How the brain remembers what happens and when

August 8, 2011

Neuroscientists at New York University have identified the parts of the brain we use to remember the timing of events within an episode.

The researchers ran animal subjects through a temporal-order memory task in which a sequence of two visual objects were presented and the subjects were required to retrieve that same sequence after a delay. To perform the task correctly, the subjects needed to remember both the individual visual items (“what”) and their temporal order (“when”). During the experiment, the researchers monitored the activity of individual brain cells in the subjects’ medial temporal lobe (MTL).

Their results showed that two main areas of the MTL are involved in integrating “what” and “when”: the hippocampus and the perirhinal cortex. The hippocampus, which is known to have an important role in a variety of memory tasks, provides an incremental timing signal between key events, giving information about the passage of time from the last event as well as the estimated time toward the next event. The perirhinal cortex appeared to integrate information about what and when by signaling whether a particular item was shown first or second in the series.

Their findings provide insight into the specific patterns of brain activity that enable us to remember both the key events that make up our lives and the specific order in which they happened, the researchers said.

Ref.: Yuji Naya and Wendy A. Suzuki, Integrating What and When Across the Primate Medial Temporal Lobe, Science, 5 August 2011: 773-776 [DOI: 10.1126/science.1206773]