Non-invasive, opsin-free mid-infrared modulation activates cortical neurons and accelerates associative learning

Effect of terahertz waves on the aggregation behavior of neurotransmitters

Understanding the dynamics of neurotransmitters is crucial for unraveling synaptic transmission mechanisms in neuroscience. In this study, we investigated the impact of terahertz (THz) waves on the aggregation of four common neurotransmitters through all-atom molecular dynamics (MD) simulations. The simulations revealed enhanced nicotine (NCT) aggregation under 11.05 and 21.44 THz, with a minimal effect at 42.55 THz. Structural analysis further indicated strengthened intermolecular interactions and weakened hydration effects under specific THz stimulation. In addition, enhanced aggregation was observed at stronger field strengths, particularly at 21.44 THz. Furthermore, similar investigations on epinephrine (EPI), 5-hydroxytryptamine (5-HT), and γ-aminobutyric acid (GABA) corroborated these findings. Notably, EPI showed increased aggregation at 19.05 THz, emphasizing the influence of vibrational modes on aggregation. However, 5-HT and GABA, with charged or hydrophilic functional groups, exhibited minimal aggregation under THz stimulation. The present study sheds some light on neurotransmitter responses to THz waves, offering implications for neuroscience and interdisciplinary applications.

Resonating with Cellular Pathways: Transcriptome Insights into Nonthermal Bioeffects of Middle Infrared Light Stimulation and Vibrational Strong Coupling on Cell Proliferation and Migration

Middle infrared stimulation (MIRS) and vibrational strong coupling (VSC) have been separately applied to physically regulate biological systems but scarcely compared with each other, especially at identical vibrational frequencies, though they both involve resonant mechanism. Taking cell proliferation and migration as typical cell-level models, herein, we comparatively studied the nonthermal bioeffects of MIRS and VSC with selecting the identical frequency (53.5 THz) of the carbonyl vibration. We found that both MIRS and VSC can notably increase the proliferation rate and migration capacity of fibroblasts. Transcriptome sequencing results reflected the differential expression of genes related to the corresponding cellular pathways. This work not only sheds light on the synergistic nonthermal bioeffects from the molecular level to the cell level but also provides new evidence and insights for modifying bioreactions, further applying MIRS and VSC to the future medicine of frequencies.

Ultrafast light-driven metasurfaces with an ultra-broadband frequency agile channel for sensing

Active terahertz metasurface devices have been widely used in communication technology, optical computing and biosensing. However, numerous dynamically tunable metasurfaces are only operating at a single frequency point or in a narrow range, limiting the further possibility of the devices to meet contemporary broad-spectrum biosensing requirements. In this paper, a novel compact biosensor is proposed with an ultrawide resonance frequency agile channel shifted from 0.82 to 1.85 THz, with a tuning functionality up to 55.7%. In addition, under optical pumping irradiation, the modulator with ultra-fast response is able to complete the ultra-wideband resonant mode conversion from the Fano mode to the electromagnetically induced transparency (EIT) mode within 4 ps, and achieves a frequency shift sensitivity of 118 GHz RIU-1 and 247 GHz RIU-1 at 0.82 and 1.85 THz, respectively. This mechanism implements both refractive index and conductivity sensing functions, which provide a wealth of sensing information. Thus, this work presents the possibility of realising the detection of ultra-wide fingerprint spectra and can be extended to a wider range of optical fields.

Two-photon imaging of excitatory and inhibitory neural response to infrared neural stimulation

Significance

Pulsed infrared neural stimulation (INS, 1875 nm) is an emerging neurostimulation technology that delivers focal pulsed heat to activate functionally specific mesoscale networks and holds promise for clinical application. However, little is known about its effect on excitatory and inhibitory cell types in cerebral cortex.

Aim

Estimates of summed population neuronal response time courses provide a potential basis for neural and hemodynamic signals described in other studies.

Approach

Using two-photon calcium imaging in mouse somatosensory cortex, we have examined the effect of INS pulse train application on hSyn neurons and mDlx neurons tagged with GCaMP6s.

Results

We find that, in anesthetized mice, each INS pulse train reliably induces robust response in hSyn neurons exhibiting positive going responses. Surprisingly, mDlx neurons exhibit negative going responses. Quantification using the index of correlation illustrates responses are reproducible, intensity-dependent, and focal. Also, a contralateral activation is observed when INS applied.

Conclusions

In sum, the population of neurons stimulated by INS includes both hSyn and mDlx neurons; within a range of stimulation intensities, this leads to overall excitation in the stimulated population, leading to the previously observed activations at distant post-synaptic sites.

Molecular tools for recording and intervention of neuronal activity

Observing the activity of neural networks is critical for the identification of learning and memory processes, as well as abnormal activities of neural circuits in disease, particularly for the purpose of tracking disease progression. Methodologies for describing the activity history of neural networks using molecular biology techniques first utilized genes expressed by active neurons, followed by the application of recently developed techniques including optogenetics and incorporation of insights garnered from other disciplines, including chemistry and physics. In this review, we will discuss ways in which molecular biological techniques used to describe the activity of neural networks have evolved along with the potential for future development.

