Contrast Enhancement and Distributed Encoding by Bipolar Cells in the Retina

1998 ◽  
Vol 80 (3) ◽  
pp. 1070-1081 ◽  
Author(s):  
Dwight A. Burkhardt ◽  
Patrick K. Fahey
Keyword(s):  
Contrast Enhancement ◽  
Linear Range ◽  
Bipolar Cells ◽  
Horizontal Cells ◽  
Ambystoma Tigrinum ◽  
High Contrast ◽  
Cone Photoreceptors ◽  
Large Signal ◽  
Contrast Gain ◽  
Contrast Response

Burkhardt, Dwight A. and Patrick K. Fahey. Contrast enhancement and distributed encoding by bipolar cells in the retina. J. Neurophysiol. 80: 1070–1081, 1998. Responses of bipolar cells, cone photoreceptors, and horizontal cells were recorded intracellularly in superfused eyecup preparations of the tiger salamander ( Ambystoma tigrinum). Contrast flashes of positive and negative polarity were applied at the center of the receptive field while the entire retina was light adapted to a background field of 20 cd/m2. For small contrasts, many bipolar cells showed remarkably high contrast gain: up to 15–20% of the bipolar response was evoked by a contrast step of 1%. There was considerable variation from cell to cell but, on average, no striking differences in contrast gain were found between the depolarizing (Bd) and hyperpolarizing (Bh) bipolar cells. Quantitative comparisons of contrast/response measurements for cone photoreceptors and cone-driven bipolars suggest that the high contrast gain of bipolars is the consequence of a 5–10 × amplification of small signals across the cone → bipolar synapse. Bipolar cells had a very restricted linear range of response and tended to saturate at stimulus levels that were within the linear range of the cone response. The contrast/response of horizontal cells was similar to that of cones and differed markedly from that of Bh cells. For steps of equal contrast, the latency of the Bh cells was ∼20 ms shorter than that of the Bd cells regardless of the contrast magnitude. For both bipolar cells and cones, the effect of contrast polarity on latency seems largely due to the absolute value of the light step, Δ L. In the large signal domain, properties of the contrast responses of bipolar cells varied appreciably, both within and between the Bd and Bh classes. Cells of either class could be positive- or negative-contrast dominant. These and additional results show that in the light-adapted retina, the bipolar population is functionally diverse and has the potential to provide a rich substrate for distributed encoding of visual images.

Effects of light adaptation on contrast processing in bipolar cells in the retina

2001 ◽  
Vol 18 (4) ◽  
pp. 581-597 ◽  
Author(s):  
PATRICK K. FAHEY ◽  
DWIGHT A. BURKHARDT
Keyword(s):  
Light Adaptation ◽  
Dynamic Range ◽  
Horizontal Cell ◽  
Bipolar Cells ◽  
Horizontal Cells ◽  
Background Intensity ◽  
Ambystoma Tigrinum ◽  
Background Illumination ◽  
Voltage Range ◽  
Contrast Gain

Effects of light adaptation on contrast processing in the outer retina were investigated over nearly four decades of background illumination by analyzing the intracellular responses of 111 bipolar cells, 66 horizontal cells, and 22 cone photoreceptors in the superfused eyecup of the tiger salamander (Ambystoma tigrinum). Light adaptation had striking and similar effects on the average contrast responses of the hyperpolarizing (Bh) and depolarizing (Bd) classes of bipolar cells: Over the lower two decades of background illumination, the contrast gain increased 7-fold to reach values as high as 20–30, the dynamic range and the half-maximum contrast decreased by about 60%, the total voltage range increased some 40%, and contrast dominance changed from highly positive to more balanced. At higher levels of background, most aspects of the contrast response stabilized and Weber's Law then held closely. In this background range, the contrast gain of bipolar cells was amplified some 20× relative to that of cones whereas the corresponding amplification in horizontal cells was about 6×. Differences in the growth of contrast gain with the intensity of the background illumination for cones versus bipolar cells suggest that there are at least two adaptation-dependent mechanisms regulating contrast gain. One is evident in the cone photoresponse such that an approximately linear relation holds between the steady-state hyperpolarization and contrast gain. The other arises between the voltage responses of the cones and bipolar cells. It could be presynaptic (modulation of cone transmitter release by horizontal cell feedback or other mechanisms) and/or postsynaptic, that is, intrinsic to bipolar cells. Contrast gain grew with the background intensity by a larger factor in horizontal than in bipolar cells. This provides a basis for the widely held view that light adaptation increases the strength of surround antagonism in bipolar cells. On average, the effects of light adaptation and most quantitative indices of contrast processing were remarkably similar for Bd and Bh cells, implying that both classes of bipolar cells, despite possible differences in underlying mechanisms, are about equally capable of encoding all primary aspects of contrast at all levels of light adaptation.

