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.

Non-linear temporal summation by simple cells in cat striate cortex demonstrated by failure of superposition.

Abstract: Simple cells in area 17 of the anaesthetized, paralysed cat were stimulated with stationary sinusoidal gratings whose contrast was temporally modulated in different ways. The response to a temporal waveform which was the sum of two sinusoids (1.25 Hz and 7.75 Hz) was compared with the response elicited by each component when presented alone. The responses to the high temporal frequency in the compound stimulus were relatively enhanced by the addition of the low temporal frequency; those to the low frequency were relatively depressed.

Relief of trigeminal neuralgia after percutaneous retrogasserian glycerol rhizolysis is dependent on normalization of abnormal temporal summation of pain, without general impairment of sensory perception.

Abstract: OBJECTIVE: This study was undertaken to examine the pathophysiological mechanisms of trigeminal neuralgia and the mechanisms underlying pain relief after percutaneous retrogasserian glycerol rhizolysis (PRGR). METHODS: Quantitative examination of sensory and pain perception was performed in the trigger area and the contralateral nonpainful facial skin area for 39 patients with trigeminal neuralgia who had been previously treated with PRGR and for 14 non-surgically treated patients. In a prospective study, 9 of the 14 patients were examined before and 4 to 6 weeks after PRGR. RESULTS: In the trigger area of patients who had been previously treated with PRGR for trigeminal neuralgia, we demonstrated increased temperature and tactile thresholds in pain-free patients and in patients with paroxysmal or continuous pain. Abnormal temporal summation of pain (characterized by progressive increases in pain intensity, with radiation of pain and aftersensation) was present in patients with paroxysmal or continuous pain but not in pain-free patients. In the trigger area of non-surgically treated patients with trigeminal neuralgia, we demonstrated significantly increased temperature and tactile thresholds and the presence of abnormal temporal summation of pain. The prospective study showed that pain relief after PRGR was associated with normalization of abnormal temporal summation of pain, without increased sensory loss. CONCLUSION: Partial deafferentation, with impairment of thin (C/A6) and thick (Aβ) fiber-mediated sensations and abnormal temporal summation of pain, is present in the trigger area of patients with trigeminal neuralgia. Relief of pain after PRGR depends on the normalization of abnormal temporal summation of pain, which is independent of general impairment of sensory perception. Assessment of the temporal summation of pain may serve as an important tool to record central neuronal hyperexcitability, which may play a key role in the pathophysiological changes in trigeminal neuralgia.

Nonlinear characteristics in the Frog's visual system

Abstract: The receptive fields of retinal fibers in the visual tectum of the frog are mapped with different techniques and the spatial summation characteristics are examined, by presenting stimuli of various shapes and sizes in the center of the receptive field. When the size is increased gradually from the center of the stimulus, for constant stimulus intensity, the maximum response is obtained for stimuli of approximately the size of the most responsive part of the RF. Using a clustering technique to obtain stimuli that are part of the RF and combinations of these parts, it is evident that the spatial summation characteristics are not linear. A model is developed that describes the nonlinear form of these results, based on a power law.