Weak Electrical Stimuli Research Articles

Transcranial electrical stimulation: How can a simple conductor orchestrate complex brain activity?

Transcranial electrical stimulation (tES) is one of the oldest and yet least understood forms of brain stimulation. The idea that a weak electrical stimulus, applied outside the head, can meaningfully affect neural activity is often regarded as mysterious. Here, we argue that the direct effects of tES are not so mysterious: Extensive data from a wide range of model systems shows it has appreciable effects on the activity of individual neurons. Instead, the real mysteries are how tES interacts with the brain's own activity and how these dynamics can be controlled to produce desirable therapeutic effects. These are challenging problems, akin to repairing a complex machine while it is running, but they are not unique to tES or even neuroscience. We suggest that models of coupled oscillators, a common tool for studying interactions in other fields, may provide valuable insights. By combining these tools with our growing, interdisciplinary knowledge of brain dynamics, we are now in a good position to make progress in this area and meet the high demand for effective neuromodulation in neuroscience and psychiatry.

Study on characteristics of the electric‐field‐sensitive hydrogel inspired by jelly in the ampullae of Lorenzini of elasmobranchs

AbstractThe elasmobranchs can sense the weak electric field signals of marine environment and other lives to adjust follow‐up activities by the jelly in their ampullae of Lorenzini, which provides a new research route for the development of ocean exploration, locating of underwater object, underwater navigation and communication. Inspired by such a characteristic of jelly, this paper presents a novel electric‐field‐sensitive hydrogel in response to weak electric field stimuli in surroundings. The hydrogel is made from I‐carrageenan (IC) and cellulose nanocrystals (CNCs) by the way of blending. The effects of CNCs on the performances of hydrogels have been investigated via the characterization of both IC/CNC blending hydrogel and pure IC hydrogel. Swelling experiments show that the equilibrium swelling ratio of hydrogel is positively related to the mass ratio of IC to CNCs. Electric field sensitivity experiments indicates that the IC/CNC blending hydrogel has a higher sensitivity than the pure IC hydrogel by comparing the bending angles of hydrogels under different electric fields, and the maximum bending angle, 0.5°, of blending hydrogel remains under the 1 mV/cm electric field. The blending hydrogel sensitive to weak electric field stimuli in this paper may provide an alternative strategy to develop intelligent response‐type materials for applications of efficient underwater sensors and actuators.

Marine mammal sensory systems: Special issue overview.

Marine mammals are a unique group of organisms that are secondarily adapted to the aquatic environment. Their specific lifestyle requires numerous adaptations of anatomy and physiology in general, and sensory physiology in particular. During the course of evolution, marine mammal senses changed to fit with the specific requirements of underwater sensing, while at the same time retaining aerial sensing to various degrees. In this special issue, state of the art science in the field of marine mammal sensory research is reported for representatives of all marine mammal groups, unfortunately with the exclusion of the polar bear. The articles focus on somatosensation of the glabrous skin of cetaceans and mechanoreception, including haptics, hydrodynamics, and acoustics, to chemoreception. Articles even deal with electroreception, highlighting that the bottlenose dolphin can perceive weak electric stimuli, and vision, indicating that harbor seals are able to derive temporal information from an optical stimulus. Altogether this special issue illustrates the diversity of research in the field regarding sensory systems, species, or experimental approaches. The strength of this special issue lies in the combination of carefully conducted anatomical studies paired with observations and behavioral studies attempting to relate "form" and "function" as well as in the many impulses and future avenues mentioned by numerous contributions.

Effect of Mindful Observation Attitude on Perception and Avoidance thresholds of Weak Electrical Stimuli at the Body Surface

Effect of Mindful Observation Attitude on Perception and Avoidance thresholds of Weak Electrical Stimuli at the Body Surface

Solvent-free ionic silica nanofluids: Smart lubrication materials exhibiting remarkable responsiveness to weak electrical stimuli

