Proprioception: Blurring the boundaries of central and peripheral control

New research has shown that mechanosensitive neurons in the lateral spinal cord of the adult zebrafish sense lateral bending and inhibit both their rostrally-located counterparts and the central-rhythm-generating networks across the midline. The interplay of central and peripheral neural mechanisms has never been seen to be so tight

Hans-Joachim Pfluger: scientist, citizen, cosmopolitan OBITUARY

On January 25, 2022, Professor Hans-Joachim Pfluger passed away. Hans-Joachim Pfluger conducted research in the field of neuroethology, with a focus on the development, anatomy, and function of sensorimotor networks underlying insect locomotion. As founding member and one of the presidents of the German Neuroscience Society, Hans-Joachim Pfluger was a driving force behind the development of the Neurosciences in Germany and Europe. This obituary reflects on his curriculum vitae. It shall honor his scientific and professional achievements, and importantly, also his wonderful personality, which makes this loss so sad across the manifold levels of his life and his legacy, the family, the professional and the scientific community

Insect motor control: methodological advances, descending control and inter-leg coordination on the move

Modern approaches, including high performance video, neurophysiology, and neurogenetics, allow to analyze invertebrate behavior on all levels of generation and performance in an unprecedented way. They allow observation and classification of behavior in controlled conditions, dissection of behavioral sequencing, identification of levels of processing and locations of associated sub-networks and, finally, identification of neuronal components and topologies contributing to specific aspects of behaviors. Recently conceptual and methodological progress has contributed to unraveling the neural structures underlying descending control of insect behavior as well as the mechanisms in charge of generating coordinated locomotor movements of the invertebrate extremities during walking. This brief review summarizes some of the most exciting new findings in these areas of research from the past years

Network Modularity: Back to the Future in Motor Control

Optogenetic analysis has revealed the existence of multiple rhythm-generating neural networks that drive leg motoneuron pools in the lumbar spinal cord of rodents. These findings extend the concept of a modular neural network organization for locomotion from invertebrates and lower vertebrates to mammals

Distributed processing of load and movement feedback in the premotor network controlling an insect leg joint

In legged animals, integration of information from various proprioceptors in and on the appendages by local premotor networks in the central nervous system is crucial for controlling motor output. To ensure posture maintenance and precise active movements, information about limb loading and movement is required. In insects, various groups of campaniform sensilla (CS) measure forces and loads acting in different directions on the leg, and the femoral chordotonal organ (fCO) provides information about movement of the femur-tibia (FTi) joint. In this study, we used extra- and intracellular recordings of extensor tibiae (ExtTi) and retractor coxae (RetCx) motor neurons (MNs) and identified local premotor nonspiking interneurons (NSIs) and mechanical stimulation of the fCO and tibial or trochanterofemoral CS (tiCS, tr/fCS), to investigate the premotor network architecture underlying multimodal proprioceptive integration. We found that load feedback from tiCS altered the strength of movement-elicited resistance reflexes and determined the specificity of ExtTi and RetCx MN responses to various load and movement stimuli. These responses were mediated by a common population of identified NSIs into which synaptic inputs from the fCO, tiCS, and tr/fCS are distributed, and whose effects onto ExtTi MNs can be antagonistic for both stimulus modalities. Multimodal sensory signal interaction was found at the level of single NSIs and MNs. The results provide evidence that load and movement feedback are integrated in a multimodal, distributed local premotor network consisting of antagonistic elements controlling movements of the FTi joint, thus substantially extending current knowledge on how legged motor systems achieve fine-tuned motor control. NEW & NOTEWORTHY Proprioception is crucial for motor control in legged animals. We show the extent to which processing of movement (fCO) and load (CS) signals overlaps in the local premotor network of an insect leg. Multimodal signals converge onto the same set of interneurons, and our knowledge about distributed, antagonistic processing is extended to incorporate multiple modalities within one perceptual neuronal framework

Body side-specific changes in sensorimotor processing of movement feedback in a walking insect

Feedback from load and movement sensors can modify timing and magnitude of the motor output in the stepping stick insect. One source of feedback is stretch reception by the femoral chordotonal organ (fCO), which encodes such parameters as the femorotibial (Fri) joint angle, the angular velocity, and its acceleration. Stimulation of the fCO causes a postural resistance reflex. during quiescence, and can elicit the opposite, so-called active reaction (AR), which assists ongoing flexion during active movements. In the present study, we investigated the role of fCO feedback for the difference in likelihood of generating ARs on the inside vs. the outside during curve stepping. We analyzed the effects of fCO stimulation on the motor output to the FTi and the neighboring coxa-trochanter and thorax-coxa joints of the middle leg. In inside and outside turns, the probability for ARs increases with increasing starting angle and decreasing stimulus velocity; furthermore, it is independent of the total angular excursion. However, the transition between stance and swing motor activity always occurs after a specific angular excursion, independent of the turning direction. Feedback from the fCO also has an excitatory influence on levator trochanteris motoneurons (MNs) during inside and outside turns, whereas the same feedback affects protractor coxae MNs only during outside steps. Our results suggest joint- and body side-dependent processing of fCO feedback. A shift in gain may be responsible for different AR probabilities between inside and outside turning, whereas the general control mechanism for ARs is unchanged. NEW & NOTEWORTHY We show that parameters of movement feedback from the tibia in an insect during curve walking are processed in a body side-specific manner, and how. From our results it is highly conceivable that the difference in motor response to the feedback supports the body side-specific leg kinematics during turning. Future studies will need to determine the source for the inputs that determine the local changes in sensory-motor processing

Descending control of locomotor circuits

Animals have developed different locomotor strategies to explore and survive in their environment by walking, flying, or swimming. Even though the biomechanics are different, the neural control of these movements is very similar in all vertebrate species. In this review, we provide an overview of the descending central control of locomotion in vertebrates with an emphasis on recent findings in the field. We discuss how different cell populations in the spinal cord control the intensity of locomotion. We then outline exciting findings on the heterogeneity of reticulospinal cells and their role in controlling different locomotor aspects. Furthermore, we review specific roles of different cell groups in the mesencephalic locomotor region (MLR) and describe newly found descending inputs to the MLR