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B B Lee

Publications and source records attributed to B B Lee.

At least 127 records · Page 7Linked to original sources
PubMed1987

Simulation of responses of spectrally-opponent neurones in the macaque lateral geniculate nucleus to chromatic and achromatic light stimuli.

The responses of spectrally opponent, parvocellular-layer cells in the lateral geniculate nucleus of the macaque vary with stimulation along all three dimensions of colour space (luminance, dominant wavelength and purity). Here, the responses of different cell types to light stimuli successively replacing a white adaptation field are simulated mathematically by a simple model using known cone spectral sensitivities. Hyperbolic response functions with two adjustable parameters relate cone excitation with the output signals of each cone mechanism. For the majority of cells, differences of outputs of two cone mechanisms, receiving inputs from L- and M-cones, describe responses to chromatic and achromatic stimuli. For each opponent combination of cone inputs, either L-M or M-L, two cell types were found. Off-centre cells had lower maximum firing rates of their on-component, but were the more sensitive of the two groups, preferring dark colours, whereas on-centre cells showed better responsiveness to brighter stimuli. For all four cell types, the predictions of the equations replicated well the responses measured to stimuli varying along all three dimensions of colour space. The quantification of cell responses presented here provides possibilities for studying suprathreshold coding of colour and lightness, and the model can help to link physiology with the psychophysics of colour vision.

Animals↗
PubMed1987

Mesopic spectral responses and the Purkinje shift of macaque lateral geniculate nucleus cells.

Spectral responsiveness of different classes of macaque LGN cells at eccentricities smaller than 12 degrees was studied at low light intensities. Cone thresholds of cells varied from 1 to 10 td. Rod inputs were found in all classes of cells, including inhibitory inputs in some cells. Rod inputs were not apparent above 10-40 td, giving a total mesopic range of about 1-40 td. Strong rod-mediated responses could be evoked in broadband phasic cells and in spectrally opponent cells excited by short wavelengths. Only weak if any excitatory responses could be evoked by short wavelengths at scotopic levels in spectrally opponent long-wavelength excited cells. Hence, rod inputs do not confound the spectral responsiveness of cells because no spectrally opponent cell excited by long-wavelength stimuli at photopic levels became significantly responsive to short wavelength stimuli at mesopic or scotopic intensities. The so-called "rod color" may be blue. An increase in the dominance of wide-band cell responses that may explain the Bezold-Brücke hue shift was observed at higher stimulus radiances at wavelengths near 450 and 650 nm.

Animals↗
PubMed1987

Thresholds to chromatic spots of cells in the macaque geniculate nucleus as compared to detection sensitivity in man.

1. The relation between wavelength and psychophysical threshold for chromatic spots on a white background provides evidence for the existence of chromatic channels in the primate visual system. To find the physiological substrate of this task, we compared increment thresholds of different cell types in the macaque lateral geniculate nucleus with human psychophysical thresholds to the same stimuli, using two spot sizes, 4 and 0.4 deg. 2. At different wavelengths, different opponent cell classes in the parvocellular layers of the nucleus were most sensitive, so that at long wavelengths (greater than 600 nm) red on-centre cells were most sensitive, while at short wavelengths (less than 500 nm) S-cone, blue on-centre cells were most sensitive, from 500 to about 550 nm green on-centre cells being most sensitive. A rare cell type with inhibition from S-cones was most sensitive at about 570 nm, although its maximum contrast increment sensitivity was poor compared with that of other cell types. Variation in strength of cone opponency caused a considerable range in threshold in each of the opponent cell classes of the parvocellular layers. 3. On- and off-centre cells from the magnocellular layers were more sensitive than opponent cells to white and yellow spots (as is the case with achromatic gratings). 4. With different wavelengths and spot sizes, the most sensitive cells found approached (to within 0.1-0.3 log units) human psychophysical sensitivity, suggesting that the most sensitive cells available may underlie detection. 5. Measurements of psychophysical chromatic discrimination thresholds, both with nearly monochromatic spots and with spots of differing saturation (purity), support this hypothesis. When magnocellular cell sensitivity corresponded to psychophysical threshold, a suprathreshold stimulus, capable of activating opponent cells, was required for chromatic discrimination.

Animals↗
PubMed1986

Colour and brightness signals of parvocellular lateral geniculate neurons.

