Thermal effects on neurons during stimulation of the brain

Focused Ultrasound Modulates Dopamine in a Mesolimbic Reward Circuit

Dopamine is a neurotransmitter that plays a significant role in reward and motivation. Dysfunction in the mesolimbic dopamine pathway has been linked to a variety of psychiatric disorders, including addiction. Low-intensity focused ultrasound (LIFU) has demonstrated effects on brain activity, but how LIFU affects dopamine neurotransmission is not known. Here, we applied three different intensities (6.5, 13, and 26 W/cm2 ISPPA) of 2-min LIFU to the prelimbic cortex (PLC) and measured dopamine in the nucleus accumbens (NAc) core using fast-scan cyclic voltammetry. Two minutes of LIFU sonication at 13 W/cm2 to the PLC significantly reduced dopamine release by ~50% for up to 2 h. However, double the intensity (26 W/cm2) resulted in less inhibition (~30%), and half the intensity (6.5 W/cm2) did not result in any inhibition of dopamine. Anatomical controls applying LIFU to the primary somatosensory cortex did not change NAc core dopamine, and applying LIFU to the PLC did not affect dopamine release in the caudate or NAc shell. Histological evaluations showed no evidence of cell damage or death. Modeling temperature rise demonstrates a maximum temperature change of 0.5°C with 13 W/cm2, suggesting that modulation is not due to thermal mechanisms. These studies show that LIFU at a moderate intensity provides a noninvasive, high spatial resolution means to modulate specific mesolimbic circuits that could be used in future studies to target and repair pathways that are dysfunctional in addiction and other psychiatric diseases.

Enhancing biocompatibility of the brain-machine interface: A review

In vivo implantation of microelectrodes opens the door to studying neural circuits and restoring damaged neural pathways through direct electrical stimulation and recording. Although some neuroprostheses have achieved clinical success, electrode material properties, inflammatory response, and glial scar formation at the electrode-tissue interfaces affect performance and sustainability. Those challenges can be addressed by improving some of the materials' mechanical, physical, chemical, and electrical properties. This paper reviews materials and designs of current microelectrodes and discusses perspectives to advance neuroprosthetics performance.

Microfabrication Technologies for Nanoinvasive and High-Resolution Magnetic Neuromodulation

The increasing demand for precise neuromodulation necessitates advancements in techniques to achieve higher spatial resolution. Magnetic stimulation, offering low signal attenuation and minimal tissue damage, plays a significant role in neuromodulation. Conventional transcranial magnetic stimulation (TMS), though noninvasive, lacks the spatial resolution and neuron selectivity required for spatially precise neuromodulation. To address these limitations, the next generation of magnetic neurostimulation technologies aims to achieve submillimeter-resolution and selective neuromodulation with high temporal resolution. Invasive and nanoinvasive magnetic neurostimulation are two next-generation approaches: invasive methods use implantable microcoils, while nanoinvasive methods use magnetic nanoparticles (MNPs) to achieve high spatial and temporal resolution of magnetic neuromodulation. This review will introduce the working principles, technical details, coil designs, and potential future developments of these approaches from an engineering perspective. Furthermore, the review will discuss state-of-the-art microfabrication in depth due to its irreplaceable role in realizing next-generation magnetic neuromodulation. In addition to reviewing magnetic neuromodulation, this review will cover through-silicon vias (TSV), surface micromachining, photolithography, direct writing, and other fabrication technologies, supported by case studies, providing a framework for the integration of magnetic neuromodulation and microelectronics technologies.

Large-Scale, High-Density MicroLED Array-Based Optogenetic Device for Neural Stimulation and Recording

Optogenetics has emerged as a pivotal tool in neuroscience, enabling precise control of neural activity through light stimulation. However, the current microLED arrays lack sufficient density and scalability. This study proposes an innovative optogenetic device capable of integrating hundreds of microLEDs and electrocorticography (ECOG) electrodes. Individual or multiple microLEDs in the device can be selectively controlled with a custom controller. The light intensity of microLEDs decreases with increasing brain tissue penetration while maintaining a low temperature rise during pulse stimulations. In addition, interference from microLED pulses on ECOG electrode recordings could be alleviated with local mean subtraction data processing. The optogenetic device enables high-quality neural signal recording and triggers a significant enhancement in neural activity following light stimulation. Integration of microLED arrays and ECOG electrodes in the optogenetic device represents a promising advancement in neuroscientific research, providing improved spatial and temporal recording and control over neural activity.