Dynamic shifts of the contrast-response function

1997 ◽  
Vol 14 (3) ◽  
pp. 577-587 ◽  
Author(s):  
Jonathan D. Victor ◽  
Mary M. Conte ◽  
Keith P. Purpura
Keyword(s):  
Gain Control ◽  
Human Vision ◽  
High Contrast ◽  
Contrast Level ◽  
Low Contrast ◽  
Contrast Gain ◽  
Contrast Response Function ◽  
Stimuli Response ◽  
Response Phase ◽  
Contrast Response

AbstractWe recorded visual evoked potentials in response to square-wave contrast-reversal checkerboards undergoing a transition in the mean contrast level. Checkerboards were modulated at 4.22 Hz (8.45-Hz reversal rate). After each set of 16 cycles of reversals, stimulus contrast abruptly switched between a “high” contrast level (0.06 to 1.0) to a “low” contrast level (0.03 to 0.5). Higher contrasts attenuated responses to lower contrasts by up to a factor of 2 during the period immediately following the contrast change. Contrast-response functions derived from the initial second following a conditioning contrast shifted by a factor of 2–4 along the contrast axis. For low-contrast stimuli, response phase was an advancing function of the contrast level in the immediately preceding second. For high-contrast stimuli, response phase was independent of the prior contrast history. Steady stimulation for periods as long as 1 min produced only minor effects on response amplitude, and no detectable effects on response phase. These observations delineate the dynamics of a contrast gain control in human vision.

Contrast encoding in retinal bipolar cells: Current vs. voltage

2003 ◽  
Vol 20 (1) ◽  
pp. 19-28 ◽  
Author(s):  
WALLACE B. THORESON ◽  
DWIGHT A. BURKHARDT
Keyword(s):  
Dynamic Range ◽  
Linear Regression Analysis ◽  
Bipolar Cells ◽  
Response Analysis ◽  
Voltage Response ◽  
Cone Voltage ◽  
Current Response ◽  
Contrast Gain ◽  
Retinal Bipolar Cells ◽  
Contrast Response

To investigate the influence of voltage-sensitive conductances in shaping light-evoked responses of retinal bipolar cells, whole-cell recordings were made in the slice preparation of the tiger salamander, Ambystoma tigrinum. To study contrast encoding, the retina was stimulated with 0.5-s steps of negative and positive contrasts of variable magnitude. In the main, responses recorded under voltage- and current-clamp modes were remarkably similar. In general agreement with past results in the intact retina, the contrast/response curves were relatively steep for small contrasts, thus showing high contrast gain; the dynamic range was narrow, and responses tended to saturate at relatively small contrasts. For ON and OFF cells, linear regression analysis showed that the current response accounted for 83–93% of the variance of the voltage response. Analysis of specific parameters of the contrast/response curve showed that contrast gain was marginally higher for voltage than current in three of four cases, while no significant differences were found for half-maximal contrast (C50), dynamic range, or contrast dominance. In sum, the overall similarity between current and voltage responses indicates that voltage-sensitive conductances do not play a major role in determining the shape of the bipolar cell's contrast response in the light-adapted retina. The salient characteristics of the contrast response of bipolars apparently arise between the level of the cone voltage response and the postsynaptic current of bipolar cells, via the transformation between cone voltage and transmitter release and/or via the interaction between the neurotransmitter glutamate and its postsynaptic receptors on bipolar cells.

scholarly journals Center/surround organization of retinal bipolar cells: High correlation of fundamental responses of center and surround to sinusoidal contrasts

2011 ◽  
Vol 28 (3) ◽  
pp. 183-192 ◽  
Author(s):  
DWIGHT A. BURKHARDT ◽  
THEODORE M. BARTOLETTI ◽  
WALLACE B. THORESON
Keyword(s):  
Receptive Field ◽  
Maximum Amplitude ◽  
High Gain ◽  
Bipolar Cells ◽  
Ambystoma Tigrinum ◽  
Response Curves ◽  
On And Off Cells ◽  
Field Organization ◽  
Receptive Field Organization ◽  
Contrast Response

