Unihemispheric memory in pigeons-knowledge, the left hemisphere is reluctant to share

Abstract

In the present study, pigeons were trained under binocular conditions in a conditional visual discrimination in which they were faced with two identical patterns arranged one above the other. In half of these stimulus pairs the animals had to peck the upper pattern, in the other half the lower one. Although only six pairs of stimuli were used, only four out of eight birds reached learning criterion. These animals needed up to 6 months of training with 3050 to 6650 trails. Then, the experiment proceeded under identical conditions using eye caps restricting vision alternatively to the left or the right eye. These monocular tests revealed that three out of four birds virtually had no knowledge of the task contingencies using their left eye (right hemisphere). Again, several thousand trials were needed to train the birds to criterion with their left eye, while they were simultaneously discriminating at a very high level with their right. These results show that memories on task contingencies are stored unihemispherically in the visually dominant left side despite extensive training with both eyes open. Additionally, it can be concluded that the subsequent read-out by the 'naive' hemisphere can be largely restricted, resulting in a 'natural split-brain' like situation in birds. It is speculated that the absence of a corpus callosum in birds restricts interhemispheric transfer of information. #

The study of hemispheric specialization for categorical and coordinate spatial relations in animals

“…This memory study suggests that visual engrams learned binocularly during training were stored, at least in part, unilaterally in the left hemisphere, although both eyes had equal access to the patterns during acquisition. Similarly Nottelmann, Wohlschläger, and Güntürkün (2002) showed that patterns learned by RE/LH can 'stay' in the left hemisphere without transfer to the other side. Thus, it is likely that the avian left hemisphere stores large amounts of acquired pattern information to which the right hemisphere has only limited access.…”

Asymmetrical Modes of Visual Bottom-Up and Top-Down Integration in the Thalamic Nucleus Rotundus of Pigeons

“…Because left rotundal lesions have a significantly higher impact on visual accuracy than those on the right (Gün-türkün and Hahmann, 1999), and because the right eye of the pigeon is superior in discriminating visual patterns in the frontal visual field (Güntürkün and Kesch, 1987;Güntürkün and Kischkel, 1992;Nottelmann et al, 2002), the longer activity durations of left-rotundal bottom-up neurons might indeed be related to the superiority of the left tectofugal system in processing of various stimulus properties.…”

Lateralization of the Avian Magnetic Compass: Analysis of Its Early Plasticity

“…This is contrary to the results of most visual discriminations tasks, which found a more efficient transfer of visual discrimination from the left eye to the right eye [43,51,52]. This is assumed to be due to the more bilateral left hemispheric visual representation in the tectofugal pathway that enables the right eye system to swiftly access left eye information [38].…”

“…Learning visual discrimination tasks takes longer with the left eye/right hemisphere than with the right eye, and in several cases of bilateral learning, the right hemisphere did not share the knowledge, but had to be trained separately (e.g., [51,52]; for review, see [53]). It is unclear whether the longer time required for the left eye/right hemisphere system to adjust to higher magnetic intensities represents a parallel case.…”