The temporal dynamics of the response of neurons in the outer retina were investigated by intracellular recording from cones, bipolar, and horizontal cells in the intact, light-adapted retina of the tiger salamander (Ambystoma tigrinum), with special emphasis on comparing the two major classes of bipolars cells, the ON depolarizing bipolars (Bd) and the OFF hyperpolarizing bipolars (Bh). Transfer functions were computed from impulse responses evoked by a brief light flash on a steady background of 20 cd/m2. Phase delays ranged from about 89 ms for cones to 170 ms for Bd cells, yielding delays relative to that of cones of about 49 ms for Bh cells and 81 ms for Bd cells. The difference between Bd and Bh cells, which may be due to a delay introduced by the second messenger G-protein pathway unique to Bd cells, was further quantified by latency measurements and responses to white noise. The amplitude transfer functions of the outer retinal neurons varied with light adaptation in qualitative agreement with results for other vertebrates and human vision. The transfer functions at 20 cd/m2 were predominantly low pass with 10-fold attenuation at about 13, 14, 9.1, and 7.7 Hz for cones, horizontal, Bh, and Bd cells, respectively. The transfer function from the cone voltage to the bipolar voltage response, as computed from the above measurements, was low pass and approximated by a cascade of three low pass RC filters (“leaky integrators”). These results for cone→bipolar transmission are surprisingly similar to recent results for rod→bipolar transmission in salamander slice preparations. These and other findings suggest that the rate of vesicle replenishment rather than the rate of release may be a common factor shaping synaptic signal transmission from rods and cones to bipolar cells.

Monocular deprivation during early development causes rearrangement of neural connections within the visual cortex that produces a shift in ocular dominance favoring the non-deprived eye. This alteration is manifested anatomically within deprived layers of the lateral geniculate nucleus (LGN) where neurons have smaller somata and reduced geniculocortical terminal fields compared to non-deprived counterparts. Experiments using monocular deprivation have demonstrated a spatial correlation between cytoskeleton alteration and morphological change within the cat LGN, raising the possibility that subcellular events mediating deprivation-related structural rearrangement include modification to the neuronal cytoskeleton. In the current study we compared the spatial and temporal relationships between cytoskeleton alteration and morphological change in the cat LGN. Cross-sectional soma area and neurofilament labeling were examined in the LGN of kittens monocularly deprived at the peak of the critical period for durations that ranged from 1 day to 7 months. After 4 days of deprivation, neuron somata within deprived layers of the LGN were significantly smaller than those within non-deprived layers. This structural change was accompanied by a spatially coincident reduction in neurofilament immunopositive neurons that was likewise significant after 4 days of deprivation. Both anatomical effects reached close to their maximum by 10 days of deprivation. Results from this study demonstrate that alteration to the neuronal cytoskeleton is both spatially and temporally linked to the gross structural changes induced by monocular deprivation.

Temporal resolution is a basic property of the visual system and critically depends upon retinal temporal coding properties which are also of importance for directional coding. Whether the temporal coding properties for directional coding derive form inherent properties or critically depend upon the temporal coding mechanisms is unclear. Here, the influence of acetylcholine and GABA upon photopic temporal coding was investigated in goldfish, using flicker stimuli, in a behavioral and an electrophysiological (ERG) approach. The goldfish temporal resolution ability decreased from more than 90% correct choices at 20 Hz flicker frequency to about 65% at 45 Hz flicker frequency with a flicker fusion frequency of approximately 39 Hz. Blockade of GABAa-receptors reduced the flicker fusion frequency to about 23 Hz, not affecting temporal resolution below 20 Hz flicker frequency. Partial blockade of nicotinic acetylcholine receptors reduced the flicker fusion frequency slightly and lowered the temporal resolution ability in the 25–30 Hz range. Blockade of muscarinic acetylcholine receptors had a smaller effect than the partial blockade of nicotinic acetylcholine receptors. In ERG-recordings, blocking GABAa-receptors increased the a- and b-wave amplitude, induced a delay, an increase and a slow fall-off of the d-wave. Blocking GABAc-receptors had little effect. Blocking GABAa- or GABAa/c-receptors changed the temporal resolution, when expressed as a linear filter, from a 3rd degree filter with resonance to a low order low-pass filter with a low upper limit frequency. The temporal transfer properties were barely changed by blocking either nicotinic or muscarinic acteylcholine receptors, although ERG-components increased in amplitude to varying degrees. The behavioral and electrophysiological data indicate the important role of GABA for temporal processing but little involvement of the cholinergic system. It is proposed that the interaction of the GABAergic amacrine cell network and bipolar cells determines the gain of the retinal temporal coding in the upper frequency range.

The retina mainly contains ganglion, bipolar and photoreceptor cells which are distributed in the ganglion cell layer (GCL), inner nuclear layer (INL) and outer nuclear layer (ONL), respectively. Whether there is an age-related loss of these retinal cells remains not well understood. Cell density and the total number of cells were two commonly used measures to evaluate such age-related changes in most previous studies and provided controversial conclusions. The use of density measures as decisive data is problematic because the total area of the retina was expanded in aging, whereas the application of the total number of cells was limited for assessing ganglion cells. In this study, thus, we wanted to test whether there is an age-related cell loss in the GCL, INL and ONL and if so, whether such a loss is correlated to the convergence ratio of these cells. We used stereological procedures to quantify the total number of cells in the three retinal nuclear layers in six young and six aged Long-Evans rats. We found that during aging, the total volume of the retina remained unchanged, but the retina became thinner. There was no cell loss in each individual nuclear layer, and the ratio of the ONL to INL to GCL was preserved.