We recorded from single neurons in the parvocellular layers of the lateral geniculate body of anesthetized monkeys. Spectral response curves of parvocellular neurons depended on the luminance ratio between the chromatic stimuli and achromatic background. From response/intensity curves, we determined the relative luminance between a coloured and an achromatic (white) light at which a given cell became non-responsive (critical luminance ratio, CLR). The spectral dependence of the CLRs of narrow (N) and wide band (W) cells with opponent receptor input showed characteristic differences. The activity of W-cells increased with luminance increase of a white light and of a coloured light in the specific spectral region of the cell (yellow-red for the long wave length sensitive WL-, and yellow-green-blue for the short wave length sensitive WS-cells), while N-cells were activated by their specific spectral light (blue for NS-cells, red for NL-cells) and by a luminance decrease of achromatic white. N-cells discriminate best between their characteristic colour and white at luminance ratios below their respective CLR, while W-cells distinguish best between a light of their characteristic colour and white at chromatic/achromatic luminance ratios above their respective CLR. Yellow sensitive W-cells with a narrow spectral sensitivity peaking around 570 nm and with only a small or no response to white light, could enable distinction between white and yellow of similar luminance. The findings are consistent with the opponency model of spectrally sensitive cells in the LGB. We discuss their implications for colour coding by parvocellular cells. N- and W-cells appear to behave complementary with respect to luminance information (N-cells may be compared to the cat's off-cells, W-cells to on-cells). S- and L-cells are complementary with respect to colour. The yellow sensitive WM-cells are critical for the discrimination of yellow and white, while cells with excitatory cone input from blue and red cones (W-SL-cells) may aid the perception of purple. The fact that, at different relative luminance ratios between a chromatic stimulus and a white background, the whole family of parvocellular cells is involved differently in coding for colour, may explain the different appearance of colours against a white background at different luminance ratios and the perception of induced colours.

Animals↗
PubMed1986

Neurones with strong inhibitory S-cone inputs in the macaque lateral geniculate nucleus.

Neurons with strong inhibitory short-wavelength sensitive cone (S-cone) inputs have been identified in the macaque geniculate using a tritanopic confusion line test, i.e. by stimulation with equiluminous stimuli which leave excitations of long- and middle-wavelength sensitive cones (L- and M-cones) constant while differentially exciting S-cones. Mathematical simulation of the responses of these cells, using known spectral sensitivities of the cone receptors, demonstrates that they receive excitation from M-cones, inhibition from S-cones, and little or no inhibition from L-cones. Excitatory and inhibitory pools are largely spatially coextensive.

Animals↗
PubMed1986

Reconstruction of equidistant color space from responses of visual neurones of macaques.

We demonstrate that a combination of responses of various types of spectrally opponent sustained cells of the macaque lateral geniculate nucleus (LGN) may be related to equidistant color space. Response curves of such cells to stimuli of different luminance ratios and wavelengths are similar to the first stage opponent coordinate functions of the new SVF color-difference formula [T. Seim and A. Valberg, Color Res. Appl. 11, 11 (1986)]. Mathematical simulation of the responses of these cells to a variety of color stimuli is possible through computation of cone excitations and subsequent sums and differences of cone signals. When the response functions thus obtained for cells are used to replace the corresponding coordinates of the SVF diagram, the distributions of equiluminous stimuli with the same sensory differences from an achromatic stimulus approximate ellipses about the white point, and loci of constant hue approximate straight lines. Improved uniformity may be obtained by linear combinations of these cells' outputs or by including more cell types with best responsiveness to other directions of color space. This indicates possible roles of LGN cell types for color scaling in primates, in that color scaling observed psychophysically is an implicit property of these cells' responses.

Animals↗
PubMed1985

A simultaneous contrast effect of steady remote surrounds on responses of cells in macaque lateral geniculate nucleus.

Steadily illuminated surrounds, remote from the receptive field centre, are shown to affect the responses of primate visual cells. Intensity-response curves of cells of the macaque lateral geniculate nucleus were measured using a successive contrast paradigm where chromatic or achromatic stimuli were presented in alternation with a white adaptation field of constant luminance. Adding white surround annuli around stimuli and adaptation field shifted the intensity-response curves to higher intensity ranges. Since response curves can be nonmonotonic, this remote surround effect can result in an increase or decrease in responsiveness (facilitation or suppression) dependent on stimulus intensity. Steady surrounds, remote from the receptive field centre, thus control cell sensitivity and responses by means of simultaneous contrast.

