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.

Cuff Algometry for Estimation of Hyperalgesia and Pain Summation

Abstract: Objective. Cuff algometry is useful to assess pain sensitivity mechanisms, but effects of cuff position and stimulation pattern are not clear. Methods. In 20 healthy volunteers, cuff pain detection threshold (PDT) and pain tolerance (PTT) were recorded with cuffs accommodating two individual chambers at four locations (eight positions) along the leg, using ramp inflation (1 kPa/s) until subjects indicated PDT and PTT. Repeated stimulations (1-s stimulation, 4-s break) with a staircase increase in stimulus intensity (5 kPa/step) were used to assess PDT and PTT on a single location. Spatial pain summation was calculated as the ratio between PTTs recorded with one chamber or simultaneously with two neighbor chambers. Temporal pain summation was assessed by repeated cuff stimulations (1-s stimulation, 1-s break) and the pain intensity was recorded on a visual analog scale (VAS); the PTT from ramp and staircase assessments were used as stimulus intensity. Results. For the most distal cuff position, the PTT was higher compared with other leg positions except when in proximity to the knee ( P < 0.01). The PDT was higher for the distal part compared with the mid-portions of the lower and upper leg ( P < 0.01). Compared with other leg locations, the spatial summation ratio was highest at the proximal lower leg ( P < 0.02). The staircase versus ramp pattern revealed higher PDT and PTT (P < 0.01), as well as pronounced temporal pain summation ( P < 0.01). Conclusion. The mid-portion of the lower leg is recommended for cuff placement, and the staircase paradigm provides relevant stimulus intensity for assessment of temporal pain summation.

Stimulus duration and the oxcillatory potentials of the human electroretinogram.

Abstract: The effect of duration of stimulus light on the threshold of oscillatory and the slow (a- and b-wave) potentials of the human ERG were assessed on light adaptation to light stimuli. On weak light adaptation induced by stimuli given at 2 min intervals there was a temporal summation of the oscillatory potentials over a range of at least 2 log units (4 msec-400msec). The threshold of the a-wave and b-wave was dependent on duration up to a critical duration of about 40 msec. On strong light adaptation by repetitive light stimulation with 15 sec intervals the oscillations were determined by intensity alone over a range of 2 log units. The a-wave revealed a similar behaviour, whereas the b-wave integrated stimuli in the temporal domain up to about 10 msec. Of main importance; the results provide evidence which is suggestive of temporal integration and discrimination being independently governed by the neurons (probably at the inner plexiform layer), which generate the oscillatory potentials.

Synthesis of a comprehensive population code for contextual features in the awake sensory cortex

Abstract: How cortical circuits build representations of complex objects is poorly understood. Individual neurons must integrate broadly over space, yet simultaneously obtain sharp tuning to specific global stimulus features. Groups of neurons identifying different global features must then assemble into a population that forms a comprehensive code for these global stimulus properties. Although the logic for how single neurons summate over their spatial inputs has been well explored in anesthetized animals, how large groups of neurons compose a flexible population code of higher-order features in awake animals is not known. To address this question, we probed the integration and population coding of higher-order stimuli in the somatosensory and visual cortices of awake mice using two-photon calcium imaging across cortical layers. We developed a novel tactile stimulator that allowed the precise measurement of spatial summation even in actively whisking mice. Using this system, we found a sparse but comprehensive population code for higher-order tactile features that depends on a heterogeneous and neuron-specific logic of spatial summation beyond the receptive field. Different somatosensory cortical neurons summed specific combinations of sensory inputs supra-linearly, but integrated other inputs sub-linearly, leading to selective responses to higher-order features. Visual cortical populations employed a nearly identical scheme to generate a comprehensive population code for contextual stimuli. These results suggest that a heterogeneous logic of input-specific supra-linear summation may represent a widespread cortical mechanism for the synthesis of sparse higher-order feature codes in neural populations. This may explain how the brain exploits the thalamocortical expansion of dimensionality to encode arbitrary complex features of sensory stimuli.

Three Models of Temporal Summation Evaluated Using Normal-Hearing and Hearing-Impaired Subjects

Abstract: Temporal summation effects were measured in normal-hearing and hearing impaired subjects using stimuli of different durations and temporal patterns. Threshold decreased with increasing stimulus dur...