Impact of fever on the outcome non-anoxic acute brain injury patients: a systematic review and meta-analysis

BACKGROUND

Fever is a common condition in intensive care unit (ICU) patients, with an incidence between 30 and 50% in non-neurological ICU patients and up to 70-90% in neurological ICU patients. We aim to perform systematic review and meta-analysis of current literature to assess impact of fever on neurological outcomes and mortality of acute brain injury patients.

METHODS

We searched PubMed/Medline, Scopus and Embase databases following the recommendations of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses statement, and we included both retrospective and prospective observational studies, interventional studies, and randomized clinical trials that had data on body temperature and fever during ICU admission. The primary endpoints were neurological outcome and mortality at any time. Secondary outcomes included: early neurological deterioration, delayed cerebral ischemia (DCI, only for patients with subarachnoid hemorrhage), large infarct or hemorrhage size, hemorrhagic transformation (only for patients with ischemic stroke). This study was registered in PROSPERO (CRD42020155903).

RESULTS

180 studies from 14692 records identified after the initial search were included in the final analysis, for a total of 460,825 patients. Fever was associated with an increased probability of unfavorable neurological outcome (pooled OR 2.37 [95% CI 2.08-2.71], I2:92%), death (pooled OR 1.31 [95% CI 1.28-1.34], I2:93%), neurological deterioration (pooled OR 1.10 [95% CI 1.05-1.15]), risk of DCI (pooled OR 1.96 [95% CI 1.73-2.22]), large infarct size (pooled OR 2.94 [95% CI 2.90-2.98]) and hemorrhagic transformation (pooled OR 1.63 [95% CI 1.34-1.97]) and large hemorrhagic volume (pooled OR 2.38 [95% CI 1.94-2.93]).

CONCLUSION

Fever was associated with poor neurological outcomes and mortality in patients with acute brain injury. Whether normothermia should be targeted in the management of all neuro critically ill patients warrants specific research.

NeuroQuantify - An image analysis software for detection and quantification of neuron cells and neurite lengths using deep learning

BACKGROUND

The segmentation of cells and neurites in microscopy images of neuronal networks provides valuable quantitative information about neuron growth and neuronal differentiation, including the number of cells, neurites, neurite length and neurite orientation. This information is essential for assessing the development of neuronal networks in response to extracellular stimuli, which is useful for studying neuronal structures, for example, the study of neurodegenerative diseases and pharmaceuticals.

NEW METHOD

We have developed NeuroQuantify, an open-source software that uses deep learning to efficiently and quickly segment cells and neurites in phase contrast microscopy images.

RESULTS

NeuroQuantify offers several key features: (i) automatic detection of cells and neurites; (ii) post-processing of the images for the quantitative neurite length measurement based on segmentation of phase contrast microscopy images, and (iii) identification of neurite orientations.

COMPARISON WITH EXISTING METHODS

NeuroQuantify overcomes some of the limitations of existing methods in the automatic and accurate analysis of neuronal structures. It has been developed for phase contrast images rather than fluorescence images. In addition to typical functionality of cell counting, NeuroQuantify also detects and counts neurites, measures the neurite lengths, and produces the neurite orientation distribution.

CONCLUSIONS

We offer a valuable tool to assess network development rapidly and effectively. The user-friendly NeuroQuantify software can be installed and freely downloaded from GitHub at https://github.com/StanleyZ0528/neural-image-segmentation.

