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PubMed1992

Infants with myelomeningocele: visual recognition memory and sensorimotor abilities.

The cognitive development was explored of 29 infants with myelomeningocele. Although as a group they tended to be less likely to demonstrate visual recognition memory than a matched control group, excluding the more severely cognitively impaired infants from analysis rendered this difference non-significant. Infants with myelomeningocele demonstrated more verbal imitation on the Uzgiris-Hunt Assessment Scales than the controls, but there were no statistically significant differences between the groups on the Objects Permanence, Schemes, or Objects in Space subscales. The two groups did not differ on the majority of demographic and environmental variables examined, suggesting that group differences may be due to differences in biomedical variables. However, within the myelomeningocele group, environmental variables correlated with the majority of the cognitive measures, while correlations between cognitive performance and both demographic and biomedical variables were at chance level.

Apgar Score↗
PubMedDate not supplied

The influence of high-frequency stimulation of the midbrain reticular formation on the interaction of neurons of the neocortex.

The influence of the stimulation of the midbrain reticular formation (NRT) at a frequency of 75-100 Hz, current strength 33-400 microA, on the interaction of neurons of the visual and sensorimotor areas of the neocortex of rabbits was investigated. Cross- and autocorrelation histograms of the impulse sequences were plotted. Stimulation of the NRT led to an increase in the number of pairs of neurons functioning in correlation and an increase in the probability of discharges of neurons one after the other with delays from 100 to 400 msec as compared with resting wakefulness. The mechanisms of the interaction of the cells were not altered in the process. Comparison with previously obtained data made it possible to conclude that activation of the NRT may lead to specific changes in the interaction of neurons which are observable during pseudoconditioning and at the beginning of the development of a conditioned reflex.

Animals↗
PubMed1996

Development of spontaneous locomotor behaviors in the opossum, Monodelphis domestica.

The development of spontaneous locomotor behaviors was studied in the opossum Monodelphis domestica. The newborn opossum performs alternate, rhythmic movements with its forelimbs to crawl on the mother's belly where it attaches to a nipple, and its hindlimbs are little more than embryonic buds. The forelimbs retain the above movements for about 3 weeks, while the hindlimbs begin to move late in the second week. When detached from the nipple at 2-3 weeks, the pup can support its weight on the forelimbs and pivot around its hindquarter. Around the fourth week, the young can detach from the mother, its hindlimbs can support weight and linear locomotion appears, but the four limbs are not well coordinated. However, it can swim with coordinated movements of all limbs. Coordination when walking appears around the sixth week. During development, the duration of the step cycle decreases significantly. The durations of the stance and swing phases of the step cycle decrease in absolute terms, but swing increases as a percentage of the step cycle. The results are discussed in relation to the development of nervous and skeletomuscular components as well as sensorimotor reflexes.

Animals↗
PubMed1999

How efficient are central mechanisms for the learning and retention of coincident timing actions?

We compared the adaptive strategy and retention capacity of a deafferented subject and control subjects when intercepting, with a sliding-throw, an apparent movement coming at various speeds. Subjects were submitted to five practice sessions (30 trials per session) and to a retention test. The throwing kinematics was analysed, and spatial and temporal performance errors were measured. With practice, the deafferented subject showed modifications in movement initiation strategies and throwing patterns. With a slow apparent movement, the deafferented subject's initial behavior was characterized by short movement initiation and movement times. With practice, she showed an important increase in movement time in session 5, allowing longer visual control and leading to better temporal and spatial accuracy than that shown in session 1. In the retention session, the deafferented patient showed a late movement initiation strategy, similar to that of the control subjects. This increased movement initiation time was accompanied by an improved temporal accuracy compared to the deafferented subject's early results. However, spatial accuracy improvement was labile and could not be maintained over the retention interval. At the fast speed, all temporal components of the response, namely, movement initiation time (MIT), movement time (MT), and disk travel time (DTT), were similar for the deafferented and control subjects. Overall, the deafferented subject reduced her temporal error through practice, though without attaining the control subjects' accuracy. However, with a fast-moving stimulus, she showed a deteriorated spatial accuracy, even doubling her spatial errors at retention. In brief, the deafferented subject achieved proper temporal (perceptivo-cognitive) lasting control of her interceptive action, whereas spatial (sensorimotor) regulation raised mnemonic problems.

