Washington ? Using a powerful microscope, Karel Svoboda, a brain scientist at the Janelia Farm Research Campus in Ashburn, Va., peers through a plastic window in the top of a mouse’s head to watch its brain’s neurons sprout new connections — a vivid display of a living brain in action.

Ryan LaLumiere, a neurologist at the Medical University of South Carolina in Charleston, trains cocaine-addicted rats to suppress their craving — a technique he says may help human addicts.

Elizabeth Kensinger, the director of a neuroscience lab at Boston College, uses an MRI machine to picture the brains of Boston College hockey players as they remember high points and low points from the hockey season — the better to understand the effect of strong emotions on memory.

The work is shedding new light on how the brain handles memory storage, loss, fear, addiction and aging. Some explore the role of sleep — even a brief nap — in consolidating long-term memories. Others are building colorful wiring diagrams, nicknamed “Brainbows,” that use different shades to show which neurons connect with which.

The human brain contains some 100 billion neurons that are connected by an elaborate network of tiny wires called axons and dendrites.

Neurons communicate by passing chemical signals from axons to dendrites at junctions known as synapses.

The sender neuron sends a chemical transmitter, called glutamate, across the synaptic gap. The receiver neuron responds by firing a tiny jolt of electricity.

The brain responds to life experiences by adjusting the strength of individual synapses and by changing the pattern of connections between neurons. Scientists say this “plasticity” of the brain is the key to how animals and people learn, remember and forget.

Researchers are gaining new insights into various processes and problems of memory. For example:

• Alzheimer’s disease:

Li-Huei Tsai, the director of the Picower Institute for Learning and Memory in Cambridge, Mass., found a gene in mice that she said is a prime target for a drug that could treat, or even reverse, the effects of Alzheimer’s. She was able to restore lost memories in mice that had been drugged to produce Alzheimer’s-like symptoms.

• Sleep:

Recent work by William Fishbein, a psychologist at City College of New York, showed that even “a brief daytime nap” improves memory.

College students who napped did better on a memory test than those who stayed awake all day, he said.