Seconds before a memory pops
up, certain nerve cells jolt
into collective action. The discovery of this signal, described in the Aug. 16 Science, sheds light on the mysterious brain processes that store
and recall information.
Electrodes implanted in the
brains of epilepsy patients picked up neural signals in the hippocampus, a key
memory center, while the patients were shown images of familiar people and
places, including former President Barack Obama and the Eiffel Tower in Paris. As
the participants took in this new information, electrodes detected a kind of
brain activity called sharp-wave ripples, created by the coordinated activity
of many nerve cells in the hippocampus.
Later blindfolded, the patients
were asked to remember the pictures. One to two seconds before the participants
began describing each picture, researchers noticed an uptick in sharp-wave
ripples, echoing the ripples detected when the subjects had first seen the
That echo suggests that these
ripples are important for learning new information and for recalling it later, Yitzhak
Norman of the Weizmann Institute of Science in Rehovot, Israel, and colleagues
write in the study.
Earlier studies suggested that
these ripples in the hippocampus were important for forming memories. But it
wasn’t clear if the ripples also had a role in bringing memories to mind. In another
recent study, scientists also linked synchronized ripples in two parts of the
brain to better memories of word pairs (SN Online: