A study published in the Proceedings of the National Academy of Sciences this week shows that preschool children whose mothers display nurturing behaviors have a larger hippocampus than their peers.

The hippocampus is a part of the brain tied to memory, learning and stress regulation, suggesting such behavior can have significant effects on abilities related to how a child learns and performs at school.

Researchers identified the correlation after placing children ages 3 to 6 and their mothers in a scenario meant to mimic the stressors of real life: Children were presented with a brightly wrapped gift and told they had to wait for their mothers to fill out a series of forms before they could open it.

The mothers who offered support to their (likely impatient) children and helped them deal with their frustration were rated as being nurturing. Those who either ignored or scolded their children were not.

Four years later, researchers did MRI scans of the children who participated in the earlier scenario. They discovered that children from mothers rated "nurturing" had hippocampi 10 percent larger than others.

Read more: Mom’s love good for child’s brain

Think gym class isn't important? A review of 14 studies involving 12,000 children suggests that physical activity promotes significantly better academic performance.

According to researchers, this may be for a few reasons. Exercise may help kids' brains by increasing blood flow to the brain. Activity may also make kids happier and ready to sit down and learn in the classroom. Or sports may be teaching them the discipline necessary to work hard at academics.

Read more: Active children 'get better grades'

University of California, Berkeley researchers have found that individuals from lower socioeconomic classes may be better adept at recognizing signs of distress and are quicker to express compassion than their upper class counterparts.

Results from a survey of 148 UC Berkeley students showed that individuals from lower class backgrounds report feeling compassion more often than their middle and upper class peers. Researchers also performed experiments to monitor the heart rates of 64 students as they watched emotionally charged videos about families coping with childhood cancer. They found that while both groups reacted similarly to neutral videos, the lower class group showed a calming response typical of that experienced when the body prepares itself to take care of another person.

In a final experiment, 106 students were divided into pairs that competed against each other in stressful mock job interviews. Results showed that lower class interviewees felt their competitors were experiencing more stress and reported a greater deal of compassion and sympathy.

ABSTRACT: Class and compassion: Socioeconomic factors predict responses to suffering.

Legalizing same sex marriage is linked to a 13 percent drop in clinic visits, say researchers from Columbia University Mailman School of Public Health.

Surveying patients at a community-based clinic in Massachussetts, they found that visits for stress-related conditions such as hypertension and depression were significantly reduced following the passage of the state's same-sex marriage law. Examining the clinic's billing records, they discovered health costs were simultaneously reduced 14 percent.

Read more: Same-Sex Marriage Laws Reduce Doctor Visits and Health Care Costs for Gay Men

Fetal brains develop according to the environment they will enter based on the mental state of their mothers, shows a study on mothers and babies from the University of California-Irvine.

Surprisingly, researchers found that babies thrived best when their mothers' mental state stayed consistent before and after birth. This was true even for depressed mothers. Changes in mental state, whether going from happy to sad or sad to happy, slowed the children's development.

According to the researchers, the findings suggest that pregnant women should be screened and treated for depression.

Between 10 and 20 percent of women will experience depression during pregnancy and up to 20 percent will become depressed after birth.

Read More: Sensing Mom's Psychological State From Within The Womb