Applications of 2D Nanomaterials in Neural Interface

Neural interfaces are crucial conduits between neural tissues and external devices, enabling the recording and modulation of neural activity. However, with increasing demand, simple neural interfaces are no longer adequate to meet the requirements for precision, functionality, and safety. There are three main challenges in fabricating advanced neural interfaces: sensitivity, heat management, and biocompatibility. The electrical, chemical, and optical properties of 2D nanomaterials enhance the sensitivity of various types of neural interfaces, while the newly developed interfaces do not exhibit adverse reactions in terms of heat management and biocompatibility. Additionally, 2D nanomaterials can further improve the functionality of these interfaces, including magnetic resonance imaging (MRI) compatibility, stretchability, and drug delivery. In this review, we examine the recent applications of 2D nanomaterials in neural interfaces, focusing on their contributions to enhancing performance and functionality. Finally, we summarize the advantages and disadvantages of these nanomaterials, analyze the importance of biocompatibility testing for 2D nanomaterials, and propose that improving and developing composite material structures to enhance interface performance will continue to lead the forefront of this field.

Fluorescent Nanodiamonds for High-Resolution Thermometry in Biology

Optically active color centers in diamond and nanodiamonds can be utilized as quantum sensors for measuring various physical parameters, particularly magnetic and electric fields, as well as temperature. Due to their small size and possible surface functionalization, fluorescent nanodiamonds are extremely attractive systems for biological and medical applications since they can be used for intracellular experiments. This review focuses on fluorescent nanodiamonds for thermometry with high sensitivity and a nanoscale spatial resolution for the investigation of living systems. The current state of the art, possible further development, and potential limitations of fluorescent nanodiamonds as thermometers will be discussed here.

Local variation in brain temperature explains gender-specificity of working memory performance

Introduction

Exploring gender differences in cognitive abilities offers vital insights into human brain functioning.

Methods

Our study utilized advanced techniques like magnetic resonance thermometry, standard working memory n-back tasks, and functional MRI to investigate if gender-based variations in brain temperature correlate with distinct neuronal responses and working memory capabilities.

Results

We observed a significant decrease in average brain temperature in males during working memory tasks, a phenomenon not seen in females. Although changes in female brain temperature were significantly lower than in males, we found an inverse relationship between the absolute temperature change (ATC) and cognitive performance, alongside a correlation with blood oxygen level dependent (BOLD) signal change induced by neural activity. This suggests that in females, ATC is a crucial determinant for the link between cognitive performance and BOLD responses, a linkage not evident in males. However, we also observed additional female specific BOLD responses aligned with comparable task performance to that of males.

Discussion

Our results suggest that females compensate for their brain's heightened temperature sensitivity by activating additional neuronal networks to support working memory. This study not only underscores the complexity of gender differences in cognitive processing but also opens new avenues for understanding how temperature fluctuations influence brain functionality.

Optical constraints on two-photon voltage imaging

Significance

Genetically encoded voltage indicators (GEVIs) are a valuable tool for studying neural circuits in vivo, but the relative merits and limitations of one-photon (1P) versus two-photon (2P) voltage imaging are not well characterized.

Aim

We consider the optical and biophysical constraints particular to 1P and 2P voltage imaging and compare the imaging properties of commonly used GEVIs under 1P and 2P excitation.

Approach

We measure the brightness and voltage sensitivity of voltage indicators from commonly used classes under 1P and 2P illumination. We also measure the decrease in fluorescence as a function of depth in the mouse brain. We develop a simple model of the number of measurable cells as a function of reporter properties, imaging parameters, and desired signal-to-noise ratio (SNR). We then discuss how the performance of voltage imaging would be affected by sensor improvements and by recently introduced advanced imaging modalities.

Results

Compared with 1P excitation, 2P excitation requires ∼ 10 4 -fold more illumination power per cell to produce similar photon count rates. For voltage imaging with JEDI-2P in the mouse cortex with a target SNR of 10 (spike height to baseline shot noise), a measurement bandwidth of 1 kHz, a thermally limited laser power of 200 mW, and an imaging depth of > 300    μ m , 2P voltage imaging using an 80-MHz source can record from no more than ∼ 12 neurons simultaneously.

