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At least 343 records · Page 19Linked to original sources
PubMed2003

Connecting mirror neurons and forward models.

Two recent developments in motor neuroscience are promising the extension of theoretical concepts from motor control towards cognitive processes, including human social interactions and understanding the intentions of others. The first of these is the discovery of what are now called mirror neurons, which code for both observed and executed actions. The second is the concept of internal models, and in particular recent proposals that forward and inverse models operate in paired modules. These two ideas will be briefly introduced, and a recent suggestion linking between the two processes of mirroring and modelling will be described which may underlie our abilities for imitating actions, for cooperation between two actors, and possibly for communication via gesture and language.

Models, Neurological↗
PubMed2005

A learning rule for the emergence of stable dynamics and timing in recurrent networks.

Neural dynamics within recurrent cortical networks is an important component of neural processing. However, the learning rules that allow networks composed of hundreds or thousands of recurrently connected neurons to develop stable dynamical states are poorly understood. Here I use a neural network model to examine the emergence of stable dynamical states within recurrent networks. I describe a learning rule that can account both for the development of stable dynamics and guide networks to states that have been observed experimentally, specifically, states that instantiate a sparse code for time. Across trials, each neuron fires during a specific time window; by connecting the neurons to a hypothetical set of output units, it is possible to generate arbitrary spatial-temporal output patterns. Intertrial jitter of the spike time of a given neuron increases as a direct function of the delay at which it fires. These results establish a learning rule by which cortical networks can potentially process temporal information in a self-organizing manner, in the absence of specialized timing mechanisms.

Action Potentials↗
PubMed2002

Spatiotemporal spike encoding of a continuous external signal.

Interspike intervals of spikes emitted from an integrator neuron model of sensory neurons can encode input information represented as a continuous signal from a deterministic system. If a real brain uses spike timing as a means of information processing, other neurons receiving spatiotemporal spikes from such sensory neurons must also be capable of treating information included in deterministic interspike intervals. In this article, we examine functions of neurons modeling cortical neurons receiving spatiotemporal spikes from many sensory neurons. We show that such neuron models can encode stimulus information passed from the sensory model neurons in the form of interspike intervals. Each sensory neuron connected to the cortical neuron contributes equally to the information collection by the cortical neuron. Although the incident spike train to the cortical neuron is a superimposition of spike trains from many sensory neurons, it need not be decomposed into spike trains according to the input neurons. These results are also preserved for generalizations of sensory neurons such as a small amount of leak, noise, inhomogeneity in firing rates, or biases introduced in the phase distributions.

Action Potentials↗
PubMed1986

[Connections between neurons of sympathetic ganglia and the myenteric nerve plexus of the mammalian colon].

By means of retrograde transport of the fluorescent marker primulin the initial part of the sympathetic innervation of the myenteric nervous plexus of the descending colon has been characterized in cats and guinea pigs. When primulin is injected into the myenteric nervous plexus, marked neurons are revealed in the caudal mesenteric ganglion, in the celiac plexus ganglia, in the sympathetic trunk ganglia. The marked nervous populations of the extramural sympathetic ganglia differ in their form, size, number of neurons and their distribution.

Animals↗
PubMed1985

Neuropeptides and other mediators in the central nervous system.

Some general principles of peptide and other transmitter actions in the CNS may be applicable to determining how central, autonomic, or blood-borne transmitter signals may regulate the responsiveness of the cells of the immune system. For the resolution of how and where transmitters act in the CNS, research in cellular neurobiology has made substantial recent progress in three specific areas of work: neuronal connectivity, synaptic mechanisms, and neuronal transmitters, Together, the new circuits, new transmitters, and new receptor mechanisms provide a rich repertoire of signaling mechanisms that transcend earlier notions of "classical" excitatory or inhibitory transmission modes and that are pertinent to regulation of immune response mechanisms.

Adenylyl Cyclases↗
PubMedDate not supplied

[Certain functional connections of neurons control the walking of the cockroach Periplaneta americana].