Solvent-free ionic nanofluids (NFs) are promising smart lubrication materials due to their remarkable stimuli responsiveness to an external electric field. In this study, four kinds of silica (SiO2) NFs with diverse corona molecule structures were successfully synthesized. Effects of NFs’ structures on their physic-chemical properties and lubricity were investigated. In particular, nanostructures of the tribofilms were comprehensively characterized for shedding light on lubricating mechanisms of the NFs. Our results demonstrate that the newly synthesized NFs exhibit excellent lubrication performance and their lubricity displays remarkable electrical responsiveness. Applying even a rather low electrical potential, e.g. 1.5 V, gives rise to significant and immediate friction reduction. Moreover, lubricity and electrical responsiveness of the NFs are closely dependent on structures of the corona layers. Interestingly, our work provides direct evidence that feeding NFs onto the friction zone expedites growth of a robust tribofilm consisting mainly of SiO2 nanoparticles and tribochemical products. This work opens up new opportunities for tuning structures and functionalities of boundary layers of numerous motion components by tailoring architectures of NFs and controlling the electrical stimuli.

Voltage-dependent gating of SV channel TPC1 confers vacuole excitability

In contrast to the plasma membrane, the vacuole membrane has not yet been associated with electrical excitation of plants. Here, we show that mesophyll vacuoles from Arabidopsis sense and control the membrane potential essentially via the K+-permeable TPC1 and TPK channels. Electrical stimuli elicit transient depolarization of the vacuole membrane that can last for seconds. Electrical excitability is suppressed by increased vacuolar Ca2+ levels. In comparison to wild type, vacuoles from the fou2 mutant, harboring TPC1 channels insensitive to luminal Ca2+, can be excited fully by even weak electrical stimuli. The TPC1-loss-of-function mutant tpc1-2 does not respond to electrical stimulation at all, and the loss of TPK1/TPK3-mediated K+ transport affects the duration of TPC1-dependent membrane depolarization. In combination with mathematical modeling, these results show that the vacuolar K+-conducting TPC1 and TPK1/TPK3 channels act in concert to provide for Ca2+- and voltage-induced electrical excitability to the central organelle of plant cells.

Prepulse inhibition of the blink reflex is abnormal in functional movement disorders.

Patients with functional movement disorders also typically have functional somatic symptoms, including pain, fatigue, and sensory disturbance. A potentially unifying mechanism for such symptoms is a failure in processing of sensory inputs. Prepulse inhibition is a neurophysiological method that allows for the study of preconscious somatosensory processing. The objective of this study was to assess prepulse inhibition in patients with functional movement disorders and healthy control subjects. We analyzed the effect of a weak electrical stimulus to the index finger (prepulse) on the magnitude of the R2 response of the blink reflex induced by electrical stimuli delivered to the supraorbital nerve in 22 patients with clinically established functional movement disorders and 22 matched controls. Pain, depression, anxiety, and obsessive-compulsive symptoms were assessed using self-rated questionnaires. In addition, in patients we assessed motor symptom severity. Prepulses suppressed the R2 response of the blink reflex in both groups, by 36.4% (standard deviation: 25.6) in patients and by 67.3% (standard deviation: 16.4) in controls. This difference was significant (P < 0.001). There was no significant correlation between motor and nonmotor symptom measures and prepulse inhibition size. Impaired prepulse inhibition of the blink reflex suggests an abnormal preconscious processing of somatosensory inputs, which can be interpreted within predictive coding accounts of both functional movement disorders and functional somatic syndromes. Our results, along with previous findings of a reduced prepulse inhibition in fibromyalgia syndrome, support a possible unified pathophysiology across functional neurological and somatic syndromes with noteworthy implications for diagnostic classification and development of novel biomarkers and treatments. © 2019 International Parkinson and Movement Disorder Society.

Biases in tactile localization by pointing: compression for weak stimuli and centering for distributions of stimuli.

