MEMORY
CONSOLIDATION AND HIPPOCAMPUS | ALCOHOLIC KORSAKOFF’S SYNDROME AND
DIENCEPHALIC AMNESIA
According
to an old concept of how the long-term memory develops after initial
acquisition is referred to as consolidation.
However, from a cognitive neuroscience perspective, consolidation is conceived
of as biological changes that underlie the long-term retention of learned
information, and we can ask what brain structures and systems support this
process.
Because
damage to the medial temporal lobe does not wipe out most of the declarative
memories formed over a lifetime, we know that the hippocampus is not the storehouse
of stored knowledge. Rather, the medial temporal lobe appears to support the
process of forming new memories; that is, the hippocampal region is critical
for the consolidation of information in long term memory. The strongest
evidence that the hippocampus is involved in consolidation comes from the fact
that amnesics have retrograde amnesia for memories from one to a few years
prior to the damage to the medial temporal lobe or diencephalon, a pattern that
does not support a storage role but rather a role in consolidation.
What
might consolidation involve at the neural level? One idea is that consolidation
strengthens the associations between multiple stimulus inputs and activations
of previously stored information. The hippocampus is hypothesised to coordinate
this strengthening, but the effects are believed to take place in the
neocortex. The idea is that once consolidation is complete, the hippocampus is
no longer required for storage or retrieval. Nonetheless, keep in mind that
although the memories are stored in the neocortex, the hippocampus is crucial
for consolidation.
Alcoholic Korsakoff’s Syndrome and Diencephalic Amnesia
The
medial temporal lobe is not the only area of interest in human memory. Amnesia
emerges from brain damage in other regions too. For example, damage to midline
structures of the diencephalon of the brain causes amnesia. The prime structures
are the dorsomedial nucleus of the thalamus and the mammillary bodies. Damage
to these midline subcortical regions can be caused by stroke, tumors, and
metabolic problems like those brought on by chronic alcoholism as well as by
trauma.
In
the last half of the nineteenth century, the Russian psychiatrist Sergei Korsakoff reported
an anterograde and retrograde amnesia associated
with alcoholism. Long term alcohol abuse can lead to vitamin
deficiencies that cause brain damage. Patients suffering from alcoholic
Korsakoff’s syndrome have degeneration in the diencephalon, especially the
dorsomedial nucleus of the thalamus and the mammillary bodies. It remains
unclear whether the dorsomedial thalamic nucleus, the mammillary bodies, or
both are necessary for the patients’ amnesia. Yet, damage to the diencephalon
can produce amnesia.
References:
Gazzaniga, M.S., Ivry, R., & Mangun, G.R.
(2002). Cognitive Neuroscience: The Biology of the Mind. New York: W.W. Norton.
Gleitman, L. R.,
Liberman, M., & Osherson, D. N. (Eds.)(2000). An Invitation to Cognitive
Science, 2nd Ed. Cambridge, MA: MIT Press.
Levinthal, C.F.
(1990). Introduction to Physiological Psychology. New Jersey: Prentice Hall.
Sternberg, R.J.
(2009). Applied Cognitive Psychology: Perceiving, Learning, and Remembering.
London: Cengage
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