Home About us Contact
|
Home About us Contact | ||
|
|
||
One Pattern (one + pattern)
Selected AbstractsEvidence for functional compartmentalization of trigeminal muscle spindle afferents during fictive mastication in the rabbitEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 4 2000K. -G. Abstract Primary afferent neurons innervating muscle spindles in jaw-closing muscles have cell bodies in the trigeminal mesencephalic nucleus (NVmes) that are electrically coupled and receive synapses. Each stem axon gives rise to a peripheral branch and a descending central branch. It was previously shown that some spikes generated by constant muscle stretch fail to enter the soma during fictive mastication. The present study examines whether the central axon is similarly controlled. These axons were functionally identified in anaesthetized and paralysed rabbits, and tonic afferent firing was elicited by muscle stretch. For the purpose of comparison, responses were recorded extracellularly both from the somatic region and from the central axon in the lateral brainstem. Two types of fictive masticatory movement patterns were induced by repetitive stimulation of the masticatory cortex and monitored from the trigeminal motor nucleus. Field potentials generated by spike-triggered averaging of action potentials from the spindle afferents were employed to determine their postsynaptic effects on jaw-closing motoneurons. Tonic firing of 32% NVmes units was inhibited during the jaw-opening phase, but spike frequency during closing was almost equal to the control rate during both types of fictive mastication. A similar inhibition occurred during opening in 83% of the units recorded along the central branch. However, firing frequency in these was significantly increased during closing in 94%, probably because of the addition of antidromic action potentials generated by presynaptic depolarization of terminals of the central branch. These additional spikes do not reach the soma, but do appear to excite motoneurons. The data also show that the duration and/or frequency of firing during the bursts varied from one pattern of fictive mastication to another. We conclude that the central axons of trigeminal muscle spindle afferents are functionally decoupled from their stem axons during the jaw-closing phase of mastication. During this phase, it appears that antidromic impulses in the central axons provide one of the inputs from the masticatory central pattern generator (CPG) to trigeminal motoneurons. [source] Computational constraints between retrieving the past and predicting the future, and the CA3-CA1 differentiationHIPPOCAMPUS, Issue 5 2004Alessandro Treves Abstract The differentiation between the CA3 and CA1 fields of the mammalian hippocampus is one of the salient traits that set it apart from the organization of the homologue medial wall in reptiles and birds. CA3 is widely thought to function as an autoassociator, but what do we need CA1 for? Based on evidence for a specific role of CA1 in temporal processing, I have explored the hypothesis that the differentiation between CA3 and CA1 may help solve a computational conflict. The conflict is between pattern completion, or integrating current sensory information on the basis of memory, and prediction, or moving from one pattern to the next in a stored sequence. CA3 would take care of the former, while CA1 would concentrate on the latter. I have found the hypothesis to be only weakly supported by neural network simulations. The conflict indeed exists, but two mechanisms that would relate more directly to a functional CA3-CA1 differentiation were found unable to produce genuine prediction. Instead, a simple mechanism based on firing frequency adaptation in pyramidal cells was found to be sufficient for prediction, with the degree of adaptation as the crucial parameter balancing retrieval with prediction. The differentiation between the architectures of CA3 and CA1 has a minor but significant, and positive, effect on this balance. In particular, for a fixed anticipatory interval in the model, it increases significantly the information content of hippocampal outputs. There may therefore be just a simple quantitative advantage in differentiating the connectivity of the two fields. Moreover, different degrees of adaptation in CA3 and CA1 cells were not found to lead to better performance, further undermining the notion of a functional dissociation. © 2004 Wiley-Liss, Inc. [source] Patterns of variability in the satellite microwave sounding unit temperature record: comparison with surface and reanalysis dataINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 15 2003Giovanni Sturaro Abstract Principal component analysis is applied to global temperature records to study the differences in the patterns of variability between surface and troposphere. Surface, Microwave Sounding Unit (lower troposphere, channel 2 and channel 4) and National Centers for Environmental Prediction,National Center for Atmospheric Research reanalysis thickness data are studied in the common period 1979,2000. The patterns of variability are classified into