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.

Temporal integration of pungency

Abstract: Four experiments explored possible temporal summation in olfaction and the common chemical sense. In one experiment, participants judged the perceived magnitude of various concentrations and durations (1.25 - 3.75 s) of the pungent odorant ammonia and the nonpungent odorant isoamyl butyrate. The perceived magnitude of ammonia increased during an inhalation whereas the magnitude of isoamyl butyrate did not. Time-intensity trading relations for ammonia indicated nearly perfect temporal summation. In another experiment, modulation of the concentration of ammonia during an inhalation led to assessments of perceived magnitude that confirmed the high degree of temporal summation seen in the first experiment. That is, approximately equal time-integrated mass of inhaled ammonia led to approximately equal perceived intensity. A third experiment indicated that temporal summation for ammonia arose from its pungency rather than from its odor, a fourth that trigeminally-mediated reflex apnea in response to ammonia also exhibits temporal summation. The degree of temporal summation measured with the reflex came very close to that assessed psychophysically. When stimulated with ammonia, the common chemical sense behaves more like a total mass detector than a concentration detector. The investigation raises the possibility that the short-term sensory reaction to most pungent stimuli may follow this simple rule.

The analgesic effect of codeine as compared to imipramine in different human experimental pain models

Abstract: The hypoalgesic effect of single oral doses of 100 mg imipramine and 125 mg codeine was evaluated in a randomised, placebo-controlled, double-blind, 3-way cross-over experiment including 18 healthy volunteers. Pain tests were performed before and 90, 180, 270, 360 and 450 min after medication. The tests included determination of pain tolerance thresholds to pressure, pain detection/tolerance thresholds to single electrical sural nerve stimulation and pain summation at tolerance threshold to repetitive electrical sural nerve stimulation (temporal summation) and pain experienced during the cold pressor test, rated as peak pain intensity, pain average intensity and discomfort. Compared to placebo, imipramine significantly increased pressure pain tolerance threshold (P=0.03) and increased pain tolerance threshold (P=0.05) and pain summation threshold (P=0.03), but not pain detection threshold to electrical stimulation. Imipramine did not cause significant changes in pain perception during the cold pressor test. Codeine significantly increased pressure pain tolerance threshold (P=0.02), pain detection (P=0.04) and pain tolerance threshold (P=0.01) and pain summation threshold (P=0.02) to electrical stimulation. In addition, codeine reduced the pain experienced during the cold pressor test (P=0.04–0.003). It is concluded that both imipramine and codeine inhibit temporal pain summation, whereas only codeine reduces cold pressor pain. Pain summation may be a key mechanism in neuropathic pain. Imipramine has a documented effect on such pain conditions on temporal summation. The present study showed that codeine also inhibits temporal summation, which is in line with the clinical observations indicating that opioids relieve neuropathic pain.

Research papers Spatial summation for pain perception: interaction of inhibitory and excitatory mechanisms

Abstract: To study the relation between size of the surface stimulated and perceived pain intensity (spatial summation effect), subjects sequentially immersed predetermined segments of the surface of their arm, between the fingertips and the shoulder, in circulating nociceptive hot water. Immersion sessions were of three types: (i) increasing session (immersion beginning at fingertips and increasing to shoulder); (ii) decreasing session (immersion beginning at shoulder and decreasing to fingertips); and (iii) whole arm 1 increasing session (preliminary immersion of the whole arm up to shoulder, followed by an increasing session from fingertips to shoulder). Results showed a positive spatial summation effect (pain perception positively correlated to the size of the surface stimulated) during both the decreasing session and the whole arm 1 increasing session. However, no spatial summation effect was found during the increasing session (fingertips to shoulder). In addition, pain perceived for a surface area was less intense during the decreasing session compared to the increasing session. One possible explanation for the lack of a spatial summation effect during the increasing session is that inhibitory mechanisms are gradually recruited at the same time as excitatory afferences, thus ‘canceling out’ any measurable spatial summation effect. The results obtained during the decreasing session and the whole arm 1 increasing session may be explained by inhibitory mechanisms being fully recruited at the beginning of the session with the immersion of the largest surface area (whole arm). The results are a shift of the pain perception curve and a positive relation between the surface stimulated and pain perception. q 2002 International Association for the Study of Pain. Published by Elsevier Science B.V. All rights reserved.

Temporal Summation and Its Limit for Wavelength Changes: An Analog of Bloch's Law for Color Vision

Abstract: Temporal summation and its limits were studied at subjective threshold by varying the pulse duration t of (a) constant-luminance pulse changes of wavelength Δλ, and (b) constant-wavelength pulse changes of luminance ΔL. Threshold depends on Δλ and ΔL for pulse durations longer than about 150–300 and 60 ms, respectively. Psychophysical sensitivity to a pulse of wavelength change improved as pulse duration was increased for short pulses, but was unaffected by pulse duration for long pulses. Although there are departures from full temporal summation for pulse durations longer than roughly 20 ms, a formal analog of Bloch’s law tΔλ = constant gives a fair description of the wavelength-pulse data for short pulses. The critical duration for wavelength pulses (tcw) is much longer than the critical duration for luminance pulses (tcL) at any given mean wavelength. Although tcL does not depend on mean wavelength, tcw is roughly twice as long in the blue-green as in the red. These data bear on the question of what part is played in color vision by the neural encoding of information in the time domain. They can provide fresh empirical tests of current theories of color vision. The findings are tentatively interpreted (a) in terms of different critical events in Walraven’s luminosity and chromaticity channels; these critical events are supposed to limit temporal summation for luminance pulses and wavelength pulses, respectively, and (b) from the viewpoint that central neural processing plays an important part in (task dependent) summation.