Conclusions

Due to the stringent photon-count requirements of voltage imaging and the modest voltage sensitivity of existing reporters, 2P voltage imaging in vivo faces a stringent tradeoff between shot noise and tissue photodamage. 2P imaging of hundreds of neurons with high SNR at a depth of > 300    μ m will require either major improvements in 2P GEVIs or qualitatively new approaches to imaging.

Focused Ultrasound Modulates Dopamine in a Mesolimbic Reward Circuit

Dopamine is a neurotransmitter that plays a significant role in reward and motivation. Dysfunction in the mesolimbic dopamine pathway has been linked to a variety of psychiatric disorders, including addiction. Low-intensity focused ultrasound (LIFU) has demonstrated effects on brain activity, but how LIFU affects dopamine neurotransmission is not known. Here, we applied three different intensities (6.5, 13, and 26 W/cm 2 I sppa ) of 2-minute LIFU to the prelimbic region (PLC) and measured dopamine in the nucleus accumbens (NAc) core using fast-scan cyclic voltammetry. Two minutes of LIFU sonication at 13 W/cm 2 to the PLC significantly reduced dopamine release by ∼ 50% for up to 2 hours. However, double the intensity (26 W/cm 2 ) resulted in less inhibition (∼30%), and half the intensity (6.5 W/cm 2 ) did not result in any inhibition of dopamine. Anatomical controls applying LIFU to the primary somatosensory cortex did not change NAc core dopamine, and applying LIFU to the PLC did not affect dopamine release in the caudate or NAc shell. Histological evaluations showed no evidence of cell damage or death. Modeling of temperature rise demonstrates a maximum temperature change of 0.5°C with 13 W/cm 2 , suggesting that modulation is not due to thermal mechanisms. These studies show that LIFU at a moderate intensity provides a noninvasive, high spatial resolution means to modulate specific mesolimbic circuits that could be used in future studies to target and repair pathways that are dysfunctional in addiction and other psychiatric diseases.

Bioenergetic myths of energy transduction in eukaryotic cells

The study of energy transduction in eukaryotic cells has been divided between Bioenergetics and Physiology, reflecting and contributing to a variety of Bioenergetic myths considered here: 1) ATP production = energy production, 2) energy transduction is confined to mitochondria (plus glycolysis and chloroplasts), 3) mitochondria only produce heat when required, 4) glycolysis is inefficient compared to mitochondria, and 5) mitochondria are the main source of reactive oxygen species (ROS) in cells. These myths constitute a 'mitocentric' view of the cell that is wrong or unbalanced. In reality, mitochondria are the main site of energy dissipation and heat production in cells, and this is an essential function of mitochondria in mammals. Energy transduction and ROS production occur throughout the cell, particularly the cytosol and plasma membrane, and all cell membranes act as two-dimensional energy conduits. Glycolysis is efficient, and produces less heat per ATP than mitochondria, which might explain its increased use in muscle and cancer cells.

Sleep-wake body temperature regulates tau secretion in mice and correlates with CSF and plasma tau in humans

The sleep-wake cycle regulates interstitial fluid and cerebrospinal fluid (CSF) tau levels in both mouse and human by mechanisms that remain unestablished. Here, we reveal a novel pathway by which wakefulness increases extracellular tau levels in mouse and humans. In mice, higher body temperature (BT) associated with wakefulness and sleep deprivation increased CSF tau. In vitro, wakefulness temperatures upregulated tau secretion via a temperature-dependent increase in activity and expression of unconventional protein secretion pathway-1 components, namely caspase-3-mediated C-terminal cleavage of tau (TauC3), and membrane expression of PIP2 and syndecan-3. In humans, the increase in both CSF and plasma tau levels observed post-wakefulness correlated with BT increase during wakefulness. Our findings suggest sleep-wake variation in BT may contribute to regulating extracellular tau levels, highlighting the importance of thermoregulation in pathways linking sleep disturbance to neurodegeneration, and the potential for thermal intervention to prevent or delay tau-mediated neurodegeneration.