The number of L cones in the retina normally exceeds that of the M cones. Because normal color vision does not depend on the ratio of L- and M-photoreceptors, their signals must undergo an alteration in gain before being analyzed in the cortex. Previous studies have shown that this gain must take place before the cortex, but after the bipolar/amacrine cell layer of the retina. The aim of this study was to obtain topographical information about L- and M-cone activity at the ganglion cell layer using multifocal pattern electroretinography (mfPERG). A standard (black and white) stimulus was used, as well as stimuli modulating only the long wavelength-sensitive (L) or only the middle wavelength-sensitive (M) cones. The L:M ratio was calculated from the amplitude of the L-cone isolating mfPERG to that of the M-cone isolating mfPERG of 10 trichromats. Both the positive and negative components of the waveform were analyzed. Additional recordings of single cone modulated mfERGs were obtained from nine of the 10 subjects. We also recorded from one protanope and one deuteranope. The L:M cone amplitude ratios for both deflections of the mfPERG in the trichromats were around unity (medians 1.18 and 1.16, respectively) for the central 8° of retina. In the peripheral retina between 12.8° and 26°, this ratio increased to 1.42 for the positive component, and 1.37 for the negative component. The median L:M cone amplitude ratios for the mfPERG were higher and ranged between 1.00–2.78 in the central 8° and 1.29–2.78 in the periphery. The results indicate that a major gain adjustment of the retinal signals takes place at the ganglion cell level, and that the ratio is higher at eccentric locations than in the central retinal area.

Visual spatial attention has been described as a process that favors the processing of sensory information that falls into the “spotlight of attention.” Recent studies have provided support for an ability to split this attentional focus to selectively process spatially separate locations. Using functional magnetic resonance imaging, the signature for the presence of multiple spotlights is the presence of multiple retinotopically specific foci of activation in striate and extrastriate visual areas. We used this approach to investigate the presence of such separable activations as a function of the eccentricity of the spatial foci of attention. Visual stimuli consisted of letters and digits displayed in rapid serial visual presentation (RSVP). Five RSVP streams were presented simultaneously, one in the center of the visual field and one in each visual field quadrant. Subjects had to deploy their attention either to a single peripheral location or two non-contiguous regions performing a match-mismatch judgment. The results show that dividing attention leads to multiple spotlights of attention for central as well as more peripheral locations of the visual field. However, depending on the exact location and width of the attentional spotlights, resulting activation maps might reveal merged activation patterns even in the presence of distinct attentional spotlights.

Neighboring retinal ganglion cells often spike synchronously, but the possible function and mechanism of this synchrony is unclear. Recently, the strength of the fast correlation between ON-OFF directionally selective cells of the rabbit retina was shown to be stimulus dependent. Here, we extend that study, investigating stimulus-dependent correlation among multiple ganglion-cell classes, using multi-electrode recordings. Our results generalized those for directionally selective cells. All cell pairs exhibiting significant spike synchrony did it for an extended edge but rarely for full-field stimuli. The strength of this synchrony did not depend on the amplitude of the response and correlations could be present even when the cells' receptive fields did not overlap. In addition, correlations tended to be orientation selective in a manner predictable by the relative positions of the receptive fields. Finally, extended edges and full-field stimuli produced significantly greater and smaller correlations than predicted by chance respectively. We propose an amacrine-network model for the enhancement and depression of correlation. Such an apparently purposeful control of correlation adds evidence for retinal synchrony playing a functional role in vision.

Humans discriminate approaching objects from receding ones shortly after birth, and optic flow associated with self-motion may activate distinctive brain networks, including the human MT+ complex. We sought evidence for evoked brain activity that distinguished radial motion from other optic flow patterns, such as translation or rotation by recording steady-state visual evoked potentials (ssVEPs), in both adults and 4–6 month-old infants to direction-reversing optic flow patterns. In adults, radial flow evoked distinctive brain responses in both the time and frequency domains. Differences between expansion/contraction and both translation and rotation were especially strong in lateral channels (PO7 and PO8), and there was an asymmetry between responses to expansion and contraction. In contrast, infants' evoked response waveforms to all flow types were equivalent, and showed no evidence of the expansion/contraction asymmetry. Infants' responses were largest and most reliable for the translation patterns in which all dots moved in the same direction. This pattern of response is consistent with an account in which motion processing systems detecting locally uniform motion develop earlier than do systems specializing in complex, globally non-uniform patterns of motion, and with evidence suggesting that motion processing undergoes prolonged postnatal development.

The thalamic reticular nucleus (TRN) supplies an important inhibitory input to the dorsal thalamus. Previous studies in non-primate mammals have suggested that the visual sector of the TRN has a lateral division, which has connections with first-order (primary) sensory thalamic and cortical areas, and a medial division, which has connections with higher-order (association) thalamic and cortical areas. However, the question whether the primate TRN is segregated in the same manner is controversial. Here, we investigated the connections of the TRN in a New World primate, the marmoset (Callithrix jacchus). The topography of labeled cells and terminals was analyzed following iontophoretic injections of tracers into the primary visual cortex (V1) or the dorsal lateral geniculate nucleus (LGNd). The results show that rostroventral TRN, adjacent to the LGNd, is primarily connected with primary visual areas, while the most caudal parts of the TRN are associated with higher order visual thalamic areas. A small region of the TRN near the caudal pole of the LGNd (foveal representation) contains connections where first (lateral TRN) and higher order visual areas (medial TRN) overlap. Reciprocal connections between LGNd and TRN are topographically organized, so that a series of rostrocaudal injections within the LGNd labeled cells and terminals in the TRN in a pattern shaped like rostrocaudal overlapping “fish scales.” We propose that the dorsal areas of the TRN, adjacent to the top of the LGNd, represent the lower visual field (connected with medial LGNd), and the more ventral parts of the TRN contain a map representing the upper visual field (connected with lateral LGNd).