Electrophysiology publications

Purpose: To reduce amplitude variability of auditory evoked potentials (AEPs) we developed a circuit that generates an electric calibration pulse (CalPulse) following each evoking sound presentation. We aim to determine if external CalPulse signals can function as a reliable calibration reference for AEP amplitude measurements. Methods: The CalPulse circuit was integrated with an AEP recording montage. The amplitude and morphology of two CalPulse signals (square wave and sine wave) was first assessed in vitro with electrodes submerged in saline. Repeatability of the two signals was then compared in vivo using five (3 male/2 female) 4-month-old CBA/CAJ mice and four unique auditory brainstem response (ABR) configurations. Sine wave CalPulse amplitudes were subsequently used to adjust raw ABR wave-1 amplitudes in a sample of 38 (19 male/19 female) CBA/CaJ mice. Variability in adjusted wave-1 amplitudes was compared with raw amplitudes. Measurements were repeated every month for 4 months (8 to 11 months old) to evaluate its potential as a tool to detect age-related changes in auditory function. Results: Wave quality examinations indicate that both CalPulse signal types are stable in vitro, with the sine wave signal being more repeatable when recorded in vivo. Sine wave CalPulse amplitudes correlated positively with ABR wave-1 amplitudes. Normalizing wave-1 amplitudes with CalPulse measures significantly reduced within-subject variability. Normalized wave-1 amplitudes showed a significant decrease at 10 months of age consistent with age-related cochlear synaptopathy, while uncalibrated wave-1 amplitudes from the same recordings failed to detect this decrease. Conclusion: Our new calibration circuit can be used to improve diagnostic sensitivity of AEP measures.

A large body of literature has shown that sensory neurons typically exhibit adaptation to repetitive stimulation. However, adaptation alone does not account for the ability of sensory systems to remain vigilant to the environment in spite of repetitive sensory stimulation. Here, we investigated single neuron responses to sequences of sounds repeatedly delivered from a particular spatial location. Instead of inducing adaptation, repetitive stimulation evoked long-lasting and location-specific facilitation (LSF) in firing rate of nearly 90% of recorded neurons. The LSF decreased with decreasing presentation probability and diminished when sounds were randomly delivered from multiple spatial locations. Intracellular recordings showed that repetitive sound stimulation evoked sustained membrane potential depolarization. Computational modeling showed that increased arousal, not decreased inhibition, underlies the LSF. Our findings reveal a novel form of contextual modulation in the marmoset auditory cortex that may play a role in tasks such as auditory streaming and the cocktail party effect.

Restoring upper limb function is critical in individuals with central paralysis, and hand control is a priority in patients with neurological impairments. Functional electrical stimulation with implantable electrodes targeting the peripheral nervous system has the potential to selectively recruit hand muscles and generate multiple functional hand movements. However, the implantation of electrodes in the forearm or elbow areas requires multiple incisions for surgery, and elbow joint movements cannot be performed. In this study, we designed and implanted two epineural cuffs on the median and radial nerves in the distal brachial plexus of a single Japanese macaque ( Macaca fuscata ) monkey. The cuffs were successfully placed via an axillary approach using a single incision. Electrical stimuli were applied to innervate the contraction patterns of the hand, forearm, and triceps muscles relevant to the median and radial nerves. The evoked potentials of the target muscles electrically stimulated the distal brachial plexus to reliably and selectively innervate the upper limb muscles at the functional group level. Our results demonstrated that the distal brachial plexus can be a useful stimulation site for upper limb muscle contraction and that the axillary approach enables electrode placement to peripheral nerves required for upper limb control.