Modulatory Effects on Laminar Neural Activity Induced by Near-Infrared Light Stimulation with a Continuous Waveform to the Mouse Inferior Colliculus In Vivo

Infrared neural stimulation (INS) is a promising area of interest for the clinical application of a neuromodulation method. This is in part because of its low invasiveness, whereby INS modulates the activity of the neural tissue mainly through temperature changes. Additionally, INS may provide localized brain stimulation with less tissue damage. The inferior colliculus (IC) is a crucial auditory relay nucleus and a potential target for clinical application of INS to treat auditory diseases and develop artificial hearing devices. Here, using continuous INS with low to high-power density, we demonstrate the laminar modulation of neural activity in the mouse IC in the presence and absence of sound. We investigated stimulation parameters of INS to effectively modulate the neural activity in a facilitatory or inhibitory manner. A mathematical model of INS-driven brain tissue was first simulated, temperature distributions were numerically estimated, and stimulus parameters were selected from the simulation results. Subsequently, INS was administered to the IC of anesthetized mice, and the modulation effect on the neural activity was measured using an electrophysiological approach. We found that the modulatory effect of INS on the spontaneous neural activity was bidirectional between facilitatory and inhibitory effects. The modulatory effect on sound-evoked responses produced only an inhibitory effect to all examined stimulus intensities. Thus, this study provides important physiological evidence on the response properties of IC neurons to INS. Overall, INS can be used for the development of new therapies for neurological disorders and functional support devices for auditory central processing.

An optrode array for spatiotemporally-precise large-scale optogenetic stimulation of deep cortical layers in non-human primates

Optogenetics has transformed studies of neural circuit function, but remains challenging to apply to non-human primates (NHPs). A major challenge is delivering intense, spatiotemporally-precise, patterned photostimulation across large volumes in deep tissue. Such stimulation is critical, for example, to modulate selectively deep-layer corticocortical feedback circuits. To address this need, we have developed the Utah Optrode Array (UOA), a 10×10 glass needle waveguide array fabricated atop a novel opaque optical interposer, and bonded to an electrically addressable µLED array. In vivo experiments with the UOA demonstrated large-scale, spatiotemporally precise, activation of deep circuits in NHP cortex. Specifically, the UOA permitted both focal (confined to single layers/columns), and widespread (multiple layers/columns) optogenetic activation of deep layer neurons, as assessed with multi-channel laminar electrode arrays, simply by varying the number of activated µLEDs and/or the irradiance. Thus, the UOA represents a powerful optoelectronic device for targeted manipulation of deep-layer circuits in NHP models.

Transcranial Functional Ultrasound Imaging Detects Focused Ultrasound Neuromodulation Induced Hemodynamic Changes in Mouse and Nonhuman Primate Brains In Vivo

Focused ultrasound (FUS) is an emerging noinvasive technique for neuromodulation in the central nervous system (CNS). To evaluate the effects of FUS-induced neuromodulation, many studies used behavioral changes, functional magnetic resonance imaging (fMRI) or electroencephalography (EEG). However, behavioral readouts are often not easily mapped to specific brain activity, EEG has low spatial resolution limited to the surface of the brain and fMRI requires a large importable scanner that limits additional readouts and manipulations. In this context, functional ultrasound imaging (fUSI) holds promise to directly monitor the effects of FUS neuromodulation with high spatiotemporal resolution in a large field of view, with a comparatively simple and flexible setup. fUSI uses ultrafast Power Doppler Imaging (PDI) to measure changes in cerebral blood volume, which correlates well with neuronal activity and local field potentials. We designed a setup that aligns a FUS transducer with a linear array to allow immediate subsequent monitoring of the hemodynamic response with fUSI during and after FUS neuromodulation. We established a positive correlation between FUS pressure and the size of the activated area, as well as changes in cerebral blood volume (CBV) and found that unilateral sonications produce bilateral hemodynamic changes with ipsilateral accentuation in mice. We further demonstrated the ability to perform fully noninvasive, transcranial FUS-fUSI in nonhuman primates for the first time by using a lower-frequency transducer configuration.

