Neurons Shift During Repeated Navigation Of Identical Paths

In a caller study, Northwestern University neurobiologists recovered nan brain's soul GPS changes each clip we navigate a familiar, fixed environment.

This intends that if personification walks nan aforesaid way each time - and nan way and surrounding conditions stay identical - each locomotion still activates different "map-making" encephalon cells, aliases neurons.

Not only does this find shed ray connected nan basal enigma of really nan encephalon processes and stores spatial memories, but it besides could person profound implications for scientists' knowing of memory, learning and moreover aging.

The study will publish on Wednesday (July 23) successful nan diary Nature.

Our study confirms that spatial memories successful nan encephalon aren't unchangeable and fixed. You can't constituent to 1 group of neurons successful nan encephalon and say: 'That representation is stored correct there.' Instead, we're uncovering that memories are passed among neurons. The nonstop aforesaid acquisition will impact different neurons each time. It's not a abrupt change, but it slow evolves."

Daniel Dombeck, study's elder author, Northwestern University

Dombeck is simply a professor of neurobiology and nan Wender-Lewis Teaching and Research Professor astatine Northwestern's Weinberg College of Arts and Sciences. The study was a collaboration among Dombeck and 3 members of his laboratory: Jason Climer, Heydar Davoudi and Jun Young Oh. Climer, who is 1 of nan study's co-first authors, is now an adjunct professor of molecular and integrated physiology astatine nan University of Illinois, Urbana-Champaign.

A representation mystery

Located heavy wrong nan brain's temporal lobe, nan hippocampus stores memories related to spatial navigation. For decades, neurobiologists thought nan aforesaid hippocampal neurons encoded memories of nan aforesaid places. In different words, nan way personification mightiness return from their chamber to their room should activate nan nonstop aforesaid series of neurons during each midnight locomotion for a solid of water.

About 10 years ago, however, scientists imaged mice's brains arsenic they ran done a maze. Even arsenic nan mice ran done nan aforesaid maze time aft day, different neurons fired during each run. Scientists wondered if nan results were a fluke.

"People successful nan section started to wonderment if nan mice were genuinely having nan aforesaid acquisition during each tally done nan maze," Dombeck said. "Maybe they tally faster connected immoderate days. Maybe nan smells alteration from time to day. Maybe location are subtle, unavoidable biology aliases behavioral differences that alteration nan wide experience."

'We controlled for everything we perchance could'

To probe these questions, Dombeck and his squad designed an research that gave them unprecedented power complete nan mice's sensory input. First, nan squad employed a cutting-edge multisensory virtual reality strategy - previously developed successful Dombeck's laboratory - to guarantee nan animals' knowledgeable identical ocular cues. Then, nan mice ran done nan virtual maze connected treadmills, ensuring precise measurement of speed. Finally, nan scientists put cones connected nan mice's noses to supply identical smells for each session.

After moving nan research respective times, nan results were clear. Even successful a highly reproducible virtual world, nan encoded neurons still drifted. The uncovering confirmed that nan brain's spatial maps are inherently dynamic, perpetually updating sloppy of really fixed a abstraction mightiness be.

"We controlled for everything we perchance could," Dombeck said. "I was convinced we were going to get nan other consequence and show that memories really are identical for nan aforesaid space. But it turns out, they are not. A somewhat different group of neurons activated each time."

Implications for aging

Although fewer patterns arose passim nan people of nan experiment, Dombeck and his squad did announcement 1 accordant factor. The astir excitable neurons, which were much easy activated, maintained much unchangeable spatial memories passim aggregate runs done nan virtual maze. Because neuron excitability decreases pinch age, nan uncovering could thief scientists understand nan domiciled of aging arsenic it relates to nan brain's expertise to encode caller memories.

"Some neurons do look to beryllium amended astatine holding onto nan original representation than others," Dombeck said. "Really excitable neurons look to shop memories nan best. The ones that occurrence much weakly are nan ones that extremity up changing. So location does look to beryllium immoderate mini constituent of nan original representation that's still location successful this mini fraction of neurons."

Dombeck and his squad are still pondering why nan activated neurons alteration moreover though nan abstraction remains precisely nan same. Although he's still unsure, Dombeck said nan logic mightiness beryllium related to time.

"Even if you person nan nonstop aforesaid experience, it has to beryllium occurring astatine a different time," Dombeck said. "If I hike nan aforesaid way twice, and it's identical some times, I astir apt still want to retrieve that I did nan aforesaid hike twice. It's imaginable that nan encephalon forces america to return very akin experiences that hap astatine different times and retrieve them successful somewhat different ways. That gives america entree to memories of those individual experiences."

The study, "Hippocampal representations drift successful unchangeable multisensory environments," was supported by nan National Institutes of Health (grant number R01MH101297, T32AG020506 and 1F32NS116023).