Adaptation, Physiological↗
PubMed1985

A comparison of visual responses of cat lateral geniculate nucleus neurones with those of ganglion cells afferent to them.

We compared visual responses of cat lateral geniculate nucleus (l.g.n.) neurones with those of retinal ganglion cells providing their afferent inputs. Quantitative studies were made on twenty such pairs; eight X on-centre, seven Y on-centre, two X off-centre and three Y off-centre pairs. Receptive field centre locations of cell pairs with correlated activities were very closely superimposed, having a mean centre displacement of 1.6 minutes of arc for X cells and 11 minutes of arc for Y cells. With flashed spots and annuli, responses of l.g.n. cells were almost always smaller than those of their retinal afferents, with peaks and troughs in ganglion cell responses being faithfully followed in the geniculate neurones. This is consistent with almost all impulses from the l.g.n. cell being triggered by the afferent feeding its centre. With spots of different sizes and contrasts, modulation of responses by l.g.n. inhibition was obvious, but effects were complex. With moving bright-bar stimuli, although response histograms were clearly reshaped to some extent in the l.g.n., peak firing rates under different stimulus conditions were often merely attenuated by a constant factor for most l.g.n. cells in comparison with their retinal inputs. For velocity tuning curves, a few cell pairs showed selective attenuation at high speeds, while others showed it at low speeds. All the latter group appeared to have more than one major excitatory afferent. These changes in velocity tuning occurred across the X/Y classification, so that differences in velocity preference of the X and Y systems is more blurred in the l.g.n. than in the retina.

Action Potentials↗
PubMed1984

Importance of cytotoxic lymphocytes during cytomegalovirus infection in renal transplant recipients.

Thirty renal transplant recipients were studied prospectively to evaluate the relationship of cytomegalovirus-specific cytotoxic lymphocyte responses to clinical outcome during cytomegalovirus infection. Cytomegalovirus infection developed in 20 patients; of these 20, 14 had cytomegalovirus-specific cytotoxic lymphocyte responses whereas six did not. Clinical findings (fever, leukopenia, thrombocytopenia, or elevations in serum transaminase levels) were significantly more frequent among patients without responses than among patients with responses (p less than 0.001), and prolonged viremia and complications of infection including superinfection, interstitial pneumonitis, pancreatitis, and death occurred exclusively among patients without responses. Acute allograft dysfunction during infection was experienced by four patients without responses but by only one patient with response (p = 0.02), indicating that the virus-specific cytotoxic response did not result in a renal immunopathologic condition, and may have protected against virus-induced injury to the graft. In seven of nine patients with responses who shed virus, cytotoxic responses occurred within one week of detection of activation of virus shedding. Absence of cytotoxic responses correlated with prior high-dose, intravenous methylprednisolone treatment, and apparently resulted from inhibition of cytotoxic T cell precursors. Immunosuppressive treatment to inhibit graft rejection should be minimized, and methods should be developed that do not inhibit cytomegalovirus-specific cytotoxic T cell responses.

Antibodies, Viral↗
PubMed1983

Linear signal transmission from prepotentials to cells in the macaque lateral geniculate nucleus.

Prepotentials preceding a neuronal action potential were recorded extracellularly in the lateral geniculate nucleus (LGN) of the macaque. Although prepotentials are found less frequently in the macaque than in the cat LGN, their electrical characteristics are similar, suggesting that they represent the arrival of impulses in a retinal afferent, as in the cat. The visual response properties of prepotentials and associated cells were similar under a variety of conditions, indicating that, apart from some response attenuation, little signal processing takes place in macaque LGN. A constant fraction of prepotentials above a threshold frequency gave rise to neuronal action potentials independent of the stimuli used, so that the frequency of cell action potentials was linearly related to the frequency of prepotentials. Since the maintained discharge rates of a cell and its prepotential always fell on the linear relation, the net responses of a cell and its prepotential to visual stimuli were approximately proportional to one another.

Action Potentials↗
PubMed1983

The responses of cells in macaque lateral geniculate nucleus to sinusoidal gratings.

