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PubMed2002

Nonlinear cortical modulation of muscle fatigue: a functional MRI study.

Muscle fatigue has been studied for over a century, but almost no data are available to indicate how the brain perceives fatigue and modulates its signals to the fatiguing muscle. In this study, brain activation was measured by functional magnetic resonance imaging (fMRI) during a sustained (2-min) maximal-effort handgrip contraction while handgrip force and finger muscle electromyographic (EMG) data were recorded simultaneously by a magnetic resonance environment-adapted force-EMG measurement system. The results showed decoupled progresses in brain and muscle activities when muscle was fatigued and correlated behaviors among the cortical areas being analyzed. While handgrip force and EMG signals declined in parallel during the course of muscle fatigue, fMRI-measured brain activities first substantially increased and then decreased. This similar signal modulation occurred not only in the primary sensorimotor areas but also in the secondary and association cortices (supplementary motor, prefrontal, and cingulate areas). The nonlinear changes of brain signal may reflect an early adjustment to strengthen the descending command for force-loss compensation and subsequent inhibition by sensory feedback as fatigue became more severe. The close association in the activation pattern in many cortical regions may reflect integrated processing of information in the brain.

Afferent Pathways↗
PubMedDate not supplied

Cerebello-thalamic synapses and motor adaptation.

The cerebellum's influence on voluntary movement is mediated, in large part, through the cerebello-thalamo-cortical (CTC) pathway. Of particular relevance here are those neurons in the cerebellar nuclei that project, via thalamus, to pyramidal tract neurons in primary motor cortex. Several lines of evidence implicate cerebello-thalamic (CT) synaptic plasticity as a neural substrate underlying movement adaptation in adult animals. CT synapses exhibit a number of structural characteristics suggestive of a capacity for both formation of new synapses, and alterations in efficacy of transmission across existing synapses. Long-term potentiation can be evoked across CT synapses in vitro by high frequency stimulation, albeit in young animals. Evidence regarding the contribution of CT synaptic plasticity to two different types of movement adaptation in adult animals is conflicting. Adaptation involving a strengthening and re-coordination of voluntary movement is associated with an increase in density of CT synaptic boutons and an increase in number of synaptic vesicles available for immediate neurotransmitter release within each bouton. On the other hand, adaptation involving associative conditioning of a reduced sensorimotor neural circuit is associated with plasticity at thalamo-cortical but not CT synapses. These conflicting findings may reflect differences in the extent of synaptic re-organization that occurs at thalamic versus cortical levels, differences in the neural circuitry mediating each behavior, and/or differences in the spatio-temporal convergence of activity in the thalamus during the adaptive processes. It is concluded that CT synaptic plasticity can underlie movement adaptation if the adaptation requires reorganization of the cerebellum's influence on cerebral cortex.

Adaptation, Physiological↗
PubMed1980

Adaptation to visual--motor rearrangement of mentally retarded individuals: relationship to Adaptive Behavior Scale scores.

Thirty-five institutionalized, mentally retarded individuals navigated an obstacle course while viewing through an optical prism that displaced the visual field (visual--motor rearrangement). The degree of adaptation to visual--motor rearrangement was assessed and compared with scores on a research version of the Adaptive Behavior Scale (ABS). The results showed that those individuals who produced the expected patterns of prismatic visual--motor adaptation scored significantly higher on ABS Factors I and II but not III. Factors I and II include a number of items that depend upon sensorimotor integration. Thus, an explicit experimental technique for assessing sensorimotor adaptation was found to support the utility and validity of ABS assessment of mentally retarded individuals.

Adaptation, Psychological↗
PubMed1999

Cortical neurite outgrowth and growth cone behaviors reveal developmentally regulated cues in spinal cord membranes.

Corticospinal axon outgrowth in vivo and the ability to sprout or regenerate after injury decline with age. This developmental decline in growth potential has been correlated with an increase in inhibitory myelin-associated proteins in older spinal cord. However, previous results have shown that sprouting of corticospinal fibers after contralateral lesions begins to diminish prior to myelination, suggesting that a decrease in growth promoting and/or an increase in inhibitory molecules in spinal gray matter may also regulate corticospinal axon outgrowth. To address this possibility, we carried out in vitro experiments to measure neurite outgrowth from explants of 1-day-old hamster forelimb sensorimotor cortex that were plated onto membrane carpets or membrane stripe assays prepared from white or gray matter of 1-to 22-day-old cervical spinal cord. On uniform carpets and in the stripe assays cortical neurites grew robustly on young but not older membranes from both white and gray matter. Mixtures of membranes from 1- and 15-day spinal cord inhibited neurite outgrowth, suggesting that the presence of inhibitory molecules in the 15-day cord overwhelmed permissive or growth promoting molecules in membranes from 1-day cord. Video microscopic observations of growth cone behaviors on membrane stripe assays transferred to glass coverslips supported this view. Cortical growth cones repeatedly collapsed at borders between permissive substrates (laminin or young membrane stripes) and nonpermissive substrates (older membrane stripes). Growth cones either turned away from the older membranes or reduced their growth rates. These results suggest that molecules in both the gray and white matter of the developing spinal cord can inhibit cortical neurite outgrowth.

