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

2008

Phil. Trans. R. Soc. B

Brain asymmetries are a widespread phenomenon among vertebrates and show a common behavioural pattern. The right hemisphere mediates more emotional and instinctive reactions, while the left hemisphere deals with elaborated experience-based behaviours. In order to achieve a lateralized behaviour, each hemisphere needs different information and therefore different representations of the world. However, how these representations are accomplished within the brain is still unknown. Based on the pigeon's visual system, we present experimental evidence that lateralized behaviour is the result of the interaction between the subtelencephalic ascending input directing more bilateral visual information towards the left hemisphere and the asymmetrically organized descending telencephalic influence on the tecto-tectal balance. Both the bilateral representation and the forebrain-modulated information processing might explain the left hemispheric dominance for complex learning and discrimination tasks.

Section: Asymmetries Of Ascending Descending and Commissural Systemsmentioning

confidence: 80%

Ascending and descending mechanisms of visual lateralization in pigeons

Valencia-Alfonso

Verhaal

2008

Phil. Trans. R. Soc. B

“…Electrophysiological data show that the left as well as the right nucleus rotundus are more strongly affected by the left visual wulst than by the right one [4,22]. It is conceivable that such a weak right hemispheric modulation is the result of suppressive subtelencephalic interactions.…”

Section: Introductionmentioning

confidence: 99%

A morphological study of the nucleus subpretectalis of the pigeon

Freund

Brain Research Bulletin

Manns

2008

In pigeons, the tectofugal system is functionally as well as structurally lateralized. So for example the right nucleus rotundus is less modulated by right forebrain influences than the left nucleus rotundus by the left ones. This functional lateralization pattern may depend on a dynamic balance between left and right tectal processing. Apart from inhibitory interactions at tectal level, suppressive influences might directly affect rotundal neurons by GABAergic input from a cluster of nuclei, the bed nuclei of the tecto-thalamic tract. A major afferent of these nuclei is the side branch of the tectorotundal projection which is of bilateral origin and which is involved in the regulation of ipsilateral as well as bilateral visual processing. Hence, an important role of the bed nuclei could be the interhemispheric communication and in turn the mediation of functional asymmetries. In a first step to unravel asymmetric influences of these nuclei, the present study investigated if the largest of the bed nuclei, the nucleus subpretectalis displays morphological asymmetries in the pigeon. We found that the nucleus subpretectalis in fact exhibits asymmetric cell sizes with larger cell bodies on the left side. This asymmetrical pattern was not present in dark-incubated animals indicating that cell size asymmetries within nucleus subpretectalis are induced by asymmetric photic stimulation during embryonic development.

“…Since pigeons raised under these conditions usually show a normal visual asymmetry, it is evident that these large numbers of very short light pulses are sufficient to provoke anatomical asymmetries. Since a recent study showed the visual Wulst to exert asymmetrical control over the tectofugal system (Folta et al, 2004), it is likely, that asymmetrical light input induces asymmetries both in the tectofugal and in the thalamofugal system.…”

Section: Discussionmentioning

confidence: 99%

“…Apart from tectal (Güntürkün, 1997b;Manns and Güntürkün, 1999b;Skiba et al, 2002) and rotundal (Manns and Güntürkün, 1999a) cell size differences, the tectorotundal projection is asymmetrically organised with more tectal fibres ascending from the right tectum to the left rotundus than vice versa (Güntürkün et al, 1998). Additionally, top-down projections from the Wulst modulate tectofugal processing in an asymmetrical way (Folta et al, 2004).…”

Section: Introductionmentioning

confidence: 99%

“Let There be Light!” pigeon eggs are regularly exposed to light during breeding

Buschmann

Manns

2006

Behavioural Processes

Light stimulation before hatching initiates the emergence of avian visual lateralisation. Since several studies show that birds benefit from being lateralised, we can conjecture that their clutch is being exposed to light during breeding. We tested this assumption in pigeons with a semi-natural setup where the animals were systematically recorded using a movement detection system throughout their breeding period. The results show that pigeon pairs perform their relieves in a regular way by abandoning their clutch for a mean of about 55 s at approximately every 43 min. Thus, the developing visual pathways are repetitively stimulated by light for cumulatively over 3 h before the breeding period ends. It becomes apparent that both the duration as well as the repetitions of light stimulation play a crucial role in the onset of visual asymmetry.