Where Long-Term Memory is Stored: Cerebral Cortex in Brain Harbors Thoughts

First Posted: Aug 28, 2013 07:22 AM EDT
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Where are memories stored? That's a good question. The location and exactly how our memories are encoded in our nervous system are challenging topics for researchers. Now, scientists have discovered that a specific form of memory associations is encoded in the cerebral cortex.

The hippocampus has long been considered a center in the brain for the long-term storage of spatial associations. Yet these latest findings show that it doesn't store all memories. This, in particular, is a game changer since is suggests that the motor cortical circuits itself is used as memory storage rather than the hippocampus.

In order to understand a little bit more about memory, the researchers examined the behavior of genetically modified mice, in which NMDA receptors are turned off only in the motor cerebral cortex. These NMDA receptors bind the neurotransmitter glutamate to the synapses and become active when several signals feed into one synapse at the same time. In other words, they're the central molecular elements of learning processes.

During the study, the researchers taught animals with and without NMDA receptors to link a tone with a subsequent electrical stimulus of the eyelid.

"After a learning phase, the animals' reflex is to close their eye when they hear just the tone," said Mazahir T. Hasan, one of the researchers, in a news release. "Without NMDA receptors in the primary motor cerebral cortex, the genetically modified mice on the other hand cannot remember the connection between the tone and the electrical stimulus, and therefore they keep their eyes open despite the tone."

So what did they find? It turns out that synaptic plasticity no longer functions without the NMDA receptors. This seemed to indicate that, in fact, it's the cerebral cortex that's the storage site for some forms of memory rather than the hippocampus.

In fact, the findings are a huge step forward for memory research. They show that the cerebral cortex is the region where memory associations are linked and stored. This could help with treatments and the study of neurological diseases such as amnesia, Alzheimer's disease and dementia.

The findings are published in the journal Nature Communications.

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