Functional Segregation of the Entopallium in Pigeons

Abstract

In birds, the entopallium is the primary telencephalic target of the major visual ascending route called the tectofugal pathway. Often functionally compared to the primate geniculo-striate pathway and its subsequent telencephalic (cortical) regions, the latter processes visual information in a parallel fashion in terms of anatomy, physiology, and function. Little is known, however, about the exact mechanism of whether or how information is segregated or integrated in the avian tectofugal pathway including the telencephalon. Testing four pigeons, we examined whether or not color, form, and motion information is selectively processed by different portions of the entopallium. Each learned three distinct visual tasks requiring discrimination of different combinations of color, form and motion cues. After learning and pre-lesion testing, two pigeons received lesions to the anterior portion of the entopallium and two received lesions to the posterior entopallium. During post-lesion testing the pigeons with anterior lesions exhibited significant deficits in those tasks most dependent on color and form discrimination, but showed no deficit on a task that had involved discriminating among forms that were moving. Pigeons with posterior lesions showed a different pattern of deficits, exhibiting significant reductions in discriminating both moving and static forms, but little or no deficits in color discrimination. These divergent profiles of effects for each lesion suggest there is a functional segregation of visual information processing in the pigeon telencephalon. This indicates a convergence between birds and primates regarding the parallel processing and separation of information within their phylogenetically distinct major visual pathways.

Keywords: birds; lesion; visual system.

Figure 1

Representative examples of the stimuli tested in the three different tasks. The top row shows example of shape and color-based texture displays used in the localization task. The variably-located target could be made from different combinations of eight colors and eight shapes. The middle row shows examples of the two shapes tested in the dynamic shape discrimination task. On each trial, a single shape was randomly located in different random orientations on the monitor. The bottom row shows the set of 16 two-shape compounds used in the where/what task. For each bird, a different stimulus was designated correct. When paired with different foils, the task required the pigeon to discriminate the identity and relative locations of the shapes.

Figure 2

Transverse sections through the telencephalon of #4H in the anterior entopallial lesion group and #1A in the posterior entopallial lesion group. The numbers A11.0 – A8.5 indicate the anterior-posterior coordinates. Black areas represent regions of necrosis/gliosis. BG: basal ganglia; E: entopallium; HA: hyperpallium apicale; M: mesopallium, N: nidopallium.

Figure 3

Shown are the pre- and post-lesion color and shape target localization accuracies in the texture-based localization task for each type of lesion. The bars show average performance in each condition, while the individual symbols show the results for each pigeon individually.

Figure 4

Shown are the pre- and post-lesion cumulative reaction time distributions in two different tasks. The top row shows the reaction times for the texture localization task, while the bottom row shows comparable data from the where/what task.

Figure 5

Shown are the pre- and post-lesion discrimination ratios in the dynamic shape discrimination for each type of lesion. The bars show average performance in each condition, while the individual symbols show the results for each pigeon individually. The dashed line shows chance discrimination.

Figure 6

Shown are the pre- and post-lesion choice accuracies in the where/what discrimination task for each type of lesion. The bars show average performance, while the individual symbols show the results for each pigeon individually. The dashed line shows chance discrimination.