Light‐dependent development of the tectorotundal projection in pigeons

Abstract

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Steroid hormones influence light‐dependent development of visual projections to the forebrain (Commentary on Letzner et al., 2020)

“…The asymmetry develops in the midline‐crossing neuronal axons projecting from each optic tectum to its contralateral nucleus rotundus, and it develops in response to light exposure of the embryo. This finding invites comparison to development of visual asymmetry in precocial species, as indeed discussed by Letzner et al (2020). Such comparisons are particularly useful if they reveal differences in visual development.…”

“…As Letzner et al (2020) mentioned, development of asymmetry of the thalamofugal system in the chick embryo is modulated by sex hormone levels. The first suggestion that this may be so came from evidence of the thalamofugal asymmetry being less marked in females than in males (Rajendra & Rogers, 1993; Rogers & Deng, 2005), seen also as a lesser strength of asymmetry of visual behaviour in females than in males (e.g.…”

“…In their important paper, Letzner et al (2020) have reported convincing evidence of asymmetry in the tectofugal projections of the pigeon, an altricial species. The asymmetry develops in the midline‐crossing neuronal axons projecting from each optic tectum to its contralateral nucleus rotundus, and it develops in response to light exposure of the embryo.…”

“…In the pigeon, asymmetry develops by loss of projections from the light‐stimulated, left tectum to the right nucleus rotundus (Letzner et al, 2020), whereas in the chicken it develops by growth of projections from the light‐stimulated left thalamus to the right hyperpallium of the forebrain (Rogers, Adret, & Bolden, 1993; Figure 1). In chicks, we know that the sensitive period for asymmetrical development of the thalamofugal projections is limited to a brief period just before hatching and, once established, is not influenced by rearing in the dark or light after hatching (Rogers & Bolden, 1991; Rogers & Deng, 2005).…”

Brain Lateralization and Cognitive Capacity

“…As Xiao and Güntürkün [116] argue, the neurones in this commissure are largely excitatory and, hence, the left side should step up activity of the right side, thereby acting as a balance against the dominant role of the left hemisphere in colour discrimination. To understand this more completely, it is necessary to know that, in pigeons, the left hemisphere receives visual inputs from both eyes (the tectofugal visual system), whereas the right hemisphere receives inputs mostly from the left eye [117,118]. In domestic chicks, it is the other visual system (the thalamofugal system) that is lateralized: in this visual system, the Wulst region of the right hemisphere receives strong inputs from both eyes, whereas the left Wulst receives input mainly from the right eye [79].…”