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.

Spatial and temporal summation in the human dark-adapted retina

Abstract: A coherent set of absolute-threshold data is presented for circular flashes with a diameter of 5–343 min of arc, a flash duration of 32–1000 msec, and at eccentricities between 7 and 50 deg in the temporal retina. A reduction in the flash interval from 4 to 1 sec causes a threshold elevation for eccentricities exceeding 15 deg for all other stimulus parameters. It is shown that local adaptation affects the measurements significantly, especially when long-lasting stimuli and large eccentricities exist. The results can be described with the help of a quanta-coincidence model if adaptational properties are included.

Noninvasive assessment of the facilitation of the nociceptive withdrawal reflex by repeated electrical stimulations in conscious dogs.

Abstract: Objective—To investigate the facilitation of the nociceptive withdrawal reflex (NWR) by repeated electrical stimuli and the associated behavioral response scores in conscious, nonmedicated dogs as a measure of temporal summation and analyze the influence of stimulus intensity and frequency on temporal summation responses. Animals—8 adult Beagles. Procedures—Surface electromyographic responses evoked by transcutaneous constant-current electrical stimulation of ulnaris and digital plantar nerves were recorded from the deltoideus, cleidobrachialis, biceps femoris, and cranial tibial muscles. A repeated stimulus was given at 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, and 1.1 × It (the individual NWR threshold intensity) at 2, 5, and 20 Hz. Threshold intensity and relative amplitude and latency of the reflex were analyzed for each stimulus configuration. Behavioral reactions were subjectively scored. Results—Repeated sub-It stimuli summated and facilitated the NWR. To elicit temporal summation, significantly lower int...

Separate Inhibitory and Excitatory Components Underlying Receptive Field Organization in Superficial Medullary Dorsal Horn Neurons

Abstract: Extracellular recording has shown that dorsal horn neurons can have an inhibitory surround outside their excitatory receptive field, but cannot reveal inhibitory inputs within the excitatory field, or show the underlying excitatory and inhibitory synaptic inputs that determine net output. To study the underlying components of receptive field organization, in vivo patch-clamp recording was used to compare the size and distribution of subthreshold, suprathreshold, and inhibitory fields, in neurons in the mouse superficial medullary dorsal horn that were characterized by their responses to noxious and innocuous mechanical facial stimulation. Subthreshold excitatory fields typically extended some distance beyond the borders of the suprathreshold field, and also commonly exhibited broader stimulus selectivity, in that the majority of nociceptive-specific neurons exhibited subthreshold responses to brush. Separate voltage-clamp recording of excitatory and inhibitory inputs using different holding potentials revealed that inhibition could be evoked from both within and outside the excitatory field. In nociceptive neurons, inhibition tended to be maximal at the excitatory receptive field center, and was usually greater for pinch than brush, although the selectivity for pinch versus brush was not as great as with excitatory responses. Based on current data on dorsal horn organization, we propose that the localized peak of inhibition at the excitatory field center could be mediated by local interneurons, while the more widespread surrounding inhibition may depend on supraspinal circuitry.