Behavior of larval and juvenile bullfrogs (Rana catesbeiana) following chronic spinal transection

The behavior of larval and juvenile bullfrogs (Rana catesbeiana) was examined for 32 days following cervical spinal transection. The threshold for cutaneously elicited hindlimb withdrawal was not changed at either stage of development but righting reflexes were abolished. Forelimb postural support of juveniles was abolished by the transection but recovered within 3 days. Hindlimb posture was normal and hopping could be elicited by stimulation of the rump with a blunt wire probe. Undulatory swimming of larvae was abolished by the transection but began to recover approximately 1 week later. The hindlimbs of larvae were very active following the transection and displayed long sequences of coordinated stepping in response to a variety of stimuli. Gross examination of the spinal cord in situ after 32 days suggested that fibers may have grown across the transection site. Retransection at the site of the original transection on Postoperative Day 33 had no discernable effect on the behavior juveniles or on the stepping of larvae, but it abolished recovered swimming of larvae. Deafferentation of lumbar segments of larvae eliminated stepping but had no effect on swimming. Deafferentation of cervical segments eliminated forelimb support in juveniles. These results suggest that recovery of larval swimming depends at least in part upon the growth of fibers across the transection site. Stepping of spinal larvae appears to be mediated by proprioceptive reflexes rather than by central pattern generators, and in the normal animal is probably under the control of descending inhibition. Recovery of posture and hopping in juveniles was much more rapid than that described for adult frogs and does not depend on growth across the transection site.     

DNA methylation and behavioral changes induced by neonatal spinal transection

Although the importance of epigenetic mechanisms in behavioral development has been gaining attention in recent years, research has largely focused on the brain. To our knowledge, no studies to date have investigated epigenetic changes in the developing spinal cord to determine the dynamic manner in which the spinal epigenome may respond to environmental input during behavioral development. Animal studies demonstrate that spinal cord plasticity is heightened during early development, is somewhat preserved following neonatal transection, and that spinal injured animals are responsive to sensory feedback. Because epigenetic alterations have been implicated in brain plasticity and are highly responsive to experience, these alterations are promising candidates for molecular substrates of spinal plasticity as well. Thus, the current study investigated behavioral changes in the development of weight-bearing locomotion and epigenetic modifications in the spinal cord of infant rats following a neonatal low-thoracic spinal transection or sham surgery on postnatal day (P)1. Specifically, global levels of methylation and methylation status of the brain-derived neurotrophic factor (Bdnf) gene, a neurotrophin heavily involved in both CNS and behavioral plasticity, particularly in development, were examined in lumbar tissue harvested on P10 from sham and spinal-transected subjects. Behavioral results demonstrate that compared to shams, spinal-transected subjects exhibit significantly reduced partial-weight bearing hindlimb activity. Molecular data demonstrate group differences in global lumbar methylation levels as well as exon-specific group differences in Bdnf methylation. This study represents an initial step toward understanding the relationship between epigenetic mechanisms and plasticity associated with spinal cord and locomotor development.     

Embodied emotion concepts: How generating words about pride and disappointment influences posture

Embodiment theories predict that activating conceptual knowledge about emotions can be accompanied by re‐experiencing bodily states, since simulations of sensory, motor, and introspective experiences form the foundation of conceptual representations of emotion. In the present study, we examine whether the activation of the specific emotion concepts of pride and disappointment are embodied in the sense that they are accompanied by changes in posture. Participants generated words associated with pride and disappointment while posture height was measured. Results show that during the generation of disappointment words participants decreased their posture height more than when participants generated pride words. This finding suggests that the activation of conceptual knowledge about disappointment can lead to a spontaneous expression of the associated body posture. In contrast to posture changes along the vertical axis, movement along the horizontal axis was not influenced by concept activation. In addition to bodily simulation the data also indicated introspective simulation, since feelings of disappointment increased after generating disappointment words. The current study provides the first evidence for the claim that the activation of conceptual knowledge about emotion can instantiate spontaneous simulations at a behavioral level. Copyright © 2008 John Wiley & Sons, Ltd.     

Prey behaviour across antipredator adaptation types: how does growth trajectory influence learning of predators?

