There are many different types of memory one can talk about.
One of the main distinctions is between semantic and episodic
memory. With episodic memory, the subject not only has the
memory, but can remember something about the setting in
which the remembered information was learned. Conversely,
with semantic memory, the subject cannot recall the context
of the initial learning.
The nature of episodic memory, however, is far more complex.
It has specifically to do with the ability for a person
to travel back in time to re-experience remembered events.
In this way, episodic memory links experience of the past,
present and future. The term autonoetic (from the Greek
word Gnosis) consciousness means awareness of subjective
experiences in the past, present and future. Autonoetic
consciousness is a special feature of episodic memory; the
different types of consciousness associated with semantic
memory and procedural memory are termed noetic (knowing)
and anoetic (without knowledge) respectively.
Experimentally, one can ask subjects whether they "remember"
something or "know" it, thereby distinguishing between autonoetic
and noetic (i.e., without the re-experiencing the event)
awareness. Others have shown dissociations in the brain
regions involved, as well as electrophysiological features,
depend upon whether the memory was rated as "remembered"
or "known." Such studies suggest that the prefrontal and
hippocampal brain regions are involved in autonoetic awareness.
These results are consistent with the HERA model, which
implicates left prefrontal cortex for semantic retrieval
and right prefrontal cortex for episodic retrieval.
A recent lesion patient, M.L., provides additional support
for this approach to the unique nature of episodic memory.
M.L. has damage to part of the right frontal cortex, and
consistent indeed, has an impaired capacity to perform episodic
memory tasks (as assessed by the remember/know paradigm).
