This image shows
entorhinal "ocean cells" (red) and "island cells" (blue).
Green fluorescence
indicates ocean cells that have been genetically altered.
Image: Takashi
Kitamura
Neuroscientists identify a brain circuit that is critical
for forming episodic memories.
(September 23, 2015) When
you remember a particular experience, that memory has three critical elements —
what, when, and where. MIT neuroscientists have now identified a brain circuit
that processes the “when” and “where” components of memory.
In this image of
the entorhinal cortex, ocean cells are labeled with green fluorescence
and island cells
with red fluorescence. Blue fluorescence indicates the cell nuclei.
Image: Takashi
Kitamura
This circuit, which connects the hippocampus and a region of
the cortex known as entorhinal cortex, separates location and timing into two
streams of information. The researchers also identified two populations of
neurons in the entorhinal cortex that convey this information, dubbed “ocean
cells” and “island cells.”
Previous models of memory had suggested that the
hippocampus, a brain structure critical for memory formation, separates timing
and context information. However, the new study shows that this information is
split even before it reaches the hippocampus.
“It suggests that there is a dichotomy of function upstream
of the hippocampus,” says Chen Sun, an MIT graduate student in brain and
cognitive sciences and one of the lead authors of the paper, which appears in
the Sept. 23 issue of Neuron. “There is one pathway that feeds temporal
information into the hippocampus, and another that feeds contextual
representations to the hippocampus.”
The paper’s other lead author is MIT postdoc Takashi
Kitamura. The senior author is Susumu Tonegawa, the Picower Professor of
Biology and Neuroscience and director of the RIKEN-MIT Center for Neural
Circuit Genetics at MIT’s Picower Institute for Learning and Memory. Other
authors are Picower Institute technical assistant Jared Martin, Stanford University
graduate student Lacey Kitch, and Mark Schnitzer, an associate professor of
biology and applied physics at Stanford.