Despite the fact that the ability of animals to avoid being consumed by predators is influenced by their behaviour, morphology and life history, very few studies have attempted to integrate prey responses across these adaptation types. Here, our goal was to address the link between life-history traits (size and growth trajectory) of tadpoles and behavioural responses to predators. Specifically, we wanted to determine whether information learned about predators was influenced by prey growth trajectory before and after learning. We manipulated the size/growth trajectory of tadpoles by raising them under different temperatures. Tadpoles raised on a slow-growth trajectory (under cold conditions) and taught to recognize a salamander subsequently showed stronger responses after 2 weeks than tadpoles that were raised on a fast-growth trajectory (under warm conditions). When we account for the effect of size (r ² = 0.22) on the responses of prey to predator cues, we find that the growth trajectory pre-learning but not post-learning influences the learned responses of the tadpoles. The differences in responses to predators may reflect differential memory associated with the predator. To our knowledge, this is the first study that has attempted to link life-history traits (size and growth rate) with learning of predators. In order to gain a comprehensive understanding of antipredator responses of prey animals, we call for additional integrative studies that examine prey anti-predator responses across adaptation types.     

Discordance in Recovery Between Altered Locomotion and Muscle Atrophy Induced by Simulated Microgravity in Rats

Exposure to a microgravity environment leads to adverse effects in motion and musculoskeletal properties. However, few studies have investigated the recovery of altered locomotion and muscle atrophy simultaneously. The authors investigated altered locomotion in rats submitted to simulated microgravity by hindlimb unloading for 2 weeks. Motion deficits were characterized by hyperextension of the knees and ankle joints and forward-shifted limb motion. Furthermore, these locomotor deficits did not revert to their original form after a 2-week recovery period, although muscle atrophy in the hindlimbs had recovered, implying discordance in recovery between altered locomotion and muscle atrophy, and that other factors such as neural drives might control behavioral adaptations to microgravity.     

Greater reinforcement rate during training increases spontaneous recovery

Spontaneous recovery occurs when a previously reinforced and recently extinguished response reemerges over the course of time, often at the beginning of a new session of extinction. Spontaneous recovery could underlie instances of treatment relapse that threaten otherwise effective behavioral interventions for problem behavior. In two experiments, we arranged multiple schedules with pigeons and a human child to assess the effects of different training reinforcer rates on spontaneous recovery. In both experiments, responding was both more resistant to extinction and more likely to relapse following training with greater reinforcement rates upon returning to extinction after time off from extinction testing. A quantitative model based on behavioral momentum theory accounted well for the data, which suggests reexposure to the extinction context following time off during extinction resulted in (1) the failure of extinction learning to generalize, and (2) greater generalization of original learning during training. The present model attempts to quantify theories attributing spontaneous recovery to changes in temporal context.     

Adaptive Dynamics of the Leg Movement Patterns of Human Infants: I. The Effects of Posture on Spontaneous Kicking

This is the first of two articles in which we describe how infants adapt their spontaneous leg movements to changes in posture or to elicitation of behaviors by a mechanical treadmill. In this article, we compare the kinematics of kicks produced by 3-month-old infants in three postures, supine, angled (45°), and vertical, and examine the changes in muscular and nonmuscular force contributions to limb trajectory. By manipulating posture we were able to assess the sensitivity of the nascent motor system to changes in the gravitational context. The postural manipulation elicited a distinct behavioral and dynamic effect. In the more upright postures, gravitational resistance to motion at the hip was 4 to 10 times greater than resistance met in the supine posture, necessitating larger muscle torques to drive hip flexion. Kicks produced in the vertical posture showed a reduction in hip joint range of motion and an increase in synchronous joint flexion and extension at the hip and knee. At the same time, hip and knee muscle torques were also more highly correlated in kicks performed in the vertical than in the supine or angled posture. This increased correlation between muscle torques at the hip and knee implicates anatomical and energetic constraints—the intrinsic limb dynamics—in creating coordinated limb behavior out of nonspecific muscle activations.     