Structural Insights and Influence of Terahertz Waves in Midinfrared Region on Kv1.2 Channel Selectivity Filter

Potassium ion channels are the structural basis for excitation transmission, heartbeat, and other biological processes. The selectivity filter is a critical structural component of potassium ion channels, whose structure is crucial to realizing their function. As biomolecules vibrate and rotate at frequencies in the terahertz band, potassium ion channels are sensitive to terahertz waves. Therefore, it is worthwhile to investigate how the terahertz wave influences the selectivity filter of the potassium channels. In this study, we investigate the structure of the selectivity filter of Kv1.2 potassium ion channels using molecular dynamics simulations. The effect of an electric field on the channel has been examined at four different resonant frequencies of the carbonyl group in SF: 36.75 37.06, 37.68, and 38.2 THz. As indicated by the results, 376GLY appears to be the critical residue in the selectivity filter of the Kv1.2 channel. Its dihedral angle torsion is detrimental to the channel structural stability and the transmembrane movement of potassium ions. 36.75 THz is the resonance frequency of the carbonyl group of 376GLY. Among all four frequencies explored, the applied terahertz electric field of this frequency has the most significant impact on the channel structure, negatively impacting the channel stability and reducing the ion permeability by 20.2% compared to the absence of fields. In this study, we simulate that terahertz waves in the mid-infrared frequency region can significantly alter the structure and function of potassium ion channels and that the effects of terahertz waves differ greatly based on frequency.

Tetherless Optical Neuromodulation: Wavelength from Orange-red to Mid-infrared

Optogenetics, a technique that employs light for neuromodulation, has revolutionized the study of neural mechanisms and the treatment of neurological disorders due to its high spatiotemporal resolution and cell-type specificity. However, visible light, particularly blue and green light, commonly used in conventional optogenetics, has limited penetration in biological tissue. This limitation necessitates the implantation of optical fibers for light delivery, especially in deep brain regions, leading to tissue damage and experimental constraints. To overcome these challenges, the use of orange-red and infrared light with greater tissue penetration has emerged as a promising approach for tetherless optical neuromodulation. In this review, we provide an overview of the development and applications of tetherless optical neuromodulation methods with long wavelengths. We first discuss the exploration of orange-red wavelength-responsive rhodopsins and their performance in tetherless optical neuromodulation. Then, we summarize two novel tetherless neuromodulation methods using near-infrared light: upconversion nanoparticle-mediated optogenetics and photothermal neuromodulation. In addition, we discuss recent advances in mid-infrared optical neuromodulation.

Terahertz Photons Inhibit Cancer Cells Long Term by Suppressing Nano Telomerase Activity

Telomeres are nanoscale DNA-protein complexes to protect and stabilize chromosomes. The reexpression of telomerase in cancer cells is a key determinant crucial for the infinite proliferation and long-term survival of most cancer cells. However, the use of telomerase inhibitors for cancer treatment may cause problems such as poor specificity, drug resistance, and cytotoxicity. Here, we discovered a nondrug and noninvasive terahertz modulation strategy capable of the long-term suppression of cancer cells by inhibiting telomerase activity. First, we found that an optimized frequency of 33 THz photon irradiation effectively inhibited the telomerase activity by molecular dynamics simulation and frequency filtering experiments. Moreover, in vitro experiments showed that telomerase activity in 4T1 and MCF-7 cells significantly decreased by 77% and 80% respectively, after 21 days of regular 33 THz irradiation. Furthermore, two kinds of cells were found to undergo aging, apoptosis, and DNA double-strand breaks caused by telomere crisis, which seriously affected the survival of cancer cells. In addition, the tumorigenicity of 4T1 cells irradiated with 33 THz waves for 21 days in in vivo mice decreased by 70%. In summary, this study demonstrates the potential application of THz modulation in nano therapy for cancer.

Advances in the Regulation of Neural Function by Infrared Light

In recent years, with the rapid development of optical technology, infrared light has been increasingly used in biomedical fields. Research has shown that infrared light could play roles in light stimulation and biological regulation. Infrared light has been used to regulate neural function due to its high spatial resolution, safety and neural sensitivity and has been considered a useful method to replace traditional neural regulation approaches. Infrared neuromodulation methods have been used for neural activation, central nervous system disorder treatment and cognitive enhancement. Research on the regulation of neural function by infrared light stimulation began only recently, and the underlying mechanism remains unclear. This article reviews the characteristics of infrared light, the advantages and disadvantages of infrared neuromodulation, its effects on improving individual health, and its mechanism. This article aims to provide a reference for future research on the use of infrared neural regulation to treat neuropsychological disorders.

