Prolonged mechanical noise restores tactile sense in diabetic neuropathic patients.

Acute application of stochastic resonance (SR), defined as a subsensory level of mechanical noise presented directly to sensory neurons, improves the vibration and tactile perception in diabetic patients with mild to moderate neuropathy. This study examined the effect of 1 hour of continuous SR stimulation on sensory nerve function. Twenty diabetic patients were studied. The effect of stimulation was measured at 2 time points, at the beginning and after 60 minutes of continual SR stimulation. This effect was measured using the vibration perception threshold (VPT) at the big toe under 2 conditions: a null (no SR) condition and active SR, defined as mechanical noise below the subject's own threshold of perception. The measurements under null and active conditions were done randomly and the examiner was blinded regarding the type of condition. Immediately after SR application, the VPT with SR in null condition was similar to baseline (32.2 +/- 13.1, P = nonsignificant) but was significantly lower during active SR (27.4 +/- 11.9) compared with both baseline (P = .018) and off position (P = .045). The 60 minutes VPT with active SR (28.7 +/- 11.1) reached significance comparing the baseline when one outlier was removed from the analysis (P = .031). It may be concluded that SR for a continuous 60-minute period can sustain the VPT improvement in diabetic patients with moderate to severe neuropathy. These results permit the conclusion that there is no short-term adaptation to the stimulation signal. Long-term application of this technique, perhaps in the form of a continually vibrating shoe insert, or insole, may result in sustained improvement of nerve function.

Enhancing sensation in diabetic neuropathic foot with mechanical noise.

OBJECTIVE: Localized low-level mechanical or electrical noise can significantly enhance tactile sensitivity in healthy young subjects and older adults. This phenomenon is termed stochastic resonance (SR). In this study, we examined the effect of SR on vibratory and tactile sensation in patients with moderate to severe diabetic peripheral neuropathy. RESEARCH DESIGN AND METHODS: A total of 20 subjects were included in the study. The vibration perception threshold (VPT) test and the Semmes-Weinstein filament (SWF) threshold at the plantar surface of the left foot and the big toe were determined under two mechanical noise stimulus conditions: null (no noise) condition and at 10% lower than each subject's mechanical noise threshold of perception. RESULTS: The baseline values (mean +/- SD) were as follows: Neuropathy Symptom Score (NSS) 5.2 +/- 2.5, Neuropathy Disability Score (NDS) 5.0 +/- 2.1, VPT 24 +/- 11 V, and SWF threshold 5.6 +/- 0.8 at the plantar surface of the foot and 5.3 +/- 0.9 at the big toe. The VPT improved significantly from 24 +/- 11 under null condition to 19 +/- 10 V with mechanical noise (P < 0.0001). Mechanical noise also significantly increased the number of detections of the SWF at the plantar surface of the foot (detection rate 66 +/- 11 vs. 59 +/- 15%, P < 0.02) but not at the big toe (63 +/- 10 vs. 61 +/- 16%, P = NS). CONCLUSIONS: Mechanical noise stimulation improves vibration and tactile perception in diabetic patients with moderate to severe neuropathy. Additional studies are required to examine the effect of long-term noise stimulation on parameters of nerve function.

Vibrating insoles and balance control in elderly people.

Somatosensory function declines with age, and such changes have been associated with diminished motor performance. Input noise can enhance sensory and motor function. We asked young and elderly participants to stand quietly on vibrating gel-based insoles, and calculated sway parameters and random-walk variables. In our 27 participants, application of noise resulted in a reduction in seven of eight sway parameters in young participants and all of the sway variables in elderly participants. Elderly participants showed greater improvement than young people in two variables, mediolateral range (p=0.008), and critical mean square displacement (p=0.012). Noise-based devices, such as randomly vibrating insoles, could ameliorate age-related impairments in balance control.

Enhancing tactile sensation in older adults with electrical noise stimulation.

Older adults often suffer from diminished somatosensation stemming from age-related neuropathy. Recently, localized low-level electrical noise stimulation was shown to enhance tactile sensitivity in healthy young subjects. Here, we hypothesized that fine-touch sensitivity in older adults can be similarly improved. Semmes-Weinstein monofilaments were used to evaluate fine-touch sensitivity on the first metatarsal phalangeal joint with four electrical stimulus conditions and a null (no-noise) condition in nine healthy elderly subjects. Electrical noise stimulation resulted in a statistically significant increase in the number of detections below the null-condition detection threshold, for five of the nine subjects, as well as across the entire population. This work suggests that electrical noise-based techniques may enable people to overcome functional difficulties due to age-related sensory loss.