Premotor-motor circuits

The recent discovery of the medullary circuit driving "hunger responses" - reduced thermogenesis and promoted feeding - has greatly expanded our knowledge on the central neural networks for energy homeostasis. However, how hypothalamic hunger and satiety signals generated under fasted and fed conditions, respectively, control the medullary autonomic and somatic motor mechanisms remains unknown. Here, in reviewing this field, we propose two hypothalamomedullary neural pathways for hunger and satiety signaling...

A vast array of motor skills can be maintained throughout life. Do these behaviors require stability of individual neuron tuning or can the output of a given circuit remain constant despite fluctuations in single cells? This question is difficult to address due to the variability inherent in most motor actions studied in the laboratory. A notable exception, however, is the courtship song of the adult zebra finch, which is a learned, highly precise motor act mediated by orderly dynamics within premotor neurons of the forebrain...

We review neuromodulation and lesion studies that address how activations in the mirror neuron system contribute to our perception of observed actions. Past reviews showed disruptions of this parieto-premotor network impair imitation and goal and kinematic processing. Recent studies bring five new themes. First, focal perturbations of a node of that circuit lead to changes across all nodes. Second, primary somatosensory cortex is an integral part of this network suggesting embodied representations are somatosensory-motor...

Little is known about the organizational and functional connectivity of the corticospinal (CS) circuits that are essential for voluntary movement. Here, we map the connectivity between CS neurons in the forelimb motor and sensory cortices and various spinal interneurons, demonstrating that distinct CS-interneuron circuits control specific aspects of skilled movements. CS fibers originating in the mouse motor cortex directly synapse onto premotor interneurons, including those expressing Chx10. Lesions of the motor cortex or silencing of spinal Chx10+ interneurons produces deficits in skilled reaching...

Descending signals from the brain play critical roles in controlling and modulating locomotion kinematics. In the Caenorhabditis elegans nervous system, descending AVB premotor interneurons exclusively form gap junctions with the B-type motor neurons that execute forward locomotion. We combined genetic analysis, optogenetic manipulation, calcium imaging, and computational modeling to elucidate the function of AVB-B gap junctions during forward locomotion. First, we found that some B-type motor neurons generate rhythmic activity, constituting distributed oscillators...

Neurophysiological studies showed that in macaques, grasp-related visuomotor transformations are supported by a circuit involving the anterior part of the intraparietal sulcus, the ventral and the dorsal region of the premotor area. In humans, a similar grasp-related circuit has been revealed by means of neuroimaging techniques. However, the majority of "human" studies considered movements performed by right-handers only, leaving open the question of whether the dynamics underlying motor control during grasping is simply reversed in left-handers with respect to right-handers or not...

UBR1 is an E3 ubiquitin ligase best known for its ability to target protein degradation by the N-end rule. The physiological functions of UBR family proteins, however, remain not fully understood. We found that the functional loss of C. elegans UBR-1 leads to a specific motor deficit: when adult animals generate reversal movements, A-class motor neurons exhibit synchronized activation, preventing body bending. This motor deficit is rescued by removing GOT-1, a transaminase that converts aspartate to glutamate...

The functional organization of human emotion systems as well as their neuroanatomical basis and segregation in the brain remains unresolved. Here, we used pattern classification and hierarchical clustering to characterize the organization of a wide array of emotion categories in the human brain. We induced 14 emotions (6 'basic', e.g. fear and anger; and 8 'non-basic', e.g. shame and gratitude) and a neutral state using guided mental imagery while participants' brain activity was measured with functional magnetic resonance imaging (fMRI)...

Singing behavior in the adult male zebra finch is dependent upon the activity of a cortical region known as HVC (proper name). The vast majority of HVC projection neurons send primary axons to either the downstream premotor nucleus RA (robust nucleus of the arcopallium, or primary motor cortex) or Area X (basal ganglia), which play important roles in song production or song learning, respectively. In addition to these long-range outputs, HVC neurons also send local axon collaterals throughout that nucleus. Despite their implications for a range of circuit models, these local processes have never been completely reconstructed...

Stroke results in enduring damage to the brain which is accompanied by innate neurorestorative processes, such as reorganization of surviving circuits. Nevertheless, patients are often left with permanent residual impairments. Cell based therapy is an emerging therapeutic that may function to enhance the innate neurorestorative capacity of the brain. We previously evaluated human umbilical tissue-derived cells (hUTC) in our non-human primate model of cortical injury limited to the hand area of primary motor cortex...

OBJECTIVE Apraxia is a cognitive-motor deficit affecting the execution of skilled movements, termed praxis gestures, in the absence of primary sensory or motor disorders. In patients affected by stroke, apraxia is associated with lesions of the lateral parietofrontal stream, connecting the posterior parietal areas with the ventrolateral premotor area and subserving sensory-motor integration for the hand movements. In the neurosurgical literature to date, there are few reports regarding the incidence of apraxia after glioma surgery...

