Scientists film how the brain makes memories, could treat PTSD

By Mark Waghorn via SWNS

Scientists have filmed how the brain makes memories.

Scans captured snapshots of past experiences in a living animal for the first time.

The amazing breakthrough offers hope of new treatments for post traumatic stress disorder (PTSD).

It could even have implications for Alzheimer's and other neurodegenerative diseases.

A US team induced a memory in young zebrafish - then mapped changes in their heads.

Brain cells 'lit up like a Christmas tree'. Learning caused connections between neurons to either proliferate or disappear.

Known as synapses, they pass messages using chemicals called neurotransmitters. It had been thought they merely altered strength.

Lead author Professor Don Arnold said: "Our probes can label synapses in a living brain without altering their structure or function, which was not possible with previous tools."

It enabled the University of Southern California researchers to image where the synapses were located.

Co-author Prof Scott Fraser said: "The microscope we built was tailored to solve this challenge and extract the knowledge we needed.

"Sometimes, you try to get such a spectacular image that you kill what you are looking at.

"For this experiment, we had to find the right balance between getting an image that was good enough to get answers, but not so spectacular that we would kill the fish with photons."

The study in Proceedings of the National Academy of Sciences also explains why some memories are stronger than others.

For instance, we remember the name of our childhood best friend - but sometimes struggle to recall that of the person we just met.

Previously, comparisons before and after memory formation were unfeasible.

The humble zebrafish is large enough to have a brain that functions like our own.

It's also small and transparent - opening a window into the organ's mysteries.

By keeping the intact fish alive, Prof Arnold and colleagues compared synapses over time.

The 12-day-old fish were first trained to link the turning on of a light with an infrared laser heating their head.

They sought to avoid this by swimming away. Fish that remembered would flick their tails.

Five hours later, the researchers observed and recorded dramatic gains and losses in the neuronal junctions.

They also altered DNA so their strength and location was marked with a fluorescent protein that glowed under a beam.

It provided them with hundreds of before and after pictures of the same individual.

Earlier experiments had only been possible on deceased specimens. Two different brains had to be compared - one conditioned, one not.

Prof Fraser said: "This is ninja imaging, we sneak in without being noticed."

Complicated algorithms processed the vast quantity of data. Existing synapses did not alter.

Instead, some were destroyed and others born - in another region of the brain.

Co-author Prof Carl Kesselman, a computer scientist, said: "For the last 40 years the common wisdom was you learn by changing the strength of the synapses. But that is not what we found in this case."

Age-related breakdown in synapses is found in dementia and other neurodegenerative diseases.

Prof Arnold said: "This was the best possible outcome we could have had.

"We saw this dramatic change in the number of synapses - some disappearing, some forming, and we saw it in a very distinct part of the brain.

"The dogma was the synapses change their strength. But I was surprised to see a push-pull phenomenon, and that we didn't see a change in synapses' strengths."

The results suggest changes in the number of synapses encode memories.

They shed fresh light on why bad memories, such as those that lead to PTSD, are so robust.

Prof Arnold said: "It has been thought memory formation mainly involves remodeling of existing synaptic connections.

"In this study, we found the formation and elimination of synapses. But we saw only small, random changes in synaptic strength of existing synapses.

"This may be because this study concentrated on associative memories, which are much more robust than other memories and are formed in a different place in the brain, the amygdala, versus the hippocampus for most other memories.

"This may someday have relevance for PTSD, which is thought to be mediated by the formation of associative memories."