In a famous surgery while in the early 1900s, Canadian neurosurgeon Wilder Penfield, attempting to treat epilepsy, found that arousing special neurons while patients were under local anesthesia caused them to vividly remember sophisticated events. The mind, then, relies on issue, Penfield concluded.
Now researchers at MIT say they place this observation for the test in an extensive study showing the direct reactivation of certain hippocampus neurons can lead to very special memory recall. And to do this, all they used was light.
“We illustrate that behaviour depending on high-level cognition, which includes the reflection of a particular memory, can be generated in a mammal by highly special physical activation of a special little subpopulation of brain cells — in this case by light,” Susumu Tonegawa, a biology and neuroscience professor at MIT, Nobel laureate and lead author of the analysis, said in a news release.
For the study, published online today in the journal Nature, researchers used optogenetics, a technique that joins genetic and optical strategies to command special events in special cells. (The tech was co-invented by MIT’s Ed Boyden, who last year proposed using optogenetics to induce light susceptibility in the retina and ultimately restore eyesight within the blind.)
Using optogenetics to arouse memory, the researchers first learned which brain cells in the hippocampus were active in a mouse exploring a new surroundings. The genes were then coupled by them activated in those brain cells using the genes for channelrhodopsin-2 (ChR2), a light-activated protein found in optogenetics.
“We desired to artificially activate a recollection less the normal essential sensory encounter, which provides experimental evidence that even ephemeral phenomena, including personal memories, reside in the physical machinery of the mind,” said coauthor Steve Ramirez, a graduate student in Tonegawa’s laboratory.
The team then used tiny optical fibers to pulse light to neurons with this particular genetic couplet so that, by seeing the neurons correlated with experiential learning light up, they may tag the physical system of neurons connected with a specific memory.
Their ultimate step was supposed to observe mice entering an environment, produce a light shock with their feet to instruct the mice to worry the environment, tag the brain cells that have been activated with ChR2, and expose only those brain cells to pulses of light in a completely different environment. Sure enough, the mice assumed defensive, immobile crouches — a hint that they were remembering the anxiety they experienced while in the first surroundings.
These findings are just preliminary, but the researchers consider that this light-induced fear demonstrates the mice were recalling the shocks from another location and time, and that light alone artificially re activated that special memory by arousing the neurons they had tagged.
Tonegawa says their findings call into question Descartes’ declaration the head is different from the body and are unable to be examined like a natural science: “He was erroneous. This experimental method will be the ultimate manner of illustrating that mind, like memory recall, relies on changes in question.”
The researchers suggest that their approach could improve the research of neurodegenerative and neuropsychiatric illnesses. “The more we understand about the transferring pieces which make up our brains,” said grad student Ramirez, “the better equipped we are to discover what happens when brain pieces break down.”