Is your memory as good as a dead rat's?
Ben W Strowbridge, associate professor of neuroscience and physiology/biophysics and PhD student Phillip Larimer of Case Western Reserve University School of Medicine were hoping to identify the specific circuits responsible for working memory.
Using isolated pieces of rodent brain tissue, Larimer discovered a way to recreate a type of working memory in vitro. He was studying a particular type of brain neuron, called mossy cells, which are part of the hippocampus.
When stimulating electrodes were inserted in the hippocampal brain slice, the spontaneous activity in the mossy cells remembered which electrode had been activated. The memory in vitro lasted about 10 seconds, about as long as many types of working memories studied in people.
"This is the first time anyone has stored information in spontaneously active pieces of mammalian brain tissue. It is probably not a coincidence that we were able to show this memory effect in the hippocampus, the brain region most associated with human memory," said Strowbridge.
The scientists measured the frequency of synaptic inputs onto the mossy cells to determine whether or not the hippocampus had retained memory.
"Memory was not evident in one cell but it was evident in a population of cells," said Strowbridge.
Larimer and Strowbridge also found the brain circuit that enabled the hippocampus to remember which input pathway had been activated.
Strowbridge's group is now looking into how much information they can store in the hippocampus.
"It took us four years to be able to reproducibly store two bits of information for 10 seconds" says Larimer. "Our findings should progress faster now that we know what to look for and have found the brain circuit that actually holds the memory."
Their study appears in Nature.