Single Unit publications

The development of motor control in primary motor cortex (M1) requires both movements and neural activity. In rats, cortical motor control first appears around postnatal day (P) 25, prior to which movements are generated by subcortical motor nuclei such as the red nucleus (RN). While these subcortically generated movements are thought to provide the activity that guides the development of M1, the specific movements associated with M1 activity and their somatotopic and temporal precision remain unknown. Here, we performed acute electrophysiological recordings of neural activity in the forelimb region of M1 of P12–24 rats as they cycled between sleep and wake and compared M1 and RN activity in P24 rats. At every age, M1 neurons exhibited somatopically precise activity during REM sleep twitches, along with strong activity during wake movements. From P12 to P24, the proportion of neurons exhibiting twitch-related activity decreased, twitch-related activity became more temporally refined, and a larger fraction of spikes occurred before movement onset. At P24, M1 showed less premovement activity than RN. Further, in contrast to the non-selective activity seen in M1, some RN neurons showed movement-selective activity patterns during wake, firing only during particular wake movements. These findings reveal that movement-related activity in M1 is somatotopically precise by P12 and temporally precise by P24. But M1 still lacks the strong premovement activity and selectivity characteristic of RN, suggesting that at P24, subcortical outputs remain the main drivers of M1’s movement-related activity.

Male bushcrickets produce complex species-specific songs to attract mating partners. Since the neuronal processing underlying song-pattern detection is not fully understood, we analysed extracellularly recorded song-induced spike responses and local field potentials across the first stage of auditory processing in the prothoracic ganglion of Mecopoda elongata. We analysed the influence of the temporal structure and of any change in amplitude of spiking and local field potentials. We presented the complete chirp and compared the neuronal response pattern with those responses evoked individually by each pulse of the chirp. Our data revealed: (i) the complete chirp leads to a transient summation in local field potentials over the time course of the chirp, and (ii) significantly fewer action potentials occur during the chirp presentation than to the individually presented pulses. Our data provide insights into the question of how an acoustical signal can be used to extract those features from sensory information that are important for auditory behaviour, such as chorus formation, species recognition, or phonotaxis.

How neuronal firing within a circuit encodes behavioural intensity, like running speed, is largely unknown. Projections from temporal association cortex (TeA) and superior colliculus (SC) to dorsal periaqueductal grey (dPAG) circuit can both trigger running behaviour. Using in vivo loose-patch recordings with circuit manipulations in mice, we quantified a firing - speed relationship and established its encoding model. Here, we report two behavioural patterns induced by circuit activation: backing away and rebound running. Mechanistically, dPAG CaMKIIα neurons receiving inputs from either TeA or SC, function as distinct “behavioural units”, controlling two “unit behaviours” of running and backing away, respectively. The unidirectional inhibition from the backing away unit to the running unit is mediated by somatostatin (SOM) neurons in dPAG, enabling transitions among four behavioural states: running, backing away, stopping, and rebound running. Both running and backing away behaviours follow a unified motor encoding model, quantified by a single-phase association equation.

A central goal in neuroscience is to clarify how neural circuits translate sensory input into adaptive behaviours. Although unisensory evoked escape circuits in mice are well defined, it remains unclear whether a single nucleus contains specialized sensory, sensory‒motor decision, and motor command neurons for escapes driven by distinct sensory cues, and how these neurons form functional microcircuits. Using multiple sensory stimuli in mice, we identified the temporal association cortex (TeA) as a critical escape hub. Combining in vivo electrophysiology, optogenetics and chemogenetics, we characterized three distinct neuron subtypes within TeA layer 5 (L5) CaMKII neurons that correspond to these three functional classes. Intratelencephalic (IT) neurons serve as sensory‒motor decision neurons, while layer matched pyramidal tract (PT) neurons projecting to the dorsal periaqueductal grey (dPAG) act as motor command neurons. We reveal a laminar IT–PT microcircuit that converts sensory input into sensory-motor decisions and commands for escape locomotion.

