Visual intensity and pattern discrimination after lesions of the thalamofugal visual pathway in pigeons (original) (raw)
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Near-field acuity after visual system lesions in pigeons. I. Thalamus
Behavioural Brain Research, 1984
Key words. visual acuity -lesions -thalamus -nucleus rotundus -nucleus opticus principalis thalami -animal psychophysics -pigeon Visual acuity determinations were made for 14 pigeons trained to discriminate high-contrast, square-wave gratings of successively higher spatial frequencies from blank stimuli of equal average luminances. The stimuli were presented according to the method of constant stimuli. Video-taped motion pictures of the key-pecking response provided a measure of the cornea-to-stimulus distance. The preoperative results indicated that the mean minimal-separable visual angle was 2.3 min (range 1.6-3.6) under conditions of photopic adaptation with the stimulus luminance at 70 cd/m z. When performance was stable, bilateral electrolytic lesions were placed in: (1) nucleus rotundus (RT), (2) nucleus opticus principalis thalami (the OPT complex); and (3) RT plus the OPT complex. Lesions confined to the OPT complex did not impair resolution threshold while lesions confined to the nucleus rotundus produced permanent threshold elevations. When the destruction of OPT and RT was combined, the deficit was more severe. The results indicated that the integrity of the tectofugal pathway of the pigeon is required for normal perfbrmance of spatial frequency discrimination near threshold. These observations suggest that nuclei containing neurons with wide receptive fields are capable of processing visual information with fine spatial detail.
Near-field acuity changes after visual system lesions in pigeons. II. Telencephalon
Behavioural Brain Research, 1984
Pigeons were trained to perform in a psychophysical task that measured their minimum-separable visual acuity. After their performance stabilized, lesions were made in telencephalic components of the visual system. In one group, lesions were made in the ectostriatum, which is the teleneephalic target of the tectofugal visual pathway. These cases showed severe to moderate losses of acuity. The magnitude of the loss was correlated with the extent of ectostriatal damage. In another group, lesions were made in the visual Wulst, a portion of which receives the ascending fibers of the thalamofugal visual pathway. Within this group, only lesions that were large and included all components of the visual Wulst were effective in decreasing visual acuity to a moderate degree. A partial correlation analysis indicated that the components of the visual Wulst that were responsible for the acuity changes were the accessory hyperstriatum and the hyperstriatum ventrale. However, lesions that were generally confined to these regions alone were ineffective. Also ineffective were lesions of the granular components of the visual Wulst, which receive the ascending thalamofugal fibers. The results raise questions about the presumed roles of the tectofugal pathway as a background-vision mechanism and the thalamofugal pathway as a fine-detail vision mechanism.
Lateral telencephalic lesions affect visual discriminations in pigeons
Behavioural Brain Research, 1984
The importance of the lateral telencephalon of the pigeon for visual performance was examined. Lesions in this area markedly impaired both the acquisition and the retention of instrumentally learned hue, intensity and pattern discriminations. Comparable lesions of the thalamofugal visual projection in the dorsoanterior telencephalon did not have an appreciable effect. Laterally lesioned pigeons showed only a minor, non-significant impairment in an instrumental auditory discrimination task. These results generally agree with findings of other authors on domestic chicks but disagree with previous work on pigeons. The visual discrimination performance of laterally lesioned subjects improved gradually over the course of days and weeks without specific experience being necessary, and after 3 months the recovery was virtually complete. The effect of lateral telencephalic lesions is discussed in connection with known visual projections within the avian endbrain and their relationship with other functional systems.
Behavioural Brain Research, 1981
The monocular and binocular performance of pigeons with bilateral, unilateral or sham lesions in the telencephalic Wulst was tested with visual discrimination tasks. Unilateral lesions yielded a marked deficit when the animals could only use the eye contralateral to the lesion. Otherwise the accomplishments of the ablated animals did not differ from that of the controls. The reciprocal inhibition of symmetrical visual brain stem centers is thought to have been unbalanced through the one-sided interruption of a known pathway descending from the Wulst.