Aging↗
PubMed1990

Chronic infusion of GABA and saline into the nucleus basalis magnocellularis of rats: II. Cognitive impairments.

In order to assess sensorimotor and/or cognitive modifications following chronic inhibition of nucleus basalis magnocellularis (NBM) neurons, rats trained in two radial maze paradigms (the classical version of the test and a modified version introducing a one-hour delay between the fourth and the fifth choice) received chronic infusion of gamma-aminobutyric acid (GABA) into the NBM area. GABA (10 and 50 micrograms/microliters/h) was infused for 3 days into the NBM contralateral to their preferred turning direction in the radial maze. Simultaneously, saline (NaCl 0.9%; 1 microliter/h) was infused into the contralateral NBM. GABA and saline infusions were alternated for the subsequent 3-day period. One week later, we investigated the rats' ability to learn a multiple trial passive avoidance task. At the dose of 50 micrograms/microliters, GABA infusion produced (1) a turning bias ipsilateral to the side first infused with GABA, (2) transitory cognitive impairments in radial maze tasks and (3) a deficit in the acquisition of the passive avoidance task. At the dose of 10 micrograms/microliters, the same behavioral deficits were observed except that (1) the turning bias was reversed by the contralateral GABA infusion and (2) cognitive impairments in the radial maze were observed only when a delay was inserted between the fourth and the fifth choice. Histologically, we found a dose-dependent gliosis in the NBM area first infused with GABA. These data suggest a reactivity of the NBM to GABAergic manipulations and the intervention of this structure in both sensorimotor and cognitive processes involved in the radial maze paradigms.

Acetylcholine↗
PubMed2005

Adult female and male zebra finches show distinct patterns of spine deficits in an auditory area and in the song system when reared without exposure to normal adult song.

Male songbirds typically require exposure to normal adult conspecific song during development in order to learn a normal song of their own. Females require exposure to conspecific song during development in order to select high-quality, learned song over the incomplete song produced by males reared in isolation. Altering males' opportunity for song learning during development affects the neuroanatomy of brain regions involved in song production (the song system), but in females the neural effects of song learning are unknown. We raised male and female zebra finches (Taeniopygia guttata) with differing amounts of exposure to singing males during development. At 120 days, we Golgi-stained their brains and measured the frequency of dendritic spines in brain areas used in song perception or production. We found that females reared with little or no exposure to song have 31% fewer dendritic spines per unit length of dendrite in caudomedial nidopallium (NCM), a brain area activated by song perception, compared to control females. The deprived females had small deficits in the frequency of spines in HVC, a region activated by song production in males. Males with limited exposure to song had a 24% lower spine density in HVC than controls but only a 10% lower density in NCM. These data support the hypothesis that NCM is important in auditory learning, while HVC is involved in sensorimotor learning, and that these capacities are differentially emphasized in the two sexes.

Animals↗
PubMed2004

Structure of dependent relationships between neurons in the sensorimotor cortex of the left and right hemispheres in rabbits in immobilization catatonia.