Terahertz Photons Improve Cognitive Functions in Posttraumatic Stress Disorder

Posttraumatic stress disorder (PTSD) is a serious psychosis leading to cognitive impairment. To restore cognitive functions for patients, the main treatments are based on medication or rehabilitation training but with limited effectiveness and strong side effects. Here, we demonstrate a new treatment approach for PTSD by using terahertz (THz) photons stimulating the hippocampal CA3 subregion. We verified that this method can nonthermally restore cognitive function in PTSD rats in vivo. After THz photon irradiation, the PTSD rats' recognitive index improved by about 10% in a novel object recognition test, the PTSD rats' accuracy improved by about 100% in a shuttler box test, the PTSD rats' numbers to identify target box was about 5 times lower in a Barnes maze test, and the rate of staying in new arm increased by approximately 40% in a Y-maze test. Further experimental studies found that THz photon (34.5 THz) irradiation could improve the expression of NR2B (increased by nearly 40%) and phosphorylated NR2B (increased by about 50%). In addition, molecular dynamics simulations showed that THz photons at a frequency of 34.5 THz are mainly absorbed by the pocket of glutamate receptors rather than by glutamate molecules. Moreover, the binding between glutamate receptors and glutamate molecules was increased by THz photons. This study offers a nondrug, nonthermal approach to regulate the binding between the excitatory neurotransmitter (glutamate) and NR2B. By increasing synaptic plasticity, it effectively improves the cognitive function of animals with PTSD, providing a promising treatment strategy for NR2B-related cognitive disorders.

Effect of Terahertz Waves on the Structure of the Aβ42 Monomer, Dimer, and Protofibril: Insights from Molecular Dynamics Simulations

Amyloid-β (Aβ) and its assemblies play important roles in the pathogenesis of Alzheimer's disease (AD). Recent studies conducted by experimental and computational researchers have extensively explored the structure, assembly, and influence of biomolecules and cell membranes on Aβ. However, the impact of terahertz waves on the structures of Aβ monomers and aggregates remains largely unexplored. In this study, we systematically investigate the molecular mechanisms by which terahertz waves affect the structure of the Aβ42 monomer, dimer, and tetramer through all-atom molecular dynamics (MD) simulations. Our findings indicate that terahertz waves at a specific frequency (42.55 THz) can enhance intramolecular and intermolecular interactions in the Aβ42 monomer and dimer, respectively, by resonating with the symmetric stretching mode of the -COO- groups and the symmetric bending/stretching mode of -CH3 groups. Consequently, the β-structure content of the Aβ42 monomer is greatly increased, and the binding energy between the monomers in the Aβ42 dimer is significantly enhanced. Additionally, our observations suggest that terahertz waves can mildly stabilize the structure of tetrameric protofibrils by enhancing the interactions among peripheral peptides. Furthermore, we also investigated the effect of the frequency of terahertz waves on the structure of Aβ42. The present study contributes to a better understanding of the impact of external fields on the biobehavior of Aβ42 peptides and may shed some light on the potential risks associated with electromagnetic field radiation.

An optical clearing imaging window: Realization of mouse brain imaging and manipulation through scalp and skull

Cortical visualization is essential to understand the dynamic changes in brain microenvironment under physiopathological conditions. However, the turbid scalp and skull severely limit the imaging depth and resolution. Existing cranial windows require invasive scalp excision and various subsequent skull treatments. Non-invasive in vivo imaging of skull bone marrow, meninges, and cortex through scalp and skull with high resolution yet remains a challenge. In this work, a non-invasive trans-scalp/skull optical clearing imaging window is proposed for cortical and calvarial imaging, which is achieved by applying a novel skin optical clearing reagent. The imaging depth and resolution are greatly enhanced in near infrared imaging and optical coherence tomography imaging. Combining this imaging window with adaptive optics, we achieve the visualization and manipulation of the calvarial and cortical microenvironment through the scalp and skull using two-photon imaging for the first time. Our method provides a well-performed imaging window and paves the way for intravital brain studies with the advantages of easy-operation, convenience and non-invasiveness.

Investigations on Na+, K+-ATPase energy consumption in ion flow of hydrophilic pores by THz unipolar stimulation

Terahertz science and technology has recently shown new application prospects in artificial intelligence. It is found that terahertz unipolar stimulation can activate cell membrane hydrophilic pores. However, the behaviors of Na+, K+-ATPase and energy consumption during this period remain unknown. This paper investigates these behaviors by Na+, K+-ATPase and electroporation models, based on the interaction theory between terahertz fields and ions at the cellular level. The effective diameters of life ions are considered in the aqueous solution. From results, Na+, K+-ATPases can be activated and stay for a while before close after the stimulation. Their life ion flows are far lower than the flows via the pores. And their power dissipation is as low as 10-11 W in both rat neostriatal neurons and guinea pig ventricular myocytes. The results keep tenable in 0.1-1.2 THz. These lay the basis for investigations of information communication mechanisms in cells under terahertz stimulation.