Afferent Pathways↗
PubMed1997

Phenotypic specification of hindbrain rhombomeres and the origins of rhythmic circuits in vertebrates.

This essay considers the ontogeny and phylogeny of the cranial neural circuitry producing rhythmic behaviors in vertebrates. These behaviors are characterized by predictable temporal patterns established by a neuronal network variously referred to as either a pacemaker, neural oscillator or central pattern generator. Comparative vertebrate studies have demonstrated that the embryonic hindbrain is divided into segmented compartments called rhombomeres, each of which gives rise to a distinct complement of cranial motoneurons and, as yet, unidentified populations of interneurons. We now propose that novel rhythmic circuits were innovations associated with the adoption of cardiac and respiratory pumps during the protochordate-vertebrate transition. We further suggest that the pattern-generating circuits of more recent innovations, such as the vocal, electromotor and extraocular systems, have originated from the same Hox gene-specified compartments of the embryonic hindbrain (rhombomeres 7-8) that gave rise to rhythmically active cardiac and respiratory circuits. Lastly, we propose that the capability for pattern generation by neurons originating from rhombomeres 7 and 8 is due to their electroresponsive properties producing pacemaker oscillations, as best typified by the inferior olive which also has origins from these same hindbrain compartments and has been suggested to establish rhythmic oscillations coupled to sensorimotor function throughout the neuraxis of vertebrates.

Animals↗
PubMed2002

Effects of transgenic overproduction of CRH on anxiety-like behaviour.

Central administration of corticotropin-releasing hormone increases anxiety-like behaviour and arousal in rodents, and increased anxiety-like behaviour has been shown in mice overproducing corticotropin-releasing hormone on an elevated plus maze and in a dark-light emergence task. However, evidence is accumulating that measures obtained from different anxiety tasks may reflect different aspects of anxiety-like behaviour in animals. We therefore tested mice overproducing corticotropin-releasing hormone in a battery of paradigms, studying spontaneous behaviour after a mild stressor, tasks of innate anxiety-like behaviour (light-dark box), lick suppression (Vogel conflict), conditioned fear, and forced swimming. Exploratory behaviour was studied in a 16-hole board task. Furthermore, pain threshold, water intake, locomotor activity and sensorimotor learning/co-ordination were tested to control for confounding factors. In line with previous findings, increased anxiety-like behaviour of transgenic mice was observed in the light-dark box paradigm. However, no differences were seen in the conflict paradigm. Conditioned fear was decreased 1 h but not 24 h after conditioning in transgenic mice, and immobility was decreased [corrected] in forced swimming in corticotropin-releasing hormone overexpressors. Locomotor activity in a novel open field and on the hole board was reduced in transgenics. Exploratory behaviour (hole pokes) was reduced during initial exploration of an unfamiliar hole board. Moreover, sensorimotor performance on a rotorod was impaired, and water intake was reduced in corticotropin-releasing hormone overproducing mice, while no changes were seen in nociception. No differences in locomotor activity were seen in a second group of mice, tested in a familiar open field. When these animals were challenged with diazepam, transgenic mice were less susceptible to the sedative effects of the drug on locomotor activity. These data suggest that corticotropin-releasing hormone overproduction leads to specific effects in a subset of anxiety paradigms, and that these transgenic mice suffer from a motor deficit in addition to altered anxiety-like behaviour/arousal.

Animals↗
PubMed2005

Effects of haloperidol, clozapine, and quetiapine on sensorimotor gating in a genetic model of reduced NMDA receptor function.

RATIONALE: Reduced N-methyl D-aspartate (NMDA) receptor function is hypothesized to contribute to the pathophysiology of schizophrenia. In order to model chronic and developmental NMDA receptor hypofunction, a mouse line was developed that expresses low levels of the NMDA R1 (NR1) subunit of the NMDA receptor. These mice show increased acoustic startle reactivity and deficits in prepulse inhibition (PPI) of acoustic startle. OBJECTIVES: The present study tested the hypothesis that these altered acoustic startle responses in the NR1 hypomorphic (NR1-/-) mice would be affected by antipsychotic drug treatment. METHODS: Mice were injected with drugs 30 min before assessment of acoustic startle responses with and without prepulse stimuli. RESULTS: Haloperidol (0.5 or 1.0 mg/kg) did not reduce the increased startle reactivity in the NR1-/- mice, but did increase PPI in both the mutant and wild type mice. Clozapine (3 mg/kg) and quetiapine (20 mg/kg) reduced startle magnitude and increased PPI in both the wild type and mutant mice. The antidepressant drug imipramine (10 and 20 mg/kg) had minimal effects on startle amplitude in NR1-/- or wild type mice. However, for the 20-mg/kg dose of imipramine, a significant increase in PPI was observed in the wild type animals, but not in the mutant mice. CONCLUSIONS: The results demonstrate that PPI can be increased in a mouse model of chronic NMDA receptor hypofunction by typical and atypical antipsychotic drugs. The similar effects of typical and atypical antipsychotic drugs to increase PPI in the wild type and mutant mice indicates that the assessment of behavior of the NR1 hypomorphic mice in the PPI paradigm offers no advantage over the wild type controls for identifying new clozapine-like drugs.

