Epithalamus of developing zebrafish

Despite our apparent perfect bilateral symmetric body plan, we all show small but conspicuous left-right asymmetries that are thought to be evolutionarily advantageous. Brain lateralisation, for instance, leads to an increase in cognitive performance. Zebrafish are useful for studying how left-right brain asymmetries arise during embryonic development and how the resultant asymmetric neuronal circuitry ultimately impacts on function and behaviour. This image shows the epithalamus of a zebrafish larvae 4 days post-fertilization. Two regions of the epithalamus (which connects the limbic system, responsible for instinct and mood, to other regions of the brain) are shown: axons of the habenular are in purple and the parapineal organ in yellow. The parapineal is an accessory organ to the pineal gland and is thought to have a rudimentary light sensitive function. It represents the most overt asymmetric feature found in any vertebrate brain, as it is only present in the left side of the epithalamus and sends axonal projections exclusively to the left habenula. Width of the image is 200 micrometres.