Illuminating the Brain: Advances and Perspectives in Optoelectronics for Neural Activity Monitoring and Modulation

Optogenetic modulation of brain neural activity that combines optical and electrical modes in a unitary neural system has recently gained robust momentum. Controlling illumination spatial coverage, designing light-activated modulators, and developing wireless light delivery and data transmission are crucial for maximizing the use of optical neuromodulation. To this end, biocompatible electrodes with enhanced optoelectrical performance, device integration for multiplexed addressing, wireless transmission, and multimodal operation in soft systems have been developed. This review provides an outlook for uniformly illuminating large brain areas while spatiotemporally imaging the neural responses upon optoelectrical stimulation with little artifacts. Representative concepts and important breakthroughs, such as head-mounted illumination, multiple implanted optical fibers, and micro-light-delivery devices, are discussed. Examples of techniques that incorporate electrophysiological monitoring and optoelectrical stimulation are presented. Challenges and perspectives are posed for further research efforts toward high-density optoelectrical neural interface modulation, with the potential for nonpharmacological neurological disease treatments and wireless optoelectrical stimulation.

Calcium Imaging Characterize the Neurobiological Effect of Terahertz Radiation in Zebrafish Larvae

(1) Objective: To explore the neurobiological effects of terahertz (THz) radiation on zebrafish larvae using calcium (Ca2+) imaging technology. (2) Methods: Zebrafish larvae at 7 days post fertilization (dpf) were exposed to THz radiation for 10 or 20 min; the frequency was 2.52 THz and the amplitude 50 mW/cm2. The behavioral experiments, neural Ca2+ imaging, and quantitative polymerase chain reaction (qPCR) of the dopamine-related genes were conducted following the irradiation. (3) Results: Compared with the control group, the behavioral experiments demonstrated that THz radiation significantly increased the distance travelled and speed of zebrafish larvae. In addition, the maximum acceleration and motion frequency were elevated in the 20 min radiation group. The neural Ca2+ imaging results indicated a substantial increase in zebrafish neuronal activity. qPCR experiments revealed a significant upregulation of dopamine-related genes, such as drd2b, drd4a, slc6a3 and th. (4) Conclusion: THz radiation (2.52 THz, 50 mW/cm2, 20 min) upregulated dopamine-related genes and significantly enhanced neuronal excitability, and the neurobiological effect of THz radiation can be visualized using neural Ca2+ imaging in vivo.

Rabies virus-based labeling of layer 6 corticothalamic neurons for two-photon imaging in vivo

Neocortical layer 6 (L6) is less understood than other more superficial layers, largely owing to limitations of performing high-resolution investigations in vivo. Here, we show that labeling with the Challenge Virus Standard (CVS) rabies virus strain enables high-quality imaging of L6 neurons by conventional two-photon microscopes. CVS virus injection into the medial geniculate body can selectively label L6 neurons in the auditory cortex. Only three days after injection, dendrites and cell bodies of L6 neurons could be imaged across all cortical layers. Ca²⁺ imaging in awake mice showed that sound stimulation evokes neuronal responses from cell bodies with minimal contamination from neuropil signals. In addition, dendritic Ca²⁺ imaging revealed significant responses from spines and trunks across all layers. These results demonstrate a reliable method capable of rapid, high-quality labeling of L6 neurons that can be readily extended to other brain regions.

High Frequency Electromagnetic Radiation Stimulates Neuronal Growth and Hippocampal Synaptic Transmission

Terahertz waves lie within the rotation and oscillation energy levels of biomolecules, and can directly couple with biomolecules to excite nonlinear resonance effects, thus causing conformational or configuration changes in biomolecules. Based on this mechanism, we investigated the effect pattern of 0.138 THz radiation on the dynamic growth of neurons and synaptic transmission efficiency, while explaining the phenomenon at a more microscopic level. We found that cumulative 0.138 THz radiation not only did not cause neuronal death, but that it promoted the dynamic growth of neuronal cytosol and protrusions. Additionally, there was a cumulative effect of terahertz radiation on the promotion of neuronal growth. Furthermore, in electrophysiological terms, 0.138 THz waves improved synaptic transmission efficiency in the hippocampal CA1 region, and this was a slow and continuous process. This is consistent with the morphological results. This phenomenon can continue for more than 10 min after terahertz radiation ends, and these phenomena were associated with an increase in dendritic spine density. In summary, our study shows that 0.138 THz waves can modulate dynamic neuronal growth and synaptic transmission. Therefore, 0.138 terahertz waves may become a novel neuromodulation technique for modulating neuron structure and function.

Engineering optical tools for remotely controlled brain stimulation and regeneration

Neurological disorders are one of the world's leading medical and societal challenges due to the lack of efficacy of the first line treatment. Although pharmacological and non-pharmacological interventions have been employed with the aim of regulating neuronal activity and survival, they have failed to avoid symptom relapse and disease progression in the vast majority of patients. In the last 5 years, advanced drug delivery systems delivering bioactive molecules and neuromodulation strategies have been developed to promote tissue regeneration and remodel neuronal circuitry. However, both approaches still have limited spatial and temporal precision over the desired target regions. While external stimuli such as electromagnetic fields and ultrasound have been employed in the clinic for non-invasive neuromodulation, they do not have the capability of offering single-cell spatial resolution as light stimulation. Herein, we review the latest progress in this area of study and discuss the prospects of using light-responsive nanomaterials to achieve on-demand delivery of drugs and neuromodulation, with the aim of achieving brain stimulation and regeneration.

