[Effect of sildenafil citrate on the cortical visual responses]. / Efecto del citrato de sildenafilo sobre las respuestas visuales corticales.

OBJECTIVE: To study the possible effect of oral sildenafil citrate on the response of cortical visual cells to visual stimulation. METHOD: Multiunit activity was recorded from cortical area V2 of one behaving monkey. Spatio-temporal receptive field maps were obtained by using a reverse cross correlation technique and white noise visual stimulation before and after oral administration of sildenafil citrate. RESULTS: The receptive field maps showed a reduction in response latency after administration of sildenafil citrate. CONCLUSIONS: Since sildenafil citrate is an inhibitor of retinal phosphodiesterase-6, an enhancement on light sensitivity in the photoreceptors is proposed as the cause of the observed reduction in response latency (Arch Soc Esp Oftalmol 2002; 77: 241-246).

Efecto del citrato de sildenafilo sobre las respuestas visuales corticales / Effect of sildenafil citrate on the cortical visual responses

Objetivo: Estudiar el posible efecto del citrato de sildenafilo oral sobre la respuesta de las células corticales visuales a la estimulación visual. Método: Se registró la actividad multiunitaria del área V2 en un mono activo. Se obtuvieron mapas espacio-temporales de los campos receptores usando una técnica de correlación cruzada inversa y estimulación visual con ruido blanco antes y después de la administración de citrato de sildenafilo. Resultados: Los mapas de los campos receptores demostraron una disminución de la latencia de respuesta después de la administración del citrato de sildenafilo. Conclusiones: Dado que el citrato de sildenafilo es un inhibidor de la fosfodiesterasa-6 presente en la retina, se propone que la causa de la disminución de latencia puede ser producida por un incremento de sensibilidad a la luz en los fotorreceptores (AU)

Receptive field organization of disparity-sensitive cells in Macaque medial superior temporal cortex.

Binocular disparities are crucial for building an accurate three-dimensional representation of the peripersonal environment in a viewer-centred frame of reference. Previous studies have shown that visual cells of the medial superior temporal cortex (MST) have large receptive fields and that they are sensitive to disparities present in large surfaces. By using a reverse cross-correlation technique in this study we tested 175 disparity-sensitive units recorded from MST in the awake Macaca mulatta monkey to determine if these large receptive fields are homogeneous in terms of disparity sensitivity. We found that the receptive fields of 50 cells (50 out of 175, 29%) showed subregions with specific disparity sensitivity. These subregions presented eccentricities from 0.8 to 22.3 degrees and their sizes varied from 1.6 to 15.3 degrees 2. This particular receptive field organization represents a suitable mechanism for encoding the location of small objects within our peripersonal space.

Binocular interaction and sensitivity to horizontal disparity in visual cortex in the awake monkey.

We evaluated the binocular interaction and horizontal disparity sensitivity in neurons recorded from macaque visual cortex. Neurons from V1 of three awake Macaca mulatta monkeys were isolated by means of extracellular recording and tested for disparity sensitivity with dynamic random dot stereograms. Neurons sensitive to horizontal disparities were stimulated both monocularly and binocularly with flashing bars and their responses quantified. ANOVA and regression tests were used for data analysis. Sixty-six cells out of 185 (66/185, 36%) showed sensitivity to horizontal disparity. Disparity sensitive cells were grouped into near (25/66, 38%), tuned inhibitory (16/66, 24%), far (13/66, 20%) and tuned excitatory (12/66, 18%). Receptive fields of tuned cells were located more centrally in the visual field than those of near and far cells. The binocular interaction in tuned inhibitory cells increased linearly along with ocular unbalance. Most of tuned excitatory cells (10/12, 83%) showed facilitatory binocular interaction, characterized by a stronger response to binocular stimulation than to the stimulation of the dominant eye. On the contrary, most of tuned inhibitory cells (14/16, 88%) showed suppressory binocular interaction, characterized by a weaker response to binocular stimulation than to the stimulation of the dominant eye. Near and far cells showed both types of interaction in similar percentages. The binocular response showed a linear relationship with the sum of both monocular responses in tuned excitatory, tuned inhibitory and near cells, but not in far cells. Sensitivity to horizontal disparity may be a result of facilitatory and suppressive interactions between left and right inputs.

Response latencies to visual stimulation and disparity sensitivity in single cells of the awake Macaca mulatta visual cortex.

The onset response latencies to dynamic random dot figures (solid figures) and dynamic random dot stereograms were measured in single units recorded from areas V1 and V2 of two awake Macaca mulatta monkeys. We studied 56 cells, 39 from V1 and 17 from V2. In 14 disparity sensitive and 13 disparity unsensitive cells from V1 the median latencies to solid figures were 59.8 and 73.6 ms, respectively, which were statistically different. In 26 disparity sensitive cells from V1 and 17 from V2 the median latencies to stereofigures were 85.6 and 97.9 ms, respectively, which were statistically different. These results indicate that V1 disparity sensitive cells may have shorter integration time than disparity unsensitive cells and that there is a transferring delay for disparity information between areas V1 and V2.

Interocular temporal delay sensitivity in the visual cortex of the awake monkey.

Due to the separation of the eyes, temporal retinal disparities are created during binocular stimulation and they have been proposed to be the basis of several stereo-visual effects. This paper studies the sensitivity of cortical neurons from area V1 to interocular temporal delay in the awake monkey (Macaca mulatta). Forty-four cells were included in this study. Temporal delay sensitivity was observed in 59% of them. About half of these temporal-delay-sensitive cells were also sensitive to the stimulation sequence of the eyes. The cells that preferred one eye to be stimulated first were termed asymmetrical (46%); those which were not sensitive to the eye sequence of stimulation were termed symmetrical (54%). No clear differences were observed in the distribution of delay-sensitive cells according to their eye dominance. Fifty-six percent of balanced cells and 65% of unbalanced cells were sensitive to interocular delay. These data underline the importance of temporal cues for depth perception.