Adaptive Dynamics of the Leg Movement Patterns of Human Infants: I. The Effects of Posture on Spontaneous Kicking

This is the first of two articles in which we describe how infants adapt their spontaneous leg movements to changes in posture or to elicitation of behaviors by a mechanical treadmill. In this article, we compare the kinematics of kicks produced by 3-month-old infants in three postures, supine, angled (45 degrees ), and vertical, and examine the changes in muscular and nonmuscular force contributions to limb trajectory. By manipulating posture we were able to assess the sensitivity of the nascent motor system to changes in the gravitational context. The postural manipulation elicited a distinct behavioral and dynamic effect. In the more upright postures, gravitational resistance to motion at the hip was 4 to 10 times greater than resistance met in the supine posture, necessitating larger muscle torques to drive hip flexion. Kicks produced in the vertical posture showed a reduction in hip joint range of motion and an increase in synchronous joint flexion and extension at the hip and knee. At the same time, hip and knee muscle torques were also more highly correlated in kicks performed in the vertical than in the supine or angled posture. This increased correlation between muscle torques at the hip and knee implicates anatomical and energetic constraints-the intrinsic limb dynamics-in creating coordinated limb behavior out of nonspecific muscle activations.     

Spontaneous epidural hematoma with cervical localization--report of a case with etiopathologic analysis

A case of spontaneous spinal epidural hematoma is reported. The 56-year-old man was hospitalized with neck pain followed by right sided Brown-Sequard syndrome at the level of C5-6 with a light rectovesical insufficiency and cervical sympathetic symptomatology. CT scan revealed right sided extradural high density mass. Following emergency operation removing the epidural hematoma ensured good recovery from the illness. The spontaneous spinal epidural hematoma is rare emergency. The exact etiology is unknown. Etiology and pathophysiology of this unusual lesion are described.     

Subacute apomorphine injections in rats: effects on components of behavioral stereotypy

This study was aimed at documenting the changes in the frequency and duration of bouts of behavior of Sprague-Dawley male rats in the open-field following each of four injections of apomorphine (Apo, 5 mg/kg, sc, immediate), or normal saline, delivered at 3-day intervals. Independent quantification of locomotion, sniffing, rearing, grooming, inactivity, gnawing, nodding, and jumping was obtained continuously throughout the 78-min sessions. Apo eliminated grooming and inactivity on all sessions. The large increases in locomotion and sniffing seen in the Apo rats compared to the saline rats on the first session were sustained throughout subsequent sessions. However, the Apo-induced potentiation of nodding of the head and gnawing, seen acutely, declined across sessions. These observations reconcile inconsistencies in the literature on subacute Apo effects. Finally, the individual differences in behavioral scores of Apo-treated rats were more stable than were those of saline-treated rats. This finding supports evidence in the literature that individual differences in neurochemistry are more likely to be predicted from the behavioral scores of Apo-challenged rats than from the scores of untreated rats.     

The effects of flooding on reducing snake fear in rhesus monkeys: 6-month follow-up and further flooding

Seven wild-reared rhesus monkeys were given two different 6-month follow-up tests to assess for spontaneous recovery of snake fear that had been somewhat reduced following 7 flooding sesions 6 months earlier. Both tests revealed essentially complete spontaneous recovery of fear. In addition, all 7 monkeys received 4 further mixed flooding sessions that involved exposure to real, toy and model snakes, and the 4 most fearful monkeys also received 3 more hours of exposure to the real snake alone. A final behavioral test following these additional flooding sessions revealed a pattern of changes very similar to that observed after the original 7 sessions 6 months earlier. In particular, there were some significant changes in the behavioral avoidance component of the fear but no changes in the behavioral disturbance component of the fear. The results are discussed in the context of earlier studies that purported to demonstrate that snake fear is easy to abolish. It is concluded that these earlier studies erred by not having tests for spontaneous recovery and by only testing for changes in the behavioral avoidance component of fear. Possible reasons for the failure to produce significant changes in the behavioral disturbance component of fear are discussed.     

Effect of Age and Level of Cognitive Function on Spontaneous and Exploratory Behaviors in the Beagle Dog

Cognitively characterized young and aged beagle dogs were administered six different spontaneous behavior tests, which provided measures of locomotion, exploration, and social interaction. Consistent with our previous findings, we obtained no overall effect of age on locomotion. We did find, however, that for the aged dogs locomotion correlated with level of cognitive function, being lowest in age-unimpaired dogs and highest in impaired dogs. Exploratory behavior, as measured by response to novelty, varied with age, with young dogs scoring the highest. Young dogs spent more time with novel toys and a person, responded more to a silhouette of a dog, and interacted more with a model dog compared to aged dogs. Among the aged dogs, age-unimpaired dogs spent the greatest amount of time sitting or standing beside a person whereas age-impaired dogs spent the most time reacting to a reflection in a mirror. The age-impaired dogs show undirected, stereotypical types of behavioral patterns. These differences in activity patterns may be linked to underlying age-associated neuropathology.     