Acoustic Stimulation↗
PubMed2005

Functional circuits mediating sensorimotor integration: quantitative comparisons of projections from rodent barrel cortex to primary motor cortex, neostriatum, superior colliculus, and the pons.

Motor performance depends on somatosensory feedback, and consistent with this finding, primary somatosensory (SI) cortex projects to several regions involved in motor control. Although the pathways mediating sensorimotor integration are known, few studies have compared their projection patterns. Therefore, in each animal, we injected two anterograde tracers into SI barrel cortex and compared the relative density and spatial extent of the labeled projections to the primary motor (MI) cortex, neostriatum, superior colliculus, and basal pons. Quantitative analysis revealed that these projections terminated most extensively in the neostriatum, to a lesser extent in MI cortex, and innervated the least amount of neuropil in the superior colliculus and pontine nuclei. Tracer overlap in the pontine nuclei was significantly higher than in the other three brains regions, and was strongly correlated with overlap in the superior colliculus, presumably because some projections to these two brain regions represent collaterals of the same neurons. The density of labeled varicosities was highest in the pons and lowest in MI. As a proportion of total labeling, densely packed clusters of labeled terminals were most prevalent in the pons, less prevalent in neostriatum and superior colliculus, and least prevalent in MI cortex. These results are consistent with physiological evidence indicating strong coherence between SI barrel cortex and the cerebellum during whisking behavior.

Animals↗
PubMedDate not supplied

Disruption of central cholinergic systems in the rat by basal forebrain lesions or atropine: effects on feeding, sensorimotor behaviour, locomotor activity and spatial navigation.

Rats with ibotenic acid lesions of the nucleus basalis magnocellularis, the origin of the extrinsic cholinergic innervation of the cortex, were examined for changes in feeding, sensorimotor behaviour, nocturnal locomotor activity, and place navigation in the Morris swimming pool task, in comparison with control rats and rats receiving the muscarinic antagonist, atropine. The lesions produced acute feeding impairments, marked by weight loss and vigorous active rejection of food and water lasting 2-4 days, sensorimotor impairments in placing and orienting, and overnight hyperactivity. A similar hyperactivity was induced by atropine, lasting approximately 6 h following the injection. Rats with lesions or receiving atropine were similarly impaired in the acquisition of the spatial navigation task, they failed to reach control levels of efficiency even once they had acquired the task, and they showed small but significant retention impairments when pretrained in the absence of either treatment. The results are discussed in terms of the lesions producing a disruption of cortical cholinergic systems, with implications for the clinical disorder of senile dementia of the Alzheimer type, and in terms of possible associated disruption to non-cholinergic systems.

Animals↗
PubMed2005

Novel oral drug administration in an animal model of neuroleptic therapy.

A novel method of oral drug administration was used in a neuroleptic animal study. Seventy male Sprague-Dawley rats were randomly subdivided into four groups, which were treated with clozapine, haloperidol, diazepam or a vehicle solution (5% sucrose solution). Oral drug treatment was achieved by training the rats to drink the drug of choice mixed with five percent sucrose or vehicle solution from a syringe. Within 3-4 weeks the haloperidol group developed vacuous chewing movement, which did not disappear with discontinuation of the drug. Significant weight gain was observed for all drug groups in relation to the control group, whereas only the diazepam group showed a significant increase in response latency on the disengage test of sensorimotor function, which disappeared with drug withdrawal. A novel means of testing the motivational status showed that all drug-treated groups engaged in eating chocolate before grooming (t=11.69, p<0.001), whereas the control group showed no specific tendency towards either task. Furthermore, there was a significant delay in grooming for the haloperidol group compared to the other drug groups and controls. In conclusion, a novel method of oral drug administration with minimum stress was introduced that was sufficient to cause the described changes in behavioural parameters. Additionally, the combination of tests used provided an efficient discrimination between the behavioural effects of clozapine, haloperidol and diazepam in rodents.

