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At least 343 records · Page 19Linked to original sources
PubMed2000

Proprioceptive population coding of two-dimensional limb movements in humans: I. Muscle spindle feedback during spatially oriented movements.

The proprioceptive coding of multidirectional ankle joint movements was investigated, focusing in particular on the question as to how accurately the direction of a movement is encoded when all the proprioceptive information from all the muscles involved in the actual movement is taken into account. During ankle movements imposed on human subjects, the activity of 30 muscle spindle afferents originating in the extensor digitorum longus, tibialis anterior, extensor hallucis longus and peroneus lateralis muscles was recorded from the lateral peroneal nerve using the microneurographic technique. In the first part of the study, it was proposed to investigate whether muscle spindle afferents have a preferred direction, as previously found to occur in the case of cortical cells, and to analyze the neural coding of the movement trajectories using a "population vector model." This model is based on the idea that neuronal coding can be analyzed in terms of a series of vectors, each based on specific movement parameters. In the present case, each vector gives the mean contribution of a population of muscle spindle afferents within one directionally tuned muscle. A given population vector points in the "preferred sensory direction" of the muscle to which it corresponds, and its length is the mean frequency of all the afferents within that muscle. Our working hypothesis was that the sum of these weighted vectors points in the same direction as the ongoing movement. The results show that each muscle spindle afferent, and likewise each muscle, has a specific preferred sensory direction, as well as a preferred sensory sector within which it is capable of sending sensory information to the central nervous system. Interestingly, the results also demonstrate that the preferred directions are the same as the directions of vibration-induced illusions. In addition, the results show that the neuronal population vector model describes the multipopulation proprioceptive coding of spatially oriented 2D limb movements, even at the peripheral sensory level, based on the sum vectors calculated from all the muscles involved in the movement. In an accompanying paper, the coding of more complex 2D movements such as those involved in drawing rectilinear and curvilinear geometrical shapes was investigated.

Adult↗
PubMed2006

Methodological considerations on the use of template matching to study long-lasting memory trace replay.

Replay of behaviorally induced neural activity patterns during subsequent sleep has been suggested to play an important role in memory consolidation. Many previous studies, mostly involving familiar experiences, suggest that such reactivation occurs, but decays quickly (approximately 1 h). Recently, however, long-lasting (up to approximately 48 h) "reverberation" of neural activity patterns induced by a novel experience was reported on the basis of a template-matching analysis. Because detection and quantification of memory-trace replay depends critically on analysis methods, we investigated the statistical properties of the template-matching method and analyzed rodent neural ensemble activity patterns after a novel experience. For comparison, we also analyzed the same data with an independent analysis technique, the explained variance method. Contrary to the recent report, we did not observe significant long-lasting reverberation using either the template matching or the explained variance approaches. The latter, however, did reveal short-lasting reactivation in the hippocampus and prefrontal cortex. In addition, detailed analysis of the template-matching method shows that, in the present study, coarse mean firing rate differences among neurons, but not fine temporal spike structures, dominate the results of template matching. Most importantly, it is also demonstrated that partial comparisons of template-matching correlations, such as used in the recent paper, may lead to erroneous conclusions. These investigations indicate that the outcome of template-matching analysis is very sensitive to the conditions of how it is applied, and should be interpreted cautiously, and that the existence of long-lasting reverberation after a novel experience requires additional verification.

Action Potentials↗
PubMed1975

[Reflex interaction between the visual and skin temperature analyzers in focal lesions at the level of the optic thalamus and brain stem].

The authors convened a clinico-physiological study of the interaction of the visual and skin temperature analyzers in patients with disturbed circulation in the deep branches of the posterior cerebral artery (the first group) and in patients with disturbed circulation in the vertebro-basillar system (the second group). Inasmuch as in the first group there was an involvement of thalamic structures, the significant disorders connected with disturbances of reflectory interaction in the visual and skin-temperature analyzers are presumably related to these structures. An insignificant change in the continuing of the visual and skin temperature analyzers in disturbances of the brain stem indicate to the limited importance of nonspecific structures of this area in the reflectory interaction of these analyzers.

Basilar Artery↗