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At least 775 records · Page 43Linked to original sources
PubMed2002

Cortical network reorganization guided by sensory input features.

Sensory experience alters the functional organization of cortical networks. Previous studies using behavioral training motivated by aversive or rewarding stimuli have demonstrated that cortical plasticity is specific to salient inputs in the sensory environment. Sensory experience associated with electrical activation of the basal forebrain (BasF) generates similar input specific plasticity. By directly engaging plasticity mechanisms and avoiding extensive behavioral training, BasF stimulation makes it possible to efficiently explore how specific sensory features contribute to cortical plasticity. This review summarizes our observations that cortical networks employ a variety of strategies to improve the representation of the sensory environment. Different combinations of receptive-field, temporal, and spectrotemporal plasticity were generated in primary auditory cortex neurons depending on the pitch, modulation rate, and order of sounds paired with BasF stimulation. Simple tones led to map expansion, while modulated tones altered the maximum cortical following rate. Exposure to complex acoustic sequences led to the development of combination-sensitive responses. This remodeling of cortical response characteristics may reflect changes in intrinsic cellular mechanisms, synaptic efficacy, and local neuronal connectivity. The intricate relationship between the pattern of sensory activation and cortical plasticity suggests that network-level rules alter the functional organization of the cortex to generate the most behaviorally useful representation of the sensory environment.

Acetylcholine↗
PubMed1984

Olivo-vestibular and cerebello-vestibular connections in albino rabbits.

This study analyzes the organization of olivo-vestibular and cerebello-vestibular projections in rabbits. Iontophoretic injections of horseradish peroxidase, placed under physiological guidance into the superior, medial and lateral vestibular nuclei, produced retrogradely labeled neurons in the dorsal cap, ventrolateral outgrowth and lateral flexure of the principal olivary nucleus, the caudal half of the medial accessory olive and the caudal three-fourths of the dorsal accessory olive. This inferior olivary labeling was strictly contralateral. The same injections labeled groups of Purkinje cells in the ipsilateral cerebellar cortex, oriented perpendicular to the long axes of the folia of lobules I-V, VId-e and VIII-X of the vermis and the flocculus. The patterns of olivo-vestibular and cerebello-vestibular connections were consistent with the general hypothesis that inferior olivary axon collaterals project to both Purkinje cells and subcortical neurons inhibited by those Purkinje cells. In addition, the analysis of flocculo-nodular and dorsal cap-ventrolateral outgrowth projections to the medial and superior vestibular nuclei suggests that these connections are discrete at the level of a pool of olivary neurons which projects to functional pools of neurons in both cerebellar cortex, and in the vestibular nuclei. Thus, it is likely that inferior olivary projections define functional networks spanning cerebellar cortex and the vestibular nuclei.

Animals↗
PubMed1998

The functional anatomy of attention to visual motion. A functional MRI study.

Attention can enhance or modulate neural responses to stimuli at early and late stages of sensory processing. We were interested in the modulatory effect of attention to visual motion on cortical responses as measured by functional MRI. Subjects were scanned during repeated presentations of identical stimuli (visual motion) while only the attentional component of the task was varied. Enhanced haemodynamic responses during attentive conditions defined an occipitoparietofrontal system, including sensory and association areas, as well as the medial thalamus and superior colliculus. Attentional modulation was not restricted to extrastriate areas (including V3a and the V5 complex) but was also evident, to a lesser degree, in early visual areas close to the calcarine fissure (V1/V2 border). Attention-related enhancement of cortical responsiveness is discussed in terms of data that implicate modulatory short-term changes in synaptic efficacy and reciprocal connections between striate, extrastriate, parietal and frontal areas. Given the similarity of our attentional network to that controlling eye movements, the results of this study are in accord with theories linking oculomotor control and attention.

Attention↗
PubMed1975

Development of specific sensory-evoked synaptic networks in fetal mouse cord-brainstem cultures.

Neurites of nerve growth factor-enhanced fetal mouse dorsal root ganglion cells can not only establish characteristic sensory synaptic network functions in dorsal regions of attached spinal cord explants, but some of the neurites may grow through the cord tissue in these cultures and make similar functional synaptic connections with specific types of "target" neurons in localized zones within nearby medulla explants.

Animals↗
PubMed2004

Neural activity when people solve verbal problems with insight.

