Topic
Summation
About: Summation is a research topic. Over the lifetime, 954 publications have been published within this topic receiving 45593 citations. The topic is also known as: summation & sum of a sequence.
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TL;DR: It is concluded that spatial summation both within and between dermatomes plays a significant role in thermal pain perception across the range from threshold to tolerance.
Abstract: Spatial summation of thermal pain has recently been reported when stimulus presentations were restricted within a single dermatome. The present study examined whether the magnitude of spatial summation of human thermal pain perception would vary when stimuli were presented within vs. between adjacent dermatomes. Noxious contact heat stimuli from 43°C to 51°C (5 sec duration) were applied to the forearm using areas of 0.21–2.10 cm2. Subjects rated the intensity and unpleasantness of pain using visual analog scales. For stimuli from 45°C to 51°C, there was a significant increase in ratings with increasing stimulus area for both intensity and unpleasantness. When two thermodes were used simultaneously in adjacent dermatomes, the ratings did not differ significantly from those for the same stimulus area in a single dermatome. We conclude that spatial summation both within and between dermatomes plays a significant role in thermal pain perception across the range from threshold to tolerance.
88 citations
TL;DR: The present results indicate that pentobarbital has remarkably selective actions on the sympathetic ganglion and indicate that blockade of ganglionic transmission by anesthetic concentrations of pentobarBital can be entirely explained by a postsynaptic action.
Abstract: The frog sympathetic ganglion has been used as a model to elucidate the cellular mechanism of barbiturate anesthesia. Anesthetic concentrations of pentobarbital markedly reduced the fast nicotinic excitatory postsynaptic potential while having no effect on the slow excitatory postsynaptic potential or slow inhibitory postsynaptic potential, even though all three synaptic potentials depend on the presynaptic release of acetylcholine. A similar differential effect was seen for nicotinic and muscarinic responses to exogenously applied agonists, while the depolarizing action of gamma-aminobutyric acid (GABA) was enhanced. These results indicate that pentobarbital has remarkably selective actions on the sympathetic ganglion and further indicate that blockade of ganglionic transmission by anesthetic concentrations of pentobarbital can be entirely explained by a postsynaptic action. The present results strengthen the concept that pentobarbital anesthesia results from a postsynaptic blockade of central excitatory synapses which increase sodium conductance coupled with a postsynaptic enhancement of GABA-mediated synaptic inhibition.
87 citations
86 citations
TL;DR: Enlargement of Ricco's area completely compensates for reduced perimetric sensitivity in early glaucoma to maintain constant threshold at Ricco’s area, suggesting an increase in signal pooling in response to ganglion cell loss.
Abstract: Purpose. The area of complete spatial summation (Ricco's area) is the largest stimulus size for which area × intensity is constant at threshold. The authors sought to investigate whether Ricco's area changes in early glaucoma to account for the decreased visual signal/noise ratio that may accompany retinal ganglion cell loss.
Methods. Spatial summation functions were measured, and Ricco's area was determined at four 10° retinal locations in 24 patients with early glaucoma (total deviation at test locations, mean, −1.3 dB; range, +2 dB to −8 dB) and 26 age-similar healthy subjects under achromatic and S-cone isolation conditions. Achromatic grating resolution acuity was measured at the same locations to estimate functional ganglion cell density.
Results. Ricco's area was enlarged in patients compared with controls for both achromatic (enlarged by: superior field, 0.57 log units, P < 0.01; inferior field, 0.72 log units, P < 0.01) and chromatic (enlarged by: superior field, 0.26 log units, P < 0.01; inferior field, 0.25 log units, P = 0.065) stimuli, with negligible vertical summation curve shifts along the intensity axis. Resolution acuity was significantly reduced in glaucoma patients in both hemifields (P < 0.001). There was a weak, but significant, relationship between Ricco's area and resolution acuity.
Conclusions. Enlargement of Ricco's area completely compensates for reduced perimetric sensitivity in early glaucoma to maintain constant threshold at Ricco's area, suggesting an increase in signal pooling in response to ganglion cell loss. The rightward displacement of the spatial summation curve indicates that perimetric stimuli should be capable of modulating in size as well as/instead of contrast, which may boost the glaucoma signal within measurement noise.
86 citations
TL;DR: In neurons of the deep cerebellar nuclei, stimulation of the nuclear tissue, as well as stimulating of the olivary tissue, induced a fast rising excitatory postsynaptic potential, followed by an inhibitory post Synaptic potential and a long-lasting excitation, suggesting that this potential was mediated by N-methyl-D-aspartate receptors.
86 citations