Wireless closed-loop deep brain stimulation using microelectrode array probes

Deep brain stimulation (DBS), including optical stimulation and electrical stimulation, has been demonstrated considerable value in exploring pathological brain activity and developing treatments for neural disorders. Advances in DBS microsystems based on implantable microelectrode array (MEA) probes have opened up new opportunities for closed-loop DBS (CL-DBS) in situ. This technology can be used to detect damaged brain circuits and test the therapeutic potential for modulating the output of these circuits in a variety of diseases simultaneously. Despite the success and rapid utilization of MEA probe-based CL-DBS microsystems, key challenges, including excessive wired communication, need to be urgently resolved. In this review, we considered recent advances in MEA probe-based wireless CL-DBS microsystems and outlined the major issues and promising prospects in this field. This technology has the potential to offer novel therapeutic options for psychiatric disorders in the future.

Multifunctional Fiber-Based Optoacoustic Emitter as a Bidirectional Brain Interface

A bidirectional brain interface with both "write" and "read" functions can be an important tool for fundamental studies and potential clinical treatments for neurological diseases. Herein, a miniaturized multifunctional fiber-based optoacoustic emitter (mFOE) is reported thatintegrates simultaneous optoacoustic stimulation for "write" and electrophysiology recording of neural circuits for "read". Because of the intrinsic ability of neurons to respond to acoustic wave, there is no requirement of the viral transfection. The orthogonality between optoacoustic waves and electrical field provides a solution to avoid the interference between electrical stimulation and recording. The stimulation function of the mFOE is first validated in cultured ratcortical neurons using calcium imaging. In vivo application of mFOE for successful simultaneous optoacoustic stimulation and electrical recording of brain activities is confirmed in mouse hippocampus in both acute and chronical applications up to 1 month. Minor brain tissue damage is confirmed after these applications. The capability of simultaneous neural stimulation and recording enabled by mFOE opens up new possibilities for the investigation of neural circuits and brings new insights into the study of ultrasound neurostimulation.

A phased array ultrasound system with a robotic arm for neuromodulation

BACKGROUND

Ultrasonic neuromodulation (UNMOD) provides a non-invasive brain stimulation. However, the high-resolution region-specificity of UNMOD with a single element transducer combined with a mechanical positioning system could have limits due to the intrinsic positioning error from mechanical systems.

OBJECTIVE/HYPOTHESIS

A phased array system could lead to highly selective neuromodulation with electronic control.

METHODS

A specialized phased-array system with a robotic arm is implemented for a rhesus monkey model. Various primary motor cortex areas related to tail, hand, and mouth were stimulated with a 200 μm step size. The ultrasonic parameters were ISPTA of 840 mW/cm2, pulse repetition frequency of 100 Hz, and a 5% duty factor at 600 kHz. The induced movement were recorded and analyzed.

RESULTS

Separate digits, mouth, and tongue motions were successfully induced by electronically controlling the focus. The identical body part movement could be induced when the focus was moved back to the identical primary motor cortex with electronic control. Accordingly, the reproducibility of UNMOD could be partially validated with rhesus monkey model.

CONCLUSION

A phased-array system appears to have a potential for the non-invasive and region-selective neuromodulation method.

Thermal safety considerations for implantable micro-coil design

Micro magnetic stimulation of the brain via implantable micro-coils is a promising novel technology for neuromodulation. Careful consideration of the thermodynamic profile of such devices is necessary for effective and safe designs.Objective.We seek to quantify the thermal profile of bent wire micro-coils in order to understand and mitigate thermal impacts of micro-coil stimulation.Approach. In this study, we use fine wire thermocouples and COMSOL finite element modeling to examine the profile of the thermal gradients generated near bent wire micro-coils submerged in a water bath during stimulation. We tested a range of stimulation parameters previously reported in the literature such as voltage amplitude, stimulus frequency, stimulus repetition rate and coil wire materials.Main results. We found temperature increases ranging from <1 °C to 8.4 °C depending upon the stimulation parameters tested and coil wire materials used. Numerical modeling of the thermodynamics identified hot spots of the highest temperatures along the micro-coil contributing to the thermal gradients and demonstrated that these thermal gradients can be mitigated by the choice of wire conductor material and construction geometry.Significance. ISO standard 14708-1 designates a thermal safety limit of 2 °C temperature increase for active implantable medical devices. By switching the coil wire material from platinum/iridium to gold, our study achieved a 5-6-fold decrease in the thermal impact of coil stimulation. The thermal gradients generated from the gold wire coil were measured below the 2 °C safety limit for all stimulation parameters tested.