People sometimes solve problems with a unique process called insight, accompanied by an "Aha!" experience. It has long been unclear whether different cognitive and neural processes lead to insight versus noninsight solutions, or if solutions differ only in subsequent subjective feeling. Recent behavioral studies indicate distinct patterns of performance and suggest differential hemispheric involvement for insight and noninsight solutions. Subjects solved verbal problems, and after each correct solution indicated whether they solved with or without insight. We observed two objective neural correlates of insight. Functional magnetic resonance imaging (Experiment 1) revealed increased activity in the right hemisphere anterior superior temporal gyrus for insight relative to noninsight solutions. The same region was active during initial solving efforts. Scalp electroencephalogram recordings (Experiment 2) revealed a sudden burst of high-frequency (gamma-band) neural activity in the same area beginning 0.3 s prior to insight solutions. This right anterior temporal area is associated with making connections across distantly related information during comprehension. Although all problem solving relies on a largely shared cortical network, the sudden flash of insight occurs when solvers engage distinct neural and cognitive processes that allow them to see connections that previously eluded them.

Adolescent↗
PubMed2004

Cortical activation and synchronization during sentence comprehension in high-functioning autism: evidence of underconnectivity.

The brain activation of a group of high-functioning autistic participants was measured using functional MRI during sentence comprehension and the results compared with those of a Verbal IQ-matched control group. The groups differed in the distribution of activation in two of the key language areas. The autism group produced reliably more activation than the control group in Wernicke's (left laterosuperior temporal) area and reliably less activation than the control group in Broca's (left inferior frontal gyrus) area. Furthermore, the functional connectivity, i.e. the degree of synchronization or correlation of the time series of the activation, between the various participating cortical areas was consistently lower for the autistic than the control participants. These findings suggest that the neural basis of disordered language in autism entails a lower degree of information integration and synchronization across the large-scale cortical network for language processing. The article presents a theoretical account of the findings, related to neurobiological foundations of underconnectivity in autism.

Autistic Disorder↗
PubMed1990

[Regulation of food intake].

Regulation of food intake is commonly treated as a negative feedback-loop. Hunger and/or appetite lead man and animals to ingest food. The subsequent meal-contingent activation of pre- and postabsorptive mechanisms then leads to satiety. The activation of oral and gastrointestinal chemo- and mechanoreceptors is important on the preabsorptive site. The gastrointestinal hormone cholecystokinin may also have a physiological satiety effect. Preabsorptive satiety mechanisms are influenced by the rate of gastrointestinal transit. The pancreatic hormone glucagon, which is released during meal taking, and various metabolites contribute to the postabsorptive regulation of food intake through activation of hepatic chemoreceptors, which are connected to the brain via predominantly vagal afferents. In addition, glucoreceptors in the brain, in particular in the nucleus of the solitary tract, contribute to food intake regulation by monitoring blood glucose concentration or, more specifically, glucose utilization. The nucleus of the solitary tract, which relays vagal afferents from gut and liver and also gustatory afferents, projects to the hypothalamus and to other forebrain structures. In this neural network the informations from the periphery are integrated by various neurotransmitters and neuropeptides, but the exact role of the substances involved is not fully understood yet. Body weight and, hence, body fat presumably affects feeding through modulation of a postabsorptive mechanism.

Animals↗
PubMed1994

Gravitational neuromorphology.

This review shows that morphological studies of the central, peripheral and autonomic nervous system of animals exposed to altered gravity yield data which are extremely significant for our understanding of the mechanisms of adaptation of the nervous system, and of the mammalian organism as a whole, to increased and decreased loading. Neuromorphological studies, correlating structure and function, indicate a decreased activity in weightlessness for spinal ganglia neurons and motoneurons of the spinal cord, as well as the neurons of the hypothalamic nuclei producing arginine vasopressin and growth hormone releasing factor. Structural changes of the somatosensory cortex and spinal ganglia suggest a decreased afferent flow to the somatosensory cortex in microgravity. The results characterize the mechanisms of structural adaptation to a decreased afferent flow in microgravity by the neurons in the hemisphere cortex and brain stem nuclei. There is also morphological evidence for an increased sensitivity of the otolith apparatus and for the development of a hyponoradrenergic syndrome in weightlessness. These studies have shown that both microgravity and the simulation of microgravity effects by tail suspension-induced structural changes in the large neurons of lumbar spinal ganglia and motoneurons of the lumbar spinal cord, which occur under conditions of nerve cell hypoactivity. The structural changes, and consequently the development of neuron hypoactivity, are expressed more extensively after microgravity than after tail suspension for the same length of time. The influence of microgravity and hypergravity on animals is expressed by opposing changes in nervous tissue structure in the spinal ganglia, spinal cord, and nodulus of cerebellar vermis. These changes indicate neuron hypoactivity under microgravity and neuron hyperactivity under 2 G. Morphological assessment of the functional state of other structures of the brain under hypergravity will require further study. Can all structural changes which occur in nerve tissue under microgravity or under hypergravity be explained on the basis of increased or decreased activity of its structural elements? The presently available data regarding the correlation of structure and functional state of cells in brain and spinal cord suggest an affirmative answer. Ultrastructural studies of the nodular cortex of the cerebellum in rats after different duration spaceflights provide what appears to be a convincing example. However, it should be pointed out that the criteria for the morphological assessment of the functional state of single nerve cells will certainly be different from those for groups of neurons connected in a nerve cell network.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1998

Analysis of neural interactions explains the activation of occipital cortex by an auditory stimulus.

