Functional cerebral asymmetries, once thought to be exclusively human, are now accepted to be a widespread principle of brain organization in vertebrates [1]. The prevalence of lateralization makes it likely that it has some major advantage. Until now, however, conclusive evidence has been lacking. To analyze the relation between the extent of cerebral asymmetry and the degree of performance in visual foraging, we studied grain-grit discrimination success in pigeons, a species with a left hemisphere dominance for visual object processing [2,3]. The birds performed the task under left-eye, right-eye or binocular seeing conditions. In most animals, right-eye seeing was superior to left-eye seeing performance, and binocular performance was higher than each monocular level. The absolute difference between left- and right-eye levels was defined as a measure for the degree of visual asymmetry. Animals with higher asymmetries were more successful in discriminating grain from grit under binocular conditions. This shows that an increase in visual asymmetry enhances success in visually guided foraging. Possibly, asymmetries of the pigeon's visual system increase the computational speed of object recognition processes by concentrating them into one hemisphere while preventing the other side of the brain from initiating conflicting search sequences of its own.

The reported activity was modulated by the temporal devaluation of the anticipated reward in addition to reward amount. Our findings contribute to the understanding of neuropathologies such as drug addiction, pathological gambling, frontal lobe syndrome, and attention-deficit disorders, which are characterized by inappropriate temporal discounting and increased impulsiveness.

Working memory, the ability to temporarily store and manipulate currently relevant information, is required for most cognitive faculties. In humans and other mammals, the prefrontal cortex (PFC) provides the underlying neural network for these processes. Within the PFC, working memory neurons display sustained elevated activity while holding active an internal representation of the relevant stimulus during its physical absence or retaining a motor plan for the forthcoming response. Working memory, however, is not a hallmark of higher vertebrates endowed with a neocortex. Birds also master complex cognitive problems invoking working memory, but they lack a laminated neocortex. Behavioral studies in pigeons show that the neostriatum caudolaterale (NCL) plays a central role in executive functions, such as working memory and response control. For neurons in the NCL of pigeons, we show activity changes during the delay of a working memory task, which were similar to those observed in PFC neurons and were related to the successful holding of information in memory and to the subsequent behavior. Thus, although the anatomical and morphological structure of the neuronal substrate in birds is radically different from the mammalian neocortical architecture, the neuronal mechanisms evolved to master equivalent cognitive demands seem to be very similar.

In birds, visual object discrimination performance is lateralized with a dominance of the right eye/left hemisphere. This asymmetry is induced by embryonic light stimulation. However, visually guided behavior, even during simple object distinction tasks, is composed of different behavioral and neural modules. Therefore, the aim of the present study was to test whether all neural subsystems involved in visual discriminations are lateralized in a similar way after prehatch visual stimulation. To examine this question, two behavioral paradigms were used which reveal complementary aspects of visually guided behavior. The first was the grain Á/grit discrimination task in which no left Á/right differences in the number of pecks, but significant differences in the number of grains can be found. Therefore, grain Á/grit discrimination reveals visuoperceptual performance but not visuomotor speed. The contrary seems to be the case for a successive pattern discrimination with a VR32 schedule. Here, the hemispheres do not differ with respect to discrimination accuracy but with regard to the number of pecks emitted. Thus, successive pattern discrimination with lean VR schedules reveals hemispheric differences in visuomotor speed without testing visuoperceptual performance. Using these two paradigms a group of light and a group of dark incubated pigeons were tested. The results show that dark incubated birds evinced no asymmetry in any measure while light incubated ones were right-eye dominant in both variables. However, light incubation induced a visual left hemispheric dominance by modulating two different processes, a left-hemispheric increase of visuoperceptual processes; and a right-hemispheric decrease for visuomotor speed. Taken together these data show that embryonic light stimulation elicits visual lateralization by differently modulating visuoperceptual and visuomotor systems in both hemispheres. #

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