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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TL;DR: It is suggested that a transmitter released from interneurons or descending fibres which are activated in part by A delta afferents, mediates a slow excitatory postsynaptic currents in substantia gelatinosa neurons and that an excitatories amino acid is implicated in the generation of the slow excited current, although the receptor appears to differ from the known ligand-gated channels.
59 citations
TL;DR: It is proposed that contrast dependency in the retinal ganglion cells results directly from a reduction in the size of the center mechanism due to an increase in contrast, and that these properties first arise in the retina and are transmitted passively through the LGN to visual cortex.
Abstract: Based on extracellular recordings from 69 lateral geniculate nucleus (LGN) cells in the anesthetized cat, we found spatial summation within their receptive fields to be dependent on the contrast of the stimuli presented. By fitting the summation curves to a difference of Gaussians model, we attributed this contrast-dependent effect to an actual change in the size of the center mechanism. Analogous changes in spatial frequency tuning were also observed, specifically increased peaks and cut-off frequencies with contrast. These effects were seen across the populations of both X and Y cell types. In a few cases, LGN cells were recorded simultaneously with one of their retinal ganglion cell (RGC) inputs (S-potentials). In every case, the RGCs exhibited similar contrast-dependent effects in the space and spatial-frequency domains. We propose that this contrast dependency in the retinal ganglion cells results directly from a reduction in the size of the center mechanism due to an increase in contrast. We also propose that these properties first arise in the retina and are transmitted passively through the LGN to visual cortex.
59 citations
TL;DR: The results support a duplex model of mechanoreception in which one of two receptor systems exhibits temporal summation in the context of vibrotactile stimulation on the thenar eminence of the hand.
Abstract: Threshold measurement and matching procedures were used to determine the amount of temporal summation at threshold and suprathreshold levels of vibrotactile stimulation on the thenar eminence of the hand. The frequency of the stimulus was 25, 40, 80, or 200 Hz. At 25 Hz, temporal summation was absent at all intensity levels. Considerable amounts of temporal summation were observed for 80- and 200-Hz stimuli, although the effects decreased as a function of intensity. At 40 Hz, no temporal summation was observed at threshold, but above threshold, a small amount was observed at all intensity levels. The results support a duplex model of mechanoreception in which one of two receptor systems exhibits temporal summation.
59 citations
TL;DR: Correlations between these results and psychophysical studies suggest that the limits on temporal summation established by the cones appear not to be substantially altered by the rest of the retina.
58 citations
58 citations