Analysis of neural interactions explains the activation of occipital cortex by an auditory stimulus. J. Neurophysiol. 80: 2790-2796, 1998. Large-scale neural interactions were characterized in human subjects as they learned that an auditory stimulus signaled a visual event. Once learned, activation of left dorsal occipital cortex (increased regional cerebral blood flow) was observed when the auditory stimulus was presented alone. Partial least-squares analysis of the interregional correlations (functional connectivity) between the occipital area and the rest of the brain identified a pattern of covariation with four dominant brain areas that could have mediated this activation: prefrontal cortex (near Brodmann area 10, A10), premotor cortex (A6), superior temporal cortex (A41/42), and contralateral occipital cortex (A18). Interactions among these regions and the occipital area were quantified with structural equation modeling to identify the strongest sources of the effect on left occipital activity (effective connectivity). Learning-related changes in feedback effects from A10 and A41/42 appeared to account for this change in occipital activity. Influences from these areas on the occipital area were initially suppressive, or negative, becoming facilitory, or positive, as the association between the auditory and visual stimuli was acquired. Evaluating the total effects within the functional models showed positive influences throughout the network, suggesting enhanced interactions may have primed the system for the now-expected visual discrimination. By characterizing both changes in activity and the interactions underlying sensory associative learning, we demonstrated how parts of the nervous system operate as a cohesive network in learning about and responding to the environment.

Acoustic Stimulation↗
PubMed1998

Exploring brain circuitry with neurotropic viruses: new horizons in neuroanatomy.

There have been substantial advances in methods for defining connections among neurons over the past quarter century. However, most tracers have been limited in their ability to define populations of functionally related neurons that contribute to a multisynaptic circuit because they are not transported across synapses. As a result, the large body of literature that has employed these tracers has established regional associations between regions that must be further explored with electron microscopy and electrophysiological methods to define the synaptic relations among constituent neurons. Recently, neurotropic alpha herpesviruses have been used to visualize ensembles of neurons that contribute to polysynaptic networks. These pathogens invade permissive cells, replicate, and pass transynaptically to infect other neurons. In effect, the viruses become self-amplifying tracers whose natural tropism and invasiveness define populations of functionally related neurons. The recent increase in the use of this experimental approach has emerged from advances in our understanding of the life cycle of these viruses and the resulting evidence in support of specific transynaptic passage of progeny virus rather than infection by lytic release into the extracellular space. This article reviews the advances that have made this a viable experimental approach and considers ways in which this method has been creatively used to illuminate aspects of nervous system circuit organization that could not be defined with conventional tracers.

Animals↗
PubMed1995

Cholinergic modulation of cortical oscillatory dynamics.

1. The effect of cholinergic modulation on cortical oscillatory dynamics was studied in a computational model of the piriform (olfactory) cortex. The model included the cholinergic suppression of neuronal adaptation, the cholinergic suppression of intrinsic fiber synaptic transmission, the cholinergic enhancement of interneuron activity, and the cholinergic suppression of inhibitory synaptic transmission. 2. Electroencephalographic (EEG) recordings and field potential recordings from the piriform cortex were modeled with a simplified network in which cortical pyramidal cells were represented by excitatory input/output functions with gain parameters dependent on previous activity. The model incorporated distributed excitatory afferent input and excitatory connections between units. In addition, the model contained two sets of inhibitory units mediating inhibition with different time constants and different reversal potentials. This model can match effectively the patterns of cortical EEG and field potentials, showing oscillatory dynamics in both the gamma (30-80 Hz) and theta (3-10 Hz) frequency range. 3. Cholinergic suppression of neuronal adaptation was modeled by reducing the change in gain associated with previous activity. This caused an increased number of oscillations within the network in response to shock stimulation of the lateral olfactory tract, effectively replicating the effect of carbachol on the field potential response in physiological experiments. 4. Cholinergic suppression of intrinsic excitatory synaptic transmission decreased the prominence of gamma oscillations within the network, allowing theta oscillations to predominate. Coupled with the cholinergic suppression of neuronal adaptation, this caused the network to shift from a nonoscillatory state into an oscillatory state of predominant theta oscillations. This replicates the longer term effect of carbachol in experimental preparations on the EEG potential recorded from the cortex in vivo and from brain-slice preparations of the hippocampus in vitro. Analysis of the model suggests that these oscillations depend upon the time constant of neuronal adaptation rather than the time constant of inhibition or the activity of bursting neurons. 5. Cholinergic modulation may be involved in switching the dynamics of this cortical region between those appropriate for learning and those appropriate for recall. During recall, the spread of activity along intrinsic excitatory connections allows associative memory function, whereas neuronal adaptation prevents the spread of activity between different patterns. During learning, the recall of previously stored patterns is prevented by suppression of intrinsic excitatory connections, whereas the response to the new patterns is enhanced by suppression of neuronal adaptation.