Sensory input-dependent gain modulation of the optokinetic nystagmus by mid-infrared stimulation in pigeons

Neuromodulation serves as a cornerstone for brain sciences and clinical applications. Recent reports suggest that mid-infrared stimulation (MIRS) causes non-thermal modulation of brain functions. Current understanding of its mechanism hampers the routine application of MIRS. Here, we examine how MIRS influences the sensorimotor transformation in awaking-behaving pigeons, from neuronal signals to behavior. We applied MIRS and electrical stimulation (ES) to the pretectal nucleus lentiformis mesencephali (nLM), an essential retinorecipient structure in the pretectum, and examined their influences on the optokinetic nystagmus, a visually guided eye movement. We found MIRS altered eye movements by modulating a specific gain depending on the strength of visual inputs, in a manner different than the effect of ES. Simultaneous extracellular recordings and stimulation showed that MIRS could either excite and inhibit the neuronal activity in the same pretectal neuron depending on its ongoing sensory responsiveness levels in awake-behaving animals. Computational simulations suggest that MIRS modulates the resonance of a carbonyl group of the potassium channel, critical to the action potential generation, altering neuronal responses to sensory inputs and as a consequence, guiding behavior. Our findings suggest that MIRS could be a promising approach toward modulating neuronal functions for brain research and treating neurological diseases.

Advances in photobiomodulation for cognitive improvement by near-infrared derived multiple strategies

Cognitive function is an important ability of the brain, but cognitive dysfunction can easily develop once the brain is injured in various neuropathological conditions or diseases. Photobiomodulation therapy is a type of noninvasive physical therapy that is gradually emerging in the field of neuroscience. Transcranial photobiomodulation has been commonly used to regulate neural activity in the superficial cortex. To stimulate deeper brain activity, advanced photobiomodulation techniques in conjunction with photosensitive nanoparticles have been developed. This review addresses the mechanisms of photobiomodulation on neurons and neural networks and discusses the advantages, disadvantages and potential applications of photobiomodulation alone or in combination with photosensitive nanoparticles. Photobiomodulation and its associated strategies may provide new breakthrough treatments for cognitive improvement.

THz-PCR Based on Resonant Coupling between Middle Infrared and DNA Carbonyl Vibrations

The carbonyl groups of deoxyribonucleotide can resonantly couple with 53 THz middle infrared, which can highly transmit water without ionization-based damage to DNA molecules. Herein, we predict that vibrational coupling with THz irradiation could lower down the hybridization landscape of nucleic acids and thus affect DNA replication. Using polymerase chain reaction (PCR) as a measure, we found that THz shining can reduce the denature temperature of DNA duplexes by about 3 °C, which allows one to conduct PCR at lower temperature, facilitating long-time amplification reaction without losing enzymatic fidelity, i.e., normal PCR should be carried out at denaturing temperature ∼4 °C higher than the melting temperature (T_m), but THz-PCR only requires temperature ∼1 °C higher than T_m due to the nonthermal effect of THz shining. Moreover, the melting time can also be shortened to 1/5 due to the enhanced vibration coupling with 53 THz irradiation. We proposed THz-PCR as an innovated DNA amplification technique with ultrahigh specificity and sensitivity and also successfully demonstrated its advantages in forensic detections.

AuNP-Modulated qPCR: An Optimized System for Detecting MIR Biophotons Released in DNA Replication

Living systems can utilize energy with a high efficiency. Biophotons are proposed to modulate biological functions with such efficiency; however, the underlying mechanism remains unexplored, especially due to the challenge of ultraweak mid-infrared (MIR) light detection and the theoretical perturbation from spontaneous MIR emission. Here, we proposed an optimized system to detect MIR biophotons generated in the hydrolysis of deoxynucleotide triphosphates (dNTPs, energy-storing molecules similar to ATP). The system used a quantitative polymerase chain reaction (qPCR) that was modulated by gold nanoparticle (AuNP) concentration and thus by the inter-AuNP distance, which depends on the concentration above. The measurements indicate that 33- and 84-THz photons are released by dNTP hydrolysis, which can drive DNA replication. Our findings provide a novel chain-reaction-based method for detecting MIR photons in solution, and pave a way for photon-based insights to understand the highly efficient energy utilization of biology.

