In Review

Imagine you’re driving through your neighborhood, with scenery of trees, houses, and sidewalks whizzing by outside your window. Now imagine a squirrel runs across the road in front of you. Will you see it in time to attempt to avoid it?

Part of the answer rests with how old you are.

One reason humans are generally good at discerning smaller moving objects in the foreground is that the brain becomes desensitized to larger background stimuli. “The human brain cannot possibly process all of the information around us,” says Duje Tadin, a professor of brain and cognitive sciences at Rochester. “Being less sensitive to things that are less important makes the brain more efficient and faster at accomplishing the more important tasks.”

For example, there are two basic ways the brain can distinguish such objects from moving backgrounds. It can enhance the objects that matter or it can suppress the background, which has the effect of enhancing the objects. The latter is “the more efficient option,” Tadin says. “Think about trying to have a conversation in a room with high background noise. It is more effective to find a way to turn off the noise than it is to just try speaking more loudly.”

In a study published in the journal Nature Communications, Tadin shows that as we age, our brains lose some of the ability to suppress background motion, therefore becoming less sensitive to smaller foreground objects. (Researchers have observed the same phenomenon in people with schizophrenia and depression.)

The differences aren’t large. Younger adults in the study took an average of 20 milliseconds to pick out moving foreground objects, while adults aged 65 and older took about 30 milliseconds. But “those extra milliseconds could make a big difference,” says Woon Ju Park, a former postdoctoral associate in Tadin’s lab and now a research associate at the University of Washington. They could mean the difference between hitting and avoiding the squirrel—or a child or a distracted pedestrian.

The good news is that with some training, older adults can narrow or eliminate the gap between them and their younger counterparts. Notably, the older participants who underwent training didn’t get better at seeing the smaller moving object; instead, they became less sensitive to the background motion, just like younger adults.

“Most of the time when you train something in the brain, things get better,” Tadin says. “This is a case where when you train something in the brain, you get better at seeing moving objects on a moving background, but you get worse at seeing the background. This showed us that these two things are really integrally connected, because when we affected one, the other one changed.”

—Lindsey Valich

Why Some African Nations Struggle with Ethnic Strife, and Others Don’t

The continent of Africa, made up of 54 nations and thousands of distinct ethnic groups, is fertile ground to examine ethnic conflict. In a paper published in the journal International Organization, Rochester political scientist Jack Paine, an expert on comparative politics and game theory, posed a simple question: why are some African nations mired in ethnic conflicts and others not? Civil wars and insurgencies have occurred in Sudan and Uganda, for example, but not in Kenya. Benin has experienced several coups and coups attempts after independence, but Côte d’Ivoire has not.

Previous researchers have looked to the postcolonial era to explain ethnic conflicts on the continent—and haven’t sufficiently explained variations within Africa, according to Paine. Taking a longer-term perspective, he found that “frequently, precolonial political organizations sowed the seeds of later discord.” African countries that include ethnic groups that were organized as states prior to European colonization are at much higher risk for violence.

During the precolonial period, Africa featured diverse forms of political organization, ranging from stateless societies, such as the Maasai in Kenya, to hierarchically organized societies with standing armies, such as the Dahomey in Benin. Centralized states often participated in violent activities to promote intergroup inequality, says Paine.

During the colonial period, ethnic groups organized as states were elevated in the colonial governance hierarchy. Ruling through existing local political hierarchies reduced colonial administrative costs. This strategy was most closely associated with British rule, which favored indirect governance.

As a result, “distinct states and identities created privileged subsets of the population that, when independence became imminent in the 1950s and 1960s, were unwilling to forge organizational ties with other ethnic groups,” Paine says.

Common policy recommendations for ending civil wars may not work without understanding these long-term factors, he warns. For example, promoting inclusive power-sharing agreements will likely not stem violence. Deepening democratic institutions to increase the credibility of power-sharing agreements—and the hope that over time the legacies of distinct statehood will lessen—provide a possible but uncertain path out of the coup and civil war trap.

—Sandra Knispel

New College Students Need Time Alone

Although new college students may fear loneliness, there’s a distinction between loneliness and time alone—and the latter is especially important for students adjusting to their new lives away from home.

That’s according to Thuy-vy Nguyen ’18 (PhD), who studied solitude—time spent alone, and without stimuli from electronic devices—as a doctoral student at Rochester. In a study published in the journal Motivation and Emotion, Nguyen, who will be an assistant professor of psychology at Durham University in England beginning this fall, found that “approaching solitude for its enjoyment and intrinsic values is linked to psychological health, especially for those who don’t feel as if they belong to their social groups”—a feeling that may come and go but is nearly universal to people thrust into a new environment. “These findings highlight the importance of cultivating the ability to enjoy and value solitary time as a meaningful experience rather than trying to disregard it or escape from it.”

—Sandra Knispel

A Deeper Look at the ‘Longevity Gene’

As humans and other mammals grow older, their DNA is increasingly prone to breaks, which can lead to gene rearrangements and mutations—hallmarks of cancer and aging. A gene called sirtuin 6 (SIRT6) is often called the “longevity gene” because of its important role in organizing proteins and recruiting enzymes that repair broken DNA. Mice without the gene age prematurely, for example, while mice with extra copies live longer.

But as SIRT6 goes about its work in a range of species, only some of the species have long lifespans. So what about SIRT6 accounts for the difference?

As they describe in the journal Cell, Rochester biology professors Vera Gorbunova and Andrei Seluanov, and Dirk Bohmann, professor of biomedical genetics, observed DNA repair in 18 rodent species with lifespans ranging from 3 years (mice) to 32 years (naked mole rats and beavers). Analyzing the molecular differences among the SIRT6 proteins in the various species, they identified five amino acids in beaver SIRT6 responsible for making it “more active in repairing DNA and better at enzyme functions” than SIRT6 in mice, Gorbunova says. When the researchers inserted beaver and mouse SIRT6 into human cells, the beaver SIRT6 better reduced stress-induced DNA damage compared to when researchers inserted the mouse SIRT6.

Although it appears that human SIRT6 is already optimized to function, “we have other species that are even longer lived than humans,” Seluanov says. Have such species—like the bowhead whale, which can live more than 200 years—evolved even more robust SIRT6 genes?

The ultimate goal of the work is to prevent age-related diseases, Gorbunova says. “If diseases happen because of DNA that becomes disorganized with age, we can use research like this to target interventions that can delay cancer and other degenerative diseases.”

—Lindsey Valich