AbstractReceptive field organization of cone-driven bipolar cells was investigated by intracellular recording in the intact light-adapted retina of the tiger salamander (Ambystoma tigrinum). Centered spots and concentric annuli of optimum dimensions were used to selectively stimulate the receptive field center and surround with sinusoidal modulations of contrast at 3 Hz. At low contrasts, responses of both the center and surround of both ON and OFF bipolar cells were linear, showing high gain and thus contrast enhancement relative to cones. The contrast/response curves for the fundamental response, measured by a Fast Fourier Transform, reached half maximum amplitude quickly at 13% contrast followed by saturation at high contrasts. The variation of the normalized amplitude of the center and surround responses was remarkably similar, showing linear regression over the entire response range with very high correlations, r2 = 0.97 for both ON and OFF cells. The contrast/response curves of both center and surround for both ON and OFF cells were well fit (r2 = 0.98) by an equation for single-site binding. In about half the cells studied, the nonlinear waveforms of center and surround could be brought into coincidence by scaling and shifting the surround response in time. This implies that a nonlinearity, common to both center and surround, occurs after polarity inversion at the cone feedback synapse. Evidence from paired whole-cell recordings between single cones and OFF bipolar cells suggests that substantial nonlinearity is not due to transmission at the cone synapse but instead arises from intrinsic bipolar cell and network mechanisms. When sinusoidal contrast modulations were applied to the center and surround simultaneously, clear additivity was observed for small responses in both ON and OFF cells, whereas the interaction was strikingly nonadditive for large responses. The contribution of the surround was then greatly reduced, suggesting attenuation at the cone feedback synapse.

Center-surround organization in bipolar cells: Symmetry for opposing contrasts

2003 ◽  
Vol 20 (1) ◽  
pp. 1-10 ◽  
Author(s):  
PATRICK K. FAHEY ◽  
DWIGHT A. BURKHARDT
Keyword(s):  
Bipolar Cell ◽  
Spatial Information ◽  
Horizontal Cell ◽  
Positive Contrast ◽  
Bipolar Cells ◽  
Ambystoma Tigrinum ◽  
Maximal Response ◽  
Response Curves ◽  
Contrast Polarity ◽  
Contrast Gain

Intracellular recordings were obtained from 73 cone-driven bipolar cells in the light-adapted retina of the tiger salamander (Ambystoma tigrinum). Responses to flashes of negative and positive contrast for centered spots and concentric annuli of optimum spatial dimensions were analyzed as a function of contrast magnitude. For both depolarizing and hyperpolarizing bipolar cells, it was found that remarkably similar responses were observed for the center and surround when comparisons were made between responses of the same response polarity and thus, responses to opposite contrast polarity. Thus, spatial information and contrast polarity appear to be rather strongly confounded in many bipolar cells. As a rule, the form of the contrast/response curves for center and surround approximated mirror images of each other. Contrast gain and C50 (the contrast required for half-maximal response) were quantitatively similar for center and surround when comparisons were made for responses of the same response polarity. The average contrast gain of the bipolar cell surround was 3–5 times higher than that measured for horizontal cells. Contrast/latency measurements and interactions between flashed spots and annuli showed that the surround response is delayed by 20–80 ms with respect to that of the receptive-field center. Cones showed no evidence for center-surround antagonism while for bipolar cells, the average strength of the surround ranged from about 50% to 155% of the center, depending on the test and response polarity. The results of experiments on the effects of APB (100 μM) on depolarizing bipolar cells suggest that the relative contribution of the feedback pathway (horizontal cell to cones) and the feedforward pathway (horizontal cell to bipolar cell) to the bipolar surround varies in a distributed manner across the bipolar cell population.

Contrast and Temporal Frequency-Related Adaptation in the Pretectal Nucleus of the Optic Tract

2005 ◽  
Vol 94 (1) ◽  
pp. 136-146 ◽  
Author(s):  
M. R. Ibbotson
Keyword(s):  
Visual Cortex ◽  
Optic Tract ◽  
Gain Control ◽  
Response Functions ◽  
High Contrast ◽  
Motion Adaptation ◽  
Contrast Gain ◽  
Contrast Gain Control ◽  
Contrast Adaptation ◽  
Contrast Response

In mammals, many cells in the retino-geniculate-cortical pathway adapt during stimulation with high contrast gratings. In the visual cortex, adaptation to high contrast images reduces sensitivity at low contrasts while only moderately affecting sensitivity at high contrasts, thus generating rightward shifts in the contrast response functions (contrast gain control). Similarly, motion adaptation at particular temporal frequencies (TFs) alters the temporal tuning properties of cortical cells. For the first time in any species, this paper investigates the influence of motion adaptation on both the contrast and TF responses of neurons in the retino-pretectal pathway by recording from direction-selective neurons in the nucleus of the optic tract (NOT) of the marsupial wallaby, Macropus eugenii. This species is of interest because its NOT receives almost all input directly from the retina, with virtually none from the visual cortex (unlike cats and primates). All NOT cells show changes in their contrast response functions after adaptation, many revealing contrast gain control. Contrast adaptation is direction-dependent, preferred directions producing the largest changes. The lack of cortical input suggests that contrast adaptation is generated independently from the cortex in the NOT or retina. Motion adaptation also produces direction-selective effects on the TF tuning of NOT neurons by shifting the location of the optimum TF. Cells that show strong adaptation to contrast also tend to show large changes in TF tuning, suggesting similar intracellular mechanisms. The data are discussed in terms of the generality of contrast adaptation across mammalian species and across unconnected brain regions within the same species.

