Spring is moving to summer; the birds are singing, the lambs are leaping, and the bioelectricity field is buzzing! This Buzz emphasizes advances in wearable electrical technologies for improving skin wound healing, artificial skin sensors, relief from tinnitus, monitoring pediatric cerebral hydrodynamics, and assessing animal well-being. It also reveals how ion channels control cancer cell metastasis and cold-induced tooth pain, and a role for sodium-glucose co-transporters in taste sensation.
A Wee Bug Zapper: A Wearable Nanogenerator to Co-deliver Electrical Stimulation and Antibiotics to Prevent Skin Wound Infection
This is particularly relevant to this Bioelectricity special issue on Microbial Electrophysiology. Du et al. describe flexible, wearable patches that use electrical stimulation to prevent skin wound bacterial infection and to aid healing.
Shuo Du, Nuoya Zhou, Ge Xie, Yu Chen, Huinan Suo, Jiangping Xu, Juan Tao, Lianbin Zhang, Jintao Zhu. Surface-engineered triboelectric nanogenerator patches with drug loading and electrical stimulation capabilities: Toward promoting infected wounds healing. Nano Energy 2021;85:106004.
Du et al. have leveraged wearable triboelectric nanogenerator (TENG) technology to configure a miniaturized electrical stimulation device intended to promote healing of cutaneous wounds and prevent bacterial infection. TENGs convert mechanical energy into electricity through the effects of triboelectrification and electrostatic induction, so mechanical body movements can power a wearable electrical stimulation device without an external power source.
Bacterial infection is a serious complication for nonhealing wounds and correlates directly with poor outcome. Previous efforts to apply TENGs in an antibacterial context have not overcome key challenges, making small devices that deliver sufficient high-intensity pulsed electric fields (lethal damage to bacterial membranes at >106 V/m) that are also safe for the wearer. Du et al. fabricated a surface-engineered electrode by growing 10 μm thick magnesium-aluminum-layered double hydroxide (LDH) nanosheets on flexible Al foils (LDH@Al). An arch-shaped TENG patch comprising two friction layers was prepared with a lower LDH@Al layer (positive in triboelectric series) and an upper flexible polytetrafluoroethylene polymer substrate (negative in triboelectric series). To demonstrate the output performance of the device an electrode with an area of 49 cm2 was prepared that lit 180 light-emitting diode (LED) lamps when struck with the palm of the hand.
To increase the device's antibacterial capacity, a hydrophilic antibiotic (minocycline) was incorporated within the LDH@Al layer (MLDH@Al). When tested in vitro, delivery of 2 V for 24 h using LDH@Al electrodes significantly inhibited growth of Escherichia coli and Staphylococcus aureus bacteria, but identical stimulation parameters using the MLDH@Al electrode doped with 5 μg/mL minocycline almost completely killed both bacterial species. Membrane damage was evident in both species, but S. aureus was more sensitive.
In vitro tests demonstrated that electrical stimulation of fibroblast cultures at 1 V (LDH@Al electrodes) doubled cell viability compared with controls, and this increased with voltage, rising to ∼4.5-fold improvement at 8 V. Furthermore, in an in vitro scratch wound assay fibroblast migration was enhanced by 2 V stimulation delivered by LDH@Al at 24 and 48 h compared with controls. Together this suggests a positive influence of electrical stimulation on fibroblast survival and migration, which could aid wound healing.
Of importance, the stimulator was then tested in vivo on full thickness wounds in adult mouse skin that were intentionally infected with S. aureus. A miniaturized TENG device was attached over the wound and the mouse's own movements generated AC voltage (0.5–4.5 V) and current (5–40 nA). Ten days after injury the wounds in the group wearing the antibiotic-containing TENG device were healed completely in contrast to those in the control group (wound area ∼31% of original), the group wearing the TENG device not loaded with antibiotic (∼10% original area), the group wearing an (inactive) LDH@Al electrode (∼30% original area), and the antibiotic-loaded (but inactive) MLDH@Al material (∼11% original area). Therefore, the combination of the antibiotic and stimulation delivered by the TENG device was more beneficial than either the antibiotic alone or the electrical stimulation alone.