In the auditory cortex, neural responses to stimuli inside receptive fields (RFs) can be further facilitated by behavioral demands, such as attending to a spatial location. It is less clear how off-RF stimuli modulate neural responses and contribute to behavioral tasks. Our recent study revealed a particular form of location-specific facilitation evoked by repeated stimulation from an off-RF location, suggesting behavioral modulation of spatial RFs. To further explore this question, we trained marmosets to attend to sound locations that were either inside or outside the RFs of auditory cortical neurons. The majority of neurons showed increased firing rates at target locations inside their RFs. Interestingly, this increase also occurred outside the RFs, sometimes exceeding the responses at the RF center during passive listening. This task-related off-RF facilitation was much more common in the caudal area than in the rostral area and the primary auditory cortex. A normalization model reproduced the off-RF facilitation using widespread suppression. The model’s prediction was confirmed by experimental observations of widespread reductions in firing rate and hyperpolarized membrane potentials for off-RF stimuli. These results suggest that behavioral task demands recruit a broader range of neurons than those that are responsive to a target sound in the passive state.

The acoustic flutter is processed through complementary monotonic rate coding and cannot be modulated by other acoustic parameters in the auditory cortex (AC). However, it remains unclear how the inferior colliculus (IC) encodes acoustic flutter, especially when changing other acoustic parameters. Here, we recorded IC neural activity in response to acoustic flutter and determined the existence of conjunctive processing between repetition rate and other acoustic parameters. We found that most IC neurons also encode the repetition rate at the flutter range through complementary monotonic rate coding. In addition, although the acoustic parameters did not change their monotonicity, most IC neurons encode both repetition rate and other acoustic parameters, different from the flutter processing in AC. Thus, complementary monotonic rate coding for acoustic flutter was widespread in the auditory system; however, coding specificity for repetition rate increased from IC to AC, and the capacity for conjunctive coding with other acoustic parameters decreased.

Background: In Parkinson's disease, motor network electrophysiology frequently exhibits excessive beta oscillations. The cornerstone of therapeutic efficacy lies in the ability to modulate these pathological oscillations. Transcranial alternating current stimulation (tACS), a non-invasive method that applies oscillating electric fields to modulate ongoing brain activity, offers a promising approach. Objective: The objective of the manuscript is to investigate the dose-dependent effects of tACS on motor network cortical neurons in a Parkinson's disease model. Methods: We recorded neuronal spike activity in the motor cortex in parkinsonian non-human primates during tACS to determine how stimulation-induced electric fields affect spike timing. Results: Strong electric fields entrained neural activity at the stimulation frequency but altered the preferred spiking phase. Conversely, weak fields disrupted beta-band synchronization by modulating spike timing and phase preference. Frequency-matched stimulation significantly enhanced entrainment when aligned with endogenous oscillatory activity. Conclusion: Thus, with appropriately chosen stimulation parameters, tACS exhibits significant potential for controlling and modulating pathological oscillatory patterns that are characteristic of many neurological disorders.

Harmonicity is a property of complex sounds such as vocalizations or music, but it remains unclear how harmonicity is processed in the auditory cortex (ACtx). Subregions of ACtx are thought to process harmonic stimuli differently. Selective responses to sound features in ACtx emerge hierarchically from primary ACtx (A1) L4 and secondary ACtx (A2) layer (L)2/3, which is believed to be the most responsive to harmonic sounds. Since harmonic stacks can range from 2 to >10 components, being more similar to naturalistic vocalizations, harmonic sensitivity might also arise hierarchically across layers and areas. We studied responses to harmonic stacks of 2–10 frequencies across A1 L4, A1 L2/3, and A2 L2/3 in adult male and female mice using in vivo two-photon microscopy. We found harmonic-sensitive neurons (HNs) responding only to harmonic stacks but not to individual frequencies in all areas at similar proportions. HNs showed highly nonlinear spectral integration of harmonic frequencies that decreased as the harmonic stacks became more complex. Specifically, onset-biased HNs showed greater nonlinearity than offset-biased HNs only in A1 L4. Moreover, HNs in A1 L4 exhibited higher signal correlation than A2 L2/3. Sound-responsive neurons in A1 L4 have the weakest noise correlation compared with A1 L2/3 and A2 L2/3. Together, harmonic sensitivity is not a unique feature of A2 L2/3 but is already established in A1 L4, where neurons robustly encode harmonic sounds through sparse connections.