Distinct regions of the frontal cortex connect with their basal ganglia and thalamic counterparts, constituting largely segregated basal ganglia-thalamo-cortical (BTC) circuits. However, any common role of the BTC circuits in different behavioral domains remains unclear. Indeed, whether dysfunctional motor and cognitive BTC circuits are responsible for motor slowing and cognitive slowing, respectively, in Parkinson's disease (PD) is a matter of debate. Here, we used an effortful behavioral paradigm in which the effects of task rate on accuracy were tested in movement, imagery, and calculation tasks in humans...

Extinction learning is an essential mechanism that enables constant adaptation to ever-changing environmental conditions. The underlying neural circuit is mostly studied with rodent models using auditory cued fear conditioning. In order to uncover the variant and the invariant neural properties of extinction learning, we adopted pigeons as an animal model in an appetitive sign-tracking paradigm. The animals firstly learned to respond to two conditioned stimuli in two different contexts (CS-1 in context A and CS-2 in context B), before conditioned responses to the stimuli were extinguished in the opposite contexts (CS-1 in context B and CS-2 in context A)...

Preparing and executing grasping movements demands the coordination of sensory information across multiple scales. The position of an object, required hand shape, and which of our hands to extend must all be coordinated in parallel. The network formed by the macaque anterior intraparietal area (AIP) and hand area (F5) of the ventral premotor cortex is essential in the generation of grasping movements. Yet, the role of this circuit in hand selection is unclear. We recorded from 1342 single- and multi-units in AIP and F5 of two macaque monkeys (Macaca mulatta) during a delayed grasping task in which monkeys were instructed by a visual cue to perform power or precision grips on a handle presented in five different orientations with either the left or right hand, as instructed by an auditory tone...

Cell- or network-driven oscillators underlie motor rhythmicity. The identity of C. elegans oscillators remains unknown. Through cell ablation, electrophysiology, and calcium imaging, we show: (1) forward and backward locomotion is driven by different oscillators; (2) the cholinergic and excitatory A-class motor neurons exhibit intrinsic and oscillatory activity that is sufficient to drive backward locomotion in the absence of premotor interneurons; (3) the UNC-2 P/Q/N high-voltage-activated calcium current underlies A motor neuron's oscillation; (4) descending premotor interneurons AVA, via an evolutionarily conserved, mixed gap junction and chemical synapse configuration, exert state-dependent inhibition and potentiation of A motor neuron's intrinsic activity to regulate backward locomotion...

Tourette syndrome (TS) is characterized by presence of chronic, fluctuating motor and phonic tics. The underlying neurobiological basis for these movements is hypothesized to involve cortical-striatal-thalamo-cortical (CSTC) pathways. Two major neurotransmitters within these circuits are γ-aminobutyric acid (GABA) and glutamate. Seventy-five participants (32 with TS, 43 controls) ages 5-12 years completed 1 H MRS at 7T. GABA and glutamate were measured in dorsolateral prefrontal cortex (DLPFC), ventromedial prefrontal cortex (VMPFC), premotor cortex (PMC), and striatum, and metabolites quantified using LCModel...

Virtual reality (VR)-based paradigms use visual stimuli that can modulate visuo-motor networks leading to the stimulation of brain circuits. The aims of this study were to compare the changes in blood-oxygenation level dependent (BOLD) signal when watching and imitating moving real (RH) and virtual hands (VH) in 11 healthy participants (HP). No differences were found between the observation of RH or VH making this VR-based experiment a promising tool for rehabilitation protocols. VH-imitation involved more the ventral premotor cortex (vPMC) as part of the mirror neuron system (MNS) compared to execution and VH-observation conditions...

Skill learning is instantiated by changes to functional connectivity within premotor circuits, but whether the specificity of learning depends on structured changes to inhibitory circuitry remains unclear. We used slice electrophysiology to measure connectivity changes associated with song learning in the avian analog of primary motor cortex (robust nucleus of the arcopallium, RA) in Bengalese Finches. Before song learning, fast-spiking interneurons (FSIs) densely innervated glutamatergic projection neurons (PNs) with apparently random connectivity...

Layer-dependent fMRI allows measurements of information flow in cortical circuits, as afferent and efferent connections terminate in different cortical layers. However, it is unknown to what level human fMRI is specific and sensitive enough to reveal directional functional activity across layers. To answer this question, we developed acquisition and analysis methods for blood-oxygen-level-dependent (BOLD) and cerebral-blood-volume (CBV)-based laminar fMRI and used these to discriminate four different tasks in the human motor cortex (M1)...

Animals adaptively respond to a tactile stimulus by choosing an ethologically relevant behavior depending on the location of the stimuli. Here, we investigate how somatosensory inputs on different body segments are linked to distinct motor outputs in Drosophila larvae. Larvae escape by backward locomotion when touched on the head, while they crawl forward when touched on the tail. We identify a class of segmentally repeated second-order somatosensory interneurons, that we named Wave, whose activation in anterior and posterior segments elicit backward and forward locomotion, respectively...