Spinal Reflex System Research Articles

Temporal self-supervised domain adaptation network for machinery fault diagnosis under multiple non-ideal conditions

Although deep learning techniques have been widely used in machinery fault diagnosis, the key issue of feature learning under multiple non-ideal conditions, i.e., strong noise interference, inconsistent data distributions and class imbalance, is not tackled effectively. Thus, a novel deep neural network (DNN) named temporal self-supervised domain adaptation network (TSSDAN) is developed for machinery fault diagnosis in this article. Firstly, a temporal self-supervised learning (TSSL) method is implemented to tackle the issue of strong noise interference and class imbalance. Secondly, a specific feature extractor, perception auto-encoder (PAE) is implemented for signal feature learning by mimicking the working mode of the biological visual system and spinal reflex system. Thirdly, a cascaded domain adaptation (CDA) method is constructed to tackle the domain shift issue by considering the feature distribution discrepancy of various domains for all perception levels. Two cases (i.e., rotor and gearbox) are used in this study to evaluate the performance of TSSDAN. The experiment results illustrate the outperformance of TSSDAN in solving the problem of deep feature learning and machinery fault diagnosis under multiple non-ideal conditions.

Low-frequency H-reflex depression in trained human soleus after spinal cord injury

After spinal cord injury (SCI), widespread reorganization occurs within spinal reflex systems. Regular muscle activity may influence reorganization of spinal circuitry after SCI. The purpose of this study is to investigate the effects of long-term soleus training on H-reflex depression in humans after SCI. Seven subjects with acute (<7 weeks) SCI (AC group) underwent testing of H-reflex depression at several frequencies of repetitive stimulation. Eight subjects (including 3 from AC) stimulated one soleus muscle daily, leaving the other leg as an untrained within-subject control. Trained limb H-reflexes were assessed during year 1 (TR1) and year 2 (TR2) of training. Untrained limbs were tested during year 2 (UN). H-reflex amplitude was lower at 1, 2 and 5Hz than at 0.1 or 0.2Hz (p<0.05). The pattern of depression differed between AC and UN (p<0.05), but not between TR2 and UN (p>0.05) despite significant adaptations in torque and fatigue resistance (p<0.05). Three subjects who began training very early after SCI retained H-reflex post activation depression, suggesting that early intervention of daily muscular activity may be important.

Developmental Learning in a Pain-Related System: Evidence for a Cross-Modality Mechanism

The nociceptive spinal reflex system performs highly precise sensorimotor transformations that require functionally specified synaptic strengths. The specification is gradually attained during early development and appears to be learning dependent. Here we determine the time course of this specification for heat-nociceptive tail withdrawal reflexes and analyze which types of primary afferents are important for the learning by applying various forms of noninvasive sensory deprivations. The percentage of erroneous heat-nociceptive tail withdrawal reflexes (i.e., movements directed toward the stimulation) decreased gradually from 64.1 +/- 2.5% (mean +/- SEM) to <10% during postnatal days 10-21. This improvement was completely blocked by anesthetizing the tail during the adaptation period, confirming that an experience-dependent mechanism is involved in the specification of synaptic strengths. However, the results show that the adaptation occurs to a significant extent despite local analgesia and protection of the tail from noxious input, provided that tactile sensitivity is preserved. Therefore, it appears that a nociceptive input is not necessary for the adaptation, and that input from tactile receptors can be used to guide the nociceptive synaptic organization during development. Sensory deprivation in the adult rat failed to affect the heat-nociceptive withdrawal reflex system, indicating that the adaptation has a "critical period" during early development. These findings provide a key to the puzzle of how pain-related systems can be functionally adapted through experience despite the rare occurrence of noxious input during early life.

Spontaneous muscle twitches during sleep guide spinal self-organization.

During development, information about the three-dimensional shape and mechanical properties of the body is laid down in the synaptic connectivity of sensorimotor systems through unknown adaptive mechanisms. In spinal reflex systems, this enables the fast transformation of complex sensory information into adequate correction of movements. Here we use a computer simulation to show that an unsupervised correlation-based learning mechanism, using spontaneous muscle twitches, can account for the functional adaptation of the withdrawal reflex system. We also show that tactile feedback resulting from spontaneous muscle twitches during sleep does indeed modify sensorimotor transformation in young rats in a predictable manner. The results indicate that these twitches, corresponding to human fetal movements, are important in spinal self-organization.