Effects of bicarbonate versus HEPES buffering on measured properties of neurons in the salamander retina

1998 ◽  
Vol 15 (2) ◽  
pp. 263-271 ◽  
Author(s):  
WILLIAM A. HARE ◽  
W. GEOFFREY OWEN
Keyword(s):  
Horizontal Cell ◽  
Bipolar Cells ◽  
Horizontal Cells ◽  
Equilibrium Potential ◽  
Ambystoma Tigrinum ◽  
Light Responses ◽  
Internal Ph ◽  
Isolated Retina ◽  
Electrophysiological Studies ◽  
Kinetics Of

Electrophysiological studies of the isolated retina involve perfusing the tissue with a physiological Ringer's. Organic pH buffers such as HEPES have become increasingly popular in recent years because for many purposes they offer a convenient and reliable alternative to the more traditional bicarbonate/CO2. In this paper, however, we report that important functional properties of rods, bipolar cells, and horizontal cells in the salamander, Ambystoma tigrinum, are sensitive to the choice of buffer and, in the case of horizontal cells, that sensitivity is acute. In bicarbonate/CO2 Ringer's, the dark potential of the horizontal cell was typically near −50 mV and saturating light caused it to hyperpolarize to about −75 mV. On switching to HEPES-buffered Ringer's at the same pH, horizontal cells depolarized in darkness to about −20 mV, close to the chloride equilibrium potential, and the kinetics of their light responses changed. The cone-driven components of light responses increased in size relative to rod-driven components. Saturating lights still hyperpolarized the cells to −75 mV, however. Horizontal cells, being coupled via gap junctions, form a syncytium and syncytial length constants, measured in bicarbonate/CO2 Ringer's, were generally in the range 150–225 μm. On switching to HEPES-buffered Ringer's, length constants increased substantially to 250–330 μm. All these changes were reversible. We discuss our findings within the context of the cell's ability to regulate its internal pH.

Retinal bipolar cells: Contrast encoding for sinusoidal modulation and steps of luminance contrast

2004 ◽  
Vol 21 (6) ◽  
pp. 883-893 ◽  
Author(s):  
DWIGHT A. BURKHARDT ◽  
PATRICK K. FAHEY ◽  
MICHAEL A. SIKORA
Keyword(s):  
Cell Types ◽  
Luminance Contrast ◽  
Bipolar Cells ◽  
Horizontal Cells ◽  
Maximal Response ◽  
Strong Nonlinearity ◽  
Pass Filter ◽  
Low Contrast ◽  
Sinusoidal Modulation ◽  
Contrast Gain

Contrast encoding for sinusoidal modulations of luminance contrast was investigated by intracellular recording in the intact salamander retina. In what appears to be the first study of this kind for vertebrate bipolar cells, responses of the central receptive-field mechanism of cone-driven cells to modulation of 3 Hz were analyzed quantitatively via both signal averaging and a Fast Fourier Transform (FFT) while the retina was light adapted to 20 cd/m2. Depolarizing and hyperpolarizing bipolar cells showed very similar encoding. Both responded with sinusoidal waveforms whose amplitude varied linearly with modulation depths ranging up to 7–8%. The slope of the modulation/response curve was very steep in this range. Thus, the contrast gain was high, reaching values of 6–7, and the half-maximal response was achieved at modulations of 9% or less. At modulations above ∼15%, the responses typically showed strong compressive nonlinearity and the waveform was increasingly distorted. At maximum modulation, the higher harmonics of the FFT constituted about 30% of the amplitude of the fundamental. Measurements were also made for cones and horizontal cells. Both cell types showed predominantly linear responses and low contrast gain, in marked contrast to bipolar cells. These results suggest that the high contrast gain and strong nonlinearity of bipolar cells largely arise postsynaptic to cone transmitter release. Further experiments were performed to compare responses to contrast steps versus those to sinusoidal modulation. In the linear range, we show that the contrast gains of cones and horizontal cells are low and virtually identical for both steps and sinusoidal modulations. In bipolar cells, on the other hand, the contrast gain is about two times greater for steps than that for the 3-Hz sine waves. These results suggest that mechanisms intrinsic to bipolar cells act like a high-pass filter with a short time constant to selectively emphasize contrast transients over slower changes in contrast.

