psychology& neuroscience
Learning from Fruit Flies: How Memory Steers Action By Sneha Makhijani
Image by Howard Vindin. [CC-BY-SA 4.0]
T
he fruit fly has created quite a buzz in the world of neuroscience and learning. Similar to the way humans are now conditioned to hear a notification and pick up their phone, animals show different behavioral responses to the same sensory input, depending on past experiences and current contexts. Learning is a permanent change in behavior that results from experience. One of the earliest learning techniques is classical conditioning, a learning process in which a neutral, unconditioned stimulus is paired with a conditioned response to naturally evoke a response. While the initial experiments were first done on dogs, the field of neuroscience is slowly understanding how synaptic plasticity, a change that occurs at the junctions of different neurons, and memory is steering this learning response. UNC-Chapel Hill’s Dr. Toshihide Hige is one of the scientists doing pioneering research on the neurophysiology and learning behavior in the fruit fly – Drosophila melanogaster. The brain enables flexibility to change its structure through mechanisms at the levels of synaptic plasticity, neural circuit, and behavior, where the neural circuit is a population of neurons that carry out a specific function. Dr. Hige first got involved in synaptic physiology during his PhD research. Using electrophysiology in mammalian systems, he studied the neural circuit basis of behavior in animals. As Dr. Hige progressed in his research, he started to use Drosophila melanogaster as a model organism. Although Dr. Toshihide Hige, PhD fruit flies have about 100,000 neu-
rons, which is 1000 times fewer than that of mice, some of the important circuit motifs remain conserved across all animals, both in sensory circuits and higher-order brain areas. Circuit motifs are connectivity patterns between specific cell types across different species and brain areas. Simpler model organisms, such as Drosophila melanogaster, have small brains but exhibit a wide range of sophisticated, adaptive behaviors. Fruit flies make for an easier reading of the neural circuit and they offer a larger selection of which circuit brain area to use, with fewer pathways of each of the brain circuits. Genetic tools can label specific neuron types in every area of the brain, and such tools can also manipulate neuronal activity and address its molecular basis. Furthermore, the whole-brain connectome data is readily available and allows for an easier link between synaptic plasticity and behavior by understanding Drosophila neural circuits. Whole-brain connectome data is essentially a comprehensive map of the various neural connections in the brain that act as a wiring diagram of an organism’s nervous system. There is a pair of structures in the brain of insects called Corpora Pedunculate, or mushroom bodies. The structures are
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Figure 1. Circuit diagram of the Drosophila mushroom body
