Random noise stimulation in the treatment of patients with neurological disorders

Random noise stimulation technique involves applying any form of energy (for instance, light, mechanical, electrical, sound) with unpredictable intensities through time to the brain or sensory receptors to enhance sensory, motor, or cognitive functions. Random noise stimulation initially employed mechanical noise in auditory and cutaneous stimuli, but electrical energies applied to the brain or the skin are becoming more frequent, with a series of clinical applications. Indeed, recent evidence shows that transcranial random noise stimulation can increase corticospinal excitability, improve cognitive/motor performance, and produce beneficial aftereffects at the behavioral and psychological levels. Here, we present a narrative review about the potential uses of random noise stimulation to treat neurological disorders, including attention deficit hyperactivity disorder, schizophrenia, amblyopia, myopia, tinnitus, multiple sclerosis, post-stroke, vestibular-postural disorders, and sensitivity loss. Many of the reviewed studies reveal that the optimal way to deliver random noise stimulation-based therapies is with the concomitant use of neurological and neuropsychological assessments to validate the beneficial aftereffects. In addition, we highlight the requirement of more randomized controlled trials and more physiological studies of random noise stimulation to discover another optimal way to perform the random noise stimulation interventions.

Arp2/3-dependent mechanical control of morphogenetic robustness in an inherently challenging environment

Epithelial sheets undergo highly reproducible remodeling to shape organs. This stereotyped morphogenesis depends on a well-defined sequence of events leading to the regionalized expression of developmental patterning genes that finally triggers downstream mechanical forces to drive tissue remodeling at a pre-defined position. However, how tissue mechanics controls morphogenetic robustness when challenged by intrinsic perturbations in close proximity has never been addressed.

Using Drosophila developing leg, we show that a bias in force propagation ensures stereotyped morphogenesis despite the presence of mechanical noise in the environment. We found that knockdown of the Arp2/3 complex member Arpc5 specifically affects fold directionality while altering neither the developmental nor the force generation patterns. By combining in silico modeling, biophysical tools, and ad hoc genetic tools, our data reveal that junctional myosin II planar polarity favors long-range force channeling and ensures folding robustness, avoiding force scattering and thus isolating the fold domain from surrounding mechanical perturbations.

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Drosophila developing leg folding is extremely robust

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Fold orientation becomes variable in Arp2/3 knockdown condition

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Arp2/3 controls junctional myosin II planar polarity

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Myosin II planar polarity ensures fold robustness through force channeling

Tissue-Scale Mechanical Coupling Reduces Morphogenetic Noise to Ensure Precision during Epithelial Folding

Morphological constancy is universal in developing systems. It is unclear whether precise morphogenesis stems from faithful mechanical interpretation of gene expression patterns. We investigate the formation of the cephalic furrow, an epithelial fold that is precisely positioned with a linear morphology. Fold initiation is specified by a precise genetic code with single-cell row resolution. This positional code activates and spatially confines lateral myosin contractility to induce folding. However, 20% of initiating cells are mis-specified because of fluctuating myosin intensities at the cellular level. Nevertheless, the furrow remains linearly aligned. We find that lateral myosin is planar polarized, integrating contractile membrane interfaces into supracellular "ribbons." Local reduction of mechanical coupling at the "ribbons" using optogenetics decreases furrow linearity. Furthermore, 3D vertex modeling indicates that polarized, interconnected contractility confers morphological robustness against noise. Thus, tissue-scale mechanical coupling functions as a denoising mechanism to ensure morphogenetic precision despite noisy decoding of positional information.

Mechanical Noise Improves the Vibration Perception Threshold of the Foot in People With Diabetic Neuropathy

BACKGROUND

Mechanical noise may improve somatosensation at the dorsal side of the foot, but the effect at the plantar side of the foot, the side most at risk for foot ulceration, is unknown. Moreover, techniques used in research so far have several problems that limit applicability in daily practice. Piezoelectric actuators may provide mechanical noise with better clinical applicability. We assessed the effects of piezoelectric actuators generating mechanical noise on the vibration perception threshold (VPT) at the plantar side of the foot in people with diabetic neuropathy.

METHODS

Double-blind within-subjects design in a controlled laboratory setting including participants with diabetic neuropathy (N = 40; 18 male; mean age 69.6 years; mean duration of diabetes 14.1 years; mean BMI 30.5). VPT was measured at three plantar foot locations with and without mechanical noise applied via piezoelectric actuators.

RESULTS

Mechanical noise improved VPT at metatarsophalangeal joint (MTP) 1 (left 39.3V vs 43.5V; right 39.0 vs 42.6 V), MTP5 (left 37.5V vs 41.7V; right 34.5V vs 40.8V) and the heel (left 40.0V vs 44.0V; right 39.3V vs 41.0V), all P < .001.

CONCLUSIONS

Mechanical noise improves VPT at the plantar side of the foot in people with diabetic neuropathy. This is an important step for further development of insoles using mechanical noise that may have the potential to improve VPT and decrease the risk of foot ulceration.