214 Self and the Phenomenon of Life
b2726 Self and the Phenomenon of Life: A Biologist Examines Life from Molecules to Humanity “9x6”Table 10.2. Types of Memory According to Duration
A. Short-term: Usually less than an hour. Message resides in ongoing interactions
between the prefrontal cortex (with involvement of other neocortical areas), and the
hippocampus. Involves transient synaptic functional changes without permanent
structural alteration.
B. Long-term: At least a day but usually months and years, up to a lifetime. For
declarative memory, hippocampus serves as a way station for transfer of memory traces
to distributed neocortical areas for permanent storage, where long-lasting structural
changes take place. The transition process involves gene activation and protein
synthesis. Recall depends on conscious executive effort of the prefrontal cortex in
mobilizing memory traces stored in multimodal brain areas, including the associative
cortical centers such as the parietal cortex.
Note: Both declarative and non-declarative memories can be short-term or long-term.
only two minutes. Short-term memory can be compared to a notepad
while long-term memory is like a filing cabinet. The conversion from
short- to long-term memory is called memory consolidation or fixation,
and is hippocampus-dependent.^6
Amnesia is defined as the loss of memory, either from a deficit in
storing information or in recall. Amnesia due to a storage problem is
called anterograde amnesia, whereas that due to defect in retrieval is
called retrograde. HM’s amnesia was primarily anterograde as he could
not form any new memory after surgery. In retrograde amnesia, a per-
son cannot remember what happened in the past. Many people recov-
ering from head trauma cannot recall the event immediately before the
impact, as in an automobile accident. More severe cases of retrograde
amnesia extend far into years past. In HM’s case, many (but not all) of his
childhood memories were preserved after brain surgery.
Amnesia can also be classified as global or focal. A global amne-
sia covers all types of experience. However, even with the global type,
some categories of experience are more severely affected than others.
For example, time is usually lost first, followed by place, then by per-
son. An Alzheimer’s patient will first forget the time (“what day of the
week is today?”), then the place (“where are you now?” or “Where do
you live?”), and lastly, persons (“Have you seen this man before?”). This