By GREGORY ZELLER //
Straight from the hippocampus (and the horse’s mouth) comes a new research paper in the journal Science, highlighting landmark innovations in human brain mapping.
Published Aug. 16 by the peer-reviewed academic journal of the American Association for the Advancement of Science, “Hippocampal Sharp-Wave Ripples Linked to Visual Episodic Recollection in Humans” carries a heavy title but a simple synopsis: real-time mapping of specific brain neurons that fire when humans form visual memories, and again when they recollect them.
The study, a collaboration of the Feinstein Institute for Medical Research and Israel’s Weizmann Institute of Science, involved a series of brain-electrode experiments performed on volunteer epilepsy patients.
Though the research is not directly epilepsy-related, this particular cohort already has electrodes in place for monitoring seizure activity in the brain – tools that also plug into the work of Northwell Health Epilepsy Surgery Director Ashesh Mehta and his collaborators at the Feinstein Institute and abroad.
The sensitive electrodes, a carefully curated collection of visual stimuli and a singularly human ability have given Mehta and co. unique insights into human brain-mapping functions – and unprecedented understanding of how (and where) memories are stored.
Most current knowledge of human brain functionality “derives from animal work,” the researcher noted, but no matter how closely rodent or primate or some other mammalian brain mimics the human noggin, “none of them have the higher-developed brain that makes us uniquely human.”
“The advantage of being able to talk is critical,” Mehta said. “Humans can. Monkeys can’t.”
The science, of course, is slightly thicker than that: electrophysiological events, intracranial recordings, synchronized neuronal activity, conscious cognition and so forth.
But for the researchers – including Mehta, also director of the Feinstein Institute’s Laboratory for Human Brain Mapping – the connection between hippocampal “sharp-wave ripples” and the formation/recollection of visual memories is crystal clear.
One primary finding: When you see someone’s face and then later recall it, you’re “activating the same set of neurons,” according to Mehta.
“When you first see it, it’s your eyes that drive the neuron activity,” the scientist said. “But when you recall it, it’s these hippocampal waves that stimulate the neuron activity.
“It’s these ripples in the hippocampus that create the experience of recognizing something like a face,” he added.
For the non-neuroscience PhD out there, it works thusly: Volunteer patients were shown pictures of landmarks and faces, essentially creating a series of new memories, and their brains, already wired with epilepsy-focused electrodes, were closely monitored.
The patients were subsequently asked to remember the faces – Smiling or not? Looking left or right? – and to remember details about the landmarks.
The process of recalling the pictures spiked “sharp-wave ripple” activity in the hippocampus – sometimes in one area, sometime in another, each relating to SWR activity that spiked when the individual memories were formed.
In essence: a brain-mapping breakthrough that shows researchers precisely where memories of different stimuli are stored in all that gray matter.
“There are different areas of the brain that seem to respond preferentially to faces,” Mehta told Innovate LI. “And an area just near it that responds to places. And other areas that respond to words, and to [everyday objects], and to body parts.
“These are all very common stimuli that we see in our visual world daily,” he added. “And there are groups of neurons that cluster in certain areas, and respond to those different classes of stimuli.”
The experiments engendered several key findings. For one thing, the SWR rate during picture viewing – known also “memory encoding” – closely predicted subsequent recall performance, meaning the more SWR activity during encoding, the better the recollection.
Researchers also detected a “transient increase” in the SWR rate preceding the patients’ verbal recollections. In essence, the patients’ memories spiked as they prepared to talk about them.
That real-time data furthers the mapping precision – and precision is the name of the game here, according to Mehta, who suggests that a “better sense of the functional areas of the brain” could give surgeons a more accurate roadmap when they’re forced to go in.
“The brain areas we don’t want to remove when we do surgery,” he added. “Where we want to spare as much as possible.”
With several related studies completed and/or under review by other scientific journals, what Mehta called a “unique patient population” – pre-wired for brain scans and plenty ready to talk about it – stands out in this next step of neuroscience.
And while the research isn’t necessarily directed toward epilepsy treatments, those talkative volunteers are furthering several brain-related sciences – including potential new treatments for their own afflictions, according to Mehta.
“This could also help us understand how to treat their particular form of epilepsy,” he added. “So, they’re helping people in general, but they’re also helping themselves.”