OFF-center Ganglion Research Articles

Life imitates op art

The beautiful, undulating orientation maps in visual cortex have motivated many developmental models. A new study finds that this functional organization could be seeded in the retina by moire interference between mosaics of ON-center and OFF-center retinal ganglion cells.

Convergence and segregation of the multiple rod pathways in mammalian retina.

Using a multidisciplinary approach, we demonstrate that three different pathways are responsible for the transmission of rod signals across the mouse retina. Each pathway serves a primarily nonoverlapping range of stimulus intensities, with ganglion cells receiving either segregated or convergent inputs. For both on-center (ON) and off-center (OFF) ganglion cells, the primary rod pathway carries signals with the lowest threshold, whereas the secondary rod pathway is less sensitive by approximately 1 log unit. In addition, OFF signaling uses a tertiary rod pathway that is approximately 1 log unit less sensitive than the secondary. Although some ganglion cells received rod inputs exclusively from one of the pathways, others showed convergent inputs. Using pharmacological and genetic approaches, we defined classes of ON and OFF ganglion cells for which the scotopic inputs derive only from the primary pathway or from both primary and secondary pathways. In addition, we observed a class of OFF ganglion cell receiving mixed input from primary and tertiary pathways. Interestingly, OFF ganglion cells receiving convergent inputs from all three rod pathways or from the secondary and tertiary pathways together were never observed. Overall, our data show a complex arrangement of convergence and segregation of rod inputs to ganglion cells in the mammalian retina.

The midget pathways of the primate retina.

Midget ganglion cells in the foveal slope, parafovea, near periphery and far periphery of human and monkey retinas have been studied by electron microscopy (EM). Five human foveal ganglion cells were reconstructed and found to share input from seven midget bipolar cells. The OFF center ganglion cells were in a one to one relationship with their midget bipolar cells. But the ON center cells received input from two to three midget bipolar cells, of which one was dominant in terms of numbers of ribbon synapses directed at the midget ganglion cell dendrites. In the human parafovea every midget ganglion cell received input from only one midget bipolar cell (previously published, Kolb and DeKorver, 1991). At 4 mm of eccentricity, the near peripheral ON midget ganglion cell received input from three midget bipolar cells and thus from three cones. In far peripheral retina (12 mm) the ON midget ganglion cell received input from three to four midget bipolar cells. The peripheral midget bipolar cells probably contacted three cones each: therefore between nine and 12 cones could have input to such midget ganglion cell. The relationship of the increasing dendritic field size and increasing convergence of cones to the midget ganglion cells with eccentricity from the fovea is discussed in terms of color processing and resolution.

Neural Mechanisms of Visual Perception

It is more than half a century ago since Keffer H Hartline published his classical receptive fields studies of single optic nerve fibres in the frog. World War II intervened and the full impact of his work did not become apparent until the early fifties, when Horace Barlow extended Hartline's analysis in the frog and Stephen W Kuffler showed the on-centre and off-centre type ganglion cells in the cat retina. The next advances were made in the late fifties when Jerome Lettvin and Humberto Maturana described cells in the frog tectum with very complex response properties and when David Hubel and I discovered that cells in the cat striate cortex were sensitive to orientation of contours and binocular stimulation. Vision research has gone a long distance since that time—nonetheless we have just begun the long journey towards a detailed mechanistic understanding of the neural basis of visual perception. In this lecture I discuss the processing of visual information at the level of the striate cortex in the cat and monkey, and describe technical advances that have greatly facilitated the analysis of the neural mechanisms of visual perception.

Simulation of visual cortex development under lid-suture conditions: enhancement of response specificity by a reverse-Hebb rule in the absence of spatially patterned input.

In this report, I show that a reverse-Hebb synaptic modification rule leads to the enhancement of response specificity of simulated visual cortex neurons in the absence of spatial patterning of the afferent activity. Although it is clear that receptive fields in the visual cortex can be modified by experience, many studies have shown a substantial increase of response specificity in cats deprived of pattern vision by lid suture, leading some to conclude that receptive field properties are essentially hard-wired. The hard-wired vs. experience-dependent controversy can be resolved by assuming that while Hebb-type plasticity is responsible for developmental synaptic changes, the organization of presynaptic activity which exists under conditions of visual deprivation is sufficient to drive the neurons towards greater specificity (Linsker 1986a-c; Miller 1989, 1992; Miller et al. 1989). As a reverse-Hebb rule enhances response specificity by balancing the push-pull system of ON- and OFF-center afferents, the sufficient condition is that the activity of ON- and OFF-center retinal ganglion cells be negatively correlated, a condition which will be met by diffuse illumination as seen through sutured eyelids. Unlike the models of Linsker and Miller and colleagues, which are based on a standard-Hebb rule, the model presented here does not require the presence of a "Mexican hat" spatial patterning of the afferent correlations, which has not been observed experimentally.

Effects of vasoactive intestinal peptide on ganglion cells in the rabbit retina.

The effects of vasoactive intestinal peptide (VIP) on the extracellularly recorded activity of ganglion cells were studied in superfused rabbit retinas. VIP, applied to the bathing solution, significantly increased the maintained activity of both OFF-center and ON-center brisk ganglion cells. The transient, excitatory responses of these cells to flashes of light (spots or annuli centered over the receptive field) were either unaffected or moderately reduced. VIP did not affect the responses of most ON/OFF directionally selective ganglion cells to a moving light stimulus. Furthermore, maintained activity of most of these cells remained absent. Effects of VIP on the light responses of ganglion cells were pronounced in retinas that were bathed with the dopamine D1 antagonist (+)-SCH 23390. For OFF-center brisk ganglion cells, VIP brought out both the center and surround excitatory responses that were selectively reduced by (+)-SCH 23390. Similarly, VIP brought out the leading edge responses that were reduced by (+)-SCH 23390 in ON/OFF directionally selective ganglion cells to a moving light stimulus. VIP did not however reverse the effects of (+)-SCH 23390 on ON-center brisk ganglion cells. It is argued that VIP counteracts the effects of (+)-SCH 23390 on OFF-center brisk ganglion cells and ON/OFF directionally selective ganglion cells by stimulating adenylate cyclase activity in dopamine-receptive cells of the retina.

Superior colliculus cell responses to to electrical stimulation of the retina.

Superior colliculus cell discharges in response to electrical stimulation of the retina were investigated in rabbit. In contrast with the responses at the optic tract level both polarities evoked discharges of equal latencies suggesting a convergence of ON- and OFF-centre retinal ganglion cells upon one collicular unit. Three typical patterns of responses could be distinguished. Thus, 40% of cells reacted with a burst, 47% with a prolonged discharge, and 5% responded by a transient inhibition. The responses of the remaining cells could not be classified.