Prior to a new University study, scientists didn’t believe that a cell could change its behavior.
But in a recently released study that examined how the brain changes as people learn, researchers found that cells can change their behavior.
The collaborative study between two University laboratories also found that the brain contains more synaptic plasticity — the ability to undergo change that promotes learning and memory — than previously believed, according to a March 18 University of Michigan Health System press release.
Geoffrey Murphy, lab director and an associate professor of molecular and integrative physiology, described the surprising cell behavior discovered in the study.
“For example, if you’re waiting for someone to show up, you modify your behavior,” Murphy said. “For us, as an organism, that’s pretty easy, but for a single neuron cell, it’s extraordinary. That makes us think that there must be some third party. It’s a really complex event that appears to happen sort of beyond what you’d expect an individual cell to know.”
Murphy said what they discovered during their research wasn’t initially the main focus of the study.
“This was sort of a side project from those experiments,” Murphy said. “We were interested in knowing how those newborn neurons contribute to the cellular phenomena that we think involves acquiring memories.”
The study investigated the role of newborn neurons and synaptic plasticity in the brain, he said.
“Synaptic plasticity is a broad term used to indicate how changes occur in the brain — and specifically to this study — how neurons change and interact in the brain,” Murphy said.
Jack Parent, director of the University’s Neurodevelopment and Regeneration Laboratory and an associate professor of neurology, wrote in an e-mail interview that new nerve cells are born in adult brains and “are thought to play a specific role in certain types of learning and memory.”
Murphy explained that new neurons constantly replenish themselves in the hippocampus region of the brain — a crucial part of the brain associated with short- and long-term memory.
“One of the reasons that this region is so important is because it is required for acquiring memories,” Murphy said. “And specifically we call them declarative memories — these are memories for people, places, events.”
Genetically modified mice were used to conduct the study, Murphy said. The mice were given a toxic compound that prevented new neurons from developing so the scientists could examine their synaptic plasticity. The team then removed the brains from the mice to examine how their synaptic plasticity was affected, according to Murphy.
“We wanted to see what would happen if we permanently suppressed neurons,” he said. “We expected the synaptic plasticity to go away forever.”
But the results came as a surprise, Murphy said.
“What we found was that the synaptic plasticity actually comes back, in the absence of neurons,” he said. “The network sort of rearranges itself to accommodate the loss of those newborn neurons.”
However, Murphy said he was still unsure why the synaptic plasticity returned to the mice.
“If you turn off the birthing of neurons, the ones that are born right before that are more likely to survive,” he said. “We don’t really understand how that happens.”
Parent described how new nerve cells play a roll in learning and memory.
“Our new findings suggest that the new nerve cells born in the adult brain likely play a very important role in learning and memory, a role so important that when we get rid of the adult-born nerve cells, the mature cells can be recruited to act like immature nerve cells,” Parent wrote. “It is kind of like teaching an old dog new tricks — the mature nerve cells become less “inhibited” and more plastic (or malleable) when we get rid of the young cells.”
The study is different than other studies conducted on this topic because it considers long-term responses of the brain, Murphy said.
If scientists are able to pinpoint the signals that govern the relationship between newborn neurons and synaptic plasticity, they may be able to do something if the brain is damaged or aging, Murphy said.
Parent wrote the discoveries from the study will lead to major changes in the field of neurodevelopment and regeneration, including some changes in his own lab.
“Much of my laboratory now focuses on generating stem cells by reprogramming mature cells, such as skin cells, and making the stem cells into nerve or heart cells,” Parent wrote. “We are taking skin cells from patients with specific disorders to study how the diseases are caused and identify new treatments.”
Stephen Maren, director of the University’s Neuroscience Graduate Program, wrote in an e-mail interview that the study provides potential insight into the brain’s ability to overcome disruptions.
“The work is quite exciting because it reveals that the brain can compensate for a variety of insults — in this case, a genetic manipulation that prevents new cells from being born in the hippocampus,” Maren wrote. “It suggests that there are molecular mechanisms involved in re-establishing normal brain function after it is perturbed. Understanding these mechanisms may inform new clinical interventions for brain insults.”