Journal of neurophysiology最新文献

In the rat, the activity of laryngeal adductor muscles, the crural diaphragm, and sympathetic vasomotor neurons is entrained to the post-inspiratory (post-I) phase of the respiratory cycle, a mechanism thought to enhance cardiorespiratory efficiency. The identity of the central neurons responsible for transmitting respiratory activity to these outputs remains unresolved. Here we explore the contribution of the Kölliker-Fuse/Parabrachial nuclei (KF-PBN) in the generation of post-I activity in vagal and sympathetic outputs under steady-state conditions and during acute hypoxemia, a condition that potently recruits post-I activity. In artificially ventilated, vagotomised and urethane-anesthetised rats, bilateral KF-PBN inhibition by microinjection of the GABA_A receptor agonist isoguvacine evoked stereotypical responses on respiratory pattern, characterised by a reduction in phrenic nerve burst amplitude, a modest lengthening of inspiratory time, and an increase in breath-to-breath variability, while post-I vagal nerve activity was abolished and post-I sympathetic nerve activity diminished. During acute hypoxemia, KF-PBN inhibition attenuated tachypnoeic responses and completely abolished post-I vagal activity while preserving respiratory-sympathetic coupling. Furthermore, KF-PBN inhibition disrupted the decline in respiratory frequency that normally follows resumption of oxygenation. These findings suggest that the KF-PBN is a critical hub for the distribution of post-I activities to vagal and sympathetic outputs and is an important contributor to the dynamic adjustments to respiratory patterns that occur in response to acute hypoxia. While KF-PBN appears essential for post-I vagal activity, it only partially contributes to post-I sympathetic nerve activity, suggesting the contribution of multiple neural pathways to respiratory-sympathetic coupling.

When speakers learn to change the way they produce a speech sound, how much does that learning generalize to other speech sounds? Past studies of speech sensorimotor learning have typically tested the generalization of a single transformation learned in a single context. Here, we investigate the ability of the speech motor system to generalize learning when multiple opposing sensorimotor transformations are learned in separate regions of the vowel space. We find that speakers adapt to a non-uniform "centralization" perturbation, learning to produce vowels with greater acoustic contrast, and that this adaptation generalizes to untrained vowels, which pattern like neighboring trained vowels and show increased contrast of a similar magnitude.

The pathological and physiological process of spinal cord injury is complex, and there is currently no effective treatment method. Magnetic stimulation is an emerging electromagnetic therapy method in recent years, and studies have shown its potential to reduce cell apoptosis. This study used an improved Allen's method to replicate an incomplete spinal cord injury rat model, and repetitive magnetic stimulation (rMS) intervention was performed on the rats for 21 days. The research plan consists of two parts. The first part aims to observe the effects of rMS on motor function and neuronal cell apoptosis in rats. The Basso-Beattie-Bresnahan (BBB) score results indicate that rMS promotes the recovery of motor function in rats; H&E staining showed that rMS improved spinal cord structural damage and inflammatory infiltration; TUNEL and NeuN staining suggest that rMS can reduce cell apoptosis and promote neuronal cell survival. The second part aims to explore the mechanism of action of rMS. Immunofluorescence staining showed that after rMS intervention, the positive counts of PI3K and Akt increased, whereas the positive counts of caspase-3 decreased. Western blot showed that after rMS intervention, the expression of phospho-phosphatidylinositol-3 kinase (p-PI3K)/PI3K, phospho (p)-Akt/Akt, and Bcl-2 increased, whereas the expression of Bcl-2-associated X protein (Bax) and caspase-3 decreased. In summary, rMS can significantly reduce cell apoptosis in the damaged spinal cord and promote neuronal cell survival. Its mechanism of action may be related to promoting the expression of PI3K/Akt pathway proteins, upregulating the antiapoptotic protein Bcl-2, downregulating the proapoptotic protein Bax, and thereby inhibiting the expression of apoptotic protein caspase-3. NEW & NOTEWORTHY Spinal cord injury is a serious disabling central nervous system disease. Recently, research on magnetic stimulation therapy for spinal cord injury has been increasing, and its potential has gradually attracted the attention of experts. This study found that repetitive magnetic stimulation (rMS) can improve motor function and reduce neuronal apoptosis in spinal cord injury rats. The mechanism may be related to increasing the expression of phosphatidylinositol-3 kinase (PI3K)/Akt protein, thereby inhibiting cell apoptosis and promoting neuronal survival.

