Alzheimer's disease

Hippocampus minds the memory gap

NYU (US)—The brain’s hippocampus appears to play a pivotal role in stitching together disparate elements and experiences to create cohesive memories, according to a new study. The findings could have implications for treating conditions such as Alzheimer’s disease and amnesia.

Researchers Lila Davachi, assistant professor in New York University’s department of psychology and its Center for Neural Science, and graduate student Bernhard Staresina, wanted to find out if the hippocampus acted as the “glue” that turned seemingly unrelated experiences into memory. Their findings appear in the latest issue of the journal Neuron.

“Our results show that a core function of the hippocampus is the capacity to bridge gaps between elements of our experiences so that we may later remember them,” explains Davachi. “But they may also explain the role of this portion of brain more broadly in memory and cognition.

“All kinds of functions, such as spatial navigation, memory, and vivid imagery, depend upon the ability to bridge gaps in our experience and thoughts. If the hippocampus is the glue that holds together our experiences, this can explain the role of this region in other forms of memory and thought.”

In order to transform an experience into a memory, the individual, disparate elements of that experience that unfold across space and time need to be somehow compiled into a singular memory.

Researchers have previously determined that the brain’s hippocampus, which is located in the medial temporal lobe, plays a significant role in memory. But its contributions to linking together individual experiences into a larger, singular memory—or associative memory—had not been well understood.

In the study, subjects were shown a series of visuals composed of different elements, an object and a background color, for example. Subjects were then asked to recall the object separately and in combination with its associated color. Under some conditions, subjects could only recall the previously presented object (unlinked memory); under others, they were able to remember both the object and its associated color (a linked memory).

The researchers then used functional magnetic resonance imaging (fMRI) which gauged which parts of the brain were active under the linked and unlinked memory conditions. The results showed that there was significant hippocampus activity when the subjects successfully formed linked memories, but not when the elements were separately encoded.

The results also may explain the role of the hippocampus in a broader sense as far as memory and cognition go, Davachi notes, because a range of functions depend on the ability to bridge gaps in experience and thought.

“As we learn more about how the brain forms memories, we can better understand what makes them go awry and then explore behavioral and neurological remedies,” concludes Davachi.

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