The dream of modifying a person's dreams has just gotten a step closer, as MIT scientists were able to manipulate what lab rats "saw" in their sleep using audio cues.
Scientists have known that during sleep, a part of the brain called the hippocampus "replays" the day's events in a process that might help solidify a person's memories. The same has been shown in rats that dream about running through mazes after a day's work in a lab at MIT.
In the new MIT study, researchers Matthew Wilson and Daniel Bendor trained rats to run through a maze using audio cues, with one sound directing the animals to a reward on the right side of the track, and another sound leading the rats to a reward on left.
The rat brains showed specific patterns of activation of certain sets of neurons in the hippocampus depending on whether they ran to the right or the left side of the maze. These neurons, so-called place cells, tell the rats where they are spatially and are known to fire in certain patterns when a rat is in a particular location.
When the animals went to sleep, the researchers re-analyzed the neural activity in the hippocampus; during non-REM sleep, the researchers played about once every five to 10 seconds a random sound, including the two sounds associated with the two sides of the maze. "When the sound associated with the left side of the maze was played, the dream content switched to memories of running down the left side of the maze," Wilson told LiveScience. "When the sound associated with the right side was played, the dream content switched to the right side of the maze."
Even though the sounds were played for less than a second, the influence on dream content persisted, Wilson said, for five to 10 seconds. "[S]o the sounds were not simply driving the dream content, but seemed to be biasing or selecting the memories that would be subsequently replayed," he said.
This same phenomenon didn't show up when the rats were awake and not in the maze.
"When we played the sounds while the animals were just sitting quietly and 'thinking' but not sleeping, we were not able to influence replayed memory content," Wilson said.
The study, detailed online Sept. 2 in the journal Nature Neuroscience, suggest memories could be modified during sleep. "This could be thought of as a simple form of dream engineering and opens up the possibility of more extensive control of memory processing during sleep to enhance selected memories and to block or modify unwanted memories," Wilson and Bendor write.
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