Peripheral and brain-produced sex hormones exert sex-specific regulation of hippocampal cognitive function. Estrogens produced by neuronal aromatase regulate inhibitory neurons (INs) and hippocampal-dependent memory in adult female mice, but not in males. How and when this sex effect is established and how peripheral and brain sources of estrogens interact in the control of hippocampal INs is currently unknown. Using ex vivo electrophysiology, fiber photometry, molecular analysis, estrous cycle monitoring, and neonatal hormonal manipulations, we unveil estrous cycle-dependent and estrous cycle-independent features of CA1 parvalbumin (PV) INs and hippocampal inhibition in adult female mice. Before puberty, aromatase is expressed in PV INs and regulates synaptic inhibition in female but not in male mice. Neonatal testosterone administration altered prepubertal female mouse hippocampus-dependent memory, PV IN function and estrogenic regulation of adult female synaptic inhibition and PV IN perineuronal nets. Our results suggest that sex differences in brain-derived estrogen regulation of CA1 inhibition are established by organizational effects of neonatal gonadal hormones and highlight the role of INs as mediators of the sexual differentiation of the hippocampus.

The medial prefrontal cortex (mPFC) and hippocampus are critical for memory retrieval, decision making, and emotional regulation. While ventral CA1 (vCA1) shows direct and reciprocal connections with mPFC, dorsal CA1 (dCA1) forms indirect pathways to mPFC, notably via the thalamic reuniens nucleus (Re). Neuroanatomical tracing has documented structural connectivity of this indirect pathway through Re however, its functional operation is largely unexplored. Here, we used in vivo and in vitro electrophysiology along with optogenetics to address this question. Whole-cell patch-clamp recordings in acute mouse brain slices revealed both monosynaptic excitatory responses and disynaptic feedforward inhibition at Re–mPFC synapses. However, we also identified a prolonged excitation of mPFC by Re. These early monosynaptic and late recurrent components are in marked contrast to the primarily feedforward inhibition characteristic of thalamic inputs to the neocortex. Local field potential recordings in mPFC brain slices revealed prolonged synaptic activity throughout all cortical lamina upon Re activation, with the late excitation enhanced by blockade of parvalbumin neurons and GABA A Rs. In vivo Neuropixels recordings in head-fixed awake mice revealed a similar prolonged excitation of mPFC units by Re activation. In summary, Re output produces recurrent feedforward excitation within mPFC suggesting a potent amplification system in the Re–mPFC network. This may facilitate amplification of dCA1->mPFC signals for which Re acts as the primary conduit, as there is little direct connectivity. In addition, the capacity of mPFC neurons to fire bursts of action potentials in response to Re input suggests that these synapses have a high gain.

Dopamine (DA) signals to the striatum play critical roles in shaping and sustaining stimulus-reward associations. In primates, however, the dynamics of the DA signals remain unknown since conventional methods are not necessarily appropriate in terms of the spatiotemporal resolution or chemical specificity sufficient for detecting the DA signals. In our study, fiber photometry with a fluorescent DA sensor was employed to identify reward-related DA transients in the monkey striatum. This technique, which directly monitors local DA release, reveals a reward prediction error signal in the anterior putamen originating from midbrain DA neurons. Further, DA transients in the head of the caudate nucleus exhibit a value-based response to reward-predicting stimuli. These signals have been found to arise from two separate groups of DA neurons in the substantia nigra pars compacta. The present results demonstrate that fluorescence DA monitoring is applicable to detect DA signals in the primate striatum for investigating their roles.

Steady-state auditory evoked potentials are useful for studying the human auditory system and diagnosing hearing disorders. Identifying the generators of these potentials is essential for interpretation of data and for determining appropriate clinical and research applications. Here we infer putative generators of a steady-state potential measured from an electrode on the eardrum and compare this potential with the traditional envelope following response (EFR) measured from an electrode on the high forehead (N = 18, 10 female). We hypothesized that responses from the eardrum electrode would be consistent with an auditory nerve (AN) compound action potential (CAP) evoked by each cycle of the stimulus envelope, resulting in a potential we call CAPENV. Steady-state potentials were evoked by a 90 dB peSPL, 3000-Hz puretone carrier whose envelope was modulated by a tone sweep with frequencies from 20 to 160 Hz or 80 to 640 Hz. We calculated group delay to infer potential generators. We also compared the empirically measured CAPENV with simulated CAPENV from a humanized model of AN responses. Response latencies and model simulations support the interpretation that CAPENV is generated by the AN rather than hair cell or brainstem generators for all modulation frequencies tested. Conversely, latencies for the traditional EFR were consistent with a shift from cortical to brainstem generators as the modulation frequency increased from 20 to 200 Hz. We propose that CAPENV may be a fruitful tool for assessing AN function in humans with suspected AN fiber loss and/or temporal coding disorders.

