However, Salk scientists and their collaborators have discovered the memory capacity of the human brain is “10 times more than previously thought,” according to an article published in Science News magazine.
According to the journal entry published January 20, Salk scientists used high-powered computers to reconstruct brain tissue in the hippocampus in order to determine the sizes of connections (synapses). The researchers discovered there are 26 discrete sizes of synapses capable of sending signals to neighboring neurons.
“This is a real bombshell in the field of neuroscience,” says Terry Sejnowski, Salk professor and co-senior author of the paper, which was first 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.”
It’s known that memories and thoughts are really just patterns of electrical and chemical activity in the brain. Branches of neurons behave like electrical wire interacting at specific junctions called synapses. An axon — think of it as an output wire — from one neuron connects to an input “wire” (a dendrite) of a second neuron. The brain’s signals or messages fire across the synapse in the form of chemicals called neurotransmitters that instruct the receiving neuron whether to pass on an electrical signal to thousands more neurons.
Besides helping scientists determine the brain’s actual capacity for processing memory, the study answers a longstanding question as to how the brain is so energy efficient and could help engineers build computers that are incredibly powerful but also conserve energy. The bottom line for laymen is that there are a whole lot more sizes and quantities of synapses than previously known, which means the odds of a healthy brain running out of memory is quite remote, no matter what its owner does to fill it with information and know-how.
“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,” says Kristen Harris, co-senior author of the work and professor of neuroscience at the University of Texas, Austin. “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.”
The newfound complexity of the brain’s duplicitous synapses opens the door to new discoveries about the organ that directs our bodies through life and it may aid in the construction of supercomputers. “The implications of what we found are far-reaching,” adds Sejnowski. “Hidden under the apparent chaos and messiness of the brain is an underlying precision to the size and shapes of synapses that was hidden from us.”
According to the study each neuron can have thousands of these synapses with thousands of other neurons. The Salk team was building a 3D reconstruction of rat hippocampus tissue (the memory center of the brain) when it made the groundbreaking discovery. At times a single axon from one neuron formed two synapses firing into a single dendrite of a second neuron confirming that the first neuron was sending a duplicate message to the receiving neuron. Before the study it was known synapses ranged in sizes a factor of 60 between the smallest and largest and that most are small. Salk scientists assumed the newly discovered synapses would be small and about the same size.
“We were amazed to find that the difference in the sizes of the pairs of synapses were very small, on average, only about eight percent different in size. No one thought it would be such a small difference. This was a curveball from nature,” says Tom Bartol, a Salk staff scientist involved in the project.