Habituation is a crucial sensory filtering mechanism whose dysregulation can lead to a continuously intense world in disorders with hypersensitivity. Although habituation is often termed the simplest form of learning, its circuit mechanisms remain elusive. Conventional peripheral explanations fail to fully account for long-term habituation in complex sensory environments, leading to theories proposing top-down regulation. Here we evaluated two competing top-down mechanistic explanations for habituation in mice (growth in predictive filtering and waning of novelty-driven amplification) and identified an unexpected role for the orbitofrontal cortex (OFC) in predictive filtering. After daily sound exposure, neural habituation in the primary auditory cortex (A1) was reversed by inactivating the OFC. Top-down projections from the OFC, but not other frontal areas, carried predictive signals that grew with daily sound experience and suppressed A1 via somatostatin-expressing inhibitory neurons. Thus, prediction signals from the OFC cancel out anticipated stimuli by generating their 'negative images' in sensory cortices.

Norepinephrine (NE) is an important mediator of sympathetic activity that influences breathing. At the level of the inspiratory neural network, the preBötzinger complex (preBötC), NE modulation orchestrates changes in neuronal network dynamics that influence the stability of inspiratory rhythmogenesis. While this phenomenon has largely been attributed to NE-modulation of intrinsic excitability of inspiratory preBötC neurons, NE is also capable of modulating synaptic drive. Here, we resolve how NE affects synaptic properties and changes the activity dynamics of interconnected preBötC neurons in rhythmic brainstem slice preparations. Increased network burst amplitude and frequency coincided with enhanced inspiratory drive currents at the single neuron level. This increased drive was blocked by the NMDA receptor (NMDAR) antagonist, APV. Our in silico modeling indicated that synaptic calcium entry via NDMAR is key to maintaining network synchrony during this elevated state of excitability. This was consistent with our multi-electrode array studies revealing that NE-dependent NMDAR activity enhances and preserves synchrony during inspiratory network bursts. This synaptic mechanism may be a critical determinant for shaping inspiratory drive associated with changed neuromodulatory environments. Significance Statement This study demonstrates a previously undescribed synaptic mechanism by which noradrenergic modulation recruits NMDAR activity and shifts inspiratory network dynamics leading to a stable network state where synchronization is preserved among inspiratory neurons. This may be a critical mechanism preventing ventilatory instability when sympathetic activity is enhanced.

Brain systems mediating responses to previously encountered threats provide critical survival functions. Fear memory and extinction are underpinned by neural representations in the basolateral amygdala (BLA) 1–7 , but the contribution of non-neuronal cells, including astrocytes, to these processes remains unresolved. Here, using in vivo calcium (Ca 2+ ) imaging and causal astrocyte manipulations, we find that BLA astrocytes dynamically track fear state and support fear memory retrieval and extinction. By combining astrocyte manipulations with in vivo BLA neuronal Ca 2+ imaging and electrophysiological recordings, we show that astrocyte Ca 2+ signalling enables neuronal encoding of fear memory retrieval and extinction, and readout through a BLA–prefrontal circuit. Our findings reveal a key role for astrocytes in the generation and adaptation of fear-state-related neural representations, revising neurocentric models of critical amygdala-mediated adaptive functions.