Administration, Oral↗
PubMed2005

Structural covariance in the human cortex.

The morphology of the human cortex varies remarkably across individuals, regardless of overall brain size. It is currently unclear whether related cortical regions covary in gray matter density, as a result of mutually trophic influences or common experience-related plasticity. We acquired a structural magnetic resonance imaging scan from 172 subjects and extracted the regional gray matter densities from 12 readily identifiable regions of interest involved in sensorimotor or higher-order cognitive functions. We then used these values to predict regional densities in the remaining areas of the cortex, using voxel-based morphometry. This revealed patterns of positive and negative covariance that provide insight into the topographical organization of multiple cortical regions. We report that the gray matter density of a region is a good predictor of the density of the homotopic region in the contralateral hemisphere, with the striking exception of primary visual cortex. Whereas some regions express patterns of regional covariance that are mirror symmetrical relative to the interhemispheric fissure, other regions express asymmetric patterns of regional covariance. Finally, patterns of covariance are remarkably consistent between males and females, with the exception of the left amygdala, which is positively associated with the left and right anterior inferior temporal cortex in males and with the right angular gyrus in females. Our study establishes that the density of different cortical regions is coordinated within an individual. The coordinated variations we report are likely to be determined by both genetic and environmental factors and may be the basis for differences in individual behavior.

Adult↗
PubMed1997

The influence of dosing volume on the toxicity of p,p'-DDT.

In the IPCS Collaborative Study on Neurobehavioral Screening Methods, the "Top Dose" (TD) of p,p'-DDT (oral gavage, in corn oil) was determined to be different depending on the volume of administration: TD = 87 mg/kg when delivered in 1 ml/kg (i.e., 87 mg/ml) vs. TD = 130.5 mg/kg when given at 5 ml/kg (26.1 mg/ml). Two acute dose-response studies were conducted, the only difference being the doses used (pre-established percentages of the TD) and dosing volume (1 and 5 ml/kg); a third study was conducted using a single dose and varying the dosing volume (1 and 5 ml/kg). In the higher-volume study, dose-response curves for almost all the affected endpoints were shifted to the right, and the effects of the highest dose were less severe compared to the lower-volume study. For example, tremors were observed in all rats dosed with 43.5 mg/kg at 1 ml/kg, but only in 40% of the dose group given 65.3 mg/kg at 5 ml/kg. The highest dose groups (100% TD) showed myoclonus in both studies, but the incidence was 100% at 87 mg/kg (1 ml/kg) compared to 60% at 130.5 mg/kg (5 ml/kg). The dose-response curves indicated that the effective doses were generally 2-5 times higher, i.e., less potent, using a volume of 5 ml/kg. In general, the profiles of effect were similar in that the Sensorimotor and Convulsive domains were significantly altered in both studies, but again the dose-response curves were shifted; these domains were affected by both 43.5 and 87 mg/kg at 1 ml/kg, but only by 130.5 mg/kg at 5 ml/kg. The Neuromuscular domain, however, was only affected in the 1 ml/kg study (at 87 mg/kg). These differences in outcome could be due to higher partitioning of DDT into the oil, or increased gut motility, both of which could be due to the larger volume of oil delivered. The findings illustrate the importance of knowing the pharmacokinetic properties of the compound in question, as well as standardization of such variables whenever direct comparisons of dose levels are conducted.

Animals↗
PubMed2005

Tapping, grasping and aiming in ideomotor apraxia.