Weak electrocutaneous stimuli applied to the forearm are erroneously localized toward its middle (Steenbergen P, Buitenweg JR, Trojan J, Veltink PH. Exp Brain Res 232: 597-607, 2014). We asked whether mechanical touch stimuli exhibit a similar bias and whether the bias is toward the middle of the forearm or toward the middle of the recent stimulus distribution. In experiments 1 and 2, participants ( n = 12 and n = 10) localized by pointing von Frey filaments applied to four locations on the dorsal forearm. Individually adjusted weak and strong stimuli ( experiment 1) or two levels of strong stimuli ( experiment 2) were presented in single sessions in random order. Weaker stimuli were localized with greater variability than the strong, with compression toward the middle of the forearm. Responses to the two levels of strong stimuli did not differ. In experiment 3, participants ( n = 16) were presented two spatially offset stimulus distributions (8 cm center-to-center), each offset from the forearm middle, on 2 different days. Out of four target locations comprising each distribution, two were shared. Responses to weak stimuli were compressed compared with responses to strong stimuli. Importantly, biases for the common targets had opposite directions, each being toward the middle of the distribution within which targets were presented. Responses to strong stimuli also exhibited a distribution-dependent bias, a 2-cm overall shift across the forearm midpoint. We conclude that touch localization is subject to intensity-dependent biases determined by the recent history of stimulation and possibly also by the available or perceived response space. NEW & NOTEWORTHY Recent findings show that weak electrical stimuli applied to the forearm are mislocalized toward the forearm middle, relative to strong stimuli. We found that weak mechanical stimuli are similarly mislocalized. The bias changed if, as a group, stimuli were not centered on the forearm middle: weak stimuli gravitated toward the center of prior stimulation. Localization of strong stimuli was also biased, consistent with the tendency to center responses within the available response space.

Microprocessor-based prototype bycatch reduction device reduces bait consumption by spiny dogfish and sandbar shark

Abstract Elasmobranchs contribute heavily to bycatch in longline fisheries globally, and an effective method of deterring them from baited fishing gear is needed. Electrosensory stimulus holds promise as a method of disrupting elasmobranch close-range feeding responses as their electric sense guides their final strike during prey capture. We used laboratory experiments to test the hypothesis that weak electric stimuli generated by a prototype electronic bycatch reduction device (BRD) could deter sandbar shark (Carcharhinus plumbeus) and spiny dogfish (Squalus acanthias) from eating bait. Voltage gradients &amp;lt;1 mV cm−1 at the location of bait were produced by an Arduino microcontroller powered by a 9 V battery and attached to carbon electrodes. Median bait consumption by groups of juvenile sandbar shark declined by 74% when bait was located 10 cm vs. 2 m from active electrodes. Spiny dogfish median bait consumption halved when bait was located 10 cm from active vs. inactive electrodes. Although laboratory studies often produce a larger effect for electrosensory shark deterrents than can be demonstrated during field trials, if the effects seen in our laboratory studies produced similar effects in the field, it could meet fishermen’s requirements for a BRD.

Pacing Hippocampal Sharp-Wave Ripples With Weak Electric Stimulation.

Sharp-wave ripples (SWRs) are spontaneous neuronal population events that occur in the hippocampus during sleep and quiet restfulness, and are thought to play a critical role in the consolidation of episodic memory. SWRs occur at a rate of 30–200 events per minute. Their overall abundance may, however, be reduced with aging and neurodegenerative disease. Here we report that the abundance of SWR within murine hippocampal slices can be increased by paced administration of a weak electrical stimulus, especially when the spontaneously occurring rate is low or compromised. Resultant SWRs have large variations in amplitude and ripple patterns, which are morphologically indistinguishable from those of spontaneous SWRs, despite identical stimulus parameters which presumably activate the same CA3 neurons surrounding the electrode. The stimulus intensity for reliably pacing SWRs is weaker than that required for inducing detectable evoked field potentials in CA1. Moreover, repetitive ~1 Hz stimuli with low intensity can reliably evoke thousands of SWRs without detectable LTD or “habituation.” Our results suggest that weak stimuli may facilitate the spontaneous emergence of SWRs without significantly altering their characteristics. Pacing SWRs with weak electric stimuli could potentially be useful for restoring their abundance in the damaged hippocampus.

The effects of transcranial direct current stimulation on conscious perception of sensory inputs from hand palm and dorsum.

