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Innate Essay

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Innate or learned behavioural responses can be observed in a neural representation of the sensory world. Naïve animals, which are without prior learning or experience, show an innate response to a sensory stimulus suggesting that they are mediated by genetically determined neural circuits. Most sensory stimuli, however, show an experience-dependent response, allowing an organism to respond appropriately in a variable and uncertain world. Thus, behav-ioural relevance to sensory cues is mostly acquired through learning. In Drosophila melanogaster, different forms of learning have been observed in response to a number of sensory stimuli. The mushroom body (MB), in insects, is responsible for memory formation and retrieval.

When an olfactory …show more content…

Most antennal lobe projection neurons (PNs) extend their dendrites to a single glo¬merulus while their axons bifurcate to innervate the lateral horn and the MB of the brain. The lateral horn is thought to mediate innate behaviours, whereas the MB translates olfactory sensory information into learned behavioural responses. On the activation from an odorant, PN axons synapse onto the den¬drites of the Kenyon cells (KCs) in the MB calyx. According to anatomical and physiological studies, each KC is said to receive, on an average, 6.4 inputs from a random combination of glo¬meruli which indicates that knowledge of a single input to the KC cannot provide information about all the additional inputs and these connections differ in different flies.

The γ, α′/β′, and α/β lobes of the MB are formed from three classes of KCs that extend their parallel fibers to these lobes and form synapses with a relatively small number of MB output neurons (MBONs). The MBONs extend their dendrites into the MB lobes, while their axons are projected to the neuropils which lie outside the MB. Modulatory input neurons which include the dopaminergic neurons (DANs) and octo¬paminergic neurons, also innervate the MB lobes. The MBONs and DANs extend their processes to locations such that they define spatially restricted ‘subdomains’ in each lobe.

DANs are modulatory neurons of the MB that are most prevalent.

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