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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01 Jan 1992
TL;DR: A novel physiological modeling methodology was developed that extends the extant physiological models to include time-constant and driving-force interactive effects between post-synaptic inputs and results in a difference-of-exponentials PSP function that is more realistic and flexible than the common empirically-chosen alpha function.
Abstract: The olfactory system processes complex and varied information in its detection, recognition, and memory of odors. The exact functions that the olfactory bulb plays in this processing is still largely unknown. Studies were performed to help reveal bulb functionality in the olfactory system while contributing to the set of computer methods available for the study of neural systems
One interesting property of bulbar neurons is an increase in primary cell firing thresholds with depth. Since increased odor concentrations generally result in higher frequency inputs to the bulb and thus higher summation levels of primary cell membrane potentials, this threshold gradation transforms the frequency-encoded concentration data into a spatial representation in the number of primary cells responding in a single olfactory bulb glomerular region.
Since this transformation relies on temporal summation of post-synaptic potentials (PSPs) to reflect concentration levels, direct physiological modeling of the transformation was possible while providing the added efficiency to permit the simulation of large numbers of cells and synaptic interactions. A novel physiological modeling methodology was developed for these tests that extends the extant physiological models to include time-constant and driving-force interactive effects between post-synaptic inputs. This novel method is derived using linear superposition of inputs to a lumped-circuit cell representation, resulting in a difference-of-exponentials PSP function that is more realistic and flexible than the common empirically-chosen alpha function.
Also, the effects that interneuronal dendritic spines have on bulbar inhibitions were tested using biophysical computer simulations of primary-to-granule dendrodendritic reciprocal interactions. The graded strength properties of these synapses showed that reciprocal inhibitions to primary mitral cells are facilitated by the spine structures without the need of a high gain gradation while reducing lateral inhibition to other mitral cells. Furthermore, increases in the neck axial resistance of the synapsed spine further strengthen the reciprocal response and reduce the lateral inhibition; such resistance changes could therefore result in dendrodendritic synaptic plasticities and olfactory memory operations.
3 citations
TL;DR: The report of an experimental study by Greene on this topic reached me too late for reference to be included in my recent communication2.
Abstract: THE report of an experimental study by Greene1 on this topic reached me too late for reference to be included in my recent communication2.
3 citations
TL;DR: Diminished spatial summation appears to contribute to the aging visual system’s loss of temporal discrimination for low contrast oscillating targets in oscillatory displacement thresholds.
Abstract: Purpose This study sought to determine whether a decline in spatial summation contributes to age-related deficits on oscillatory displacement thresholds (ODT's). A secondary goal was to evaluate the extent of spatial summation on a dynamic version of vernier hyperacuity. Methods The ODT's and contrast sensitivity functions (CSF's) of optimally corrected young and old observers were compared as a function of vernier target length (4, 8, or 32 min), contrast level (5 or 30%), and oscillation rate (2 or 8 Hz). Results Age deficits on ODT's were related directly to rate of oscillation, but not target contrast. No age difference was seen in ODT's for short low-contrast targets; as target length increased thresholds improved more rapidly for young than old observers; this pattern was reversed at high contrast. ODT's were related strongly and consistently to contrast sensitivity for old but not young observers. Conclusions Diminished spatial summation appears to contribute to the aging visual system's loss of temporal discrimination for low contrast oscillating targets. Spatial summation contributes more importantly to the displacement discrimination of oscillating than to static vernier targets.
3 citations