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Clocktower.Monday 26 February 2018 3:52pm

Cliff Abraham image
Professor Cliff Abraham, Co-Director of Brain Research NZ - Rangahau Roro Aotearoa.

New discoveries into how information is stored in the brain have been made by a University of Otago researcher.

Professor Cliff Abraham, Co-Director of Brain Research NZ - Rangahau Roro Aotearoa, says the study, just published in the Proceedings of the National Academy of Sciences, USA, reveals how the synapses between nerve cells can rapidly increase and decrease their structure and function during learning to maintain overall stability of memory networks.

“Memory is fundamental to all our cognitive activity. Understanding how it works is critical for identifying how it goes wrong in diseases and for developing ideas about how to correct memory disorders,'' he says.

He worked with key collaborators Professor Kristen Harris, at the University of Texas at Austin, and Professor Terence Sejnowski, of the Salk Institute, and their teams to study information storage properties of the brain.

“The brain has the capacity to store an immense amount of information at the synaptic connections between nerve cells. But whether the storage capacity of synapses could be rapidly modified by experience was not known.”

The team, funded by the National Institutes of Health, made 3D reconstructions of individual synapses and mimicked the neural activity that happens during real learning.

They found information storage capacity is “surprisingly variable across different brain regions” and that in a part of the brain important for memory, the hippocampus, the capacity for information storage is not fixed but can be enhanced by learning-related neural activity.

“The structural size of the synaptic connections changed very quickly, but in a balanced way so that the net size for the whole set of synapses did not change at all. Some contacts got bigger and this was completely matched by others getting smaller.

“The brain strengthens the connections between neurons that are co-active during an experience, while diminishing the connectivity of other sets of neurons so that when one retrieves the memory of that experience, only the correct sets of nerve cells are reactivated.

“The fact our treatment had the side effect of increasing storage capacity was also surprising. Moreover, we found that the storage capacity could vary between brain regions, and this had not been reported before,” Professor Abraham says.

The ability to have both increases and decreases in the “strength” of synaptic communication between nerve cells is essential for the correct registration and storage of experiences.

The researchers plan to undertake similar studies at longer time intervals after the learning experience to see how persistent the changes are. They also want to investigate how other synaptic inputs to the cells might adapt to the same events.

“Ultimately we want to know how these processes might be disrupted in disease conditions, and might therefore be contributing to memory disorders.”

Publication details:
Long-term potentiation expands information content of hippocampal dentate gyrus synapses. PNAS:

Cailey Bromer, Thomas M. Bartol, Jared B. Bowden, Dusten D. Hubbard, Dakota C. Hanka, Paola V. Gonzalez, Masaaki Kuwajima, John M. Mendenhall, Patrick H. Parker, Wickliffe C. Abraham, Terrence J. Sejnowski, and Kristen M. Harris.

For more information, please contact:

Professor Cliff Abraham
Co-Director, Brain Research NZ - Rangahau Roro Aotearoa
Department of Psychology
University of Otago

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