These results offer promise for wearable electrical stimulation devices that free the wearer from the requirement for an external, wired battery pack, provided they prove robust enough to maintain safe levels of stimulation for prolonged periods. Because even small frictional movements between the layers in TENGs (e.g., breathing) can generate electrical output, such devices have the potential for use in bed-bound patients, who are especially susceptible to medically recalcitrant infected pressure ulcers. The ability to dope the material layers with specific drugs provides additional exciting possibilities in the context of personalized medicine for other maladies.
Getting a Move on: An Elastin Peptide/Ion Channel Complex Regulates Pancreatic Cancer Cell Migration
Pancreatic ductal adenocarcinoma is the most common pancreatic cancer and its highly aggressive nature makes it difficult to treat. Lefebvre et al. have identified a novel membrane protein complex that promotes tumor cell migration and may provide a new therapy target.
Thibaut Lefebvre, Pierre Rybarczyk, Clara Bretaudeau, Alison Vanlaeys, Rémi Cousin, Sylvie Brassart-Pasco, Denis Chatelain, Isabelle Dhennin-Duthille, Halima Ouadid-Ahidouch, Bertrand Brassart, Mathieu Gautier. TRPM7/RPSA complex regulates pancreatic cancer cell migration. Front Cell Dev Biol 2020;8:549.
Pancreatic ductal adenocarcinoma (PDAC) is a highly metastatic cancer. Tissue remodeling in PDAC generates a stromal microenvironment of extracellular matrix components that promotes cell migration and rapid disease progression. Interaction of tumor cell membrane receptors with the extracellular matrix leads to matrix degradation and release of fragments called “matrikines,” including a subtype of elastin-derived peptides (EDPs) called “elastokines.” EDPs stimulate cancer cell migration by interacting with their membrane receptor, ribosomal protein SA (RPSA). The Bioelectricity interest relates to the involvement of the transient receptor potential melastatin-related 7 (TRPM7) ion channel in regulating PDAC cell migration and invasion.
Using a human pancreatic cancer cell line, Lefebvre et al. demonstrated that the EDPs AG-9 and VG-6 increased cell migration in a Boyden chamber assay. Mechanistically, migration required TRPM7 channel activity because it was impeded in cells transfected with an siRNA targeting TRPM7. Electrophysiological patch clamp recordings showed that AG-9 treatment reversibly stimulated magnesium-inhibited cation currents owing to TRPM7 channel activity. On a tissue level RPSA was expressed strongly in human PDAC tumors, and at the cellular level, immunostaining of TRPM7 and RPSA were colocalized in the human pancreatic cancer cell line, implying formation of a TRPM7/RPSA membrane complex after treatment with AG-9. Collectively, the data suggest that the TRPM7/RPSA complex regulates human pancreatic cancer cell migration.
The authors hypothesize that the desmoplastic stroma releases EDPs during pancreatic tumorigenesis, which induces TRPM7/RPSA complex formation in PDAC cells, promoting their migration (therefore, metastasis). This complex may therefore be a promising target for future treatments in PDAC.
Have a (M)ice TRP: Transient Receptor Potential Channel Subtype 5 Ion Channel Signaling Underpins Painful Cold Sensation in Teeth
For many people biting into something cold can be unpleasant, but the mechanism responsible for that painful sensation has been elusive. Bernal et al. used a novel ex vivo mouse jaw-nerve preparation from transgenic mice to implicate the odontoblast transient receptor potential channel subtype 5 (TRPC5) as the cold sensor in tooth pain.
