The Mechanism of Short-term Memory
Calculating the Top-down Activities of the Brain
By Scott Gibson
In a study reported on in 2012 involving monkeys looking at objects, researchers discovered that in-sync large-scale brain waves affecting various regions of the brain hold memories of objects just viewed.
So, why is that important?
According to Thomas R. Insel, director of the National Institutes of Mental Health, as quoted in a National Institutes of Health press release, ‘The Holy Grail of neuroscience has been to understand how and where information is encoded in the brain. This study provides more evidence that large scale electrical oscillations [waves] across distant brain regions may carry information for visual memories.'
For Lester Ingber—a researcher who employs the advanced digital resources of XSEDE—those types of studies by other established researchers, which have begun to emerge only in recent years, magnify a concept he's been investigating since 1981: the relationship between large-scale, or "top-down," activities in the brain and short-term memory and consciousness.
Specifically, Ingber's focus has been on what are known as multiscale neocortical (of the brain's neocortex) interactions, including calculations of short-term memory and electroencephalogram (EEG) processes, which involve measuring electric currents in the brain.
Research led by Ingber resulted in a 2010 paper in the journal Mathematical Biosciences titled "Neocortical Dynamics at Multiple Scales: EEG Standing Waves, Statistical Mechanics, and Physical Analogs," which contains calculations revealing "the influence of memory and associated attentional processes at molecular levels."
Ingber explains that his recent research, documented in a paper titled "Electroencephalographic field influence on calcium momentum waves" in the Journal of Theoretical Biology, again connects the mechanism involved in conscious attention to short-term memories with the influence of synchronous EEG-measurable brain waves at the molecular scale.
Key players in what is described in the paper are electrically excitable cells called neurons; star-shaped, multifunctional astrocytes, the most-abundant type of cell in the human brain; synapses, structures that permit the passage of electrical and chemical signals in the brain; and waves of Ca2+ (calcium ions), reproduced from astrocytes to neuron–neuron synapses, where they affect other electrical and neuromodulator (neuron-altering substance) processes.
Ingber explains the flow of influence as going from highly synchronized neuronal firings to Ca+2 waves, to astrocyte–neuron interactions, which in turn likely—although not experimentally confirmed—affect background ‘spontaneous' synaptic activity that has been observed for many years to shape short-term memory.
Ingber has mostly used the Trestles supercomputer at the San Diego Supercomputer Center (SDSC) for the research explained in his most recent paper, and he expresses gratitude for the expert technical support he has received from SDSC's Glenn Lockwood, noting that Lockwood has been "very helpful."
"The XSEDE resources make a big difference in what can be accomplished in a reasonable time frame," Ingber says. "In just 6 real hours of MPI processing time, I did a CPU-month of calculations. Some similar work I did years ago actually took a few months of constant calculations on a then-powerful Convex machine."
Ingber says research discoveries—including the demonstration that large-scale brain activity as measured by scalp EEG does, in fact, process memory—present a compelling argument for continuing to study what occurs on the large scale in the brain and verify the results experimentally.