How Memory Works (and How to Preserve It)

Bret S. Stetka, MD; Felipe De Brigard, PhD


February 13, 2015

In This Article

Editor's Note: Over 5 million Americans currently have Alzheimer disease, the most common form of dementia.[1] One third of people older than 70 years without clinical dementia have memory loss severe enough to disrupt their daily routine.[2] Medscape recently spoke with memory expert Felipe De Brigard, PhD, an assistant professor in the Center for Cognitive Neuroscience at Duke University, about our evolving understanding of how memory works and what interventions are showing promise in preventing this incredibly prevalent condition.

Medscape: For decades, textbooks have taught us that the hippocampus is the brain's "memory center." But your work and that of others suggests that, like most mental functions, it's not that simple—that multiple brain regions are involved in memory, and that the hippocampus has functions beyond memory. What is the current state of the science into how we form memories?

Felipe De Brigard, PhD: One of the most important findings in the neuroscience of memory during the past century was the observation that the hippocampus is essential for our capacity to remember life episodes. After having his hippocampi surgically removed in 1957 to treat severe epilepsy, Henry Molaison—better known by his initials H.M.—appeared to be incapable of storing new experiences. People he met after the surgery were always strangers to him, and places he visited always felt new, as did every food he tried and every event he attended. This finding made it tempting to think of the hippocampus as the "memory center."

However, the reality is way more complex. First, H.M. didn't really lose all his memory. He could still remember old personal events, as well as all sorts of facts that he had not personally experienced—for example, world news from the past and geographic information. The hippocampus, then, did not seem to be that necessary for retrieving information already stored. It seemed essential only for storing or encoding such information.

Further studies on H.M. demonstrated that he was still able to learn new procedural information, as well as form new habits and acquire new skills. So not all memory encoding was compromised.

Moreover, further studies—not only with H.M., but also other patients and healthy individuals, using various neuroimaging techniques—showed that the hippocampus appeared to be critical for other cognitive tasks in addition to episodic recollection. We now know, for instance, that we need the hippocampus to imagine possible ways in which personal events could have occurred in the past or may occur in the future, particularly when such mental simulations require the recombination of past information into coherent spatial scenes. Further studies have shown that the hippocampus is required to process certain complex spatial and visual discrimination tasks, as well as certain kinds of linguistic operations.

In sum, to say that the hippocampus is the memory center is, at best, incomplete and, at worst, misleading.


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