Visual evoked potentials and magnocellular and parvocellular segregation

2000 ◽  
Vol 17 (4) ◽  
pp. 579-590 ◽  
Author(s):  
INGER RUDVIN ◽  
ARNE VALBERG ◽  
BJØRG ELISABETH KILAVIK
Keyword(s):  
Evoked Potentials ◽  
Visual Evoked Potentials ◽  
Single Cells ◽  
High Gain ◽  
High Contrast ◽  
Low Contrast ◽  
Contrast Gain ◽  
Time To Peak ◽  
Contrast Response ◽  
Visual Evoked

We have measured visual evoked potentials (VEPs) to luminance-modulated, square-wave alternating, 3-deg homogeneous disks for stimulus frequencies ranging from 1 Hz to 16.7 Hz. The aim of the study was to determine the range of frequencies at which we could reproduce the two-branched contrast-response (C-R) curves we had seen at 1 Hz (Valberg & Rudvin, 1997) and which we interpreted as magnocellular (MC) and parvocellular (PC) segregation. Low-contrast stimuli elicited relatively simple responses to luminance increments resulting in waveforms that may be the signatures of inputs from magnocellular channels to the visual cortex. At all frequencies, the C-R curves of the main waveforms were characterized by a steep slope at low contrasts and a leveling off at 10%–20% Michelson contrast. This was typically followed by an abrupt increase in slope at higher contrasts, giving a distinctive two-branched C-R curve. On the assumption that the low-contrast, high-gain branch reflects the responsivity of magnocellular-pathway inputs to the cortex, the high-contrast branch may be attributed to additional parvocellular activation. While a two-branched curve was maintained for frequencies up to 8 Hz, the high-contrast response was significantly compromised at 16.7 Hz, revealing a differential low-pass filtering. A model decomposing the measured VEP response into two separate C-R curves yielded a difference in sensitivity of the putative MC- and PC-mediated response that, when plotted as a function of frequency, followed a trend similar to that found for single cells. Due to temporal overlap of responses, the MC and PC contributions to the waveforms were hard to distinguish in the transient VEP. However, curves of time-to-peak (delay) as a function of contrast often went through a minimum before the high-contrast gain increase of the corresponding C-R curve, supporting the notion of a recruitment of new cell ensembles in the transition from low to high contrasts.

Similar effects of carbachol and dopamine on neurons in the distal retina of the tiger salamander

1995 ◽  
Vol 12 (3) ◽  
pp. 443-455 ◽  
Author(s):  
William A. Hare ◽  
W. Geoffrey Owen
Keyword(s):  
Dopamine Release ◽  
Light Adaptation ◽  
Amacrine Cells ◽  
Bipolar Cells ◽  
Horizontal Cells ◽  
D1 Receptors ◽  
Ambystoma Tigrinum ◽  
Tiger Salamander ◽  
Retinal Neurons ◽  
D2 Dopamine Receptors

AbstractThough there is considerable evidence that dopamine is an important retinal neuromodulator that mediates many of the changes in the properties of retinal neurons that are normally seen during light adaptation, the mechanism by which dopamine release is controlled remains poorly understood. In this paper, we present evidence which indicates that dopamine release in the retina of the tiger salamander, Ambystoma tigrinum, is driven excitatorily by a cholinergic input. We compared the effects of applying carbachol to those of dopamine application on the responses of rods, horizontal cells, and bipolar cells recorded intracellularly from the isolated, perfused retina of the tiger salamander. Micromolar concentrations of dopamine reduced the amplitudes of rod responses throughout the rods' operating range. The ratio of amplitudes of the cone-driven to rod-driven components of the responses of both horizontal and bipolar cells was increased by activation of both D1 and D2 dopamine receptors. Dopamine acted to uncouple horizontal cells and also off-center bipolar cells, the mechanism in the case of horizontal cells depending only upon activation of D1 receptors. Carbachol, a specific cholinomimetic, applied in five- to ten-fold higher concentrations, produced effects that were essentially identical to those of dopamine. These effects of carbachol were blocked by application of specific dopamine blockers, however, indicating that they are mediated secondarily by dopamine. We propose that the dopamine-releasing amacrine cells in the salamander are under the control of cells, probably amacrine cells, which secrete acetylcholine as their transmitter.

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