Browsing by Subject "Ganglion cell"

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  • Donner, Kristian; Yovanovich, Carola (2020)
    From the mid-19th century until the 1980's, frogs and toads provided important research models for many fundamental questions in visual neuroscience. In the present century, they have been largely neglected. Yet they are animals with highly developed vision, a complex retina built on the basic vertebrate plan, an accessible brain, and an experimentally useful behavioural repertoire. They also offer a rich diversity of species and life histories on a reasonably restricted physiological and evolutionary background. We suggest that important insights may be gained from revisiting classical questions in anurans with state-of-the-art methods. At the input to the system, this especially concerns the molecular evolution of visual pigments and photoreceptors, at the output, the relation between retinal signals, brain processing and behavioural decision-making.
  • Donner, K.; Grönholm, M.-L. (Elsevier, 1984)
    We have reexamined the receptive fields of frog retinal ganglion cells focussing on their surround properties. Carefully excluding artifacts due to stimulation of the (Gaussian) RF center, we found that spiking responses can be elicited by step stimulation of any receptor type in the surrounds of all the classes 1–4 Maturana et al. (1960) (J. gen. Physiol. 43, 129–175). The surround responses are antagonized by the responsive center and suppressed by the inhibitory surround, but are seen because of their slower dynamics. The responsive surround differs spectrally from the center: in the latter, cones and green rods compete, in the former, their signals sum.
  • Donner, K.; Koskelainen, A.; Djupsund, K.; Hemilä, S. (Elsevier, 1995)
    The kinetics of rod responses to flashes and steps of light was studied as a function of background intensity (IB) at the photoreceptor and ganglion cell levels in the frog retina. Responses of the rod photoreceptors were recorded intracellularly in the eyecup and as ERG mass potentials across the isolated, aspartate-superfused retina. The kinetics of the retinally transmitted signal was derived from the latencies of ganglion cell spike discharges recorded extracellularly in the eyecup. In all states of adaptation the linear-range rod response to dim flashes could be modelled as the impulse response of a chain of low-pass filters with the same number of stages: 4 (ERG) or 4–6 (intracellular). Dark-adapted time-to-peak (tp, mean ± SD) at 12°C was 2.4 ± 0.6 sec (ERG) or 1.7 ± 0.4 sec (intracellular). Under background light, the time scale shortened as a power function of background intensity, IB−b with b = 0.19±0.03 (ERG) or 0.14±0.04 (intracellular). The latency-derived time scale of the rod-driven signal at the ganglion cell agreed well with that of the photoreceptor responses. The apparent underlying impulse response had tp = 2.0±0.7 sec in darkness and accelerated as IB−b with b = 0.17±0.03. The photoreceptor-to-ganglion-cell transmission delay shortened by 30% between darkness and a background delivering ca 104 photoisomerizations per rod per second. Data from the literature suggest that all vertebrate photoreceptors may accelerate according to similar power functions of adapting intensity, with exponents in the range 0.1–0.2. It is noteworthy that the time scale of human (foveal) vision in experiments on flicker sensitivity and temporal summation shortens as a power function of mean luminance with b ≈ 0.15.
  • Donner, K. (Elsevier, 1987)
    The sensitivity and intensity-response [R (log I)] functions of the receptive field center were determined by extracellular recording from frog retinal ganglion cells. The object was to study the steady-state adapting effects of peripheral background patterns: steady annuli and spinning “windmills” of light. Steady annular backgrounds could not be shown to directly effect any change of center responsiveness, only an enhancement of late response components attributable to depression of surround sensitivity. Movement of a windmill pattern shifted R(log I) functions to higher log intensities and decreased the maximal number of spikes in the response, but did not depress the saturation level of the impulse frequency. Its action thus resembled direct light-adaptation of the center.