Conscious perception of sensory signals depends in part on stimulus salience, relevance and topography. Letting aside differences at skin receptor level and afferent fibres, it is the CNS that makes a contextual selection of relevant sensory inputs. We hypothesized that subjective awareness (AW) of the time at which a sensory stimulus is perceived, a cortical function, may be differently modified by cortical stimulation, according to site and type of the stimulus. In 24 healthy volunteers, we examined the effects of transcranial direct current stimulation (tDCS) on the assessment of AW to heat pain or weak electrical stimuli applied to either the hand palm or dorsum. We also recorded the vertex-evoked potentials to the same stimuli. The assessment was done before, during and after cathodal or anodal tDCS over the parietal cortex contralateral to the hand receiving the stimuli. At baseline, AW to thermal stimuli was significantly longer for palm than for dorsum (P<0.01), while no differences between stimulation sites were observed for the electrical stimuli. Both cathodal and anodal tDCS caused a significant shortening of AW to thermal stimuli in the palm but not in the dorsum, and no effects on AW to electrical stimuli. Longer AW in the palm than in the dorsum may be attributable to differences in skin thickness. However, the selectivity of the effects of tDCS on AW to thermal stimulation of the glabrous skin reflects the specificity of CNS processing for site and type of sensory inputs.

P 30. The effects of transcranial direct current stimulation on conscious perception of sensory inputs from hand palm and dorsum

Conscious perception of sensory inputs is dependent on the salience and relevance given to them. As a consequence, there can be differences in subjective awareness (AW) of the timing of sensory perception according to site and type of the stimulus. Since this is a cortical function, it might be susceptible to modification through brain stimulation. To characterize differences in AW and investigate the effects of transcranial direct current stimulation (tDCS) on the conscious perception of sensory inputs from glabrous and hairy skin. In 14 healthy volunteers, we applied heat pain and weak electrical stimuli to the hand palm and dorsum while subjects were assessing the time of sensory perception through the Libet’s clock (Libet et al., Brain 1983;106:623–42). In brief, subjects were requested to state the position of the clock’s hand at the time they felt the stimulus. Latency of AW was calculated as the difference between the actual time at which the stimulus was issued and its subjective assessment. In order to assess whether the cortex’s role in processing sensory inputs differs for stimulus site and type, we examined the effects on AW of cathodal (inhibitory) tDCS over the parietal cortex contralateral to the hand receiving thermal and electrical stimuli. Latency of AW was significantly longer for thermal than for electrical stimuli, in correspondence with the different conduction velocity of the axons involved. It was also longer for palm than for dorsum for thermal stimulation ( p < 0.01) but no differences between stimulation site were observed for the electrical stimuli. Furthermore, tDCS induced a significant shortening of AW to thermal stimuli in the palm but not in the dorsum and no effects were seen with electrical stimuli. Longer latency of AW in the palm than in the dorsum is attributable to the thickness of the skin in the hand palm, which leads to a deeper location of the receptors. These differences are not seen with electrical stimuli because they activate directly the subcutaneous myelinated axons. The finding that tDCS caused a change in latency of AW exclusively to thermal stimulation of the glabrous skin indicates a cortical control of nociceptive inputs that is specific for hand palm and could be related to the need to hold potentially harmful objects.

OP 10. Phasic modulation of somatosensory perception by means of transcranial alternating current stimulation

Ongoing oscillations are associated with brain functions such as somatosensory perception. For example, the amplitude of the sensorimotor mu rhythm can be linked to the perception of near-detection-threshold somatosensory stimuli ( Linkenkaer-Hansen et al., 2004 ). Furthermore the phase of neuronal oscillations affects the perception of near-threshold stimuli ( Busch et al., 2009 ). Transcranial alternating current stimulation (tACS) may offer the possibility to modulate oscillatory activity. Recently it was shown that tACS increased the amplitude of visual alpha oscillations ( Zaehle et al., 2010 ) and had a phase dependent influence on auditory perception ( Neuling et al., 2012 ). We examined the effect of tACS applied at participants’ individual mu frequency on threshold levels of somatosensory perception. We hypothesized that (a) tACS modulates somatosensory perception thresholds as compared to sham and (b) perception thresholds vary as a function of the phase of tACS. In a randomized, single-blinded, crossover design, 17 participants (mean age: 27; female: 10) underwent a combined EEG/tACS experiment in two separate sessions (real or sham tACS). In the beginning, subject’s individual mu frequency was derived from the event-related desynchronization over the left somatosensory cortex (S1) induced by electric pulses to the right index finger ( Fig. 1 b). Subsequently, somatosensory detection thresholds were determined in a block of 16 min using an adaptive staircase procedure of weak electric stimuli that were presented with electrodes at the right index finger. During the second third of the task 5 min of tACS was applied at the individual mu frequency in a bilateral montage over both primary somatosensory cortices (S1). For sham, 30 s of 1 mA random noise stimulation was applied ( Fig. 1 a). Behavioral performance was assessed with respect to (i) an average effect of tACS as compared to sham and (ii) a modulation dependent on the tACS phase. No differences in the average somatosensory perception thresholds were observed between real and sham stimulation. However, during tACS, somatosensory detection thresholds changed as a function of the phase of tACS. Thresholds were differing maximally for stimuli presented at opposite phases in both maxima of the tACS signal curve( Fig. 2 ). We conclude that tACS applied at the individual mu frequency over S1 is capable of modulating perception of near-threshold somatosensory stimuli in a phase-dependent manner. Our findings suggest that functionally relevant intrinsic oscillations may be modulated using non-invasive brain stimulation.