Very few studies have investigated sensorimotor control in apraxia using tasks that differ in movement complexity. Nevertheless, there is some evidence to suggest that spontaneous behaviour, although relatively preserved, can be rather clumsy or awkward, and that patients with ideomotor apraxia may have subtle kinematic abnormalities in movements made in the laboratory. It remains unclear whether patients with ideomotor apraxia perform normally on movements such as visually guided aiming, that may not depend on higher-order, more cognitive, processes and that are relatively unguided by overlearned contexts. In this study, three different sensorimotor tasks were given to the same sample of patients with quantified apraxic disturbance. Finger tapping, goal-directed grasping and aiming with and without visual feedback were examined in these patients. A clear dissociation was found between grossly impaired gesture imitation and intact motor programming of goal-directed movements with visual feedback. Apraxic patients were, however, impaired on aiming movements without visual feedback, suggesting that apraxia is associated with an increased reliance on integration of online visual information with feedforward/feedback somatosensory and motor signals. Furthermore, patients were impaired on single finger tapping which was a surprisingly good predictor of apraxia severity.

Aged↗
PubMed2005

A comparative study with two types of elevated plus-maze (transparent vs. opaque walls) on the anxiolytic effects of midazolam, one-trial tolerance and fear-induced analgesia.

The phenomenon known as one-trial tolerance (OTT) to the anxiolytic effects of benzodiazepines observed in rats submitted to the elevated plus-maze test (EPM) is considered to be due to the emergence of phobic states across the test/retest sessions. Antinociception is a usual component of the defense reaction. Until now, no study has examined antinociception and OTT together in freely behaving rats in the EPM. This work is a new approach looking at the sensorimotor gatings underlying OTT through the examination of the changes in reactivity to noxious stimuli during OTT development. We used the tail-flick test to assess the reactivity of rats to noxious stimulus during the effects of midazolam in test/retest sessions using two types of EPM, one with opaque (standard EPM) and another one with transparent walls (modified EPM). The authors had previously shown that this modified test caused an overall stressful situation more related to anxiety while the standard test coursed with a mixture of anxiety and high fear levels. In both plus mazes, the study was conducted in two experiments: (i) midazolam before the first trial, and (ii) midazolam before the second trial. In each experimental condition the effects of midazolam were tested under two doses (0.5 and 1.0 mg/kg) against a control group that received injections of saline. The anxiolytic effects of midazolam were more pronounced in animals tested in the modified EPM than in the standard EPM. Stressful stimuli present in both types of maze were able to elicit one-trial tolerance to midazolam on re-exposure. However, anxiolytic-insensitive behaviors in the first and the reduction in exploratory activity in the second trial are more pronounced in the standard EPM indicating that this test is more prone to transfer fear-related states across trials than the modified maze test. Antinociception is not present upon the re-exposure of rats to the EPM. These findings show that animals tested in the modified EPM showed higher sensitivity to the anxiolytic effects of midazolam than the standard EPM. Antinociception was not a concomitant of the shift in the emotional state present in the retest sessions of the EPM. These results are in agreement with the premises that repeated stressful experience leads to anxiolytic-insensitive fear state different from anxiety.

Analgesia↗
PubMed1995

Upright, correlated random walks: A statistical-biomechanics approach to the human postural control system.

The task of maintaining erect stance involves a complex sensorimotor control system, the output of which can be highly irregular. Even when a healthy individual attempts to stand still, the center of gravity of his or her body and the center of pressure (COP) under his or her feet continually move about in an erratic fashion. In this study, we approach the problem of characterizing postural sway from the perspective of random-walk theory. Specifically, we analyze COP trajectories as one-dimensional and two-dimensional random walks. These analyses reveal that over short-term intervals of time during undisturbed stance the COP behaves as a positively correlated random walk, whereas over long-term intervals of time it resembles a negatively correlated random walk. We interpret this novel finding as an indication that during quiet standing the postural control system utilizes open-loop and closed-loop control schemes over short-term and long-term intervals, respectively. From this perspective, our approach, known as stabilogram-diffusion analysis, has the advantage that it leads to the extraction of COP parameters which can be directly related to the steady-state behavior and functional interaction of the neuromuscular mechanisms underlying the maintenance of erect stance. (c) 1995 American Institute of Physics.

Journal Article↗
PubMed2006

Network analysis of single-subject fMRI during a finger opposition task.