Cell types are the basic units of the cerebral cortex. Broad and narrow spike waveforms (BW and NW) are the primary criteria for classifying putative excitatory and inhibitory cortical neurons, particularly in non-human primates where genetic accessibility is limited. We have classified cell types in the auditory cortex of marmosets using spike waveforms and firing patterns and identified a new type of neuron: the NW-burst neuron. NW-burst neurons are excitatory, as they drive but do not suppress the firing of connected neurons. Furthermore, NW-burst neurons displayed shorter response latencies, lower response variability, smaller receptive fields, stronger correlations between spatial and non-spatial selectivity, and higher decoding accuracy than other neurons. Together, these findings suggest that cortical NW-burst neurons in non-human primates represent a distinct excitatory cell type. Significance Statement Classifying cell types in non-human primates is challenging due to limited genetic tools. Traditionally, neurons with narrow spikes are assumed to be inhibitory. Challenging this view, we analyzed 1,816 high-quality single units in the marmoset auditory cortex and discovered that narrow-spike burst-firing neurons were excitatory. These neurons exhibited shorter response latencies, smaller receptive fields, and higher decoding accuracy. Crucially, they showed a positive correlation between "where" and "what" selectivity, defying the standard trade-off between spatial and non-spatial response properties. These findings reveal a specific excitatory cell type in the auditory cortex of a non-human primate species that integrates sound information with high temporal fidelity and feature selectivity.

Atypical sensory processing is a common feature of autism, yet the neural computations that give rise to these differences, particularly in relation to biological sex and etiological origin, remain unclear. Here we examine predictive auditory processing at the single-neuron level in the inferior colliculus of two adult rat models of autism: a genetic model with a heterozygous Grin2b deletion (Grin2b + /-) and an environmental model based on prenatal valproic acid exposure. We recorded neuronal responses to an auditory oddball paradigm and a cascade control sequence across lemniscal and non-lemniscal IC divisions under high-intensity stimulation, allowing us to derive indices of repetition suppression, prediction error and neuronal mismatch. Using generalized linear mixed-effects models that accounted for animal identity, inferior colliculus division, sex, and rat model, followed by hierarchical group-level comparisons, we identified robust alterations in predictive processing in both autism-like models. These effects varied across inferior colliculus divisions and differed between sexes, revealing distinct phenotype-specific signatures. The results indicate that sex and etiology jointly modulate early auditory computations in autism. More broadly, our findings highlight the translational value of predictive coding frameworks and support the use of complementary animal models to capture neurobiological heterogeneity across the autism spectrum.

The flexibility of human vocal production is well studied, but the direct role of the auditory system in regulating vocalizations in rodents remains largely unexplored. We show that during vocalizations, a fraction of rat auditory cortex neurons shows pre-call activity and different patterns of responses during calls and playback of calls. Additionally, we classified five auditory cortical vocalization responses: pre-call activated, onset activated, onset suppressed, ramping activated and ramping suppressed neurons. Intriguingly, onset suppressed cells can predict vocalization duration and occurrence. Injecting the auditory cortex with muscimol (GABA_A receptor agonist) prolonged vocalizations, while injecting the auditory cortex with gabazine (GABA_A receptor antagonist) shortened them. Similar reductions in call duration were observed during external white-noise stimulation of the auditory cortex and/or other auditory brain structures, resembling the effects of gabazine. Together, neuronal recordings, pharmacological interference and noise induced vocal modifications indicate direct modulation of vocal productions by the rat auditory cortex.

Reward processes have traditionally been ascribed to dopamine (DA)–associated circuits. While external stimuli, such as food and drugs of abuse, are activators of DA-neuron activity, growing evidence indicates that interoceptive signals also play a critical role. Among these, the gut-brain vagal axis has emerged as a key regulator, although its precise contribution to mesolimbic DA signaling and behavior remains unclear. Here, we combine complementary ex vivo and in vivo approaches across multiple scales to show that gut-brain vagal tone is essential for gating mesolimbic DA system activity and functions, modulating DA-dependent molecular and cellular processes, and scaling both food- and drug-induced reinforcement. These findings challenge the traditional brain-centric view of reward processing, supporting a more integrated model in which vagus-mediated interoceptive signals intrinsically shape motivation and reinforcement. By uncovering the influence of gut-brain vagal communication on DA functions, this work provides insights into the neurobiology of adaptive and maladaptive reward, with broad relevance for eating disorders and addiction.

