Brain's Recuperative Powers May Be Greater Than Previously Thought, Rutgers U/Science Daily 
Contrary to long-held popular belief, our brains may not
only produce new brain cells or neurons throughout life, but the
newly generated neurons quickly become involved in the formation
of new memories – a fact that may have positive implications
for the recuperative powers of our own brains when damaged by
stroke or other disease or trauma.
In a study published today in the March 15 issue of the journal
Nature, Rutgers psychology professor Tracey J. Shors and Princeton
psychology professor Elizabeth Gould found that newly generated
neurons in the hippocampus area of animal brains help form new
memories.
Despite what is generally believed, scientists in recent years
have learned that the brains of vertebrate animals, a category
ranging from amphibians to humans, continue to produce new neurons
throughout life. What was not known was whether the newly
generated cells are actively involved in memory formation.
To find out, Shors and Gould studied the thousands of neurons
produced daily in the hippocampus area of rat brains, an area that
controls a form of memory known as trace conditioning, in which
the animal must learn to associate stimuli that are separated in
time. The researchers discovered that when they reduced the
production of new hippocampus cells via a drug inhibitor, the rats
were no longer able to form certain types of new memories.
This occurred even though mature hippocampus neurons remained
functionally intact. On the other hand, when the researchers
stopped administering the drug inhibitor, thus restoring the
hippocampus area's ability to generate new cells, the ability to
acquire trace memories was also restored.
"It appears that the new neurons become involved in memory
about a week to two weeks after they are generated and they are
involved in memories normally handled by the hippocampus," says
Shors.
The team also noted that the reduction of new hippocampal cells
had no apparent effect on memory that depends on other parts of
the brain.
Although the researchers studied only the hippocampus, their
research implies that the brain's recuperative powers may be far
greater than previously thought. "We've known for some time that
the brain generates new cells throughout life," says Shors. "These
results suggest that one of the functions of these new cells is
related to the process of memory formation."
In an earlier study, the two researchers demonstrated the
nostrum, "use it or lose it." In the earlier study of rat brains,
they found that while most new brain cells die within weeks of
their generation, putting them to work through hippocampal-related
learning improved their survival rate.
Neurogenesis In The Adult Is Involved In The Formation Of Trace Memories, Nature
Excerpt: The vertebrate brain continues to
produce new neurons throughout life. In the rat hippocampus,
several thousand are produced each day, many of which die within
weeks. Associative learning can enhance their survival; however,
until now it was unknown whether new neurons are involved in
memory formation. (…)
These results indicate that newly generated neurons in the
adult are not only affected by the formation of a
hippocampal-dependent memory, but also participate in it.
Defibrillation Efficacy and Quantification of Activation Patterns in a Canine Heart Failure Model, Circulation
Background—Little is known about the effects of
heart failure (HF) on the defibrillation threshold (DFT) and the
characteristics of activation during ventricular fibrillation
(VF).
Methods and Results—HF was induced by rapid right
ventricular (RV) pacing for at least 3 weeks in 6 dogs. Another 6
dogs served as controls. Catheter defibrillation electrodes were
placed in the RV apex, the superior vena cava, and the great
cardiac vein (CV). An active can coupled to the superior vena cava
electrode served as the return for the RV and CV electrodes. DFTs
were determined before and during HF for a shock through the RV
electrode with and without a smaller auxiliary shock through the
CV electrode. VF activation patterns were recorded in HF and
control animals from 21x24 unipolar electrodes spaced 2 mm apart
on the ventricular epicardium. Using these recordings, we computed
a number of quantitative VF descriptors. DFT was unchanged in the
control dogs. DFT energy was increased 79% and 180% (with and
without auxiliary shock, respectively) in HF compared with control
dogs. During but not before HF, DFT energy was significantly
lowered (21%) by addition of the auxiliary shock. The VF
descriptors revealed marked VF differences between HF and control
dogs. The differences suggest decreased excitability and an
increased refractory period during HF. Most, but not all,
descriptors indicate that VF was less complex during HF,
suggesting that VF complexity is multifactorial and cannot be
expressed by a scalar quantity.
Conclusions—HF increases the DFT. This is partially
reversed by an auxiliary shock. HF markedly changes VF activation
patterns.