Dependence in the activity of sensorimotor cortex neurons recorded simultaneously in the left and right hemispheres was detected in rabbits in baseline conditions, during the state of immobilization ("animal hypnosis"), and recovery of animals from this state. In baseline conditions, the total percentage of dependent relationships between close-lying (within 50 microm) neurons in the left hemisphere was significantly smaller than in the right hemisphere and did not change either in the state of immobilization or on recovery from it. The total percentage of dependent relationships between close-lying neurons in the right hemisphere decreased significantly during immobilization and returned to baseline levels on recovery from this state. The percentage of dependent relationships between distant (500 microm) neurons in immobilization, conversely, showed no change in the cortex of the right hemisphere, though it changed significantly in the cortex of the left hemisphere, returning to baseline values when the rabbits recovered from this state. Further analysis showed that this cortical interhemisphere asymmetry was based on the asymmetrical activity of individual neurons and small neuronal populations. Thus, changes in the structure of dependent relationships between neurons in microareas of the cortex of the left and macroareas of the cortex of the right hemisphere could be in different directions, while changes in microareas of the right hemisphere and macroareas of the left hemisphere were synergistic. Thus, asymmetry was detected at different levels of neuronal combinations (neuron pairs, micro- and macrogroups of neurons), which suggests mosaicism in neuron structure, which ultimately leads to overall functional asymmetry in "animal hypnosis." Some changes in the structure of dependent relationships between sensorimotor cortex neurons arising in "animal hypnosis" persisted or even became more marked after recovery of animals from this state.

Action Potentials↗
PubMed1998

Brain-behavior correlations in hemispatial neglect using CT and SPECT: the Sunnybrook Stroke Study.

OBJECTIVE: Structural and functional lesion localization in patients with hemispatial neglect. DESIGN: Location and severity of brain damage on CT and SPECT correlated with neglect performance as assessed with a battery of drawings, line bisection, and line and shape cancellation subtests. PATIENTS: Participants included 120 consecutive stroke patients with a single right-hemisphere-damaged lesion on CT who were admitted to the Acute Stroke Care Unit at Sunnybrook Health Science Centre. Of these, 88 also had a SPECT. RESULTS: On CT, 82 patients with neglect (compared with 38 without neglect) had more extensive damage in the parietal and sensorimotor cortex and white matter fiber bundles, including the posterior-superior longitudinal and inferior-frontal fasciculi (p < 0.05). Parietal and anterior cingulate damage best predicted neglect score using the CT data (p < 0.05), and regional blood flow in the parietal cortex best predicted neglect score using the SPECT data (p < 0.05) after controlling for the influence of age and lesion size on multiple linear regression. CONCLUSIONS: Damage in the parietal and anterior cingulate cortex and posterior white matter fiber bundles correlated with hemispatial neglect. Combining structural- and functional-imaging techniques with neurobehavioral analysis can elucidate brain-behavior relationships.

Age Factors↗
PubMed2003

Burst-induced synaptic depression and its modulation contribute to information transfer at Aplysia sensorimotor synapses: empirical and computational analyses.

The Aplysia sensorimotor synapse is a key site of plasticity for several simple forms of learning. Plasticity of this synapse has been extensively studied, albeit primarily with individual action potentials elicited at low frequencies. Yet, the mechanosensory neurons fire high-frequency bursts in response to even moderate tactile stimuli delivered to the skin. In the present study, we extend this analysis to show that sensory neurons also fire bursts in the range of 1-60 Hz in response to electrical stimuli similar to those used in behavioral studies of sensitization. Intracellular stimulation of sensory neurons to fire a burst of action potentials at 10 Hz for 1 sec led to significant homosynaptic depression of postsynaptic responses. The depression was transient and fully recovered within 10 min. During the burst, the steady-state depressed phase of the postsynaptic response, which was only 20% of the initial EPSP of the burst, still contributed to firing the motor neuron. To explore the functional contribution of transient homosynaptic depression to the response of the motor neuron, computer simulations of the sensorimotor synapse with and without depression were compared. Depression allowed the motor neuron to produce graded responses over a wide range of presynaptic input strength. In addition, enhancement of synaptic transmission throughout a burst increased motor neuron output substantially more than did preferential enhancement of the initial phase of a burst. Thus, synaptic depression increased the dynamic range of the sensorimotor synapse and can, in principle, have a profound effect on information processing.

Action Potentials↗
PubMed2005

A scientific paradigm for consciousness: a theory of premotor relations.