Effects of fornix transection on spontaneous and trained non-matching by monkeys

Three monkeys with fornix transection and three normal control monkeys performed a series of tasks which were variations of delayed non-matching. Experiment 1 showed that even at short retention intervals fornix transection impaired the spontaneous tendency to explore novel objects. Experiment 2 provided differential reward for non-matching and showed that the fornix-transected monkeys learned and performed non-matching normally even though the sample-match retention intervals were long throughout the experiment. Experiment 3 showed that non-matching performance was transiently more disrupted in fornix-transected than in normal monkeys when the testing procedure was changed, in a variety of ways, while maintaining the basic non-match rule. Experiment 4 required the monkeys to discriminate objects they had displaced from objects they had seen but not displaced; fornix transection produced in this task a substantial and stable impairment. These four experiments require a revised interpretation of the effects of fornix transection upon recognition memory and exploration. Particularly they contradict the hypothesis, suggested by previous experiments, that fornix transection produces a defect in discrimination of stimulus familiarity in long-term but not in short-term memory. They suggest rather that fornix transection impairs memory of instrumental responses.     

The stability and interest consonance of lateral postural--motor biases in rats: results and implications

Each of six different tests of lateral postural-motor asymmetries was repeatedly administered to 126 rats. Directional reliability was found for rotatory swimming, open-field exploration, and stepping down from a beam. Neonatal posture, turn in an unbaited T maze, and orientation to tail pinch proved not to be reliable across days. The behavioral asymmetries in the open-field and step-down tests were directionally consonant with each other, but neither was related to the asymmetry exhibited in rotatory swimming, implying the existence of at least two independent asymmetrical neural substrates underlying the behaviors. Neither sample-wide directional biases nor major sex differences in bias were found. The sexes were, however, differentially influenced in direction on some tests by the number of males in their natal litters, implying a role for intrauterine exposure to androgens in predisposing rats toward some left- or right-biased behaviors.     

USING TIME DELAY TO PROMOTE SPONTANEOUS SPEECH IN AN AUTISTIC CHILD

One of the frequently observed deficits in autistic children is their lack of spontaneous speech. We used a multiple baseline across behaviors to investigate the effectiveness of a time delay procedure for inducing spontaneous speech in a 10-year-old male autistic child during play. We first taught the child to imitate the experimenter's verbal prompts that described the child's motor response. Once the child reached criteria on imitation, we implemented baseline wherein an immediate verbal prompt for speech was provided after each of the child's motor responses. Intervention consisted of a gradual delay in the presentation of the verbal prompts. The time delay effectively increased the child's spontaneous speech on trained items; some generalization to untrained items also occurred, but only within the same behavioral class of car play. Generalization was also observed across settings. Spontaneous speech remained at high levels during the 4-month maintenance for the behavior of car play but decreased for a second behavior. Decreases in the child's response latencies suggest that spontaneous speech may be an anticipatory verbal response.     

Different mechanisms of fear extinction dependent on length of time since fear acquisition

Fear extinction is defined as a decline in conditioned fear responses (CRs) following nonreinforced exposure to a feared conditioned stimulus (CS). Behavioral evidence indicates that extinction is a form of inhibitory learning: Extinguished fear responses reappear with the passage of time (spontaneous recovery), a shift of context (renewal), and unsignaled presentations of the unconditioned stimulus (reinstatement). However, there also is evidence to suggest that extinction is an "unlearning" process corresponding to depotentiation of potentiated synapses within the amygdala. Because depotentiation is induced more readily at short intervals following LTP induction and is not inducible at all at a sufficient delay, it may be that extinction initiated shortly following fear acquisition preferentially engages depotentiation/"unlearning," whereas extinction initiated at longer delays recruits a different mechanism. We investigated this possibility through a series of behavioral experiments examining the recoverability of conditioned fear following extinction. Consistent with an inhibitory learning mechanism of extinction, rats extinguished 24-72 h following acquisition exhibited moderate to strong reinstatement, renewal, and spontaneous recovery. In contrast, and consistent with an erasure mechanism, rats extinguished 10 min to 1 h after acquisition exhibited little or no reinstatement, renewal, or spontaneous recovery. These data support a model in which different neural mechanisms are recruited depending on the temporal delay of fear extinction.     

