Somatosensory evoked potential correlates of psychophysical magnitude estimations for air-puff stimulation of the foot in man

Somatosensory Evoked Responses Elicited by Haptic Sensations in Midair

The design of human-machine interfaces (HMIs) by virtual haptics is an emerging field of research. So far, the perception of virtual haptic feedback, e.g., generated by focused ultrasound in midair has not been objectively evaluated. This paper demonstrates the feasibility of eliciting somatosensory evoked potentials (SEPs) with ultrasonic stimuli in midair for the first time. The palm was stimulated by short ultrasonic focal points generated by an ultrasound board. The results are compared with a no stimulation condition as well as with the results of a vibro tactile stimulation. The SEPs are analyzed with the wavelet phase synchronization stability (WPSS) and the M-consecutive averaged WPSS. The results indicate a clear SEP waveform elicited by ultrasound. It can be significantly differentiated from a no stimulation condition by the M-consecutive averaged WPSS. These results could enable the possibility of developing an objective evaluation method for virtual haptic feedback in HMIs.

Relating tribological stimuli to somatosensory electroencephalographic responses

The present study deals with the extraction of neural correlates evoked by tactile stimulation of the human fingertip. A reciprocal sliding procedure was performed using a home-built tribometer while simultaneously electroencephalographic (EEG) data from the somatosensory cortex was recorded. The tactile stimuli were delivered by a sliding block with equidistant, perpendicular ridges. The experiments were designed and performed in a fully passive way to prevent attentional locked influences from the subjects. In order to improve the signal-to-noise ratio (SNR) of event related single-trials (ERPs), nonlocal means in addition to 2D-anisotropic denoising schemes based on tight Gabor frames were applied. This novel approach allowed for an easier extraction of ERP alternations. A negative correlation between the latency of the P100 component of the resulting brain responses and the intensity of the underlying lateral forces was found. These findings lead to the conclusion that an increasing stimulus intensity results in a decreasing latency of the brain responses.

Somatosensory spatial attention modulates amplitudes, latencies, and latency jitter of laser-evoked brain potentials

Several studies provided evidence that the amplitudes of laser-evoked potentials (LEPs) are modulated by attention. However, previous reports were based on across-trial averaging of LEP responses at the expense of losing information about intertrial variability related to attentional modulation. The aim of this study was to investigate the effects of somatosensory spatial attention on single-trial parameters (i.e., amplitudes, latencies, and latency jitter) of LEP components (N2 and P2). Twelve subjects participated in a sustained spatial attention paradigm while noxious laser stimuli (left hand) and noxious electrical stimuli (right hand) were sequentially delivered to the dorsum of the respective hand with nonnoxious air puffs randomly interspersed within the sequence of noxious stimuli. Participants were instructed to mentally count all stimuli (i.e., noxious and nonnoxious) applied to the attended location. Laser stimuli, presented to the attended hand (ALS), elicited larger single-trial amplitudes of the N2 component compared with unattended laser stimuli (ULS). In contrast, single-trial amplitudes of the P2 component were not significantly affected by spatial attention. Single-trial latencies of the N2 and P2 were significantly smaller for ALS vs. ULS. Additionally, the across-trial latency jitter of the N2 component was reduced for ALS. Conversely, the latency jitter of the P2 component was smaller for ULS compared with ALS. With the use of single-trial analysis, the study provided new insights into brain dynamics of LEPs related to spatial attention. Our results indicate that single-trial parameters of LEP components are differentially modulated by spatial attention.

Perceptibility of large and sequential changes in somatosensory information during leaning forward and backward when standing

11 healthy young men served as subjects in two experiments on perceptibility of (1) large changes in foot pressure and muscle activity induced by body leaning and (2) sequential changes in pressure at the first toe and the head of the first metatarsalis when leaning forward. The effects of reduced sensitivity on that perceptibility were also studied by repeating the experiments while cooling localized plantar areas of the sole (the head of the first metatarsalis, the first toe, and the heel). Under the normal (noncooled) condition, all subjects accurately perceived maximum pressure at the head of the first metatarsalis, but most subjects misperceived the second large increase in pressure at the first toe and in muscle activity as the first large increase. Under the cooling condition, localized cooling did not affect the perceptibility of maximum pressure at the head of the first metatarsalis or the activity in the tibialis anterior, but the perceptibility of pressure at the first toe and activity of the abductor hallucis were reduced. There were individual differences in perceptibility of activity of the rectus femoris when the heel was cooled. Perceptibility of sequential changes in the pressure was affected differently by the localized cooling of each region. Given these findings, we discussed the role and interrelatedness of pressure sensation in perceiving large and sequential changes in somatosensory information while standing and leaning forward and backward.

Somatosensory evoked potentials to a threshold air-puff can predict stimulus detection in human subjects

Somatosensory evoked potentials (SEPs) and reaction time (RT) were studied following a threshold intensity air-puff stimulation of the skin in nine subjects. We delivered brief air-puffs, at the threshold intensity of about 50% detection probability, to the volar surface of the right hand at the base of the index finger. The SEPs were averaged separately for detected and undetected stimuli. Prior to the SEP data collection, RTs to the same intensity threshold stimulus were measured. P300 SEP late component was recorded in response to detected stimuli and was not to undetected stimuli. However, in one subject, P300 was associated with undetected stimuli, suggesting errors in the psychophysical task. The peak latency of P300 was 316+/-29 ms (mean+/-SD) and earlier than the average RT (390+/-43 ms). These results demonstrate that SEPs can correctly predict perception of the threshold air-puff stimulus.

Differential temporal coding of the vibratory sense in the hand and foot in man

OBJECTIVE

We studied the difference in the temporal tuning function of the vibratory senses between the hand and foot in man by using steady-state somatosensory evoked potentials (S-SEPs) to vibratory stimulation.

METHODS

Vibratory stimuli were applied to the palm and sole, and the S-SEPs were then recorded in 8 normal subjects. A total of 200 responses were recorded from 4 electrodes including the ipsi-and contralateral somatosensory areas of the hand and foot. The amplitude of the first harmonic component (1F) was obtained by a Fourier analysis. The effect of modulation frequency (17-30 Hz) on the 1F at a stimulus intensity of 0.05 N was studied.

RESULTS

The amplitudes of the S-SEPs were the greatest in the contralateral hand and foot areas. The mean 1F amplitudes of the palm S-SEPs as a function of the modulation frequency showed a narrow tuning curve with a peak near 21 Hz while those of the sole demonstrated a broad tuning curve.

CONCLUSION

Our results suggest the differential temporal coding of the vibratory sense in the hand and foot areas of the somatosensory cortex in man. This is probably caused by the different characteristics in the receptors situated in the hand and foot.