A critical speed for gating of tactile detection during voluntary movement

This study addressed the paradoxical observation that movement is essential for tactile exploration, and yet is accompanied by movement-related gating or suppression of tactile detection. Knowing that tactile gating covaries with the speed of movement (faster movements, more gating), we hypothesized that there would be no tactile gating at slower speeds of movement, corresponding to speeds commonly used during tactile exploration (<200mm/s). Subjects (n=21) detected the presence or absence of a weak electrical stimulus applied to the skin of the right middle finger during two conditions: rest and active elbow extension. Movement speed was systematically varied from 50 to ~1,000mm/s. No subject showed evidence of tactile gating at the slowest speed tested, 50mm/s (rest versus movement), but all subjects showed decreased detection at one or more higher speeds. For each subject, we calculated the critical speed, corresponding to the speed at which detection fell to 0.5 (chance). The mean critical speed was 472 mm/s and >200mm/s in almost all subjects (19/21). This result is consistent with our hypothesis that subjects optimize the speed of movement during tactile exploration to avoid speeds associated with tactile gating. This strategy thus maximizes the quality of the tactile feedback generated during tactile search and improves perception.

Effect of repeated and prolonged stress stimuli on the plasma prolactin concentration in sheep.

The effect of repeated and prolonged stress-stimuli applied during 3 days on the plasma prolactin concentration in sheep, in anoestrous, prooestrous and pregnant animals were studied. The following results were obtained: Repeated and prolonged weak electric stimuli applied in the form of footshocks in sheep during 3 days elicited a rise of mesor plasma concentration. The magnitude and the onset of this rise was not associated and dependent on the physiological state of animals. The mesor values of plasma prolactin concentration in all groups of animals except prooestrous ewes on the day following stimulation returned to their prestressing levels. Repeated and prolonged stimuli disturbed circadian rhythm of prolactin secretion existing only in prooestrous ewes, i.e. they caused its disappearance on the days during stimulation and its reappearance on the day following stimulation but at an accelerated and inverse time of the day to that found before stimulation. The induced rise of plasma prolactin concentration in anoestrous and pregnant ewes on the days during electric stimulation showed, according to Cosinor analysis, all features characteristic for acrophase of the circadian rhythm. This phenomenon may be considered as induced acrophase in stress condition.

Evoked magnetic fields as a tool to optimize therapeutic electrical stimulation of the sacral surface

Magnetoencephalography (MEG) was used to measure the somatosensory evoked fields in six healthy males undergoing sacral surface therapeutic electrical stimulation, a recently introduced treatment for chronic urinary dysfunction. This study was performed to investigate the utility of MEG to optimize the stimulation parameters. Strong or weak electrical stimuli were applied to small or large surface electrodes placed over the bilateral sacral surfaces. The peak latency and strength of the equivalent current dipole were evaluated at the first peak originating from the primary somatosensory cortex (M30). There was no difference in M30 latency in response to stimulation intensity or electrode size. However, a larger equivalent current dipole strength was obtained in response to higher stimulus intensities, which indicated a more effective stimulus on the sacral surface. The present MEG study shows that stronger stimuli given through large electrodes evoke larger responses than small stimuli through small electrodes. The study also suggests that MEG can be used as an objective tool to monitor whether therapeutic stimulation parameters are appropriate.