Adaptation, Physiological↗
PubMed2003

New neural circuits for robot phonotaxis.

W. Grey Walter built robotic systems to improve understanding of biological systems. In that tradition, this paper reports ongoing work on a robot model of cricket sound localization. The main advances are the inclusion of a much larger range of neuroethological detail, and the investigation of multimodal influences on the behaviour. The former allows exploration of the functionality of identified neurons in the insect, including the possible roles of multiple sensory fibres, mutually inhibitory connections, and brain neurons with pattern-filtering properties. The latter focuses on the inclusion of an optomotor stabilization response, and how this might improve tracking, particularly under conditions of random disturbance.

Animal Communication↗
PubMed2004

Posture-related oscillations in human cerebellar thalamus in essential tremor are enabled by voluntary motor circuits.

The mechanism of essential tremor (ET) is unclear. Animal models of tremor and functional imaging studies in ET predict that the cerebellum and a cerebellar recipient thalamic nucleus (ventral intermediate, Vim) should exhibit oscillatory activity during rest and during tremor due to abnormal olivo-cerebellar activity. Physiologic responses of 152 single neurons were recorded during awake mapping of the ventral thalamus in seven patients with ET prior to thalamotomy. During postural tremor, spectral cross-correlation analysis demonstrated that 51% of the neurons studied exhibited a concentration of power at tremor frequency that was correlated with electromyography, i.e., tremor neurons. During rest, thalamic neurons did not exhibit tremor-frequency activity. Among the three thalamic nuclei surveyed, Vim had a significantly higher proportion of tremor neurons than did the principal somatic sensory nucleus (ventral caudal, Vc) or a pallidal recipient thalamic nucleus (ventral oral posterior, Vop). Neurons related to active movement (voluntary neurons) had significantly greater tremor-related activity than did nonvoluntary neurons. These findings are not consistent with a model of continuous olivo-cerebellar driving of the motor cortex through thalamic connections. Instead ET may be facilitated by motor circuits that enable tremor-related thalamic activity during voluntary movement. Additionally, a subgroup of tremor neurons with proprioceptive inputs were identified that may allow sensory feedback to access the central tremor network.

Action Potentials↗
PubMed2001

Functional connectivity and working memory in schizophrenia: an EEG study.

A leading hypothesis suggests that schizophrenic patients suffer from a disconnection syndrome. A failure in functional connectivity curtails the cortical integration and network activation needed to perform working memory tasks. Simulations with neural network models also indicate that connectivity is crucial for simulation of working memory asks. Multichannel EEG correlation-coefficient estimations are considered as a reliable measurement of connectivity patterns among cortical regions. In this study EEG samples are obtained selectively at the delay epochs of a delayed response working memory task. Results of correlation-coefficient estimations indicate a lack of statistically significant changes between non-task and task conditions in frontal, certain parietal, temporal and central channels. These findings propose that schizophrenics probably "fail" to activate the neural networks of the fronto-temporal regions. These are the networks involved in computation of the working memory task. Interestingly also good performers schizophrenics failed to activate these networks suggesting that the connectivity function is more relevant to the disorder than to task performance. If distinct deficits in cortical network activations would correlate with mental disorders it would be relevant to diagnosis and treatment of psychiatric disorders.

Brain↗
PubMed2004

Freeze-dried poly(D,L-lactic acid) macroporous guidance scaffolds impregnated with brain-derived neurotrophic factor in the transected adult rat thoracic spinal cord.