Ultrafast Modulation of THz Waves Based on MoTe2-Covered Metasurface

The sixth generation (6G) communication will use the terahertz (THz) frequency band, which requires flexible regulation of THz waves. For the conventional metallic metasurface, its electromagnetic properties are hard to be changed once after being fabricated. To enrich the modulation of THz waves, we report an all-optically controlled reconfigurable electromagnetically induced transparency (EIT) effect in the hybrid metasurface integrated with a 10-nm thick MoTe₂ film. The experimental results demonstrate that under the excitation of the 800 nm femtosecond laser pulse with pump fluence of 3200 μJ/cm², the modulation depth of THz transmission amplitude at the EIT window can reach 77%. Moreover, a group delay variation up to 4.6 ps is observed to indicate an actively tunable slow light behavior. The suppression and recovery of the EIT resonance can be accomplished within sub-nanoseconds, enabling an ultrafast THz photo-switching and providing a promising candidate for the on-chip devices of the upcoming 6G communication.

A corticostriatal projection for sound-evoked and anticipatory motor behavior following temporal expectation

The ability to form predictions based on recent sensory experience is essential for behavioral adaptation to our ever-changing environment. Predictive encoding represented by neuronal activity has been observed in sensory cortex, but how this neuronal activity is transformed into anticipatory motor behavior remains unclear. Fiber photometry to investigate a corticostriatal projection from the auditory cortex to the posterior striatum during an auditory paradigm in mice, and pharmacological experiments in a task that induces a temporal expectation of upcoming sensory stimuli. We find that the auditory corticostriatal projection relays both sound-evoked stimulus information as well as predictive signals in relation to stimulus timing following rhythmic auditory stimulation. Pharmacological experiments suggest that this projection is required for the initiation of both sound-evoked and anticipatory licking behavior in an auditory associative-learning behavioral task, but not for the general recognition of presented auditory stimuli. This auditory corticostriatal projection carries predictive signals, and the posterior striatum is critical to the anticipatory stimulus-driven motor behavior.

Terahertz refractive phenotype of living cells

Cellular refractive index is a vital phenotypic parameter for understanding the cell functional activities. So far, there remains technical challenges to obtain refractive index of viable cells at the terahertz frequency in which contains rich information closely related to their physiological status. Here we introduce a label-free optical platform for interrogating cellular phenotypes to measure the refractive index of living cells in near-physiological environments by using terahertz spectroscopy with the combination of cellular encapsulation in a confined solution droplet. The key technical feature with cells encapsulated in aqueous droplets allows for keeping cellular viability while eliminating the strong adsorption of solvent water to terahertz signal. The obtained high signal-to-noise ratio enables to differentiate different cell types (e.g., E. coli, stem cell and cancer cell) and their states under stress conditions. The integrating of terahertz spectroscopy to droplet microfluidic further realizes automated and high-through sample preparation and detection, providing a practical toolkit for potential application in cellular health evaluation and phenotypic drug discovery.

Engineering graphene-based electrodes for optical neural stimulation

Graphene-based materials (GBMs) have been investigated in recent years with the aim of developing flexible interfaces to address a range of neurological disorders, where electrical stimulation may improve brain function and tissue regeneration. The recent discovery that GBM electrodes can generate an electrical response upon light exposure has inspired the development of non-genetic approaches capable of selectively modulating brain cells without genetic manipulation (i.e., optogenetics). Here, we propose the conjugation of graphene with upconversion nanoparticles (UCNPs), which enable wireless transcranial activation using tissue-penetrating near-infrared (NIR) radiation. Following a design of experiments approach, we first investigated the influence of different host matrices and dopants commonly used to synthesize UCNPs in the electrical response of graphene. Two UCNP formulations achieving optimal enhancement of electrical conductivity upon NIR activation at λ = 780 or 980 nm were identified. These formulations were then covalently attached to graphene nanoplatelets following selective hydroxyl derivatization. The resulting nanocomposites were evaluated in vitro using SH-SY5Y human neuroblastoma cells. NIR activation at λ = 980 nm promoted cell proliferation and downregulated neuronal and glial differentiation markers, suggesting the potential application of GBMs in minimally invasive stimulation of cells for tissue regeneration.

Output characteristics of 3-8 µm mid-infrared source based on BaGa4Se7 crystal

An optical parametric oscillator based on B a G a ₄ S e ₇ crystal is constructed for use as a 3-8 µm mid-infrared source. The output characteristics of the light source, including wavelength tuning, beam quality, and energy stability, are studied, which are usually concerned differently in spectral analysis, imaging, and laser processing. When the light source operates far from the threshold, the mid-infrared output is poor in beam quality and good in energy stability, and the contradiction should be addressed in practice. The results provide guidance on the selection of operating parameters and performance optimization for the application of the B a G a ₄ S e ₇ based mid-infrared source in various settings.