geographical regions and compared. The series of their time coefficients are correlated to assess the existence of common and significant climate-change signals in the form of climatic trends. The objective is to identify the physical processes determining the records' variations and the differences between the surface and the satellite records that might be related to the discrepancy in their globally averaged trend. Major differences were found in the Tropics, where the surface warming is not paralleled in any other record. The surface record has two major patterns over the Tropics, one of which is connected to El Niño,southern oscillation. Satellite variability is instead described by only one pattern, most probably deriving from the merging of the two distinct patterns found for the near-surface records. In the eastern Antarctic a higher troposphere and lower stratosphere negative trend is found connected to ozone depletion. This signal prevails in the satellite record, despite evidence that it is confined only above 500 hPa. A pattern over Siberia is linked to the ,Euro-Siberian oscillation', i.e. the change in the pressure field determining the tracks of the Atlantic storms over the area Copyright © 2003 Royal Meteorological Society [source] Quasispecies analysis of novel HIV-1 recombinants of subtypes A and G reveals no similarity to the mosaic structure of CRF02_AG,JOURNAL OF MEDICAL VIROLOGY, Issue 9 2007Rebecca L.R. Powell Abstract HIV-1 circulating recombinant form (CRF) 02_AG is responsible for greater than 65% of HIV-1 infections in Cameroon and is widespread across West and West-Central Africa. The parental subtypes A1 and G cocirculate in this part of Africa, and high rates of infection predispose to the generation of AG unique recombinant forms (URFs). Little is known as to whether A1 and G can recombine and thrive in vivo with breakpoints other than those characteristic of CRF02_AG. In this study, six unique recombinant viruses of subtypes A1 and G were identified in two individuals in Cameroon. A 1.5 kb fragment of the reverse transcriptase (RT) region of pol (HXB2 location 2,612,4,159) and the entire env gene (HXB2 location 6,202,9,096) were evaluated by phylogenetic and breakpoint analyses. Each URF was found to have breakpoints different than CRF02_AG, indicating that A and G gene segments are functionally compatible with more than one pattern of recombination. Furthermore, contemporaneous, cultured viruses from these individuals were analyzed, revealing different proportions of URFs compared to those found in plasma, possibly indicating compart mentalization and/or phenotypic variation among the URFs. CRF02_AG emerged from West-Central Africa to become a highly successful viral strain. As such, monitoring the spread of newly emerging AG recombinants is critical not only for understanding the epidemiology of HIV-1, but also in the design of future therapeutics and vaccines appropriate to this part of Africa, and globally. J. Med. Virol. 79:1270,1285, 2007. © Wiley-Liss, Inc. [source] Bimanual coordination in Parkinson's disease: Deficits in movement frequency, amplitude, and pattern switchingMOVEMENT DISORDERS, Issue 1 2002Winston D. Byblow BHK Abstract Six patients with idiopathic Parkinson's disease (PD) and six age-matched controls participated in a variety of rhythmic bimanual coordination tasks. The main goal of the task was to perform inphase or antiphase patterns of pronation and supination of the forearms at a specified tempo, and to switch from one pattern to the other upon presentation of a visual cue. The availability of advance information was varied to examine whether deficits would emerge under choice versus pre-cue constraints. In pre-cue conditions, the subjects knew in advance which hand would be cued to initiate pattern change. In choice conditions, the cued hand was not known until the imperative stimulus was presented. Overall, the PD patients made movements with significantly lower frequencies and smaller amplitudes relative to controls. Patients exhibited spontaneous pattern switching from antiphase to inphase at significantly lower movement frequencies than controls. During intentional switching trials, the control group was significantly faster at initiating pattern change. PD and control groups differed in the time to initiate pattern switching to a greater extent under choice conditions, suggesting that patients used advance information to increase the speed of their response. The control group exhibited a preference for spontaneous switching and intentional switching through the subdominant hand. Patients exhibited a switching preference using the impaired limb (whether or not it was subdominant). The control group made more correct responses when the subdominant side was either pre-cued or presented in choice conditions. The patients maintained the subdominant/impaired side advantage under pre-cue conditions but not choice. In the maintenance of rhythmic movement, individuals with PD were able to use advance information in terms of both speed and accuracy. © 2001 Movement Disorder Society. [source] | ||||||||||