Salk Institute researchers have found that the brain’s memory capacity is far higher than previously thought — as much as a 1,000 standard computer hard drives.

A scientific paper released this week about the size of neural connections suggests the brain’s memory capacity is equal to 1,000,000 gigabytes, or a “pentabyte” of data.

“This is a real bombshell in the field of neuroscience,” said Terry Sejnowski, Salk professor and co-senior author of the paper, which was published in eLife. “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,” Sejnowski added.

Salk reserarchers Terry Sejnowski (left), Cailey Bromer and Tom Bartol. Courtesy Salk Institute

Scientists believe our memories and thoughts are the result of patterns of electrical and chemical activity in the brain. A key part of the activity happens when branches of neurons, much like electrical wire, interact at certain junctions, known as synapses. Each neuron can have thousands of these synapses with thousands of other neurons.

The Salk team using a 3D reconstruction of rat hippocampus tissue — the memory center of the brain — found that there are about 26 categories of sizes of synapses, rather than just a few.

“Our data suggests there are 10 times more discrete sizes of synapses than previously thought,” said Tom Bartol, a Salk staff scientist.

In computer terms, 26 sizes of synapses correspond to about 4.7 “bits” of information. Previously, it was thought that the brain was capable of just one to two bits for short and long memory storage in the hippocampus.

Other authors on the paper were Cailey Bromer of the Salk Institute; Justin Kinney of the McGovern Institute for Brain Research; and Michael A. Chirillo and Jennifer N. Bourne of the University of Texas, Austin.

The Salk Institute for Biological Studies in La Jolla is one of the world’s preeminent basic-research institutions. Founded in 1960 by polio vaccine pioneer Jonas Salk, the institute is an independent nonprofit organization and architectural landmark.

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