Spinal Sensorimotor Transformation: Relation between Cutaneous Somatotopy and a Reflex Network

The projection of primary afferents onto spinal interneurons constitutes the first step in sensorimotor transformations performed by spinal reflex systems. Despite extensive studies on spinal somatotopy, uncertainties remain concerning the extent and significance of representational overlap and relation to spinal reflex circuits. To address these issues, the cutaneous projection from the hindpaw and its relation to the topography of lamina V neurons encoding withdrawal reflex strength ("reflex encoders") was studied in rats. Thin and coarse primary afferent terminations in laminas II and III-IV, respectively, were mapped by wheat germ agglutinin-horseradish peroxidase and choleragenoid tracing. The functional weights of these projections were characterized by mapping nociceptive and tactile field potentials and compared with the topography of reflex encoders. Both anatomical and physiological data indicate that thin and coarse skin afferent input is spatially congruent in the horizontal plane. The representation of the hindpaw in the spinal cord was found to be intricate, with a high degree of convergence between the projections from different skin sites. "Somatotopic disruptions" such as the representation of central pads medial to that of the digits were common. The weight distribution of the cutaneous convergence patterns in laminas III-IV was similar to that of lamina V reflex encoders. This suggests that the cutaneous convergence and features such as somatotopic disruptions have specific relations to the sensorimotor transformations performed by reflex interneurons in the deep dorsal horn. Hence, the spinal somatotopic map may be better understood in light of the topography of such reflex systems.

A mathematical analysis of the force-stiffness characteristics of muscles in control of a single joint system.

Feldman (1966) has proposed that a muscle endowed with its spinal reflex system behaves as a non-linear spring with an adjustable resting length. In contrast, because of the length-tension properties of muscles, many researchers have modeled them as non-linear springs with adjustable stiffness. Here we test the merits of each approach: Initially, it is proven that the adjustable stiffness model predicts that isometric muscle force and stiffness are linearly related. We show that this prediction is not supported by data on the static stiffness-force characteristics of reflexive muscles, where stiffness grows non-linearly with force. Therefore, an intact muscle-reflex system does not behave as a non-linear spring with an adjustable stiffness. However, when the same muscle is devoid of its reflexes, the data shows that stiffness grows linearly with force. We aim to understand the functional advantage of the non-linear stiffness-force relationship present in the reflexive muscle. Control of an inverted pendulum with a pair of antagonist muscles is considered. Using an active-state muscle model we describe force development in an areflexive muscle. From the data on the relationship of stiffness and force in the intact muscle we derive the length-tension properties of a reflexive muscle. It is shown that a muscle under the control of its spinal reflexes resembles a non-linear spring with an adjustable resting length. This provides independent evidence in support of the Feldman hypothesis of an adjustable resting length as the control parameter of a reflexive muscle, but it disagrees with his particular formulation. In order to maintain stability of the single joint system, we prove that a necessary condition is that muscle stiffness must grow at least linearly with force at isometric conditions. This shows that co-contraction of antagonist muscles may actually destabilize the limb if the slope of this stiffness-force relationship is less than an amount specified by the change in the moment arm of the muscle as a function of joint configuration. In a reflexive muscle where stiffness grows faster than linearly with force, co-contraction will always lead to an increase in stiffness. Furthermore, with the reflexive muscles, the same level of joint stiffness can be produced by much smaller muscle forces because of the non-linear stiffness-force relationship. This allows the joint to remain stable at a fraction of the metabolic energy cost associated with maintaining stability with areflexive muscles.

Afferent control of posture and gait

Investigations of the complex movements involved in human posture and gait have been restricted to the description of the efferent arm of the movement, in the form of biomechanical data and muscle electromyographic (EMG) activity. The extent to which the latter, while being generated by a central program, was also influenced by spinal reflex systems became evident when fast movements were studied, such as running and jumping (Dietz et al., 1979; Dietz and Noth, 1978) or falling forward onto extended arms (Dietz et al., 1981). In addition, when unexpected displacements were induced during posture and gait (Berger et al., 1984), they evoked rapid appropriate and powerful EMG responses. The nature of these spinal reflex mechanisms, their afferent sources and their pathways, has remained a matter for debate. From experiments in the cat, many spinal reflex connections and interneuronal circuits involved in motor control are known (for review see Baldissera et al., 1981). Furthermore, there exists the possibility for selection of afferent information by presynaptic inhibition of afferent pathways to the spinal cord (Schmidt, 1971). However, little emerges from these experiments about the functional significance of different reflex pathways in the control of locomotion and it remains questionable if these spinal mechanisms can validly be transferred to the bipedal gait of man.

