230 Self and the Phenomenon of Life
b2726 Self and the Phenomenon of Life: A Biologist Examines Life from Molecules to Humanity “9x6”10.10 Dialogue between the Neocortex
and Hippocampus
According to the systems theory of memory consolidation, declarative
memory starts as transient changes in the conscious brain, assembling a
variety of sensory inputs, using the prefrontal cortex as the coordination
center and the parietal cortex as the associative center. Every day we
receive countless information that involves time, place, emotion, inten-
tion, personal relations, and many others. For these fleeting experiences
to become long-term memory, the information from widely distributed
neocortical networks must be exported to the hippocampus, where they
are filtered, extracted, categorized, and coded. In effect, the hippocam-
pus fuses incoming information into a coherent trace. Consolidation con-
sists of gradually returning the memory trace to the neocortex for perma-
nent storage, by repeatedly activating the hippocampo-cortical pathway.
This is accompanied by activation of the genes, first in the hippocampus,
then in the cortical areas. This time-dependent storage process takes
hours or days to accomplish, depending on the species and the emotional
accompaniment of the experience. During this consolidation period the
memory trace is vulnerable to disruption, either by drugs or interference
with other experiences. As the memory trace “matures,” the role of the
hippocampus gradually (but not totally) recedes to the background, leav-
ing the cortical areas alone to sustain the permanent memory. However,
there is evidence that even long after memory consolidation, the hippo-
campus is still needed to keep the old memories intact.^41
In real life we rarely learn things that are totally new. More often
new information is mingled with pre-existing ones. To avoid perturba-
tion of the old knowledge, deposition of new facts requires the retrieval
of the old ones for integration and assimilation. This involves parallel
encoding in both the neocortex and hippocampus. Therefore, every
input from new experiences results in reorganization and strengthen-
ing of the old ones.^42 This scenario is consistent with the concept that
hippocampal neurogenesis during learning results in the rewiring of the
existing network.