Consciousness has become a holy grail for scientific research only in the last few decades. In spite of the extensive recent research in the field agreement on a correct approach to a theory has been elusive. We all have an intuitive idea of what we mean by the term and at the very least relate awareness to a descriptive phenomenology. I present a theory of consciousness based on motor capacity. An organism may exert control through movement and any action it performs on its surroundings results in a reaction. This type of reafference generated by movement provides the organism with a unique opportunity to compare perceptual information, for example, a retinal image of a ball with what the body is telling the agent about the object. In other words, limb movements will describe a certain physical distance to the object and the shape will be conveyed by the arc described around it by any part of the body that comes into contact with it. The reafference, also called motor efference copy, can modulate neocortical networks strictly associated with concurrent perceptual information via input to thalamocortical projections. Concurrent perceptual and motor reafferent input provide the critical organizing principles bestowing on a neural assembly the capacity of conscious awareness. The cortical neural coding represents an interactive history and is what I call a premotor relation. It avoids the trap of behaviorism by emphasizing a developmental causality such that, once the networks are established no further motoric component is required. Supportive evidence for this position comes from the classic psychological studies of perceptual adaptation to distorting lenses facilitated by movement and elegant animal experiments dissociating sensorimotor development from visual exposure. One of the most innovative and useful conceptions advanced in the paper is a component theory of motor efference copy analyzing the two key parameters of any action namely force and proprioceptive change. There is massive neocortical input to the basal ganglia and cerebellum and recent research has implicated cognitive roles for these structures. I propose they serve the respective component parameters of motor efference copy. Finally, a theory of premotor relations provides a model for understanding how dysfunction in the basal ganglia and cerebellum relates to cognitive features of schizophrenia and autism, respectively. Motor dysfunction figures prominently in the early literature on these syndromes and I make the case for a fundamental causal connection between motor and cognitive symptoms.

Brain↗
PubMed2003

Neurobehavioral changes resulting from recombinase activation gene 1 deletion.

Recombinase activation gene 1 (RAG-1) function is essential for V(D)J recombination in T-cell-receptor and immunoglobulin rearrangements whereby the immune system may encode memories of a vast array of antigens. The RAG-1 gene is also localized to neurons in the hippocampal formation and related limbic regions that are involved in spatial learning and memory as well as other parameters of neurobehavioral performance. Since the unique ability to encode memory is shared by the immune system and the brain, we tested the hypothesis that loss of the RAG-1 gene in the brain would influence learning and memory performance and examined several different domains of behavior in RAG-1-knockout and control mice. Compared to control mice, RAG-1-knockout mice exhibited increased locomotor activity in an open field under both dim and bright lighting conditions and decreased habituation (reduction in the expected decline in locomotor activity with increasing familiarity with the novel environment in a 1-h test session) in bright lighting. RAG-1-knockout mice also showed reduced levels of fearfulness for some measures of fear-motivated behavior in both the open-field behavior test and elevated-plus maze test. Contrary to our hypothesis, no differences in spatial learning and memory were found between the groups, although modest differences were observed visible-platform testing in the Morris water maze. Neither prepulse inhibition, a measure of sensorimotor gating, nor reflexive acoustic startle responses differed between the RAG-1-knockout and control mice. It remains to be determined if these changes are due to the loss of RAG-1 gene expression in the brain, are due to the absence of the gene in the immune system (e.g., the loss of cytokines with neuromodulatory activities), or are due to some combination of both effects. Study of the neurobiological actions of RAG-1 in the brain may provide new insights into important processes involved in normal brain function and disease.

Animals↗
PubMedDate not supplied

Evolutionary robotics: a new scientific tool for studying cognition.

We survey developments in artificial neural networks, in behavior-based robotics, and in evolutionary algorithms that set the stage for evolutionary robotics (ER) in the 1990s. We examine the motivations for using ER as a scientific tool for studying minimal models of cognition, with the advantage of being capable of generating integrated sensorimotor systems with minimal (or controllable) prejudices. These systems must act as a whole in close coupling with their environments, which is an essential aspect of real cognition that is often either bypassed or modeled poorly in other disciplines. We demonstrate with three example studies: homeostasis under visual inversion, the origins of learning, and the ontogenetic acquisition of entrainment.

Animals↗
PubMed1977

Sensorimotor organization in reach and prehension: a development model.

A model is presented to depict the organization of the reflex, visual, voluntary motor, and perceptual-cognitive systems in the development of reach and prehension during the first year of life. Five components of hand skills are identified based upon a review of infant scales and observational studies, and the sequential occurrence of behaviors leading to the development of these components is graphically presented. These sequences are juxtaposed to enable the reader to view the temporal relationship of the systems at various stages in the development of reach and prehension in the infant. Items in the models are operationally defined. An explanation is included to clarify the nature and the sequence of events involved in the culmination of mature hand skills. The model should be useful in the identification, analysis, and remediation of deficits in reach and prehension often noted in children with developmental disabilities.

Child Development↗
PubMed1990

Feeding behavior of 6- to 12-month-old infants: assessment and sources of parental information.