The analysis of functional magnetic resonance imaging (fMRI) data has typically relied on univariate methods to identify areas of brain activity related to cognitive and behavioral task performance. We investigated the ability of multivariate network analysis using a modified form of principal component analysis, the Scaled Subprofile Model (SSM), applied to single-subject fMRI data to identify patterns of interactions among brain regions over time during an anatomically well-characterized simple motor task. We hypothesized that each subject would exhibit correlated patterns of brain activation in several regions known to participate in the regulation of movement including the contralateral motor cortex and the ipsilateral cerebellum. EPI BOLD images were acquired in six healthy participants as they performed a visually and auditorally paced finger opposition task. SSM analysis was applied to the fMR time series on a single-subject basis. Linear combinations of the major principal components that predicted the expected hemodynamic response to the order of experimental conditions were identified for each participant. These combinations of SSM patterns were highly associated with the expected hemodynamic response, an indicator of local neuronal activity, in each participant (0.84 </= R(2) </= 0.97, all P's < 0.0001). As predicted, the combined pattern in each subject was characterized most prominently by relatively increased activations in contralateral sensorimotor cortex and ipsilateral cerebellum. Additionally, all subjects showed areas of relatively decreased activation in the ipsilateral sensorimotor cortex and contralateral cerebellum. The application of network analysis methods, such as SSM, to single-subject fMRI data can identify patterns of task-specific, functionally interacting brain areas in individual subjects. This approach may help identify individual differences in the task-related functional connectivity, track changes in task-related patterns of activity within or between fMRI sessions, and provide a method to identify individual differences in response to treatment.

Acoustic Stimulation↗
PubMed2005

NT-3 expression from engineered olfactory ensheathing glia promotes spinal sparing and regeneration.

Adenoviral (AdV) vectors encoding neurotrophin-3 (AdV-NT-3) or the bacterial marker enzyme beta-galactosidase (LacZ gene) were used to transduce olfactory ensheathing glia (OEG) cultures. AdV vector-transduced OEG expressed high levels of recombinant neurotrophin as shown by in situ hybridization and enzyme-linked immunosorbent assay techniques. The biological activity of vector-derived NT-3 was determined in a dorsal root ganglia neurite outgrowth assay. Engineered cell suspensions were then injected into adult Fischer 344 rat spinal cord immediately after unilateral cervical (C4) corticospinal tract (CST) transection. Transplanted animals received a total of 200,000 cells; either non-transduced OEG or OEG transduced with AdV vectors encoding NT-3 or LacZ, respectively. At 3 months after injury, lesion volumes were significantly smaller in all OEG-transplanted rats when compared with control (medium-injected) rats. Anterograde tracing of the lesioned CST projection, originating from the contralateral sensorimotor cortex, showed a significantly greater number of distal CST axons only in OEG-NT-3-transplanted rats. Behavioural analysis was performed on all rats using open field locomotion scoring, and a forelimb reaching task with Eshkol-Wachman movement notation. Analysis of behavioural tests revealed no significant differences in recovery between experimental groups, although movement analysis indicated that possible compensatory mechanisms were occurring after OEG implantation. The results demonstrate that OEG transplantation per se can promote tissue sparing after injury, but, after appropriate genetic modification, these olfactory-derived cells become far more effective in promoting long-distance maintenance/regeneration of lesioned adult CST axons.

Adenoviridae↗
PubMed1999

Synaptogenesis in the brachial and lumbosacral enlargements of the spinal cord in the postnatal opossum, Monodelphis domestica.

Synaptic proteins were localized in light microscopy on sections of the brachial and lumbosacral enlargements of the spinal cord of postnatal opossums, Monodelphis domestica, to determine whether their expression correlates with the development of major motor pathways and simple motor behaviors. The tissues were fixed, cryoprotected, frozen, cut in 15-micrometer sections, and processed immunohistochemically using antibodies against synaptophysin, synaptotagmin-I, or SNAP-25. Immunolabeling was observed in the presumptive white matter before the presumptive gray matter, suggesting that the proteins are evidenced in growing axons before the onset of synaptogenesis, and it was observed in presumed propriospinal axons before most presumed descending axons of supraspinal origin. In the newborn opossum, the immunolabeling was scant in the gray matter and was limited to the periphery of the ventral horn, and indeed few synapses were seen in electron microscopy in nonexperimental material. Labeling increased in intensity and spread throughout the gray matter until 5-7 weeks, when it was no longer found in the white matter and resembled the adult pattern of labeling. Considering the location and relative intensity of the immunolabeling for the three proteins over time in the two enlargements, synaptogenesis occurs according to three general gradients: rostrocaudal, ventrodorsal, and lateromedial. These gradients match those of spinal cord and limb development, and of the growth of descending axons into the cord. Synaptogenesis is most intense when the spinal sensorimotor reflexes begin to be expressed.

Animals↗