Coordinated neuronal activity plays an important role in information processing and transmission in the brain. While ensembles’ activity provides a more specific and less noisy version of sensory stimulus information than single neurons, their role in information transmission in the auditory pathway remains unclear. We investigated the effects of ensemble activity in the medial geniculate body (MGB) on the activation of neurons in the primary auditory cortex (A1) in female rats. MGB ensembles synchronized within narrow time windows more effectively induced A1 responses than single neurons or ensembles defined in broader time windows. This was facilitated by the convergence of ensemble inputs onto target neurons. Transmission efficacy was higher for narrow-spiking (NS) A1 neurons compared with broad-spiking (BS) neurons. Cortical UP states in isolation had no discernable effect on the transmission efficacy of thalamic cNEs. These findings highlight neuronal ensembles as focal functional units that enhance information transmission in the brain.

The basal ganglia play a key role in visual perceptual decisions. Despite being the primary target in the basal ganglia for inputs from the visual cortex, the posterior striatum's (PS) involvement in visual perceptual behavior remains unknown in rodents. We reveal that the PS direct pathway is largely segregated from the dorsomedial striatum (DMS) direct pathway, the other major striatal target for the visual cortex. We investigated the role of the PS in visual perceptual decisions by optogenetically stimulating striatal medium spiny neurons in the direct pathway (D1-MSNs) of male and female mice performing a visual change-detection task. PS D1-MSN activation robustly biased visual decisions in a manner dependent on visual context, timing, and reward expectation. We examined the effects of PS and DMS direct pathway activation on neuronal activity in the superior colliculus (SC), a major output target of the basal ganglia. Activation of either direct pathway rapidly modulated SC neurons but mostly targeted different SC neurons and had opposite effects. These results demonstrate that the PS in rodents provides an important route for controlling visual decisions, in parallel with the better-known DMS and with distinct anatomical and functional properties.

Reduction in neuronal firing from wake to sleep, i.e., sleep firing rate homeostasis (sFRH), is essential for restorative sleep. Sleep dysfunction is common in Parkinson's disease (PD), but sFRH has not been investigated. Here, using a within-subject design in the nonhuman primate model of PD, we report that thalamocortical sFRH is disrupted in parkinsonism. These findings can inform therapeutic approaches tailored to normalize sFRH and reestablish restorative sleep in PD.

How positive and negative affective stimuli interact in the brain to influence behavioral outcomes remains poorly understood. Here, we show that recall of a positively valenced reward-associated cue (reward-conditioned stimulus, CS Rew +) can prevent or reverse fear generalization in mice. Modification of generalized fear by recall of a CS Rew + is dependent on the midbrain dopamine system and the regulation of discriminatory fear encoding by the central amygdala (CeA). Precisely timed, transient elevations in dopamine are necessary to reverse fear generalization and nondiscriminatory fear encoding in the CeA. Recall of a positive association is also effective at enhancing the extinction of a conditioned fear response in a dopamine-dependent manner. These data demonstrate that recall of a positive experience can be an effective means to suppress generalized fear and show that dopamine projections to the CeA are an important neural substrate for this phenomenon.

This work presents three open datasets featuring various levels of processing, containing neural recordings from the auditory cortex of rats. These recordings were obtained during experiments using the auditory oddball paradigm before, during and after the local microiontophoretic application of acetylcholine. The primary objective of these datasets is to investigate how the brain processes predictable versus unexpected auditory stimuli, and the role of cholinergic inputs during such processing. The data include multi-unit recordings of neuronal activity during the presentation of standard and deviant tones, classified by stimulus type and cortical sub-region. These resources enable quantitative investigations of deviance detection, stimulus-specific adaptation, cholinergic modulation and predictive-coding mechanisms at multiple temporal scales.