[Paleopsych] SW: On Cognitive Memory
checker at panix.com
Wed May 25 00:50:17 UTC 2005
Neuroscience: On Cognitive Memory
The following points are made by Yasushi Miyashita (Science 2004
1) Since the pioneering observations on patient H.M., who developed a
severe and selective deficit in the formation of explicit (or
declarative) memory after a bilateral resection of the medial temporal
lobe (i.e., the hippocampus and nearby regions), subsequent studies of
patients have located the source of various types of impairment in
explicit memory in many brain areas (1). Notably, although patients
with localized frontal lobe lesions do not have an amnesia typically
observed in patients with medial temporal lobe lesions, they do
exhibit impairments in memory of temporal context or temporal order,
memory of the source of facts or events, or metamemory (i.e.,
knowledge about one's memory capabilities and about strategies that
can aid memory) (2-4).
2) The identified brain-wide distributed network, called here the
"cognitive memory system", is composed of three major subsystems,
namely, the medial temporal lobe, the temporal cortex, and the frontal
cortex. Although the ultimate storage sites for explicit memories
appear to be in the cortex [but see (5) for another strong position],
the medial temporal lobe plays a critical enabling role necessary for
storage to take place. Domain-specific cortical regions in the
temporal lobes are reactivated during remembering and contribute to
the contents of a memory. The reactivation process is mediated by
various signals, such as the top-down signal from the prefrontal
cortex or the backward signal from the limbic cortex. Frontal regions
mediate the strategic attempts for retrieval and encoding and also
monitor its outcome, with the dissociated frontal regions making
functionally separate contributions.
3) This large-scale cognitive network was initially identified in
humans by using neuropsychology and functional imaging. However,
molecular, cellular, and network components of this cognitive system
have been systematically dissected by recent technical advancements,
particularly in animal studies. These include cell type-restricted
gene manipulations in mice, a combination of molecular biology and
single-unit recording in monkeys, and a sophisticated scan design of
event-related functional magnetic resonance imaging (fMRI) in humans.
4) In summary:
a) A brain-wide distributed network orchestrates cognitive memorizing
and remembering of explicit memory (i.e., memory of facts and events).
The network was initially identified in humans and is being
systematically investigated in molecular/genetic, single-unit, lesion,
and imaging studies in animals.
b) The types of memory identified in humans are extended into animals
as episodic-like (event) memory or semantic-like (fact) memory. The
unique configurational association between environmental stimuli and
behavioral context, which is likely the basis of episodic-like memory,
depends on neural circuits in the medial temporal lobe, whereas memory
traces representing repeated associations, which is likely the basis
of semantic-like memory, are consolidated in the domain-specific
regions in the temporal cortex. These regions are reactivated during
remembering and contribute to the contents of a memory.
c) Two types of retrieval signal reach the cortical representations.
One runs from the frontal cortex for active (or effortful) retrieval
(top-down signal), and the other spreads backward from the medial
temporal lobe for automatic retrieval. By sending the top-down signal
to the temporal cortex, frontal regions manipulate and organize
to-be-remembered information, devise strategies for retrieval, and
also monitor the outcome, with dissociated frontal regions making
functionally separate contributions.
d) The challenge is to understand the hierarchical interactions
between these multiple cortical areas, not only with a correlational
analysis but also with an interventional study demonstrating the
causal necessity and the direction of the causality.
1. L. R. Squire, D. L. Schacter, Neuropsychology of Memory (Guilford,
New York, ed. 3, 2002)
2. D. T. Stuss, D. F. Benson, The Frontal Lobes (Raven, New York,
3. J. M. Fuster, The Prefrontal Cortex: Anatomy, Physiology, and
Neuropsychology of the Frontal Lobe (Lippincott-Raven, Philadelphia,
4. M. Petrides, in Handbook of Neuropsychology, F. Boller, J. Grafman,
Eds. (Elsevier, Amsterdam, 2000).
5. J. O'Keefe, L. Nadel, The Hippocampus as a Cognitive Map (Oxford
Univ. Press, Oxford, 1978).
ON THE NEUROBIOLOGY OF LEARNING AND MEMORY
The following points are made by H. Okano et al (Proc. Nat. Acad. Sci.
1) The authors state they define memory as a behavioral change caused
by an experience, and they define learning as a process for acquiring
memory. According to these definitions, there are different kinds of
memory. Some memories, such as those concerning events and facts, are
available to our consciousness; this type of memory is called
"declarative memory". However, another type of memory, called
"procedural memory", is not available to consciousness. This is the
memory that is needed, for example, to use a previously learned skill.
We can improve our skills through practice: with training, the ability
to play tennis, for example, will improve. Declarative memory and
procedural memory are independent: there are patients with impaired
declarative memory whose procedural memory is completely normal.
Because of this fact, current researchers believe there must be
separate mechanisms for each type of memory, and that these separate
mechanisms probably also require separate brain areas as well.
2) The *cerebrum and *hippocampus are considered important for
declarative memory, and the *cerebellum is considered important for
procedural memory. The current belief is that memory requires
alterations in the brain. The most popular candidate site for memory
storage is the *synapse, where nerve cells communicate with each
other. A change in the transmission efficacy at the synapse (called
"synaptic plasticity") has been considered to be the cause of memory,
and a particular pattern of synaptic usage or stimulation
(conditioning stimulation) is believed to induce synaptic plasticity.