L. Bernal, P. Sotelo-Hitschfeld, C. König, V. Sinica, A. Wyatt, Z. Winter, A. Hein, F. Touska, S. Reinhardt, A. Tragl, R. Kusuda, P. Wartenberg, A. Sclaroff, J. D. Pfeifer, F. Ectors, A. Dahl, M. Freichel, V. Vlachova, S. Brauchi, C. Roza, U. Boehm, D. E. Clapham, J. K. Lennerz, K. Zimmermann. Odontoblast TRPC5 channels signal cold pain in teeth. Sci Adv 2021;7:eabf5567.
To carry out its main function of breaking down food the outer layer of each tooth is a hard, mineralized material in contrast to the inner core (pulp), which contains dense networks of blood vessels and nerves that enter through the root. The dentin, a dense calcium matrix comprising most of the tooth volume, sits between the enamel and the pulp. It is laid down and maintained by postmitotic odontoblast cells that reside at the outer margin of the pulp and extend tubular processes into fluid-filled channels in the dentin. Specialized trigeminal nerve ramifications form the “plexus of Raschkow” near the odontoblast cell bodies, extending sensory nerve terminals onto the odontoblast processes within the dentin tubules. This permits the plexus to monitor painful sensations and to regulate inflammatory events.
It has been proposed that external thermal or mechanical stimuli can activate sensory nerve endings inside the teeth because the dentinal canals provide a hydraulic link between the stimulus and the nerve endings at the pulp–dentin boundary. But evidence for that model is incomplete. Transient receptor potential (TRP) ion channels are implicated in temperature sensing because some subtypes are activated by cooling and TRPM8 and TRPA1 subtypes act together as temperature sensors in skin. However, acutely isolated human odontoblasts express only TRPM8, not TRPA1, and in rat teeth the roles of TRPM8 and TRPA1 in situ are unclear. The TRPC5 ion channel subtype is present in trigeminal and dorsal root ganglion neurons and is cold sensitive in a heterologous expression system, but whether it is a cold sensor in native cells was not known. Therefore, Bernal et al. explored the roles of TRPA1, TRPM8, and TRPC5 ion channels in cold sensing in teeth.
Initial experiments used transgenic TRPC5, TRPA1, and TRPM8 null mice in an inflammatory tooth pain model that exploited a paradoxical increase in sucrose consumption to measure pain. Only in the TRPC5−/− mice was sucrose consumption reversed to the levels of uninjured controls, indicating that TRPC5 channel is relevant to inflammatory pain.
For functional examination of the entire tooth sensory system, Bernal et al. developed a novel intact mouse mandible-inferior alveolar nerve (jaw nerve) ex vivo preparation to record action potentials from the inferior alveolar nerve upon cold stimuli. When the intact jaw was exposed to cold, high levels of tooth action potential activity were detected in cold receptors. Adding pharmacological TRPC5 channel blockers to the preparation reduced the cold responses by ∼59% but drugs that modulate TRPM8 had no effect. In jaw-nerve preparations made from TRPC5/A1 double-knockout animals, the cold responses were reduced to <3%, and pharmacological modulation of TRPM8 channels had no effect. Collectively, the data indicate that TRPC5 and TRPA1 are sufficient for cold sensation in healthy intact teeth.
TRPC5 protein was quantified in trigeminal neurons using multiphoton microscopy in retrogradely labeled whole trigeminal neurons of reporter mice expressing tau-green fluorescent protein under the control of the TRPC5 promoter. In the mandibular and maxillary branches, which have the largest density of dental primary afferent neurons, 3.5% of the dental primary afferent neurons were TRPC5+. Together with electrophysiological recordings from cultured neurons, the data demonstrate that TRPC5 is present in the cells and that they have membrane channels with characteristics of TRPC5, but in healthy teeth TRPC5 cold responses are relatively small.