Thousands of species use vocal signals to communicate with one another. Vocalizations carry rich information, yet characterizing and analyzing these complex, high-dimensional signals is difficult and prone to human bias. Moreover, animal vocalizations are ethologically relevant stimuli whose representation by auditory neurons is an important subject of research in sensory neuroscience. A method that can efficiently generate naturalistic vocalization waveforms would offer an unlimited supply of stimuli with which to probe neuronal computations. Although unsupervised learning methods allow for the projection of vocalizations into low-dimensional latent spaces learned from the waveforms themselves, and generative modeling allows for the synthesis of novel vocalizations for use in downstream tasks, we are not aware of any model that combines these tasks to synthesize naturalistic vocalizations in the waveform domain for stimulus playback. In this paper, we demonstrate BiWaveGAN: a bidirectional generative adversarial network (GAN) capable of learning a latent representation of ultrasonic vocalizations (USVs) from mice. We show that BiWaveGAN can be used to generate, and interpolate between, realistic vocalization waveforms. We then use these synthesized stimuli along with natural USVs to probe the sensory input space of mouse auditory cortical neurons. We show that stimuli generated from our method evoke neuronal responses as effectively as real vocalizations, and produce receptive fields with the same predictive power. BiWaveGAN is not restricted to mouse USVs but can be used to synthesize naturalistic vocalizations of any animal species and interpolate between vocalizations of the same or different species, which could be useful for probing categorical boundaries in representations of ethologically relevant auditory signals.NEW & NOTEWORTHY A new type of artificial neural network is presented that can be used to generate animal vocalization waveforms and interpolate between them to create new vocalizations. We find that our synthetic naturalistic stimuli drive auditory cortical neurons in the mouse equally well and produce receptive field features with the same predictive power as those obtained with natural mouse vocalizations, confirming the quality of the stimuli produced by the neural network.

In addition to the essential structural and catalytic functions of zinc, evolution has adopted synaptic zinc as a neuromodulator. In the brain, synaptic zinc is released primarily from glutamatergic neurons, notably in the neocortex, hippocampus, amygdala, and auditory brainstem. In these brain areas, synaptic zinc is essential for neuronal and sensory processing fine-tuning. But what niche does zinc fill in neural signaling that other neuromodulators do not? Here, we discuss the evolutionary history of zinc as a signaling agent and its eventual adoption as an essential neuromodulator in the mammalian brain. We then attempt to describe the unique roles that zinc has carved out of the vast and diverse landscape of neuromodulators.

Peripheral nerve stimulation (PNS) and motor point stimulation (MPS) are noninvasive techniques used to induce muscle contraction, aiding motor function restoration in individuals with neurological disorders. Understanding sensory inputs from PNS and MPS is crucial for facilitating neuroplasticity and restoring impaired motor function. Although previous studies suggest that MPS could induce Ia-sensory inputs less than PNS, experimental evidence supporting this claim is insufficient. Here, we implemented a conditioning paradigm combining transcutaneous spinal cord stimulation (tSCS) with PNS or MPS to investigate their Ia-sensory inputs. This paradigm induces postactivation depression of spinal reflexes associated with transient decreases in neurotransmitter release from Ia-afferent terminals, allowing us to examine the Ia-sensory input amount from PNS and MPS based on the depression degree. We hypothesized that MPS would induce less postactivation depression than PNS. Thirteen individuals underwent MPS and PNS on the soleus muscle as conditioning stimuli, with tSCS applied to the skin between the spinous processes (L1-L2) as test stimuli. PNS- and MPS-conditioned spinal reflexes were recorded at five interstimulus intervals (ISIs) and four intensities. Results revealed that all PNS conditioning showed significant decreases in spinal reflex amplitudes, indicating postactivation depression. Furthermore, PNS conditioning exhibited greater depression for shorter ISIs and higher conditioning intensities. In contrast, MPS conditioning demonstrated intensity-dependent depression, but without all-conditioning depression and clear ISI dependency as seen in PNS conditioning. In addition, PNS induced significantly greater depression than MPS across most conditions. Our findings provide experimental evidence supporting the conclusion that MPS activates Ia-sensory nerves less than PNS.NEW & NOTEWORTHY Peripheral nerve stimulation (PNS) and motor point stimulation (MPS) induce neuroplasticity, but differences in their effects on Ia-sensory inputs are unclear. We investigated their Ia-sensory inputs using a conditioning paradigm with spinal reflexes. Results showed that PNS conditioning significantly inhibited spinal reflexes than MPS conditioning, indicating greater postactivation depression due to Ia-sensory nerve activation. These findings provide experimental evidence that MPS activates Ia-sensory nerves to a lesser extent than PNS, enhancing our understanding of neuroplasticity.

