Two pupillo-constrictor areas in the occipital cortex of the cat

Neurons in the nucleus praetectalis olivaris (NPO) were antidromically identified by electrical stimulation of the nucleus of Edinger-Westphal (EW), the location of preganglionic pupilloconstrictor motoneurons. Electrical stimulation within the NPO leads to bilateral pupil constriction. Single neurons recorded in the NPO respond tonically to light stimuli, and their discharge frequency increases linearly with logarithmic increase in light intensity. This characteristic identifies NPO neurons as luminance detectors. They have large receptive fields mostly lying in the upper and contralateral quadrant of the visual field.Cats with impaired binocular vision show a significantly reduced binocular summation of the pupillary light reflex (BSP), i.e. the increase of pupil constriction during binocular illumination when compared to monocular illumination is less than in normal animals. The investigation of ocular dominance and subthreshold binocular interactions in the NPO of normal and innate microstrabismic cats revealed two possible mechanisms for BSP and its reduction in strabismic subjects. First, the percentage of neurons increasing their discharge rate by illuminating either eye is significantly reduced in the NPO of innate microstrabismic cats (6.6%) when compared to normal cats (22% of all neurons tested). Second, in most NPO neurons of normal cats the subthreshold influence of the ipsilateral eye leads to an increase in neuronal activity during binocular stimulation when compared to monocular stimulation of the contralateral eye (binocular summation). The subthreshold influence of the ipsilateral eye in most NPO neurons of microstrabismic cats, however, is inhibitory, i.e. the neuronal discharge rate during binocular stimulation is decreased when compared to monocular stimulation of the contralateral eye (binocular inhibition). However, there is no significant correlation between BSP and binocularity in the NPO in individual animals. This suggests that BSP may be additionally influenced by visual structures other than NPO.

Section: Introductionmentioning

confidence: 87%

Section: Introductionmentioning

confidence: 94%

The pupillary light reflex in normal and innate microstrabismic cats, I: Behavior and receptive-field analysis in the nucleus praetectalis olivaris

Distler

Hoffmann

1989

“…Electrical stimulation of certain visual cortical areas revealed a cortical influence upon constriction of the pupil in various mammals (rabbit: Imai et al, 1984;Inoue & Kiribuchi, 1985; cat: Barris, 1936;Shoumura et al, 1982;monkey: Jampel, 1960). However, it was suggested that this cortical influence would not concern the pupillary light reflex, but rather the pupil constriction which occurs during the near reflex.…”

Section: Introductionmentioning

confidence: 99%

The pupillary light reflex in normal and innate microstrabismic cats, II: Retinal and cortical input to the nucleus praetectalis olivaris

Distler

Hoffmann

1989

The anatomical substrate of the pupillary light reflex was investigated in normal and innate microstrabismic cats using anatomical methods as well as electrical stimulation. The bilateral retinal input to the nucleus praetectalis olivaris (NPO), the pretectal relay station in the subcortical pupilloconstrictor pathway, was identified to come from the ventral retina where the upper visual field is represented. Orthodromic electrical stimulation revealed that retinal information is transmitted to on-tonic neurons in the NPO mainly via slowly conducting axons probably originating from W- and X-type retinal ganglion cells.For the first time, a direct cortical input to on-tonic neurons in the NPO could be demonstrated. This cortical input originates from caudolateral parts of the occipital cortex. Putative input structures are those subdivisions of areas 19 and 20a where the upper part of the visual field is represented.A direct, predominantly contralateral projection with a weak ipsilateral component from NPO to the nucleus of Edinger-Westphal, and an interhemispheric connection between the NPOs could be demonstrated. With respect to the anatomical connections as described in this study, no differences between normal and innate microstrabismic cats could be found.The results are discussed with respect to the binocular summation of the pupillary light reflex and its reduction in subjects with impaired binocular vision.

“…Both of these brain regions contain neurons with large receptive fields (Benedek et al, 1983;Chalupa et al, 1983;Godfraind et al, 1972;Spear & Bauman, 1975;Palmer et al, 1978;Zumbroich et al, 1986), and both have rich connections with area 20a and area 20b (Cavada & Reinoso-Suarez, 1983;Kuchiiwa et al, 1984;Raczkowski & Rosenquist, 1983;Sherk, 1986;Symonds & Rosenquist, 1984). Even so, it is of interest to note that on the efferent side, electrical stimulation experiments have shown that the region surrounding the confluence of the transition zones is involved in constriction of the pupil (Barris, 1936;Shoumura et al, 1982;Wang et al, 1931). This stripe is thought to be a marker in areas 17 and 18 for the termination of fibers arising from layers A, Al and C in the lateral geniculate nucleus and from the medial interlaminar nucleus.…”

Section: Discussionmentioning

confidence: 99%

“…This stripe is thought to be a marker in areas 17 and 18 for the termination of fibers arising from layers A, Al and C in the lateral geniculate nucleus and from the medial interlaminar nucleus. Support for this idea is provided by the known connections with the parts of the lateral suprasylvian regions (Shoumura et al, 1982) shown by electrical stimulation experiments to evoke lens accommodation (Bando et al, 1981). Exactly how the inputs from the different sources interact in the creation of large receptive fields is unclear.…”

Section: Discussionmentioning

confidence: 99%

Receptive fields of neurons at the confluence of cerebral cortical areas 17, 18, 20 a, and 20 b in the cat

Payne

Siwek

1990

The activity of neurons was recorded extracellularly at the junction of visual cortical areas 17, 18, 20a, and 20b in the cat. The receptive fields of these neurons were striking for their size, which ranged from a diameter of more than 40 deg of visual angle to the complete visual field of the contralateral eye. It is speculated that these large receptive fields may be generated by perturbations in the individual maps as the four areas merge together.