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A new study by neuroscientists United States Massachusetts Institute of Technology (MIT) in Cambridge, reveals the brain circuitry that controls how memories are associated with positive or negative emotions. Scientists found they could reverse the emotional association of specific memories by manipulating brain cells with optogenetics, a technique that uses light to control the activity of neurons. | Young people with depression have brain networks “hyperconnected”
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. <- - Google_ad_section_end (name = noticia_entradilla)!> results described in the number of Thursday magazine Nature , demonstrated that a neuronal circuit connecting the hippocampus and the amygdala plays a critical role in the association of emotion with a memory. This pathway could provide a target for new drugs to help treat conditions such as posttraumatic stress disorder (PTSD), researchers advance.
“In the future, one may be able to develop methods to help people remember positive memories stronger than the negative “, poses the main study author Susumu Tonegawa, Professor of Biology and Neuroscience, Director of the RIKEN-MIT Center for Neural Circuit Genetics Institute for Learning and Memory at MIT.
Memories are made of many elements, which are stored in different parts of the brain, and the context of a memory, which includes information about where held the event is stored in the cells of the hippocampus, while emotions associated with that event are on the amygdala.
Previous research has shown that many aspects of memory, including emotional associations, are malleable . Psychotherapists have taken advantage of this to help patients suffering from depression and PTSD, but the neural circuitry underlying the malleability was unknown.
In this study, the researchers set out to explore the malleability with an experimental technique that allows them to label neurons that encode a specific memory or engram. To accomplish this, marked hippocampal cells that go on during the formation of memories with a light-sensitive protein called channelrhodopsin. Thereafter, each time that these cells are activated by light, mice recall the memory encoded by this group of cells.
Reactivation of memories
Last year, the Tonegawa laboratory technique used to implant false memories in mice by reactivating engrams, while rodents were subjected to a different experience. In the new study, the scientists wanted to investigate how the context of a memory is linked to a particular emotion .
First, the protocol used etiqueado engram to mark neurons associated with a rewarding experience (for male mice, socializing with a female mouse) or an unpleasant experience (a mild electrical shock). In this first set of experiments, researchers marked memory cells in a part of the hippocampus called the dentate gyrus.
Two days later, the mice were placed in a large rectangular space for three minutes, the researchers saw what preferred midfield mice naturally. In the mice receiving fear conditioning, scientists stimulated labeled cells in the dentate gyrus with light each time the animal entered the preferred side so that these animals began to avoid increasing the area, showing . reactivation of the fear memory was successful
The memory of the reward might also revive: in the case of mice that had prepared them for the reward, the researchers stimulated them with light each time they entered the side least preferred, so that suddenly began to spend more time there, recalling fond memories.
A couple of days later, the researchers tried to reverse the emotional responses mice. For male mice that originally received fear conditioning, memory cells involved in fear memory with light for 12 minutes while the mice spent time with female mice are activated. For mice that had initially received the reward conditioning, memory cells were activated while receiving mild electric shocks.
Then the researchers put the mice back in the big stadium two areas. This time, the mice that originally received fear conditioning and had avoided the side of the field in which the cells of the hippocampus are activated by the laser, now began to spend more time in that area, when hippocampal cells were activated, showing that a pleasant association replaced the fear. This investment was also carried out on mice that were conditioned to the reward.
No change cells casolateral amygdala
Subsequently, the authors of this paper carried out the same set of experiments, but with the memory cells labeled in the basolateral amygdala, a region involved in processing emotions. This time, they could not induce a change reactivating cells, so that the mice continued to behave as they had been conditioned when memory cells were initially labeled.
This suggests that emotional associations, also called valencies, are encoded somewhere in the neuronal circuit connecting the dentate gyrus with the amygdala, the researchers said. A terrible experience reinforces the connections between the hippocampal engram and cells encoding the fear in the amygdala, but can weaken the connection later as new connections between cells in the hippocampus and amygdala encoding positive associations are formed.
“This plasticity of the connection between the hippocampus and the amygdala plays a crucial role in the switching of the valence of the memory,” said Tonegawa. These results indicate that while cells of the dentate gyrus are neutral with respect to emotion, the amygdala are precomprometidas encode the memory of fear or reward.
The researchers are now trying to discover the molecular signatures of these two types of cells of the tonsil. They are also investigating whether reviving pleasant memories have any effect on depression, with the hope of identifying new targets for drugs to treat depression and PTSD
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