The effects of poly(D,L-lactic acid) macroporous guidance scaffolds (foams) with or without brain-derived neurotrophic factor (BDNF) on tissue sparing, neuronal survival, axonal regeneration, and behavioral improvements of the hindlimbs following implantation in the transected adult rat thoracic spinal cord were studied. The foams were embedded in fibrin glue containing acidic-fibroblast growth factor. One group of animals received fibrin glue with acidic-fibroblast growth factor only. The foams were prepared by a thermally induced polymer-solvent phase separation process and contained longitudinally oriented macropores connected to each other by a network of micropores. Both foams and fibrin only resulted in a similar gliotic and inflammatory response in the cord-implant interfaces. With BDNF foam, up to 20% more NeuN-positive cells in the spinal nervous tissue close to the rostral but not caudal spinal cord-implant interface survived than with control foam or fibrin only at 4 and 8 weeks after implantation. Semithin plastic sections and electron microcopy revealed that cells and axons more rapidly invaded BDNF foam than control foam. Also, BDNF foam contained almost twice as many blood vessels than control foam at 8 weeks after implantation. Tissue sparing was similar in all three implantation paradigms; approximately 42% of tissue was spared in the rostral cord and approximately 37% in the caudal cord at 8 weeks post grafting. The number of myelinated and unmyelinated axons was low and not different between the two types of foams. Many more axons were found in the fibrin only graft. Serotonergic axons were not found in any of the implants and none of the axons regenerated into the caudal spinal cord. The behavioral improvements in the hindlimbs were similar in all groups. These findings indicated that foam is well tolerated within the injured spinal cord and that the addition of BDNF promotes cell survival and angiogenesis. However, the overall axonal regeneration response is low. Future research should explore the use of poly(D,L-lactic acid) foams, with or without axonal growth-promoting factors, seeded with Schwann cells to enhance the axonal regeneration and myelination response.

Absorbable Implants↗
PubMed2001

In vivo assessment of human visual system connectivity with transcranial electrical stimulation during functional magnetic resonance imaging.

Functional magnetic resonance imaging (fMRI) was used to investigate local and distant cerebral activation induced by transcranial electrical stimulation in order to noninvasively map functional connectivity in the human visual system. Stimulation with lateromedially directed currents and the anode 4.5 cm dorsally to the inion over the right visual cortex induced phosphenes extending into the contralateral lower quadrant of the visual field. fMRI showed a focal hemodynamic response underneath the anode in extrastriate cortex and distant coactivation in subcortical (lateral geniculate nucleus), cortical visual (striate and extrastriate), and visuomotor areas (frontal and supplementary eye fields). This pattern of activation resembles a network of presumably interconnected visual and visuomotor areas. Analysis of activation sites supplies new information about cerebral correlates of phosphenes and shows that the cortical region underneath the cranial stimulation site is not necessarily the origin of behavioral and/or perceptual effects of transcranial stimulation. We conclude that combining transcranial electrical stimulation of neural tissue with simultaneous fMRI offers the possibility to study noninvasively cerebral connectivity in the human brain.

Adult↗
PubMed2000

Electrical synapses by guided growth of cultured neurons from the snail Lymnaea stagnalis.

The ability to assemble neuronal networks with designed topology would allow uniquely defined experiments on neurocomputing. We describe a fundamental step, the controlled formation of synapses by guided outgrowth, in vitro for the first time combining simple neuritic geometry with predefined connectivity. We used neurons from the A-clusters in the pedal ganglia of the snail Lymnaea stagnalis. They were cultured on a substrate with linear patterns made by adsorption of brain-derived conditioning factors and photolithography. We induced and observed the frontal collision of two growth cones on narrow lanes. Following such encounters. individual electrical synapses formed that were sometimes strong enough for prolonged presynaptic stimulation to reach the threshold of postsynaptic firing.

Action Potentials↗
PubMed2005

Neurobehavioral aspects of cerebral white matter disorders.

The study of higher function in humans requires a consideration of all the neural tissues in the brain. Long neglected as a contributor to the organization of cognitive and emotional operations, the cerebral white matter is now the subject of substantial effort to improve understanding. Among the many approaches that can address this area usefully, the study of individuals with white matter disorders offers a wealth of clinical insights that exploits the time-tested lesion method of behavioral neurology. This process is complemented by sophisticated neuroimaging techniques that increasingly enable detailed visualization of white matter tracts as they participate in the cognitive and emotional operations of distributed neural networks. In practical terms, an appreciation of the neurobehavioral importance of white matter disorders can be of great benefit for patients seen by neurologists and psychiatrists alike, especially because early recognition and treatment often can have an important influence on outcome. In theoretical terms, a focus on the white matter and its disorders promises to expand knowledge of the brain as an extraordinarily complex organ in which the connectivity provided by white matter is central to cognition, emotion, and consciousness itself. As the details of white matter structure and function become clarified, a more complete portrait of the organ of the mind can be anticipated.

Aging↗