Group II muscle afferents and low threshold mechanoreceptive skin afferents converging onto interneurons in a common reflex pathway to α-motoneurons

In spinal cats weak stroking of the fur of the foot facilitated PSPs from group II muscle afferents in α-motoneurons. This spatial facilitation indicates that afferents from low threshold cutaneous mechanoreceptors and group II muscle afferents may converge onto common interneurons in segmental reflex pathways. The results confirm the contribution of group II muscle afferents to a multisensorial spinal reflex system for movement control.

Fixation of spinal reflexes in rats by central and peripheral sensory input.

Two methods were used to demonstrate retention of postural asymmetries after spinal cord section in adult rats. In the first preparation, postural asymmetries of the hindlimbs were induced by placing electrolytic lesions in the anterior cerebellum. Asymmetry was found to consistently outlast a spinal cord section if 45 min were allowed between brain lesion and cord section. A certain percentage of rats allowed 35 or 40 min also demonstrated the retention. In the second preparation, postural asymmetries induced by 45 min of direct hindlimb stimulation were also retained after spinal section. Rhizotomy prior to stimulation resulted in a lack of appreciable asymmetry upon termination of the stimulation. Finally, retention of a hindlimb-stimulation-induced asymmetry was observed in animals that underwent a spinal section prior to the stimulation. The present series of studies demonstrates that the "spinal fixation" phenomenon can be obtained by induction of postural alterations from central (cerebellar lesion) and peripheral (hindlimb stimulation) sources. In addition, results obtained from spinal animals indicate that retention of peripherally induced asymmetry is not crucially dependent on higher brain center activity but rather seems to be more dependent on long-term alterations that occur directly in the spinal reflex system.

Ascending long spinal actions on forelimb motoneurons in the acute spinal cat.

Ascending long spinal reflex system were investigated by means of monosynaptic reflex testing in the acutely spinalized unanesthetized cat. 1. Hindlimb nerve stimulation gave bilateral facilitatory effects on the motoneuron pools of pectoralis major and physiological flexors of the forelimb such as biceps brachii, extensor carpi radialis, extensor digitorum communis, but elicited depressive effects on the physiological extensors such as triceps brachii, flexor carpi radialis, flexor digitorum profundus. 2. In the latissimus dorsi, which is the antagonist of pectoralis major, a depressive effect was elicited by the stimulation of ipsilateral hindlimb nerves, and a facilitatory effect by contralateral stimulation. 3. These effects were evoked mainly from group II afferent fibers in muscle as well as cutaneous nerves. 4. Intracellular recordings from motoneurons of extensor carpi radialis revealed EPSPs following stimulation of hindlimb nerves with time courses corresponding to those of the facilitatory effects. We failed to detect any potential changes in the motoneurons of flexor carpi radialis following stimulation of hindlimb nerves.

EFFECTS OF BULBOCAPNINE ON SPINAL REFLEXES OF ANESTHETIZED AND SPINAL RATS

Since all of the so-called “major tranquilizers” have the ability to induce catatonic states in experimental animals, this characteristic pharmacological property is commonly being used as a clue to detecting new compounds in screening tests. However, not all compounds that produce the catalepsy in animals are “tranquilizers”. One remarkable example is bulbocapnine, an alkaloid isolated from Corydalis cava; it was first reported by Peters (1) that a catatonic state in mammals followed bulbocapnine treatment. Although it has been suggested that bulbocapnine catalepsy could serve as an experimental model for schizophrenia or Parkinson's disease, little is known of its effects on the neural components of the motor system. In earlier experiments we found that bulbocapnine selectively depressed the spinal monosynaptic reflex response in the rat with little effect on the polysynaptic neuronal systems (2). These observations have subsequently been confirmed by Willis et al. (3, 4) in the cat. The present report describes a further investigation of the actions of bulbocapnine on spinal reflex systems. The rat was employed in the present experiments so that the electrophysiological data could be accurately compared with the numerous behavioral observations in this species.