-controllable vibrating probe for somatosensory mapping of plantar afferences with fMRI.

PURPOSE: To study cerebral responses evoked from mechanoreceptors in the human foot sole using a computer-controlled vibrotactile stimulation system. MATERIALS AND METHODS: The stimulation system consisted of two stationary moving magnet actuators with indentors to gently contact and vibrate the foot sole during functional MRI (fMRI) experiments. To allow independent settings of contact force (0-20 N) and intensity of vibration (frequency range=20-100 Hz) the actuators were controlled by a digital servo loop. For fMRI experiments with complex stimulus protocols, both vibrating probes were further operated under supervisory control. RESULTS: The MR compatibility of this electromagnetic system was tested in a 1.5T scanner with an actively shielded magnet (Siemens Magnetom Sonata). Blood oxygenation level-dependent (BOLD) responses were detected in the contralateral left pre- and postcentral gyrus, bilaterally within the secondary somatosensory cortex, bilaterally within the supplementary motor cortex, and bilaterally within the anterior cingular gyrus. CONCLUSION: This stimulation device provides a new tool for identifying cerebral structures that convey sensory information from the foot region, which is of promising diagnostic value, particularly for assessing sensorimotor deficits resulting from brain lesions.

Human brain structures related to plantar vibrotactile stimulation: a functional magnetic resonance imaging study.

The purpose of this study was to investigate the sensorimotor cortex response to plantar vibrotactile stimulation using a newly developed MRI compatible vibration device. Ten healthy subjects (20-45 years) were investigated. Vibrotactile stimulation of the sole of the foot with a frequency of 50 Hz and a displacement of 1 mm was performed during fMRI (echo-planar imaging sequence at 1.5 T) using an MRI compatible moving magnet actuator that is able to produce vibration frequencies between 0 and 100 Hz and displacement amplitudes between 0 and 4 mm. The fMRI measurement during vibrotactile stimulation of the right foot revealed brain activation contralaterally within the primary sensorimotor cortex, bilaterally within the secondary somatosensory cortex, bilaterally within the superior temporal, inferior parietal, and posterior insular region, bilaterally within the anterior and posterior cingular gyrus, bilaterally within the thalamus and caudate nucleus, contralaterally within the lentiform nucleus, and bilaterally within the anterior and posterior cerebellar lobe. The advantages of the new MRI compatible vibration device include effective transmission of the stimulus and controlled vibration amplitudes, frequencies, and intensities. The results indicate that plantar vibration can be a suitable paradigm to observe activation within the sensorimotor network in fMRI. Furthermore, the method may be used to determine the optimal responsiveness of the individual sensorimotor network.

Evaluation of FES-induced knee joint moments in paraplegics with denervated muscles.

The pendulum test was applied to evaluate functional electrical stimulation (FES)-induced joint moments in paraplegics with denervated muscles. Therefore a manipulandum was connected to the knee joint and programmed to elicit gravity-induced leg oscillations. The FES-induced output torque was compensated for in order to keep the leg in a mean vertical position (knee angle 90 degrees ). A second-order dynamical model was applied to extract the elastic and viscous moments from the recorded leg oscillations. This model provided an almost adequate description of the relaxed and FES-contracted states. In the relaxed state the elastic moment was 15.3 +/- 2.37 Nm/rad and the viscous moment was 0.41 +/- 0.21 Nms/rad. The FES-induced elastic moment was 29.4 +/- 28.5 Nm/rad and the FES-induced viscous moment was 1.53 +/- 1.03 Nms/rad (N = 10, before FES-training).

Functional electrical stimulation-induced surface muscle stiffness captured by computer-controlled tonometry.

A new tonometric test system to assess surface stiffness over relaxed and activated calf muscles was developed. The mechanical arrangement consists of a skin indentor driven by a torque motor (galvo-drive) that is rigidly connected to an ankle dynamometer. The indentation depth is measured by a displacement transducer. Software routines for cyclic indentation (recording of stiffness curves), static indentation (sensing of twitch responses), and vibration (skin resonance) were implemented. A visual interface is used to capture surface stiffness during target contractions and during controlled relaxation. For functional electrical stimulation (FES) applications, the software includes a pulse train synthesizer to generate arbitrary stimulation test patterns. The system's performance was tested in FES and voluntary contraction procedures.