Scientists Identify Brain Activity Patterns in Rat Brain Involved With Memory Recall

Posted on May 5, 2012

UCSF scientists have identified patterns of brain activity in the rat brain that play a role in the formation and recall of memories and decision-making. The researchers had previously identified patterns of brain activity in the rat hippocampus. The patterns sometimes represented where an animal was in space, and, at other times, represented fast-motion replays of places the animal had been, but no one knew whether these patterns indicated the process of memory formation and recollection.

The researchers conducted an experiment that involved zapping rats that were exploring a maze with a small amount of electricity to disrupt their memory recall. The researchers built a system for detecting the underlying patterns of neuronal activity in rats. They fitted the animals with electrodes and built a system that enabled them to detect a specific pattern, called a sharp-wave ripple, in the hippocampus. Whenever they detected a ripple, they would send a small amount of electricity into another set of electrodes that would immediately interrupt the ripple event, in effect turning off all memory replay activity without otherwise affecting the brain.

In the experiment, the rats worked their way through a maze toward a reward prize of a few drops of sweetened condensed milk. The UCSF researchers knew that these sharp-wave ripples would be activated when the animals had to make choices about which direction to turn as they worked their way toward the milk. The researchers found that terminating the sharp-wave ripples disrupted the recall and subverted the rat's ability to correctly navigate the maze.

Neuroscientist Loren Frank, PhD, a associate professor of physiology and a member of the Keck Center for Integrative Neuroscience at UCSF, who led the research with Shantanu Jadhav, PhD, a post-doctoral fellow, says the experiment shows these sharp-wave ripples are critical for this type of memory recall. Through these brain waves, the rat reprocesses and replays old experiences in a fleeting instant. The researchers believe these brain waves contain lessons from the past essential for shaping the perception of the present.

Frank says, "We think these memory replay events are a fundamental constituent of memory retrieval and play a key role in human perspective and decision-making as well. These same events have been seen in memory tasks in humans, and now we know they are critical for memory in rats. We think that these fast-forward replays make up the individual elements of our own memories, which jump rapidly from event to event."

The finding gives scientists a new way to investigate fundamental processes like learning and decision-making in animals and in people. It also may help shed light on memory disorders like post-traumatic stress disorder (PTSD).

The research paper, "Awake Hippocampal Sharp-Wave Ripples Support Spatial Memory," was published here in the journal, Science.

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