Researchers are learning more about how estrogen affects female animals in hopes of determining  whether the hormone could someday be used to improve short-term learning and memory skills in women.

Studies have already established that the region of the brain called the hippocampus responds to estrogens and is involved in cognition and memory.

The Ontario research team had already found that female mice given systemic injections of the hormone improved their short-term learning skills so, in this new study, they decided to look at what happened if they injected the hormone directly into hippocampus.

Brain cells communicate by passing signals through long cell extensions called axons to tiny spines located on branches of adjacent neurons. Within minutes of adding more estrogen, the team saw huge numbers of spine synapses growing on those branches.

But, while they expected to see greater electrical activity with more spines, but were surprised to find just the opposite in treated brain tissue alone.  The scientists said they believe estrogens increase the number of synapses but that those potential connections remain silent unless they're used for learning.

“It’s the ‘use it or lose it,’ process,” say the researchers of their study, which appears in Proceedings of the National Academy of Sciences.