Voluntary, flexible stopping of speech output is an essential aspect of speech motor control, especially during natural conversations. The cognitive and neural mechanisms of speech inhibition are not well understood. Here we have recorded direct high-density cortical activity while participants engaged in continuous speech production and were visually cued to stop speaking. Neural recordings revealed distinct activity in the premotor frontal cortex correlated with stopping speech. This activity was found in largely separate cortical sites from regions encoding vocal tract articulatory movements. Moreover, this activity primarily occurred with abrupt stopping in the middle of an utterance, rather than naturally completing a phrase. Electrocortical stimulation at many premotor sites with inhibitory stop activity caused involuntary speech arrest, which contradicts previous clinical interpretations of this effect as evidence for critical centres of speech production. Together, these results suggest a previously unknown premotor cortical network that supports the inhibitory control of speech, providing implications for understanding both natural and altered speech production.

Here, we present a protocol to decode Mandarin sentences from invasive neural recordings using a brain-to-text framework. We describe steps for preparing materials, including designing the sentence corpus and setting up electrocorticography (ECoG) recording systems. We then detail procedures for decoding, such as data preprocessing, selection of speech-responsive electrodes, speech detection, syllable and tone decoding, and language modeling. We also outline performance evaluation metrics. For complete details on the use and execution of this protocol, please refer to Zhang et al.1.

We used several post hoc pooling models to investigate the ability of primate auditory cortex to leverage population coding in the detection of amplitude-modulated sounds. When cells are indiscriminately pooled, primary auditory cortex (A1) detects amplitude-modulated sounds better than middle-lateral belt (ML). When cells that decrease firing rate with increasing modulation depth are excluded, or used in a push-pull opponent fashion, detection is similar in the two areas, and macaque behavior can be approximated using reasonably sized pools.

Objective: This study aims to investigate how reproductive experience (RE) alters thermal preference and thermoregulation in female mice, with a focus on estrogen receptor alpha (ERα)-expressing neurons in the preoptic area (POA). Methods: Thermal preference and body temperature were measured in female mice with and without RE, and virgin female mice with selective deletion of ERα from the POA (ERαPOA-KO). The number and activity of ERα-expressing POA neurons (ERαPOA) were assessed using immunohistochemistry and in vitro electrophysiology in response to temperature changes and ERα agonist. Results: We showed that female mice prefer a cooler environment starting from late pregnancy and persisting long term postpartum. Female mice with RE (>4 weeks post-weaning) displayed lower body temperature and a lower thermal preferred temperature, and lost preference for warm environments (30 °C) but preserved avoidance of cold environments (15 °C). This was associated with a significant decrease in the number of ERαPOA neurons. Importantly, virgin female ERαPOA-KO mice displayed lower thermal preferred temperature and impaired warm preference, mimicking RE mice. We further found that distinct ERαPOA subpopulations can be regulated by temperature changes with or without presynaptic blockers, and by ERα agonist. More importantly, RE decreased the number of warm-activated ERαPOA neurons and reduced the excitatory effects of warmth and estrogen-ERα signaling, while cold-activated ERαPOA neurons were slightly enhanced in female mice with RE. Conclusion: Our results support that the thermosensing ability and estrogenic effects in ERαPOA neurons are regulated by reproductive experience, altering thermal preference.

Neural dynamics are thought to reflect computations that relay and transform information in the brain. Previous studies have identified the neural population dynamics in many individual brain regions as a trajectory geometry, preserving a common computational motif. However, whether these populations share particular geometric patterns across brain-wide neural populations remains unclear. Here, by mapping neural dynamics widely across temporal/frontal/limbic regions in the cortical and subcortical structures of monkeys, we show that 10 neural populations, including 2,500 neurons, propagate visual item information in a stochastic manner. We found that visual inputs predominantly evoked rotational dynamics in the higher-order visual area, TE, and its downstream striatum tail, while curvy/straight dynamics appeared frequently downstream in the orbitofrontal/hippocampal network. These geometric changes were not deterministic but rather stochastic according to their respective emergence rates. Our meta-analysis results indicate that visual information propagates as a heterogeneous mixture of stochastic neural population signals in the brain.

