A new study led by researchers at the Salk Institute revealed that the brain's ability to store memories is much more impressive than originally thought - to be exact, its capacity for memory storage is approximately 10 times larger than previous estimates.
"This is a real bombshell in the field of neuroscience," said Terry Sejnowski, co-senior author of the paper, in a press release. "We discovered the key to unlocking the design principle for how hippocampal neurons function with low energy but high computation power. Our new measurements of the brain's memory capacity increase conservative estimates by a factor of 10 to at least a petabyte, in the same ballpark as the World Wide Web."
Memories and thoughts originate from the electrical and chemical activity in our brains and the unique activities that they are the foundation of. One of the most important aspects of the brain is when the branches of our neurons interact with synapses, much like electrical wires. Electrical and chemical signals cross these synapses and send messages across neuronal networks.
"When we first reconstructed every dendrite, axon, glial process and synapse from a volume of hippocampus the size of a single red blood cell, we were somewhat bewildered by the complexity and diversity amongst the synapses," said Kristen Harris, co-senior author of the study. "While I had hoped to learn fundamental principles about how the brain is organized from these detailed reconstructions, I have been truly amazed at the precision obtained in the analyses of this report."
After creating a 3D reconstruction of a rat hippocampus tissue, the team noticed that sometimes a single axon stemming from a single neuron formed two synapses that reached out to a dendrite, indicating that a duplicate message may be sent by the first neuron. Using microscopy and computational algorithms, they reconstructed the brain to mirror its connectivity, shapes and volumes all the way down to the nanomolecular level and found that the synapses were almost identical in size.
"We were amazed to find that the difference in the sizes of the pairs of synapses were very small, on average, only about 8 percent different in size. No one thought it would be such a small difference. This was a curveball from nature," said Tom Bartol, who participated in the research.
Memory capacity is dependent on synapse size and, using this 8 percent difference, the team was able to determine that there are approximately 26 different types of synapses as opposed to just a few.
"Our data suggests there are 10 times more discrete sizes of synapses than previously thought," said Bartol.
"This is roughly an order of magnitude of precision more than anyone has ever imagined," said Sejnowski.
The findings were published in the Nov. 30 issue of eLife.