Spinal Cord Circuits

Over the past decade, research at three different levels of sensorimotor control has revealed a degree of complexity that challenges traditional hypotheses regarding servocontrol of individual muscles: (a) The connectivity of spinal circuits is much more divergent and convergent than expected. (b) The normal and reflex-induced recruitment of individual muscles and compartments of muscles is more finely controlled than was noted previously. (c) The mechanical interactions among linked skeletal segments and their often multiarticular muscles are neither simple nor intuitively obvious. We have developed a mathematical model of the cat hind limb that permits us to examine the influence of individual muscles on posture and gait. We have used linear quadratic control theory to predict the optimal distribution of feedback from a hypothetical set of proprioceptors, given different assumptions about the behavioral goals of the animal. The changes in these predictions that result from changes in the structure and control objectives of the model may provide insights into the functions actually performed by the various circuits in the spinal cord.     

Spinal cord circuits: are they mirrors of musculoskeletal mechanics?

Over the past decade, research at three different levels of sensorimotor control has revealed a degree of complexity that challenges traditional hypotheses regarding servocontrol of individual muscles: (a) The connectivity of spinal circuits is much more divergent and convergent than expected. (b) The normal and reflex-induced recruitment of individual muscles and compartments of muscles is more finely controlled than was noted previously. (c) The mechanical interactions among linked skeletal segments and their often multiarticular muscles are neither simple nor intuitively obvious. We have developed a mathematical model of the cat hind limb that permits us to examine the influence of individual muscles on posture and gait. We have used linear quadratic control theory to predict the optimal distribution of feedback from a hypothetical set of proprioceptors, given different assumptions about the behavioral goals of the animal. The changes in these predictions that result from changes in the structure and control objectives of the model may provide insights into the functions actually performed by the various circuits in the spinal cord.     

Modeling behavioral recovery following lesion induction in the rat dentate gyrus

Unilateral entorhinal lesions have enjoyed immense popularity as a model of recovery from damage. In part, the popularity has been supported the laminar organization of the hippocampal formation, which allows for the dissection of the contribution of individual afferent pathways to the recovery process. The commissural/associational pathway is of particular interest, since electrophysiological and gross anatomical data, although limited, have correlated sprouting in this pathway with behavioral recovery. Unfortunately, information relating recovery to synaptic structure is lacking. Addressing this issue, two analyses were conducted. Initially, a quantitative review of the literature reporting behavioral recovery following this type of lesion was conducted using meta-analytic techniques. Using this detailed information across decades of research, multiple linear regression analysis was conducted to address whether the morphological correlates of recovery could predict behavioral recovery. This resulted in an equation relating morphology and recovery that stood up well to several diagnostic tests. Moreover, this model suggests that synapse structure (in particular, synapse size and curvature, as well as terminal compartmentalization and the density of multi-synaptic terminals) holds a greater potential to predict behavioral recovery than increases in synapse number, which is typically seen as the optimal anatomical measure of recovery. This initial attempt to identify, quantify, and validate a model of lesion recovery is an important initial step in understanding how synaptic morphology may help mediate recovery of function.     

Conflicting processes in the extinction of conditioned taste aversion: behavioral and molecular aspects of latency,apparent stagnation,and spontaneous recovery

The study of experimental extinction and of the spontaneous recovery of the extinguished memory could cast light on neurobiological mechanisms by which internal representations compete to control behavior. In this work, we use a combination of behavioral and molecular methods to dissect subprocesses of experimental extinction of conditioned taste aversion (CTA). Extinction of CTA becomes apparent only 90 min after the extinction trial. This latency is insensitive to muscarinic and β-adrenergic modulation and to protein synthesis inhibition in the insular cortex (IC). Immediately afterwards, however, the extinguishing trace becomes sensitive to β-adrenergic blockade and protein synthesis inhibition. The subsequent kinetics and magnitude of extinction depend on whether a spaced or massed extinction protocol is used. A massed protocol is highly effective in the short run, but results in apparent stagnation of extinction in the long-run, which conceals fast spontaneous recovery of the preextinguished trace. This recovery can be truncated by a β-adrenergic agonist or a cAMP analog in the insular cortex, suggesting that spontaneous overtaking of the behavioral control by the original association is regulated at least in part by β-adrenergic input, probably operating via the cAMP cascade, long after the offset of the conditioned stimulus. Hence, the performance of the subject in experimental extinction is the sum total of multiple, sometimes conflicting, time-dependent processes.