Recent studies combining high-density surface electromyography (HD-sEMG) and ultrasound imaging have yielded valuable insights into the relationship between motor unit activity and muscle contractile properties. However, limited evidence exists on the relationship between motor unit firing properties and tendon morpho-mechanical properties. This study aimed to determine the relationship between triceps surae motor unit firing properties and the morpho-mechanical properties of the Achilles tendon (AT). Motor unit firing properties [i.e. mean discharge rate (DR) and coefficient of variation of the interspike interval (COVisi)] and motor unit firing-torque relationships [cross-correlation between cumulative spike train (CST) and torque, and the delay between motor unit firing and torque production (neuromechanical delay)] of the medial gastrocnemius (MG), lateral gastrocnemius (LG), and soleus (SO) muscles were assessed using HD-sEMG during isometric plantarflexion contractions at 10% and 40% of maximal voluntary contraction (MVC). The morpho-mechanical properties of the AT (i.e. length, thickness, cross-sectional area, and resting stiffness) were determined using B-mode ultrasonography and shear-wave elastography. Multiple linear regression analysis showed that at 10% MVC, the DR of the triceps surae muscles explained 41.7% of the variance in resting AT stiffness. In addition, at 10% MVC, COV_isi SO predicted 30.4% of the variance in AT length. At 40% MVC, COV_isi MG and COV_isi SO explained 48.7% of the variance in AT length. Motor unit-torque relationships were not associated with any morpho-mechanical parameter. This study provides novel evidence of a contraction intensity-dependent relationship between motor unit firing parameters of the triceps surae muscle and the morpho-mechanical properties of the AT. NEW & NOTEWORTHY By employing HD-sEMG, conventional B-mode ultrasonography, and shear-wave elastography, we showed that the resting stiffness of the Achilles tendon is related to mean discharge rate of triceps surae motor units during low-force isometric plantarflexion contractions, providing relevant information about the complex interaction between rate coding and the muscle-tendon unit.

Walking in natural environments requires visually guided modifications, which can be more challenging when involving sideways steps rather than longer steps. This exploratory study investigated whether these two types of modifications involve different changes in the central drive to spinal motor neurons of leg muscles. Fifteen adults [age: 36 ± 6 (SD) years] walked on a treadmill (4 km/h) while observing a screen displaying the real-time position of their toes. At the beginning of the swing phase, a visual target appeared in front (forward) or medial-lateral (sideways) of the ground contact in random step cycles (approximately every third step). We measured three-dimensional kinematics and electromyographic activity from leg muscles bilaterally. Intermuscular coherence was calculated in the alpha (5-15 Hz), beta (15-30 Hz), and gamma bands (30-45 Hz) approximately 230 ms before and after ground contact in control and target steps. Results showed that adjustments toward sideways targets were associated with significantly higher error, lower foot lift, and higher cocontraction between antagonist ankle muscles. Movements toward sideways targets were associated with larger beta-band soleus (SOL): medial gastrocnemius (MG) coherence and a more narrow and larger peak of synchronization in the cumulant density before ground contact. In contrast, movements toward forward targets showed no significant differences in coherence or synchronization compared with control steps. Larger SOL:MG beta-band coherence and short-term synchronization were observed during sideways, but not forward, gait modifications. This suggests that visually guided gait modifications may involve differences in the central drive to spinal ankle motor neurons dependent on the level of task difficulty.NEW & NOTEWORTHY This exploratory study suggests a specific and temporally restricted increase of central (likely corticospinal) drive to ankle muscles in relation to visually guided gait modifications. The findings indicate that a high level of visual attention to control the position of the ankle joint precisely before ground contact may involve increased central drive to ankle muscles. These findings are important for understanding the neural mechanisms underlying visually guided gait and may help develop rehabilitation interventions.