Responses of cells in the parvocellular (p.c.l.) and magnocellular (m.c.l.) layers of the macaque lateral geniculate nucleus to sine-wave gratings were studied. Both p.c.l. and m.c.l. cells responded best at a temporal frequency (drift rate) of 10-20 Hz. P.c.l. cells responded at temporal frequencies lower than 1 Hz; m.c.l. cells did not. With coloured- or white-black luminance-modulated gratings, responses of m.c.l. cells were weaker at low than at medium spatial frequencies. With coloured gratings, p.c.l. cell responses were not attenuated at low spatial frequencies. With white gratings a few p.c.l. cells did show such attenuation. Optimal responses from p.c.l. cells were obtained with coloured gratings; white gratings evoked weaker responses. With a grating of a colour causing suppression of a p.c.l. cell's activity, the modulation of firing was much less than with a grating of a colour excitatory for the cell. M.c.l. on- and off-centre cells responded equally well to moving gratings. The ability of p.c.l. cells to resolve fine gratings was dependent on cell type as well as on the colour of grating used. The ability of m.c.l. cells to resolve fine gratings was comparable to that of p.c.l. cells. The contrast sensitivity of m.c.l. cells was much higher than that of p.c.l. cells. This may account for their ability to resolve fine gratings, despite their larger centre size. In comparison with luminance-modulated gratings, chromatically modulated gratings could evoke larger or smaller responses, depending on p.c.l. cell type and the colours in the grating. M.c.l. cells responded poorly or not at all.

Animals↗
PubMed1983

Cell responses in dorsal layers of macaque lateral geniculate nucleus as a function of intensity and wavelength.

We studied the relationship between light intensity and cell response to various wavelengths and wavelength combinations in the dorsal, parvocellular layers of the macaque lateral geniculate nucleus. When response is plotted as a function of the logarithm of stimulus intensity, the slope and shape of curves depends on wavelength. For wavelengths near the crossover point between excitatory and suppressive responses, nonmonotonic curves are common. Consequently, the form of spectral-response functions depends on stimulus intensity. Responses to combined stimuli made up of wavelengths close together near one spectral extreme are approximately additive. If one wavelength is near the crossover point, responses are nonadditive so that a midspectral wavelength, only producing a weak excitatory response, is able to occlude more vigorous responses to wavelengths near the spectral ends. Responses of parvocellular layer cells are consistent with their being a result of linear interaction of opponent cone mechanisms, the response of each of which follows a modified hyperbolic tangent function (22). Responses to all wavelength combinations, even those showing strikingly nonadditive effects, could be predicted from the additive opponent model described above.

Animals↗
PubMed1983

Light adaptation in cells of macaque lateral geniculate nucleus and its relation to human light adaptation.

Responses of macaque lateral geniculate nucleus (LGN) cells to stimuli of different incremental intensities and wavelength compositions were studied at different levels of light adaptation from scotopic to low photopic levels. Stimuli were large in comparison with receptive-field size. Human increment thresholds were measured for comparison. The strength of responses grew in many cells from threshold up to a saturation level as a logarithmic function of incremental intensity. More complex intensity-response functions were also obtained, particularly from parvocellular layer (PCL) cells, but the shape and slope of the intensity-response function changed as a function of adaptation level only with chromatic backgrounds. As a function of adaptation level, the intensity-response functions shifted along the logarithmic abscissa but not sufficiently for a complete contrast constancy. Thus responses to any constant contrast became smaller when adaptation level decreased. The change from cone to rod responses, when possible, took place without noticeable change in shape of intensity-response functions, and much of the adaptive shift of the functions could be attributed to the change-over between rods and cones. Differences between different cells in light adaptation and dark-adapted sensitivity were large, mostly because of variation in the strength of rod input. The strongest excitatory rod inputs were found in PCL cells activated by short-wavelength light, so that the highest sensitivity at low levels of illumination occurred in blue- and blue-green-sensitive cells. The lowest increment thresholds based on cones matched the thresholds of macaque cone late receptor potentials recorded by Boynton and Whitten (3). They were also similar to human cone thresholds measured psychophysically but only for small stimulus sizes that may approximate the size of the receptive-field centers. Human sensitivity was much higher when measured with large stimulus sizes, indicating integration at post-geniculate neural levels. Light adaptation, as evaluated with respect to contrast constancy and Weber law behavior, was similarly incomplete in monkey single cells and human perception. A few cat LGN cells were studied in a control experiment; results agreed with previous findings. The light adaptation of cat cels was more complete and sensitivity higher than those observed under comparable conditions in macaque single cells and human. The maintained activity level of cells was little affected by the intensity of steady backgrounds. Thus, the steady-state hyper-polarisation of receptors was not transmitted to LGN cells.

