[Marxism] In Memory-Bank ŒDialogue,¹ the Brain Is Talking to Itself - FYI - Fascinating!

Bonnie Weinstein giobon at sbcglobal.net
Mon Dec 18 11:12:13 MST 2006


In Memory-Bank ŒDialogue,¹ the Brain Is Talking to Itself
By NICHOLAS WADE
December 18, 2006
http://www.nytimes.com/2006/12/18/science/18memory.html

New recordings of electrical activity in the brain may explain a major part
of its function, including how it consolidates daily memories, why it needs
to dream and how it constructs models of the world to guide behavior.

The recordings capture dialogue between the hippocampus, where initial
memories of the day¹s events are formed, and the neocortex, the sheet of
neurons on the outer surface of the brain that mediates conscious thought
and contains long-term memories.

Such a dialogue had been thought to exist, but no one had been able to
eavesdrop on it successfully. The new insight has emerged from recordings of
rat brains but is likely to occur in much the same way in the human brain,
which has analogous structures and the same basic principles of operation.

The finding, reported on the Web site of the journal Nature Neuroscience by
Daoyun Ji and Matthew A. Wilson, researchers at the Massachusetts Institute
of Technology, showed that during nondreaming sleep, the neurons of both the
hippocampus and the neocortex replayed memories ‹ in repeated simultaneous
bursts of electrical activity ‹ of a task the rat learned the previous day.

The researchers could interpret the memories through electrodes inserted
into the rats¹ brains, including into special neurons in the hippocampus.
These neurons are known as ³place cells² because each is activated when the
rat passes a specific location, as if they were part of a map in the brain.
The activation is so reliable that one can tell where a rat is in its cage
by seeing which of its place cells is firing.

Earlier this year Dr. Wilson reported that after running a maze, rats would
replay their route during idle moments, as if to consolidate the memory,
although the replay, surprisingly, was in reverse order of travel. These
fast rewinds lasted a small fraction of the actual time spent on the
journey.

In the findings reported today, the M.I.T. researchers say they detected the
same replays occurring in the neocortex as well as in the hippocampus as the
rats slept. The rewinds appeared as components of repeated cycles of neural
activity, each of which lasted just under a second. Because the cycles in
the hippocampus and neocortex were synchronized, they seemed to be part of a
dialogue between the two regions.

The researchers recorded electrical activity only in the visual neocortex,
the region that handles input from the eyes, but they assumed many other
regions participated in the memory replay activity. One reason is that there
is no direct connection between the visual neocortex and the hippocampus,
suggesting that a third brain region coordinates a general dialogue between
the hippocampus and all necessary components of the neocortex.

Larry Squire, a neuroscientist who studies memory at the University of
California, San Diego, noted that the replay system in the neocortex had not
been seen before. The fact that it occurred during sleep ³would certainly
provide one clue that part of the function of sleep is to let us process and
stabilize the experiences we have during the day,² Dr. Squire said.

Because the fast rewinds in the neocortex tended to occur fractionally
sooner than their counterparts in the hippocampus, the dialogue is probably
being initiated by the neocortex, and reflects a querying of the
hippocampus¹s raw memory data, Dr. Wilson said.

Brain researchers have long assumed that immediate memories are laid down in
the hippocampus and later transferred to the neocortex for long-term
storage. Dr. Wilson said the process was not just a transfer of memory,
however, but more probably a sophisticated processing of data in which the
neocortex learned selective information from the hippocampus.

³The neocortex is essentially asking the hippocampus to replay events that
contain a certain image, place or sound,² he said. ³The neocortex is trying
to make sense of what is going on in the hippocampus and to build models of
the world, to understand how and why things happen.²

These models are presumably used to direct behavior, Dr. Wilson said. They
are able to generate expectations about the world and plausibly fill in
blanks in memory.

Though the neocortex learns from the hippocampus, the raw memory traces,
from childhood onward, are not transferred and are probably retained in the
hippocampus, Dr. Wilson said. If so, the forgetfulness of age would arise
because of problems in accessing the hippocampus, not because the data has
vanished.

The subject matter of the neocortex-hippocampus dialogue in rats seems
mostly to concern recent events. This is consistent with what people report
when awoken from nondreaming sleep ‹ usually small snatches of information
about recent events. Dr. Wilson also said that the new findings, by showing
activity in the visual neocortex, confirmed that rats had humanlike dreams
with visual imagery, a possibility some researchers had doubted.






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