Both the infant's development of feeding skill and self-regulatory competence during the second 6 months of life have implications for weaning and for a weaning diet. This article examines four categories of feeding skills: taking food from a spoon; handling thicker, lumpy foods and foods that require chewing; self-feeding with fingers or a spoon; and drinking from a cup and managing the bottle. These skills are fundamental for the development of self-regulatory competence through the phases of sensorimotor modulation (from 3 months of age to approximately 9 to 12 months) and control (9 to 12 months of age). Available instruments to assess feeding skill and self-regulatory competence are described. Questions concerning feeding practices in relation to the infant's development of feeding skill and self-regulatory competence are raised. Potential conflicts between professional and lay sources, informational methods used and preferred, and the types of problems for which help is sought are discussed.

Feeding Behavior↗
PubMed1991

Role of the Mauthner cell in sensorimotor integration by the brain stem escape network.

The Mauthner neurons have become synonymous with the C start evasive response of fishes. C starts are a two-part movement pattern. First, the fish bends its body so that it has a C-like profile (stage 1) when viewed from above. Second, the fish rapidly accelerates away from its starting position (stage 2). Until recently, it has been possible to determine the contribution of Mauthner cell activity to the expression of this behavior. In this paper we focus on three of our recent papers that address this issue. Our work combines high-speed digital image analysis of the C start with chronic Mauthner cell and electromyographic recordings, lesions of the Mauthner cells, and stimulation of single Mauthner axons in swimming fishes. This work shows that the firing of the Mauthner cell results in a short-latency body contraction that orients the initial stage of the C start away from the direction of the threatening stimulus. The direction of the escape trajectory, however, is more finely tuned to stimulus angle than can be explained by the firing of just the Mauthner cell and its post-synaptic followers. Precise control of trajectory must, therefore, require participation of other neurons. These neurons together with the Mauthner cell form a system that we term the brain stem escape network. We have identified candidate neurons of this network which can now be studied at the single-cell level. Because of both its accessibility for neurophysiological study and its neuroanatomical simplicity, we assert that the brain stem escape network is a useful preparation for understanding fundamental processes of sensorimotor integration in the brain stem.

Animals↗
PubMedDate not supplied

Age-related impairments in spatial memory are independent of those in sensorimotor skills.

Seventy-five aged rats were tested for a variety of motor and cognitive tests which generated 20 separate measures of performance. Considerable variability was observed on many measures in the aged population. Multivariate analyses were performed on the data to determine 1) the extent of intercorrelations between the measures for the aged rats, and 2) whether clusters of related and/or unrelated behavioral measures could be determined. Aged rats that were impaired on measures of cognitive performance are not necessarily impaired in their motor performance and vice versa. These results demonstrate that different age-related variables affect cognitive and motor systems, and suggest that age-related declines in different functional anatomical systems, such as the limbic system and the basal ganglia may progress independently.

Aging↗
PubMed2003

Episodic neonatal hypoxia evokes executive dysfunction and regionally specific alterations in markers of dopamine signaling.

Perinatal ischemic-anoxic and prolonged anoxic insults lead to impaired dopaminergic signaling and are hypothesized to contribute, at least in part, to the pathogenesis of disorders of minimal brain dysfunction such as attention-deficit hyperactivity disorder. We hypothesized that subtle intermittent hypoxic insults, occurring during a period of critical brain development, are also pathogenic to dopaminergic signaling, thereby contributing to behavioral and executive dysfunction. Between postnatal days 7 and 11, rat pups were exposed to either 20-s bursts of isocapnic hypoxic gas, compressed air, or were left undisturbed with the dam. On postnatal days 23 pups were instrumented with electroencephalographic/electromyographic electrodes and sleep-wake architecture was characterized. Locomotor activity was assessed between postnatal days 35 and 38, learning, and working memory evaluated between postnatal days 53 and 64. Rats were killed on postnatal day 80 and tyrosine hydroxylase, vesicular monoamine transporter, dopamine transporter, and dopamine D1 receptors were quantified in the prefrontal cortex, primary sensorimotor cortex, and precommissural striatum by Western blot analyses. Post-hypoxic pups spent less time awake and more time in rapid-eye-movement sleep during the lights-on phase of the circadian cycle, were hyperlocomotive, and expressed impaired working memory. Striatal expression of vesicular monoamine transporter and D1 receptor proteins were increased in post-hypoxic rats, consistent with depressed dopaminergic signaling. These observations lead to the intriguing hypothesis that intermittent hypoxia occurring during a period of critical brain development evokes behavioral and neurochemical alterations that are long lasting, and consistent with disorders of minimal brain dysfunction.

Animals↗