Sex-dependent structural asymmetry of the medial habenular nucleus of the chicken brain.
ABSTRACT An investigation of structural asymmetry in the avian brain was conducted on the epithalamic medial habenular nucleus of the chicken. Twelve male and ten female two-day-old chickens were used for a morphometric evaluation of asymmetry. The medial habenular nucleus was measured from paraffin-wax-embedded, 8 micron-thick sections by use of a semiautomatic image analyser. The volumes of the right and left medial habenula of each animal were statistically analysed ('within animal experimental design'). The right medial habenula in males showed significant group asymmetry. In contrast, females failed to demonstrate group bias in favour of either hemisphere. However, individual females were lateralised, with either a larger right or left medial habenula. Although individuals of both sexes were lateralised, there was no significant sex difference in volume in either the right or left medial habenula. We propose that sex-linked structural asymmetry may be influenced by steroid hormonal effects in the central nervous system, and that such asymmetry could be more prevalent in the non-mammalian vertebrate brain than previously considered.
Article: The origins of cerebral asymmetry: a review of evidence of behavioural and brain lateralization in fishes, reptiles and amphibians.[show abstract] [hide abstract]
ABSTRACT: Early evidence for lateralization at a population and/or individual level in 'lower' vertebrates is reviewed. The lateralities include structural asymmetries in the epithalamus of several species of fish and amphibians, asymmetries in the location of both eyes on the same side of the head and of the dorsal/ventral crossing at optic-chiasma in flatfish, asymmetries in copulatory organs of several species of fishes, asymmetries in lung size and direction of coiling in reptiles, and asymmetrical distribution of scarring in whitefish. More recent data on functional lateralization at population level in lower vertebrates are also reviewed. These include: lateral asymmetries in the direction of turning during escape behaviour and in eye use in poeciliid fish; lateralization of pectoral stridulation sounds in catfish; neural lateralization for control of vocalization in the frogs; pawedness in toads; lateralization of courtship behaviour in newts; and lateralization of aggressive responses in lizards. Several cases of behavioural asymmetries at the individual level are also described, and possible relationships between lateralization at the individual level and fluctuating asymmetries arising from reduced heterozygosity are discussed. It is argued that the overall evidence now available supports the hypothesis of an early origin of brain lateralization in vertebrates.Neuroscience & Biobehavioral Reviews 06/1998; 22(3):411-26. · 8.65 Impact Factor
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ABSTRACT: Domestic chicks were tested for eye use while feeding on the floor in the presence of a dummy mask which could either look at the location where the chicks were feeding or in the opposite direction. Animals completely naïve of visual experience of human eyes and gaze showed a more intense fear response when directly looked at (as shown by higher latency to approach the food) and a preferential use of the left eye (mainly feeding structures in their right hemisphere) to monitor the dummy mask. This response, seemingly predisposed, could be reversed in chicks with experience of human eyes and gaze directed toward them, which showed higher latency to approach the food and preferential left eye use when the dummy mask looked away from them. The results are discussed in relation to evidence for a right hemisphere involvement in fear responses and detection of predators in the vertebrate brain.Behavioural Brain Research 03/2007; 177(1):15-21. · 3.42 Impact Factor
Article: Diencephalic asymmetries.[show abstract] [hide abstract]
ABSTRACT: Structural asymmetry in diencephalic regions has been reported in a number of studies since the pioneering observations by Kemali and Braitenberg, Atlas of the frog's brain. Springer Verlag: 1969. Anatomical differences between the left and right habenulae have been identified in many lower vertebrate species. While there are few reports of structural asymmetry in the dorsal thalamus, there is evidence that asymmetrical thalamofugal projections can be induced in the visual system of chicks by lateralized sensory stimulation prior to hatching. Finally, there have been consistent reports of differences between and right sides of the hypothalamus in their sensitivity to the effects of circulating gonadal hormones in rats. In most cases, these asymmetries are sex-linked and correspond to a lateralization of function. Although the significance of these diencephalic asymmetries is still enigmatic, their existence indicates that asymmetry is not a phylogenetically recent feature of the brain, and the left-right differences in the brain may be mediated by a common ontogenetic mechanism and may underlie the development of highly specialized functions.Neuroscience & Biobehavioral Reviews 02/1996; 20(4):637-43. · 8.65 Impact Factor