Fluorescent tracing techniques were used to reveal a sex difference in the organization of the visual thalamo-hyperpallial projections of young chicks (Adret & Rogers 1989). In male chicks, a stronger projection connecting one side of the thalamus to both hyperpallia was found to arise from the left nucleus dorsolateralis anterior thalami (DLA) than from the right DLA. No such structural asymmetry was found in females. The finding correlates with sex differences in the visually guided behavior of chicks tested with the right or left eye occluded (Rogers & Adret 1993). The work was performed in Dr. Lesley J. Rogers laboratory.

Left and right sides of the chick thalamus

Photo: University of New England

Photomicrographs of retrogradely-labelled cells in the rostral thalamus following injection of Fluorogold (FG) into the left hyperpallium (visual Wulst) and True Blue (TB) into the right. Note the higher densities of FG-labelled cells (bright cells) on the side ipsilateral to the injection side. These are located in the ventro-medial region of the nucleus dorsolateralis anterior thalami, pars lateralis (DLLv). On the side contralateral to the injection site, fewer FG-labelled cells are distributed in a dorsolateral region of DLL (DLLd). The distribution of the TB-labelled cells shows a reverse pattern with higher densities of labeled cells in the DLLv on the side ipsilateral to the injection site and fewer cells labeled in the DLLd on the side contralateral to the injection site.

With permission from Brain Research


Diagrams illustrating two theoretical models that would account for the structural asymmetry in male chicks. The source of the asymmetry may be in the contralateral projections (A) or in the ipsilateral projections (B).

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Adret P. (1989) Behavioural and neural aspects of visual lateralization in the chick. Ph.D Thesis, University of New England, Australia

Adret P. & Rogers L.J. (1989) Sex difference in the visual projections of young chicks: a quantitative study of the thalamofugal pathway. Brain Research, 478: 59-73

Rogers L.J., Adret P. & Bolden S.W. (1993) Organisation of the thalamofugal visual projections in chick embryos, and a sex difference in light-stimulated development. Experimental Brain Research, 97: 110-114

Rogers L.J. & Adret P. (1993) Developmental mechanisms of lateralization. In: Vision, Brain and Behavior in Birds (H.P. Zeigler, H.J.Bischof Eds.) pp. 227-242, MIT Press


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