ScienceDaily, May 3, 2012
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| Brain patterns through which the rats see rapid replays of past experiences are fundamental to their ability to make decisions. Disturbing those particular brain patterns impaired the animals' ability to learn rules based on memories of things that had happened in the past. (Credit: © Oleg Kozlov / Fotolia) |
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 discovery, which builds
on the team's previous findings, offers a path for studying learning,
decision-making and post-traumatic stress syndrome.
The researchers
previously identified patterns of brain activity in the rat hippocampus, a
brain region critical for memory storage. 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.
In the journal Science
this week (online May 3, 2012), the UCSF researchers demonstrated that the
brain activity is critical for memory formation and recall. Moreover, they
showed that the brain patterns through which the rats see rapid replays of past
experiences are fundamental to their ability to make decisions. Disturbing
those particular brain patterns impaired the animals' ability to learn rules
based on memories of things that had happened in the past.
"We think
these memory-replay events are central to understanding how the brain retrieves
past experiences and uses them to make decisions," said 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. "They offer insight into how a past
experience can have such a profound effect on how we think and feel."
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), which is characterized by
strong, disturbing and uncontrolled memories.
Without Links to
the Past, Rats Face Indecision
Seeking to
understand how the recall of specific memories in the brain guides our
thinking, Frank and his colleagues 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.
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 wended their
way toward their reward: a few drops of sweetened condensed milk. These signals
seem to be flashes of memory recall, said Frank, a rat's past knowledge
flooding back to inform it on what had happened in the past and where it might
go in the future. Squashing the sharp-wave ripples, the UCSF team found,
disrupted the recall and subverted the rat's ability to correctly navigate the
maze.
This shows, said
Frank, that the 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 -- lessons from the past essential for shaping their
perception of the present.
"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," he
said. "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."
Next,
the team wants to tease out information about how the rats actually use these
memory replay events to make decisions and how amplifying or blocking specific
replay events will change the way an animal learns and remembers. They also
think that these events could be important for understanding memory problems,
as when stressful memories intrude into daily life.
Story Source:
The above story is reprinted from materials provided by University of California, San Francisco (UCSF), viaNewswise. The original article was written by Jason Bardi.Note: Materials may be edited for content and length. For further information, please contact the source cited above.
Journal Reference:
- Shantanu P. Jadhav, Caleb Kemere, P. Walter German and Loren M. Frank. Awake Hippocampal Sharp-Wave Ripples Support Spatial Memory. Science, May 4, 2012 DOI: 10.1126/science.1217230
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