Early detection of gastric cancer via high-resolution terahertz imaging system

Terahertz (THz) wave has demonstrated a good prospect in recent years, but the resolution is still one of the problems that restrict the application of THz technology in medical imaging. Paraffin-embedded samples are mostly used in THz medical imaging studies, which are thicker and significantly different from the current gold standard slice pathological examination in sample preparation. In addition, THz absorption in different layers of normal and cancerous tissues also remains to be further explored. In this study, we constructed a high-resolution THz imaging system to scan non-tumorous adjacent tissue slices and gastric cancer (GC) tissue slices. In this system, a THz quantum cascade laser emitted a pulsed 3 THz signal and the transmitted THz wave was received by a THz detector implemented in a 65 nm CMOS process. The slice thickness was only 20 μm, which was close to that of the medical pathology examination. We successfully found THz transmittance differences between different layers of normal gastric tissues based on THz images, and the resolution could reach 60 μm for the first time. The results indicated that submucosa had a lower THz transmittance than that of mucosa and muscular layer in non-tumorous adjacent tissue. However, in GC tissue, THz transmittance of mucosa and submucosa was similar, caused by the decreased transmittance of mucosa, where the cancer occurs. Therefore, we suppose that the similar terahertz transmittance between gastric mucosa and submucosa may indicate the appearance of cancerization. The images obtained from our THz imaging system were clearer than those observed with naked eyes, and can be directly compared with microscopic images. This is the first application of THz imaging technology to identify non-tumorous adjacent tissue and GC tissue based on the difference in THz wave absorption between different layers in the tissue. Our present work not only demonstrated the potential of THz imaging to promote early diagnosis of GC, but also suggested a new direction for the identification of normal and cancerous tissues by analyzing differences in THz transmittance between different layers of tissue.

Numerical study on all-optical modulation characteristics of quantum cascade lasers

To explain the phenomenon of all-optical modulation of quantum cascade laser (QCL), and explore the physics in QCL's gain medium which consists of multiple of dielectric nanostructures with high refractive index under light injection, we modified the 1½-period model to calculate values of electron population and lifetime in each subband which is separated by the nanostructures, optical gain, current and number of photons in the cavity of a mid-infrared QCL modulated with near-infrared optical injection. The results were consistent with an experiment, where the injected light increases the electron population and lifetime, but does not affect the optical gain obviously. Our study can be helpful for optimizing its use and dielectric nanostructure design.

Dielectric dispersion characteristics of the phospholipid bilayer with subnanometer resolution from terahertz to mid-infrared

There is growing interest in whether the myelinated nerve fiber acts as a dielectric waveguide to propagate terahertz to mid-infrared electromagnetic waves, which are presumed stable signal carrier for neurotransmission. The myelin sheath is formed as a multilamellar biomembrane structure, hence insights into the dielectric properties of the phospholipid bilayer is essential for a complete understanding of the myelinated fiber functioning. In this work, by means of atomistic molecular dynamics simulations of the dimyristoylphosphatidylcholine (DMPC) bilayer in water and numerical calculations of carefully layered molecules along with calibration of optical dielectric constants, we for the first time demonstrate the spatially resolved (in sub-nm) dielectric spectrum of the phospholipid bilayer in a remarkably wide range from terahertz to mid-infrared. More specifically, the membrane head regions exhibit both larger real and imaginary permittivities than that of the tail counterparts in the majority of the 1–100 THz band. In addition, the spatial variation of dielectric properties suggests advantageous propagation characteristics of the phospholipid bilayer in a relatively wide band of 55–85 THz, where the electromagnetic waves are well confined within the head regions.

Inhibition of Cancer Cell Migration and Glycolysis by Terahertz Wave Modulation via Altered Chromatin Accessibility

Metastasis and metabolic disorders contribute to most cancer deaths and are potential drug targets in cancer treatment. However, corresponding drugs inevitably induce myeloid suppression and gastrointestinal toxicity. Here, we report a nonpharmaceutical and noninvasive electromagnetic intervention technique that exhibited long-term inhibition of cancer cells. Firstly, we revealed that optical radiation at the specific wavelength of 3.6 μm (i.e., 83 THz) significantly increased binding affinity between DNA and histone via molecular dynamics simulations, providing a theoretical possibility for THz modulation- (THM-) based cancer cell intervention. Subsequent cell functional assays demonstrated that low-power 3.6 μm THz wave could successfully inhibit cancer cell migration by 50% and reduce glycolysis by 60%. Then, mRNA sequencing and assays for transposase-accessible chromatin using sequencing (ATAC-seq) indicated that low-power THM at 3.6 μm suppressed the genes associated with glycolysis and migration by reducing the chromatin accessibility of certain gene loci. Furthermore, THM at 3.6 μm on HCT-116 cancer cells reduced the liver metastasis by 60% in a metastatic xenograft mouse model by splenic injection, successfully validated the inhibition of cancer cell migration by THM in vivo. Together, this work provides a new paradigm for electromagnetic irradiation-induced epigenetic changes and represents a theoretical basis for possible innovative therapeutic applications of THM as the future of cancer treatments.