Bilateral representation in the deep cerebellar nuclei

The cerebellum is normally assumed to represent ipsilateral movements. We tested this by making microelectrode penetrations into the deep cerebellar nuclei (mainly nucleus interpositus) of monkeys trained to perform a reach and grasp task with either hand. Following weak single electrical stimuli, many sites produced clear bilateral facilitation of multiple forelimb muscles. The short onset latencies, which were similar for each side, suggested that at least some of the muscle responses were mediated by descending tracts originating in the brainstem, rather than via the cerebral cortex. Additionally, cerebellar neurones modulated their discharge with both ipsilateral and contralateral movements. This was so, even when we carefully excluded contralateral trials with evidence of electromyogram modulation on the ipsilateral side. We conclude that the deep cerebellar nuclei have a bilateral movement representation, and relatively direct, powerful access to limb muscles on both sides of the body. This places the cerebellum in an ideal position to coordinate bilateral movements.

Effects of The Remote C Fibres Stimulation Induced by Capsaicin on the Blink Reflex in Chronic Migraine

The aim of this study was to test the function of the diffuse noxious inhibitory control system (DNIC) in chronic and episodic migraine, exploring the blink reflex (BR) modifications induced by topical application of capsaicin on the hand. We evaluated 11 migraine without aura (MA) and nine chronic migraine (CM) patients during the not symptomatic phase; they were compared with 14 non-headache subjects (N). The BR was elicited by weak electrical stimuli delivered to the right supraorbital nerve; it was obtained 10 min and 20 min after the application of 1 ml of 3% capsaicin in a cream base (Teofarma) on the skin of the dorsum of the right hand, and 60 min after capsaicin removal. The subjective pain sensation induced by capsaicin was significantly increased in CM with respect to both MA patients and normal subjects; the R2 area was increased in CM patients during capsaicin application, with respect to controls and MA patients, who did not exhibit any reflex alterations. These results may suggest a failure of DNIC and a disturbed control of the trigeminal reflex at the central level, linked with migraine frequency.

Stochastic Resonance in the Motor System: Effects of Noise on the Monosynaptic Reflex Pathway of the Cat Spinal Cord

In sensory systems, the presence of a particular nonzero level of noise may significantly enhance the ability of an individual to detect weak sensory stimuli through a phenomenon known as stochastic resonance (SR). The aim of this study was to demonstrate if such phenomenon is also exhibited by the motor system; in particular, in the Ia-motoneuron synapse of the cat spinal cord. Monosynaptic reflexes elicited by periodic electrical stimulation to the medial gastrocnemius nerve were recorded in the L(7) ventral root (or in single motoneurons) of decerebrated cats. Random stretches (mechanical noise) were applied to the lateral gastrocnemius plus soleus muscle by means of a closed-loop mechanical stimulator-transducer. In all cats, we observed the SR phenomenon. The amplitude of the monosynaptic reflexes (or number of action potentials recorded in the motoneurons) evoked by the weak electrical stimuli applied to the medial gastrocnemius nerve were an inverted U-like function of the mechanical noise applied to the lateral gastrocnemius plus soleus muscle. A significant maximum value in the amplitude of the monosynaptic responses was reached with a particular noise amplitude value. Numerical simulations on a model of the monosynaptic reflex pathway qualitatively reproduce this stochastic resonance behavior. We conclude that the monosynaptic reflex response elicited by Ia afferents is optimized by the noisy stretching of a synergistic muscle. Our study provides the first direct demonstration that the motor system, and not only the sensory systems, exhibits the SR phenomenon.

Microstimulation of the Midbrain Tegmentum Creates Learning Signals for Saccade Adaptation

Error signals are vital to motor learning. However, we know little about pathways that transmit error signals for learning in voluntary movements. Here we show that microstimulation of the midbrain tegmentum can induce learning in saccadic eye movements in monkeys. Weak electrical stimuli delivered approximately 200 ms after saccades in one horizontal direction produced gradual and marked changes in saccade gain. The spatial and temporal characteristics of the produced changes were similar to those of adaptation induced by real visual error. When stimulation was applied after saccades in two different directions, endpoints of these saccades gradually shifted in the same direction in two dimensions. We conclude that microstimulation created powerful learning signals that dictate the direction of adaptive shift in movement endpoints. Our findings suggest that the error signals for saccade adaptation are conveyed in a pathway that courses through the midbrain tegmentum.