How are memories saved? Where does the recording take place and how?

—Michael Saayman, Cape Town, South Africa

Michael Rugg, director of the Center for the Neurobiology of Learning and Memory at the

University of California, Irvine, provides an explanation:

UNDERSTANDING EXACTLY how the brain encodes and stores memories is one of the central, unsolved mysteries in neuroscience. Currently the most widely accepted theory is long-term potentiation (LTP)—the lasting communication established between two neurons when they are stimulated simultaneously.

As a person processes an event, two neurons pass information through a small space called a synapse. This chemical conversation triggers an intricate cascade, inviting nearby neurons to fire and ultimately creating a network of connections with varying strengths. Afterward, this pattern of connections, or memory, remains within the network of neurons that processed the event.

Although many areas of the brain contain synapses capable of creating strong patterns of connectivity, the hippocampus is a particularly favorable spot for recording memories. This brain region plays a critical role in learning new information, forming spatial memories

and storing short-term memories as long-term ones.

Memories formed with the hippocampus are especially rich because they integrate input from several areas of the brain, and the hippocampus contains densely packed layers of neurons. In addition, damage to this region and nearby areas causes profound and permanent amnesia—an inability to store new memories or to recall old ones—and is observed in patients who have Alzheimer’s disease.

How does background noise affect our concentration?

—Philip Miele, Dublin, Ohio

Mark A. W. Andrews, director and professor of physiology at Lake Erie College of Osteopathic Medicine at Seton Hill University in Greensburg, Pa., offers a reply:

BACKGROUND OR LOW-LEVEL noise in the home, work or school often disrupts people’s concentration. According to the National Institute for Occupational Safety and Health, ambient noise also affects people’s health by increasing general stress levels and aggravating stress-related conditions such as high blood pressure, coronary disease, peptic ulcers and migraine headaches. Continued exposure does not lead to habituation; in fact, the effects worsen.

Several studies have indicated that stress resulting from ongoing white noise can induce the release of cortisol, a hormone that helps to restore homeostasis in the body after a bad experience. Excess cortisol impairs function in the prefrontal cortex—an emotional learning center that helps to regulate “executive” functions such as planning, reasoning and impulse control. Some recent evidence indicates that the prefrontal cortex also stores short-term memories. Changes to this region, therefore, may disrupt a person’s capacity to think clearly and to retain information.

Though not definitive, recent research also suggests that noise-induced stress may decrease dopamine availability in the prefrontal cortex, where the hormone controls the flow of information from other parts of the body. Stress resulting from background noise, then, may decrease higher brain function, impairing learning and memory.