On isolated abdominal nervous chain of the cockroach studies have been made of the responses of motoneurones of the thoracic ganglion to electrical stimulation of afferent axons of the leg nerve under normal conditions and during application of an anticholinesterase drug, GD-7. Depending on the type of stimulated axons, monosynaptic response, as well as polysynaptic phasic and tonic responses of motoneurones were recorded. A scheme of activation of motoneurones is suggested which evokes slow contractions of muscles in cockroach extremities.

Action Potentials↗
PubMed1994

The cortical component of experience-dependent synaptic plasticity in the rat barrel cortex.

Rats were raised with altered tactile experience from P0 by removing all but one vibrissa (D1) from one side of the face (D1-spared animals). This procedure (univibrissa rearing) has previously been shown to cause neurons in cortical barrels surrounding D1 to develop greater than normal responses to D1 vibrissa stimulation and smaller than normal responses to principal vibrissa stimulation (Fox, 1992). In this study, it was found that the potentiated D1 responses could be attenuated by acute microlesions placed in the D1 barrel, while principal vibrissa responses were unchanged or even slightly elevated for the same cases. The ratio of the average D1 to principal vibrissa response was approximately proportional to the volume of tissue damaged in the D1 barrel. This result implies that the synaptic plasticity seen in cortex of D1-spared animals is due to synaptic changes that take place within the barrel cortex rather than to relay of changes occurring at a subcortical level. In addition, lesions aimed at the septum between D1 and an adjacent barrel almost completely abolished responses to D1 stimulation in that barrel, including short-latency responses (5-10 msec). Only neurons severed horizontally from D1 were affected. Neurons that maintained a connection with the D1 barrel via a bridge of septal tissue preserved their usual elevated levels of response to D1 stimulation and their aberrant short-latency responses. This result implies that pathways radiating out from the D1 barrel/column, and connecting neurons in the D1 barrel to cells in surrounding barrels, undergo synaptic plasticity induced by univibrissa rearing.

Animals↗
PubMed1995

Some data on connections of neurons of nuclei isthmi of the chicken.

After PhA-L injection into the tectum opticum of chickens, column-like labelled terminal arborizations were found in tectum and also labelled neurons of Ipc and Imc in the corresponding sections. The PhA-L labele proved the projection from both Imc and Ipc neurons to tectum; their terminal axonarborizations were clearly discernible. Column-like terminal arborizations of different sizes were found both in PHA-L and Golgi impregnated preparations. GABA immunostaining displayed GABA positive neurons in Imc. The EM-Golgi study corroborated that the axon-terminals of Imc neurons established symmetrical synapses in the tectum. The results of the present study support the existence of an inhibitory feedback loop from Imc neurons to the tectum.

Animals↗
PubMedDate not supplied

[A new cerebellar neuron: the brush or monopolar cell. Characteristics and possible function].

The basic neuronal structure and circuitry of the cerebellum has been well known since Cajal's time. In recent years, however, a number of new neuronal connections and new immunohistochemically defined neuronal subtypes and functional cerebellar modules have been described. This new morphofunctional concept of the cerebellum seems to be in agreement with its newly assumed roles in learning and memory. In this new functional structure, a new cell (the brush cell, monopolar cell or monodendritic cell, Altman and Bayer, 1977; Mugnaini, 1994) specific to the cerebellar cortex and cochlear nucleus, could be of great importance. In all species studied, including man, this cell shows very particular morphology, immunohistochemical reactivity (against calretinin, some glutamate receptors and some neurofilament antibodies) and synaptic connections. The main afferents of these neurons are the mossy fibres, which form giant synaptic structures with them. The axons of monopolar cells end either in contact with extracerebellar neurons, or terminate intracortically at other brush cells (in the form of mossy fibres) or other cortical neurons of still-unknown morphology. In every animal species examined, these monopolar cells show different embryological development. No involution of them has been seen either in senility or in neurodegenerative disease.

Animals↗