Real Space and Time Imaging of Collective Headgroup Dipole Motions in Zwitterionic Lipid Bilayers

Lipid bilayers are supramolecular structures responsible for a range of processes, such as transmembrane transport of ions and solutes, and sorting and replication of genetic materials, to name just a few. Some of these processes are transient and currently, cannot be visualized in real space and time. Here, we developed an approach using 1D, 2D, and 3D Van Hove correlation functions to image collective headgroup dipole motions in zwitterionic phospholipid bilayers. We show that both 2D and 3D spatiotemporal images of headgroup dipoles are consistent with commonly understood dynamic features of fluids. However, analysis of the 1D Van Hove function reveals lateral transient and re-emergent collective dynamics of the headgroup dipoles-occurring at picosecond time scales-that transmit and dissipate heat at longer times, due to relaxation processes. At the same time, the headgroup dipoles also generate membrane surface undulations due a collective tilting of the headgroup dipoles. A continuous intensity band of headgroup dipole spatiotemporal correlations-at nanometer length and nanosecond time scales-indicates that dipoles undergo stretching and squeezing elastic deformations. Importantly, the above mentioned intrinsic headgroup dipole motions can be externally stimulated at GHz-frequency scale, enhancing their flexoelectric and piezoelectric capabilities (i.e., increased conversion efficiency of mechanical energy into electric energy). In conclusion, we discuss how lipid membranes can provide molecular-level insights about biological learning and memory, and as platforms for the development of the next generation of neuromorphic computers.

Spatial and Amplitude Dynamics of Neurostimulation: Insights from the Acute Intrahippocampal Kainate Seizure Mouse Model

Objective

Neurostimulation is an emerging treatment for patients with medically refractory epilepsy, which is used to suppress, prevent, and terminate seizure activity. Unfortunately, after implantation and despite best clinical practice, most patients continue to have persistent seizures even after years of empirical optimization. The objective of this study is to determine optimal spatial and amplitude properties of neurostimulation in inhibiting epileptiform activity in an acute hippocampal seizure model.

Methods

We performed high-throughput testing of high-frequency focal brain stimulation in the acute intrahippocampal kainic acid mouse model of temporal lobe epilepsy. We evaluated combinations of six anatomic targets and three stimulus amplitudes.

Results

We found that the spike-suppressive effects of high-frequency neurostimulation are highly dependent on the stimulation amplitude and location, with higher amplitude stimulation being significantly more effective. Epileptiform spiking activity was significantly reduced with ipsilateral 250 μA stimulation of the CA1 and CA3 hippocampal regions with 21.5% and 22.2% reductions, respectively. In contrast, we found that spiking frequency and amplitude significantly increased with stimulation of the ventral hippocampal commissure. We further found spatial differences with broader effects from CA1 versus CA3 stimulation.

Significance

These findings demonstrate that the effects of therapeutic neurostimulation in an acute hippocampal seizure model are highly dependent on the location of stimulation and stimulus amplitude. We provide a platform to optimize the anti-seizure effects of neurostimulation, and demonstrate that an exploration of the large electrical parameter and location space can improve current modalities for treating epilepsy.

Key Points

Evaluated spatial and temporal parameters of neurostimulation in a mouse model of acute seizuresBrief bursts of high-frequency (100 Hz) stimulation effectively interrupted epileptiform activity.The suppressive effect was highly dependent on stimulation amplitude and was maximal at the ipsilateral CA1 and CA3 regions.Pro-excitatory effects were identified with high-amplitude high-frequency stimulation at the ventral hippocampal commissure and contralateral CA1.