Brightness and pattern discrimination deficits in the pigeon after lesions of nucleus rotundus
Experimental Brain Research, 1966
Pigeons were trained to peck one of two discs on which were projected visual stimuli. One brightness and three pattern discrimination problems were presented. Correct responses were rewarded with grain. After the discriminations were learned, bilateral electrolytic lesions were placed stereotaxically in 13 birds, and sham operations were performed in three birds. Those birds with lesions in nucleus rotundus demonstrated severe deficits in performance of the visual discriminations. Following prolonged post-operative retraining, a gradual return to pre-operative levels of performance was observed. The post-operative relearning proceeded at a much slower rate than the pre-operative learning. Control birds with lesions in dorsal thalamus, teleneephalon and meseneephalon, or sham operations, all showed considerable post-operative savings. On the basis of the anatomical, eleetrophysiologieal and behavioral data available at present, nucleus rotundns appears to be a thalamie relay of visual information from optic tectum to telencephalon in the bird.
Visual Neuroscience, 2014
Earlier, we reported that nucleus rotundus (Rt) together with its inhibitory complex, nucleus subpretectalis/interstitiopretecto-subpretectalis (SP/IPS), had signifi cantly higher activity in pigeons performing fi gure-ground discrimination than in the control group that did not perform any visual discriminations. In contrast, color discrimination produced signifi cantly higher activity than control in the Rt but not in the SP/IPS. Finally, shape discrimination produced signifi cantly lower activity than control in both the Rt and the SP/IPS. In this study, we trained pigeons to simultaneously perform three visual discriminations (fi gure-ground, color, and shape) using the same stimulus displays. When birds learned to perform all three tasks concurrently at high levels of accuracy, we conducted bilateral chemical lesions of the SP/IPS. After a period of recovery, the birds were retrained on the same tasks to evaluate the effect of lesions on maintenance of these discriminations. We found that the lesions of the SP/IPS had no effect on color or shape discrimination and that they signifi cantly impaired fi gure-ground discrimination. Together with our earlier data, these results suggest that the nucleus Rt and the SP/IPS are the key structures involved in fi gureground discrimination. These results also imply that thalamic processing is critical for fi gure-ground segregation in avian brain.
The Journal of Neuroscience, 2004
The aim of this study was to separate bottom-up and top-down influences within cerebral asymmetries. This was studied in the lateralized visual system of pigeons by recording from single units of the left and right diencephalic nucleus rotundus of the tectofugal pathway while visually stimulating the ipsilateral and/or contralateral eye. Analyses of response latencies revealed rotundal neurons with short and/or late response components. Cells with short latencies very likely represent bottom-up neurons participating in the ascending retinotectorotundal system. Because lidocaine injections into the visual Wulst produced a significant reduction of late response components only, neurons with long latencies were probably activated via a top-down telencephalotectorotundal system. The distribution and response characteristics of bottom-up and top-down neurons provided insight into several asymmetries of ascending and descending pathways. Asymmetries of the ascending retinotectorotundal sy...
Brain Research Bulletin, 2006
The nucleus ventrolateralis thalami (VLT) in pigeons receives direct retinal and forebrain projections and has reciprocal connections with the optic tectum. Although VLT is a component of the avian visual system, no study directly examined its connections or its cellular response characteristics. We, therefore, recorded from single units in the pigeon's VLT while visually stimulating the ipsi-and/or contralateral eye. In addition, tracing experiments were conducted to investigate its afferent connections. Electrophysiologically, we discovered three types of neurons, two of which were probably activated via a top-down telencephalotectal system (latencies > 100 ms). Type I neurons responded to uni-and bilateral and type II neurons exclusively to bilateral stimulation. Type III neurons were probably activated by retinal or retinotectal input (latencies < 27 ms) and responded to contra-and bilateral stimulation. Retrograde tracer injections into the VLT revealed an ipsilateral forebrain input from the visual Wulst, from subregions of the arcopallium, and bilateral afferents from the optic tectum. Most intriguing was the direct connection between the VLTs of both hemispheres. We suggest that the avian VLT is part of a system that integrates visuomotor processes which are controlled by both forebrain hemispheres and that VLT contributes to descending tectomotor mechanisms.