Many questions remain to be answered, such as how synaptic plasticity
is induced and how synaptic plasticity is implicated in learning and
3) One current frontier in the study of synaptic plasticity is the
attempt to clarify the role of plasticity in learning and memory. The
strategy has been to examine the correlation between synaptic
plasticity and learning by inhibiting the plasticity in a living
animal. To do this, investigators have used inhibitors for certain
molecules that are apparently required for synaptic plasticity.
Another set of useful tools involves genetically engineered mutant
mice, such as "knockout" and transgenic mice. A "knockout" mouse is a
mutant mouse that is deficient in a specific native molecule. By using
mutant mice, the relationship between synaptic plasticity and learning
ability has been examined in detail.
Proc. Nat. Acad. Sci. http://www.pnas.org
Notes by ScienceWeek:
cerebrum: What is called the "cerebrum" is the bulk of brain as seen
by the naked eye, the "great ravelled knot" that sits on top of the
phylogenetically older parts (brainstem and midbrain) of the whole
brain. The surface of the cerebrum, an enormously extended surface
because of the many deep folds of the cerebrum, is a thin sheet called
the "cerebral cortex" (cortex = rind or bark).
hippocampus: A region of the cerebral cortex in the *medial part of
the temporal lobe. In humans, among other functions, the hippocampus
is apparently involved in short-term memory, and analysis of the
neurological correlates of learning behavior in animals indicates that
the hippocampus is also involved in memory in other species.
cerebellum: The human cerebellum is about the size of a large apple,
is placed at the lower back of the head under the optic lobes of the
cerebrum, and is apparently involved in the input-output control of
automatic sensorimotor functions. If you are sitting at your breakfast
table, holding a newspaper in one hand, and using the other hand to
routinely and repetitively dip a spoon into cold cereal and bring the
cold cereal to your mouth while you read the newspaper, it is the
cerebellum which is governing the automatic feeding movements while
your cerebral cortex processes the information that you read.
synapse: In general, nerve cells have a single long extension (the
"axon") that propagates the electrical output (the action potential)
of the cell. The term "synapse" refers to the junction between the
terminal of a neuron's axon and another neuron. When studying the
synapse, the first neuron is called the "presynaptic" neuron, and the
second neuron is called the "postsynaptic" neuron.
NEUROBIOLOGY: ON THE BIOLOGICAL BASIS OF MEMORY
Notes by ScienceWeek
Exactly 100 years ago, two psychologists, G.E. Mueller and A.
Pilzecker, proposed what came to be called the
perseveration-consolidation hypothesis of memory. In studies with
human subjects, Mueller and Pilzecker found that memory of newly
learned information was disrupted by the learning of other information
shortly after the original learning, and they suggested that processes
underlying new memories initially persist in a fragile state and then
consolidate over time. This consolidation hypothesis still guides
research, particularly research in neurobiology on the time-dependent
involvement of neural systems and cellular processes enabling lasting
At the present time, the concept of "synaptic plasticity" underlies
nearly all theories of memories, the term referring to changes in the
behavior of the junction (synapse) between two nerve cells resulting
from past history.
Two prominent aspects of synaptic plasticity considered to be related
to memory are "facilitation" and "potentiation". The term
"facilitation" refers to a progressive increase in the amount of
*neurotransmitter substance released at a synapse by successive nerve
impulses (action potentials), the increase occurring during an input
barrage consisting of repetitive stimulation (stimulus train). The
term "potentiation" refers to an increase in neurotransmitter
substance released by an action potential following repetitive
stimulation of a synapse.
Both facilitation and potentiation can be long-lasting, and "long-term
potentiation" has been a focus of much research on the cellular basis
of memory, particularly in the hippocampus, a brain cortex structure
in the medial part of the temporal lobe. In humans, among other
functions, the hippocampus is apparently involved in short-term
memory, and analysis of the neurological correlates of learning
behavior in the rat indicates that the hippocampus of the rat is also
involved in memory.
The following points are made by James L. McGaugh (Science 2000
1) The author points out that the idea that synaptic mechanisms of
long-term potentiation and long-term facilitation underlie memory
remains a hypothesis.
2) The author points out that although studies of long-term
potentiation and memory have focused on the involvement of the
hippocampus, much evidence indicates that the hippocampus has only a
time-limited role in the consolidation and/or stabilization of lasting
3) The author points out that there are forms of memory that
apparently do not involve the hippocampus and that may not use any
known mechanisms of synaptic plasticity.
4) The author points out that despite theoretical conjectures, little
is known about system and cellular processes mediating consolidation
that continues for several hours or longer after learning,
consolidation that creates lifelong memories.
Concerning the above caveats, the author concludes: "These issues
remain to be addressed in this new century of research on memory
Notes by ScienceWeek:
neurotransmitter substance: Neurotransmitters are chemical substances
released at the terminals of nerve axons in response to the
propagation of an impulse to the end of that axon. The
neurotransmitter substance diffuses into the synapse, the junction
between the presynaptic nerve ending and the postsynaptic neuron, and
at the membrane of the postsynaptic neuron the transmitter substance
interacts with a receptor. Depending on the type of receptor, the
result may be an excitatory or an inhibitory effect on the
postsynaptic nerve cell.
More information about the paleopsych