In a computational reconstruction of brain tissue in the hippocampus, Salk scientists and
UT-Austin scientists found the unusual occurrence of two synapses from the axon of one
neuron (translucent black strip) forming onto two spines on the same dendrite of a second
neuron (yellow). Separate terminals from one neuron’s axon are shown in synaptic contact
with two spines (arrows) on the same dendrite of a second neuron in the hippocampus.
The spine head volumes, synaptic contact areas (red), neck diameters (gray) and number of
presynaptic vesicles (white spheres) of these two synapses are almost identical.
Credit: Salk Institute
(January 20, 2016) Data from the Salk Institute shows brain’s memory capacity is in the petabyte range, as much as entire Web
Salk researchers and collaborators have achieved critical insight into the size of neural connections, putting the memory capacity of the brain far higher than common estimates. The new work also 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.
“This is a real bombshell in the field of neuroscience,” says 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.”
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. An output ‘wire’ (an axon) from one neuron connects to an input ‘wire’ (a dendrite) of a second neuron. Signals travel across the synapse as chemicals called neurotransmitters to tell the receiving neuron whether to convey an electrical signal to other neurons. Each neuron can have thousands of these synapses with thousands of other neurons.
“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.”