Histological examination of mouse molars revealed TRPC5 labeling in predentinal odontoblasts in pulp regions adjacent to the root, with processes of TRPC5+ odontoblasts in dentinal tubules contacting sensory axons at the pulp–dentin boundary and entering tubules. TRPC5 was not in pulp fibroblasts or in sensory axons radiating through the root into the nerve plexus of Raschkow or in the inferior alveolar nerve. Therefore, TRPC5 expression was restricted to the odontoblast layer but TRPM8 and TRPA1 are more widely expressed in mouse and human teeth, suggesting a unique association between TRPC5 and odontoblasts in mice.
Bernal et al. next examined human teeth. Histological examination identified TRPC5 in the odontoblast layer, more TRPC5 than TRPM8 in sensory nerves at the pulp–dentinal margin, and TRPC5+ fibers within the sensory transduction region of dentinal tubules. Human teeth with inflammatory pulpitis had increased TRPC5 in sensory nerves and less TRPM8.
The ex vivo jaw-nerve model in transgenic mice has resolved questions about dental sensation, demonstrating that TRPC5 and TRPA1 ion channels act as molecular cold sensors in teeth, with odontoblasts serving as the site of cold transduction.
Minding the Baby: A Skin Interface Device to Monitor Pediatric Cerebral Hemodynamics Wirelessly
Continuous monitoring of cerebral hemodynamics in babies and children can be necessary for clinical care, but irritating skin adhesives and the need for wires on the monitoring device impair natural movements, prevent cuddling with carers and parents, and can interfere with clinical procedures. Rwei et al. describe a miniaturized, soft, flexible device for real-time wireless monitoring of systemic and cerebral hydrodynamics.
Alina Y. Rwei, Wei Lu, Changsheng Wu, Kelia Human, Emily Suen, Daniel Franklin, Monica Fabiani, Gabriele Gratton, Zhaoqian Xie, Yujun Deng, Sung Soo Kwak, Lizhu Li, Carol Gu, Alanna Liu, Casey M. Rand, Tracey M. Stewart, Yonggang Huang, Debra E. Weese-Mayer, and John A. Rogers. A wireless, skin-interfaced biosensor for cerebral hemodynamic monitoring in pediatric care. Proc Nat Acad Sci 117:31674–31684. DOI: 10.1073/pnas.2019786117.
The delicate tissues and vasculature of premature infants are especially prone to damage such as hemorrhage, venous obstruction, or cardiac issues and continuous monitoring of hydrodynamics is standard neonatal care. Measurements reported include oxygenation, heart rate, and other vital signs, but entanglement in wires, which could detach sensors, and the risk of skin damage by adhesive materials are problematic. This is particularly true for babies and small children who have delicate skin and do not understand the importance of keeping the device in place. Human contact and cuddling are important for welfare of babies and parents but the array of wires on existing devices can make parents and carers anxious to hold hospitalized children. Existing wireless monitoring methods (transcranial ultrasound, magnetic resonance imaging, and near infrared spectroscopy) are cumbersome and record only intermittently, so a portable wireless system is needed.
Rwei et al. describe a system comprising a photodiode array and two LEDs for simultaneous monitoring of systemic and cerebral hemodynamics. The flexible printed circuit board has a Bluetooth low-energy system and components for wireless communication and power regulation and a unit with an optical sensor. The whole device, measuring 33 × 16 × 3 mm, is encapsulated in a medical grade silicon polymer and weighs ∼2.8 g. A modular, replaceable battery is coupled to the device with magnets to facilitate replacement. The sensor unit has a pair of LEDs that emit at wavelengths of 740 and 850 nm with an array of photodiodes at source detector distances of 5, 10, 15, and 20 mm. A thin (100 μm) layer of poly-dimethylsiloxane (PDMS) forms optical widows between the sensors and the LEDs and photodiodes. An attractive aspect of the design is the use of inexpensive, readily available, off-the-shelf components.
