Brain complexity: memory capacity (Introduction)

by David Turell , Monday, January 25, 2016, 15:22 (3225 days ago) @ David Turell

This article describes dynamic changes in size and function of synapses as well as multiple double connections:-http://www.salk.edu/news-release/memory-capacity-of-brain-is-10-times-more-than-previously-thought/-"Memory capacity of brain is 10 times more than previously thought. Data from the Salk Institute shows brain's memory capacity is in the petabyte range, as much as entire Web.-***-"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 Bartol.-"Because the memory capacity of neurons is dependent upon synapse size, this eight percent difference turned out to be a key number the team could then plug into their algorithmic models of the brain to measure how much information could potentially be stored in synaptic connections.-***-"It was known before that the range in sizes between the smallest and largest synapses was a factor of 60 and that most are small.-"But armed with the knowledge that synapses of all sizes could vary in increments as little as eight percent between sizes within a factor of 60, the team determined there could be 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,” says Bartol. 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.-“'This is roughly an order of magnitude of precision more than anyone has ever imagined,” says Sejnowski.-***-"One answer, it seems, is in the constant adjustment of synapses, averaging out their success and failure rates over time. The team used their new data and a statistical model to find out how many signals it would take a pair of synapses to get to that eight percent difference.-"The researchers calculated that for the smallest synapses, about 1,500 events cause a change in their size/ability (20 minutes) and for the largest synapses, only a couple hundred signaling events (1 to 2 minutes) cause a change.-“'This means that every 2 or 20 minutes, your synapses are going up or down to the next size. The synapses are adjusting themselves according to the signals they receive,” says Bartol.-***-“'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.”-"The findings also offer a valuable explanation for the brain's surprising efficiency. The waking adult brain generates only about 20 watts of continuous power—as much as a very dim light bulb. The Salk discovery could help computer scientists build ultraprecise, but energy-efficient, computers, particularly ones that employ “deep learning” and artificial neural nets—techniques capable of sophisticated learning and analysis, such as speech, object recognition and translation."-Comment: I've mentioned the controlled variability of synapses before, but this article gives great detail. No wonder our brain is so powerful making us different in kind.