CaMKIIδ Promotes Synaptic Plasticity under Terahertz Wave Radiation by Activation of the NF-κB Pathway

Terahertz waves have been attracting more attention because of their growing applications in brain science. Most of the studies have demonstrated that terahertz waves have a certain positive impact on neurons. They can promote the growth of ganglion processes and the release of neurotransmitters, but the specific mechanism is still largely unexplored. Our study found that terahertz waves could promote neuronal excitability. Moreover, numerous differentially expressed proteins were uncovered via proteomic analysis. Among them, CaMKIIδ is a subunit of CaMKII and could promote the release of neuronal transmitters, regulate the excitability of neurons, and enhance synaptic plasticity. We further demonstrated that CaMKIIδ actively increased synaptic plasticity through the NF-κB pathway. This study provided a potential target for nerve repair and disease treatment.

Physicochemical Insights on Terahertz Wave Diminished Side Effects of Drugs from Slow Dissociation

Dopamine D2 receptors (D2Rs) are one of the most intensely investigated and well-established drug targets for neuropsychiatric disorders. Selective D2R antagonists have been developed as efficacious antipsychotic drugs. Nevertheless, the potent drugs with necessarily high affinity are prone to slow dissociation, which invokes a plethora of severe side effects such as extrapyramidal symptoms, substantial weight gain, associated diabetes, etc. This has become a major barrier in treating psychiatric patients. In this work, we propose a physical method, terahertz wave modulation, to promote the dissociation of high-affinity antipsychotics and thus diminish the side effects. We have proven that a 4.0 THz wave could reduce the affinity by 71% between the D2R and a risperidone ligand and meanwhile expand the exit via conformation modulation, which promises an accelerated dissociation of risperidone. In addition, it is estimated that the enhancement of the dissociation rate due to lowered binding by terahertz irritation could constitute up to 8 orders of magnitude, which is fairly impressive and resembles the enzyme's catalysis. Also, acceleration of the dissociation rate could be adjusted by the irritation strength. This work elaborates the terahertz wave-modulated noncovalent interactions critical in cell signaling pathways. Most importantly, it demonstrates the feasibility of terahertz technologies intervening in receptor-ligand complex regulated diseases such as neurodegenerative disorders, metabolic diseases, etc.

Ultra-broadband optical detection from the visible to the terahertz range using a miniature quartz tuning fork

We report and experimentally demonstrate a novel, to the best of our knowledge, sensitive and wideband optical detection strategy based on the light-induced thermoelastic effect in a miniature quartz tuning fork (mQTF) with low stiffness prongs. Compared with a traditional QTF, the soft prongs of the mQTF result in improved sensitivity. Experimental results demonstrate that the mQTF exhibits ∼54-fold superior sensitivity compared to a QTF, and the mQTF sensor has an ultra-broadband optical response, ranging from visible light to terahertz wavelengths. Its response time reaches 11.7 ms, and the minimum noise equivalent power (NEP) is measured to be 2.2 × 10^-9 W Hz^-1/2 at room temperature. The mQTF exhibits advantages in its cost-effectiveness, sensitivity, and ultra-broadband response, and provides a promising approach for the detection of low-dose optical and terahertz-wave radiation.

Neuromodulation of Chemical Synaptic Transmission Driven by THz Photons

Postsynaptic currents of chemical synapse are modulated by multitudinous neurotransmitters, such as acetylcholine, dopamine, glutamate, and γ-aminobutyric acid, many of which have been used in the treatment of neurological diseases. Here, based on molecular dynamics simulations and quantum chemical calculation, we propose that 30- to 45-THz photons can resonate with a variety of typical neurotransmitter molecules and make them absorb photon energy to activate the transition to high energy state, which is expected to be a new method of neural regulation. Furthermore, we verified the calculated results through experiments that THz irradiation could substantively change neuronal signal emission and enhance the frequency, amplitude, and dynamic properties of excitatory postsynaptic current and inhibitory postsynaptic current. In addition, we demonstrated the potential of neural information regulation by THz photons through 2-photon imaging in vivo. These findings are expected to improve the understanding of the physical mechanism of biological phenomena and facilitate the application of terahertz technology in neural regulation and the development of new functional materials.

Mid-infrared multispectral confocal microscope using off-axis parabolic mirrors to study epiretinal membranes

Mid-infrared (mid-IR) multispectral microscopy, especially operating at the wavelength of 5-11 µm, is an effective tool for detecting, identifying, and quantifying the structure and composition of biological tissues. Compared with that based on the optical lens, the mid-infrared microscope composed of off-axis parabolic (OAP) mirrors is low cost, simple, and suitable for longer range of wavelength without chromatic aberrations, while keeping the optical transmission efficiency. Here we report a compact and versatile mid-infrared multispectral confocal microscope based on off-axis parabolic mirrors. We also perform numerical calculations based on the vectorial diffraction theory on OAP mirrors and analyze the typical aberrations and misalignment of the OAP-based optical system. Finally, we perform multispectral imaging of the epiretinal membrane of the human eyes with the spectrum selected according to its resonance absorption peak. The system is designed to perform multispectral or even hyperspectral imaging to identify and predict potential disease.