The superior para-olivary nucleus (SPN or SPON) is a prominent nucleus in the superior olivary complex of the auditory brainstem. The cellular composition of the nucleus reportedly differs between species, but a prominent recurring feature is the unusual characteristic to not respond during a sound but at its offset. Blocking glycine has shown that sound-induced inhibition is the mechanism, but the time course of the responsible synaptic events has not been directly measured in vivo. We obtained intracellular recordings in the Mongolian gerbil (meriones unguiculatus) with patch electrodes containing biocytin, and retrieved 12 labeled neurons with large dendritic trees within and around the SPN region. We found that these neurons could be categorized into three classes that show consistency along multiple dimensions like ultrastructure, spontaneous activity, and responses to current injection and a variety of ipsi- and contralateral sounds. Fast cells fire at onset of depolarizing current, generate short-latency rebound spikes to sound or hyperpolarizing current, and show dense synaptic coverage. Slow cells show sparse synaptic coverage, sustained responses to depolarization, and inhibition with a slow time course to hyperpolarizing current or sound. Uninhibited cells form a third class which profoundly differ in their responses to sound, lacking rebound spiking. We propose that fast cells project to the inferior colliculus, and slow cells to the cochlear nucleus.

Although recent work has made headway in understanding the neural temporospatial dynamics of conscious perception, much of that work has focused on visual paradigms. To determine whether there are shared mechanisms for perceptual consciousness across sensory modalities, here we test within the auditory domain. Participants completed an auditory threshold task while undergoing intracranial electroencephalography. Recordings from >2,800 grey matter electrodes were analyzed for broadband gamma power (a range which reflects local neural activity). For perceived trials, we find nearly simultaneous activity in early auditory regions, the right caudal middle frontal gyrus, and the non-auditory thalamus; followed by a wave of activity that sweeps through auditory association regions into parietal and frontal cortices. For not perceived trials, significant activity is restricted to early auditory regions. These findings show the cortical and subcortical networks involved in auditory perception are similar to those observed with vision, suggesting shared mechanisms for conscious perception.

Closed-loop neural control is a powerful tool for both the scientific exploration of neural function and for mitigating deficiencies found in open-loop deep brain stimulation (DBS). Here, we present a protocol for artificial intelligence-guided neural control in rats using deep reinforcement learning (RL) and infrared neural stimulation (INS). We describe steps for integrating RL closed-loop control into neuroscience and neuromodulation studies. We then detail procedures for using and deploying infrared INS in chronic DBS applications. For complete details on the use and execution of this protocol, please refer to Coventry et al.1 and Coventry and Bartlett.2.

Face processing models propose gradually more complex receptive field properties culminating in invariant representations in anterior inferotemporal cortex (aITC), leading to late socio-emotionally relevant encoding in pre- and orbitofrontal cortex (POC). Top-down facilitation models, however, predict that some lower-level POC neurons respond faster than aITC. To resolve this discrepancy, we recorded from 2,459 neurons in fMRI-defined POC and aITC face patches. POC patches are more heterogeneous, containing smaller fractions of face-selective neurons than aITC and a mixture of responses to faces and non-faces. In one POC patch, face responses are surprisingly fast, outpacing those in aITC. Moreover, its responses correlate inversely with stimulus spatial frequency. Hence, our extensive data, with a large diversity of POC neurons, support both models and suggest one POC face patch might be specialized in fast, low-level face processing, which may enable (partially) invariant face representations during subsequent processing stages in inferotemporal cortex (ITC).