The system was tested in a clinical setting on eight pediatric patients ranging in age from 2 months to 15 years. A range of skin colors was included to ensure wide utility. Predicted changes in cerebral blood flow were observed in subjects at various tilted or upright positions. Cerebral oxygenation was also measured in a 4-year-old girl during a 3-min clinical hypoxia challenge, confirming parallel results using a commercial system. These results, the relative ease of manufacture and low cost make this an attractive device design that should be able to find wide application, even in low-income settings.
Enjoying the Sweet with the Salty: The Physiology Behind the Appeal of Salted Caramel!
I did not understand as a child when my granny sprinkled salt on watermelon and when my local ice cream parlor served a bowl of salted pretzels on the side. Yasumatsu et al. (2020) reveal the science behind the magical appeal of such salty-sweet combinations; enhanced sugar perception by sodium glucose transporters.
Keiko Yasumatsu, Tadahiro Ohkuri, Ryusuke Yoshida, Shusuke Iwata, Robert F. Margolskee, Yuzo Ninomiya. Sodium-glucose cotransporter 1 as a sugar taste sensor in mouse tongue. Acta Physiol 2020;230:e13529.
Type 1 receptors (T1Rs) present in the tongue and gustatory epithelia are responsible for perception of sweet taste, with subunits contributing to variation in taste perception. However, sugar detection mechanisms independent of T1Rs have been reported, with sodium-glucose cotransporter 1 being implicated as a glucose sensor in intestinal epithelia. Yasumatsu et al. used wild-type (WT) mice and mice lacking the taste receptor subunit 3 gene (T1R3-KO) to explore sugar taste sensation in mouse tongue. They used electrophysiological recordings to identify which neuronal types and T1R types are involved, as well as exploring a potential role for sodium-glucose cotransporters (SGLTs) in sugar perception in mouse tongue.
Yasumatsu et al. used whole-nerve preparations of WT mouse chorda tympani and glossopharyngeal nerves to test responses to sweet compounds and short-chain glucose polymers with and without NaCl. When 10 mmol/L NaCl was present there was a significant enhancement of responses to sugars and a glucose analogue. But this enhancement was not induced by potassium chloride, monopotassium glutamate, citric acid, quinine sulfate, SC45647 (a noncaloric sweetener), or polycose (a glucose polymer). The enhanced nerve response was reduced by application of phlorizin (a competitive SGLT inhibitor) to the tongue, implicating SGLTs in the response.
Behavioral response measurements were then performed to examine the function of SGLTs in T1R3-KO mice. Mice licked more and intake was higher for the glucose plus NaCl solution than glucose alone and that this was suppressed by phlorizin, implicating SGLTs in the behavioral response, even in the absence of T1R3 and in support of the electrophysiological data from WT animals.
Collectively, the data provide functional evidence for a role for SGLTs in sugar sensing in anterior and posterior mouse tongue and suggest that taste cells connecting distinct nerve fiber types may be “calorie-sensing” cells that serve to identify high-energy foods for animals (and humans). The demonstration that NaCl enhances the sugar-induced firing of neurons in the taste pathway and that sugar solutions with NaCl added were favored by mice over sugar alone have inspired me to bake salted caramel brownies (in the interest of science, of course).
Ringing Off: Electric Shocks to the Tongue May Quiet Tinnitus
Tinnitus, a phantom auditory sensation of constant ringing or buzzing, affects about 10–15% of the population. Its impact on individuals ranges from mildly annoying to highly debilitating, but there is no clinically effective therapeutic drug or device. Conlon et al. present evidence from a large trial suggesting that mild electrical stimulation of the tongue, paired with auditory stimulation can alleviate tinnitus, with relief that persists for up to a year.
Brendan Conlon, Berthold Langguth, Caroline Hamilton, Stephen Hughes, Emma Meade, Ciara O. Connor, Martin Schecklmann, Deborah A. Hall, Sven Vanneste, Sook Ling Leong, Thavakumar Subramaniam, Shona D'Arcy, Hubert H. Lim. Bimodal neuromodulation combining sound and tongue stimulation reduces tinnitus symptoms in a large randomized clinical study. Sci Transl Med 12:eabb2830. DOI: 10.1126/scitranslmed.abb2830.