Adaptation, Ocular↗
PubMed1983

Captopril-induced acute renal failure in a kidney transplant recipient.

A living related kidney transplant recipient with normal renal function and severe hypertension secondary to renal artery stenosis, was treated with captopril and developed reversible renal failure requiring temporary hemodialysis. This complication of captopril, an angiotensin converting enzyme inhibitor, has been reported previously in hypertensive patients with renal artery stenosis with and without a kidney transplant. It is recommended that this drug be used with caution in this setting.

Acute Kidney Injury↗
PubMed1983

Response of neurons in the cat's lateral geniculate nucleus to moving bars of different length.

It is well recognized that in the visual cortex of the cat, some of the cells (hypercomplex) are sharply tuned for the length of a bar moving backwards and forwards across their receptive fields. Other cells (simple) exhibit no such tuning but appear to respond proportionately over a range of bar lengths. The tuning seen in hypercomplex cells is already observable to a lesser degree in retinal ganglion cells. Our experiments were carried out to determine the extent of this tuning in the lateral geniculate nucleus, which relays information from the retina to the cortex. Results show that geniculate cells have tuning properties intermediate between those of ganglion cells and hypercomplex cells. By adding together a linear array of geniculate cells, it is possible to model the characteristics of a simple cell and to demonstrate that while an elongated bar gives a minimal response in hypercomplex cells, it should have little effect on the response of simple cells.

Animals↗
PubMed1982

Responses to coloured patterns in the macaque lateral geniculate nucleus: pattern processing in single neurones.

Cell responses to complex visual patterns such as compositions of broad-band (non-monochromatic) colour areas are presented. Patterns were scanned over the receptive field, and cell response at each point was recorded. "Response patterns" were constructed which display the cell transform of the stimulus pattern. Parvocellular layer (PCL) cells in the lateral geniculate nucleus, in a very sustained fashion, signal the spectral composition of areas in the pattern, cells of different classes showing different spectral responsiveness. Little or no edge enhancement was present. Magnocellular layer (MCL) cells mark luminance steps in a pattern; they are not colour-specific. Responses to monochromatic stimuli provided a reliable guide to cell responsiveness with mixed colours. However, integration by spectrally opponent mechanisms is present with broad-band colour stimulation and partly accounts for a high variability of response patterns within the same cell class. With some cells, stimulus patterns were either shown through narrow-band colour filters, or a monochromatic background was added. Response patterns to isolated wavelength components compared with those to full colour patterns revealed an almost linear additivity of individual spectral components. Adaptation to a chromatic background, on the other hand, strongly modified the effectiveness of excitatory and suppressive components in the stimulus pattern and markedly changed the structure of a response pattern compared with the non-adapted situation.

Animals↗
PubMed1982

Responses to coloured patterns in the macaque lateral geniculate nucleus: analysis of receptive field properties.

Response patterns to complex visual stimuli were further analysed. Patterns were correlated with linear or non-linear components of the stimulus pattern at various wavelengths. Resulting correlograms revealed the spatial and spectral structure of receptive fields; they showed peaks or troughs according to whether that wavelength was associated with an increase or decrease in cell firing. Spectral response curves as derived from linear correlograms were similar to those reported for monochromatic stimuli. Variability in responsiveness and crossover wavelengths was high between parvocellular layer (PCL) cells even of the same class. Spatial differences between excitatory and suppressive receptive field components, i.e. a centre-surround organisation, are not apparent in linear correlograms from PCL cells. In this respect, spectral response curves do not qualitatively change with stimulus size. Correlation in time and the derivation of impulse functions showed that, even in magnocellular layer (MCL) cells, responses to luminance steps are of mainly temporal origin and due to a transient component in the response. A description of cell responses based on linear processing accounted well for the response patterns obtained in our experiments. Of various non-linear interactions investigated, only some kind of non-linear spectral differentiation provided an improvement in the description of cell responses. This improvement, however, was only minor and not present in all cells.

Animals↗