Background: Successful seizure onset zone (SOZ) localisation for epilepsy surgery often relies upon intracranial recordings. Accurate delineation requires anatomical detail yet influences of intracranial electrode density on clinical variables have not been systematically studied. Methods: In this experimental study we compared SOZ localisation between spontaneously captured seizures on higher-density depth and grid electrode arrays (4-5 mm inter-electrode spacing) vs. lower-density resampled versions of those same seizures (8-10 mm spacing). Since traditional review of channel traces would reveal density conditions, we instead projected seizure activity data as heatmaps on patient brain reconstructions and hid electrode locations. Using a single-blinded randomised crossover design, six attending-level epileptologists viewed these visualisations from ten patients under both higher-density and lower-density conditions (n = 120 observations) and digitally annotated SOZs. Findings: Inter-rater agreement between epileptologists on annotated margins was moderate (average Cohen's kappa: 0.47) and lower for the lower-density condition (p = 0.021, mixed effects model). Scorer confidence ratings did not differ between higher- and lower-density conditions (p = 0.410). The spatial extents of annotated SOZs for higher-density recordings were 25.4% larger on average (p = 0.011) and always closer to true SOZ extents in computer simulations, relative to lower-density. Interpretation: Epileptologists using higher-density depth and subdural intracranial EEG recordings had higher inter-rater agreement and identified larger extents of SOZs compared to lower-density recordings. While further studies assessing surgical outcomes in more patients are needed, these results suggest higher densities of electrodes on already-implanted hardware may reveal sub-centimetre extensions and clearer functional contiguity of the SOZ(s) for better appraisals of pathophysiological margins in epilepsy surgery. Funding: This work was supported by the National Institutes of Health through NINDS grant K23NS110920 and through a UCSF Weill Institute for Neurosciences Pilot Award.

Recent studies show that systemic administration of a glucagon-like peptide-1 receptor (GLP-1R) agonist is sufficient to attenuate cocaine seeking. However, the neural mechanisms mediating these effects and the role of endogenous central GLP-1 signaling in cocaine seeking remain unknown. Here, we show that voluntary cocaine taking decreased plasma GLP-1 levels in rats and that chemogenetic activation of GLP-1–producing neurons in the nucleus tractus solitarius that project to the ventral tegmental area (VTA) decreased cocaine seeking. Single-nuclei transcriptomics and FISH studies revealed that GLP-1Rs are expressed primarily on GABA neurons in the VTA. Using in vivo fiber photometry, we found that the efficacy of a systemic GLP-1R agonist to attenuate cocaine seeking was associated with increased activity of VTA GABA neurons and decreased activity of VTA dopamine neurons. Together, these findings suggest that targeting central GLP-1 circuits may be an effective strategy toward reducing cocaine relapse and highlight a functional role of GABAergic GLP-1R–expressing midbrain neurons in drug seeking.

To comprehend the volumetric neural connectivity of a brain organoid, it is crucial to monitor the spatiotemporal electrophysiological signals within the organoid, known as intra-organoid signals. However, previous methods risked damaging the three-dimensional (3D) cytoarchitecture of organoids, either through sectioning or inserting rigid needle-like electrodes. Also, the limited numbers of electrodes in fixed positions with non-adjustable electrode shapes were insufficient for examining the complex neural activity throughout the organoid. Herein, we present a magnetically reshapable 3D multi-electrode array (MEA) using direct printing of liquid metals for electrophysiological analysis of brain organoids. The adaptable distribution and the softness of these printed electrodes facilitate the spatiotemporal recording of intra-organoid signals. Furthermore, the unique capability to reshape these soft electrodes within the organoid using magnetic fields allows a single electrode in the MEA to record from multiple points, effectively increasing the recording site density without the need for additional electrodes.

Episodic memory relies on the formation and retrieval of content-specific memory traces. In addition to their veridical reactivation, previous studies have indicated that traces may undergo substantial transformations. However, the exact time course and regional distribution of reinstatement and transformation during recognition memory have remained unclear. We applied representational similarity analysis to human intracranial electroencephalography to track the spatiotemporal dynamics underlying the reinstatement and transformation of memory traces. Specifically, we examined how reinstatement and transformation of item-specific representations across occipital, ventral visual, and lateral parietal cortices contribute to successful memory formation and recognition. Our findings suggest that reinstatement in temporal cortex and transformation in parietal cortex coexist and provide complementary strategies for recognition. Further, we find that generalization and differentiation of neural representations contribute to memory and probe memory-specific correspondence with deep neural network (DNN) model features. Our results suggest that memory formation is particularly supported by generalized and mnemonic representational formats beyond the visual features of a DNN.