Neuromodulation using external electrical stimulation of the nervous system is emerging as an effective treatment for conditions including seizures, anxiety, inflammation, and depression. Conlon et al. studied co-presentation of electrical stimulation of the tongue with an auditory stimulus in a cohort of 326 people with tinnitus. Subjects were provided with a neuromodulation device consisting of wireless (Bluetooth) headphones that deliver acoustic stimuli, a paddle-like device with an array of 32 electrodes for electrical stimulation of the surface of the tongue, and a battery-powered controller. Participants were given one of three types of stimulation units: (1) a device that provided pure tones (500–800 Hz) and broadband background noise synchronized precisely with the electrical pulse, (2) a device in which there was a lag of between 30 and 50 ms between sound and tongue stimuli, or (3) a device with a longer delay of 550–950 ms and tones of 100–500 Hz. Sound and tongue sensitivity were adjusted for each individual's sensitivity (tongue stimulus was perceived like “pop rocks” fizzing candy). Treatment was applied for up to 1 h at a time for at least 36 h over the 12-week period.
Of the 84% of subjects who complied with the regimen at least 75% saw an improvement within 12 weeks, as judged by standard self-assessment tinnitus questionnaires. Impressively, a follow-up after 12 months found that 80% of the participants still had lower tinnitus scores, which sustained at about the same level overall across participants.
However, there is a caveat here; the study did not include a control group lacking bimodal stimulation, so there is a possibility that the placebo effect may have confounded the outcome. A future study that explores other variables alongside appropriate controls would clarify this interesting result.
More Than Skin Deep: Somatosensors with Feedback for Artificial Skin
Human machine interfaces (e.g., prosthetic limbs) and intelligent robotics would benefit from a “skin-like” interface that mimics the pain, temperature, and pressure sensory traits of natural skin, but their complexity has presented technical challenges. Impressively, Rahman et al. have produced a functional combination of stretchable pressure sensors, phase-changing oxide films and memristor elements that display traits of real-life sensory receptor systems.
Md. Ataur Rahman, Sumeet Walia, Sumaiya Naznee, Mohammad Taha, Shruti Nirantar, Fahmida Rahman, Madhu Bhaskaran, Sharath Sriram. Artificial somatosensors: feedback receptors for electronic skins. Adv Intell Syst 2020;2:2000094.
Incorporating sensory feedback into robotics could refine functional dexterity and there are also clear advantages for medical applications. For example, prosthetic limb wearers could “feel” their prosthetic fingers or toes, or the devices could be used to restore sensation after nerve damage. However, no system yet incorporates multiple sensory feedback systems akin to skin. Existing sensor systems are often based on data processing platforms using complementary metal oxide semiconductor (CMOS) devices, but incorporating multiple sensory systems (temperature, pain, pressure) would require multiple CMOS circuit units, adding bulk. Memristors (a portmanteau of “memory” and “resistor”) offer a solution. They are an electrical circuit component that limits or regulates the flow of electrical current, they “remember” the amount of charge that previously flowed through them without expending power, they have exceptional switching performance, and they work at the sub-nanoscale, making them attractive for applications with multiple sensory units.
Rahman et al. constructed solid-state artificial somatosensors from a combination of multiple functional units: decision-making memristor based on oxygen-deficient strontium titanate SrTiO3-x (STO), a pressure sensor made of a gold-coated stretchable PDMS elastomer, and a temperature trigger of a phase-change oxide (vanadium oxide, VO2). STO serves as the memristive material, PDMS provides excellent stretch properties, and VO2 undergoes insulator to metal transition in response to temperature. This unique phase-change property of VO2 was combined with the STO memristor to create VO2–STO-based artificial thermoreceptors and nociceptors that demonstrated critical functional aspects of the native nociceptor. The STO-based resistive switching memory serves as the decision-making element to evaluate threshold levels. This mimics signals sent by native thermal neurons to nociceptors, where amplitude thresholds are checked to choose whether an action potential will be sent to the central nervous system through the spinal cord. Rahman et al. tested the system and proved that it could operate as a nociceptor under “normal” conditions as well as mimicking allodynia (produces a response signal at sub-threshold values) and hyperalgesia (stronger response at an over threshold values).
