As animals explore their environment, they learn to master it. By discovering what tends to take precedence over predator attacks, or whatever odor presupposes for dinner, they develop a kind of biological clairvoyance ̵
Student fruit flies showed the researchers that a single odor can be either appealing or disgusting to an animal, depending on when the scent has come across in relation to a reward. The study described in a report in Cell also reveals that animals can quickly revise these memories and show how this process unfolds on a cellular level view that probably not only relates to flies but also to learn across
Memory, at its most basic level, corresponds to a number of associations: Call a bell before feeding a dog, and eventually the dog will learn to salivate at the sound of the bell alone.
"In this case, the bell comes before the food and is therefore predictive of reward," says Annie Handler, a graduate student in the laboratory of Vanessa Ruta, Gabrielle H. Reem and Herbert J. Kayden Associate Professor. "But we suspect that there is not only an order of events that animals find significant. They must also be able to extract meaning from characters following a reward."
For example. If a dog hears a bell after its meal concludes, then it must develop a negative link to that sound, as it means the end of chow. Hope to understand better how timing affects memory, examining the box and acting the brain and the construction of fruit fly.
Instead of giving the animals tasty treats, the researchers used a technique called optogenetics to stimulate neurons that normally become active when an animal receives a reward, an approach that allowed them to precisely control the timing of positive feedback. . They found that if these neurons were stimulated immediately after an otherwise neutral smell, the flies developed an attraction to that smell. Conversely, if they activated the neurons just before the emitted flies to the same odor, the animals began to avoid it.
"The difference in time is only one or two seconds, but the flies constitute completely opposed associations," Handler says. "Some places in the brain are the difference in a second – whether the smell comes before or after the reward – a big difference."
That brains have a sense of timing may seem intuitive; But exactly how neurons encode events at a cellular level is far from obvious. Relatively small and simple, the flight brain provides a unique opportunity to study the neural circuits underlying this phenomenon – and that is exactly what Ruta and Handler did.
To determine how flies discriminate the time of events, the researchers monitored changes in a brain area called the fungal body. Known to be involved in associative learning, this area contains Kenyon cells bearing odor signals, dopamine neurons which carry reward signals and output neurons that regulate a fly's attraction to an odor. Kenyon cells can be either strong or weakly connected to output neurons; and dopamine strengthens the strength or synapses of these compounds. If a Kenyon cell detecting a specific odor forms a weak connection with an output neuron, the animal is attracted to that odor; However, if this synapse grows stronger, the odor will become meaningless or even aversive to the animal. Analysis of this type of compound identified Ruta and Handler a signaling pathway that can either potentiate or weaken synapse, depending on the precise time when dopamine neurons become active.
"This path is time-sensitive, so whether the dopamine neuron is activated before or after an odor makes a critical difference in the strength of compounds between cells in the fungal body," Ruta says. "And we think this is the mechanism by which the brain calculates the order of events."
By tinkering with this path, the researchers also found that they could quickly make strong synapses weak and vice versa, suggesting that memories can be deleted as quickly as they are formed. And as they analyzed flight behavior, they found additional evidence of the ability to revise mental associations.
"We did 50 trials. Each time we changed the timing of the smells relative to the reward, and each time the animal became more or less attracted to the smell, depending on what it had experienced for a moment," Handler says.
In other words, even though a fly had previously learned to associate a scent with reward, it could quickly dissolve that association if the scent failed to predict reward in future trials. Memory is not set in stone; They are rather put into synapse, which can change as an animal's environment and experiences change. In fact, this experiment emphasizes that survival depends not only on the ability to form memories but also to forget them.
"There are so many things we could remember on a daily basis that we hold onto the memories that appear to be predictive, and we throw out associations that are wrong or irrelevant," says Ruta. "When you live in a dynamic environment – both flying and people doing – it seems like a very good strategy."
New research shows how flight brain transforms odor information to produce flexible behavior
Annie Handler et al., Distinct Dopamine Receptor Pathways Underlie the Temporal Sensitivity of Associative Learning, Cell (2019). DOI: 10,1016 / j.cell.2019.05.040
Learning from experience is all in the timing (2019, June 26)
June 27, 2019
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