Collectively, the data suggest that the technology can mimic many aspects of skin somatosensory responses, but further tests will be necessary to test and further refine aspects of the device's durability and long-term performance in situ.
The Neighs Have It: Electrical Recordings from Headbands May Reveal a Horse's Inner Feelings
Assessing the well-being of animals is challenging because it depends on behavioral, rather than verbal cues, which may be misinterpreted. Stomp et al. describe a wearable telemetric device that records electrical brain activity in free moving horses as a measure of their chronic welfare state.
M. Stomp, S. d'Ingeo, S. Henry, H. Cousillas, M. Hausberger. Brain activity reflects (chronic) welfare state: Evidence from individual electroencephalography profiles in an animal model. Appl Anim Behav Sci 2021;236:105271.
The environment in which an animal is kept can affect its levels of stress, anxiety, and overall wellbeing. Not all animals, or humans, are impacted in the same way, so identifying the influence of environmental conditions on chronic welfare can be difficult. In general, repetitive stereotypical behaviors are taken to indicate compromised animal welfare, but appropriate training is required for them to be meaningful. Electroencephalogram (EEG) recordings are a promising tool in this context because in humans a link has been described between EEG recordings and affective or cognitive states.
Different EEG wave types are characterized by their frequency; delta waves (0–3 Hz) are characteristic of deep sleep, gamma waves (>30 Hz) are linked with higher arousal states, theta waves (3–8 Hz) with low arousal, alpha waves (8–12 Hz) with an active awake state, and beta waves (12–30 Hz) with moderate arousal. Assessing the ratio of different wave types generates an EEG power spectrum, with a positive internal state associated with a higher slow wave/fast wave ratio. The power spectrum also provides information about differences in activity of left versus right brain hemispheres. A limitation of EEG recording is that it requires the subject to wear scalp electrodes hard wired to a recording device, and when used in animals they are usually shaved to improve electrode contact, or in some cases invasive electrodes are implanted. These constraints prevent assessment of free moving animals in natural conditions and may influence the result by causing a degree of stress or anxiety.
Stomp et al. used a telemetric EEG recording device with five electrodes built into a headband containing a Bluetooth transmitter. The electrodes were positioned using a conductive gel on the (unshaved) forehead over the frontal and parietal bones, with the ground electrode placed behind the ear. There were two cohorts; nine horses housed in typical stables (confined) and nine spending most of their time outdoors (leisure).
Horses were found to have individualistic, but consistent EEG profiles over two testing sessions that were not correlated with age or sex. The confined animals showed more right-hemisphere gamma wave activity, which in humans can be associated with anxiety, distraction, or depression. The leisure cohort had more left-hemisphere theta waves, which in humans can be indicative of a calm, attentive mind. However, the pattern of EEG laterality was less reflective of horse welfare than the power spectrum. Horses with indication of welfare alteration (stereotypic behaviors) were characterized by an EEG profile composed mainly of bilateral gamma waves, suggesting a perception bias of the environment. The horses with more theta waves were more positive toward humans, again suggesting a calm, relaxed mindset. Overall, the authors conclude that bilateral and left hemisphere theta activity is a marker of good welfare, whereas bilateral or right hemisphere production of gamma waves alerts potential welfare concern.
This study suggests the EEG recordings in free moving animals could be used alongside behavioral observations to reveal their mental state. It might also help to clarify whether brain-wave interpretations from humans translate directly to other species.
And that's the current Buzz until next time.