http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4087081/
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| From http://www.lifehack.org/377243/science-says-silence-much-more-important-our-brains-than-thought |
This article has been cited by other articles in PMC.
Abstract
We
have previously hypothesized that the reason why physical activity
increases precursor cell proliferation in adult neurogenesis is that
movement serves as non-specific signal to evoke the alertness required
to meet cognitive demands. Thereby a pool of immature neurons is
generated that are potentially recruitable by subsequent cognitive
stimuli. Along these lines, we here tested whether auditory stimuli
might exert a similar non-specific effect on adult neurogenesis in mice.
We used the standard noise level in the animal facility as baseline and
compared this condition to white noise, pup calls, and silence. In
addition, as patterned auditory stimulus without ethological relevance
to mice we used piano music by Mozart (KV 448). All stimuli were
transposed to the frequency range of C57BL/6 and hearing was objectified
with acoustic evoked potentials. We found that except for white noise
all stimuli, including silence, increased precursor cell proliferation
(assessed 24 h after labeling with bromodeoxyuridine, BrdU). This could
be explained by significant increases in BrdU-labeled Sox2-positive
cells (type-1/2a). But after 7 days, only silence remained associated
with increased numbers of BrdU-labeled cells. Compared to controls at
this stage, exposure to silence had generated significantly increased
numbers of BrdU/NeuN-labeled neurons. Our results indicate that the
unnatural absence of auditory input as well as spectrotemporally rich
albeit ethological irrelevant stimuli activate precursor cells—in the
case of silence also leading to greater numbers of newborn immature
neurons—whereas ambient and unstructured background auditory stimuli do
not.
Keywords: Plasticity, Stem cells, Hippocampus, Mouse, Learning
Introduction
Adult
neurogenesis adds plasticity to the dentate gyrus of the hippocampus
and is involved in key functions such as pattern separation (Aimone et
al. 2010; Clelland et al. 2009) and avoidance of catastrophic interference (Appleby and Wiskott 2009; Wiskott et al. 2006)
by adding flexibility to the network in situations where novel
information has to be integrated into established representations
(Garthe et al. 2009; Dupret et al. 2008).
Adult neurogenesis is regulated by behavioral activity. Both physical
activity and exposure to a challenging environment increase adult
neurogenesis but do so by different means (Kronenberg et al. 2003).
Non-specific stimuli like physical activity enhance the proliferation
of precursor cells and lead to an increased potential in form of a
larger pool of “neuroblasts” and immature neurons that can be recruited
in case of a cognitive challenge. In contrast, exposure to an enriched
environment promotes the survival of newborn neurons. Accordingly, the
two interventions turned out to be additive in their effect (Fabel et
al. 2009).
The
new immature neurons own particular functionality in that they are more
likely to generate action potentials in response to incoming stimuli
due to their particular balance between excitatory and inhibitory input
(Marin-Burgin et al. 2012). The threshold for LTP induction is reduced in these neurons (Schmidt-Hieber et al. 2004; Snyder et al. 2001).
In fact, the LTP that is measurable in the dentate gyrus under
physiological conditions is contributed by the newborn neurons during
this critical period of their development (Garthe et al. 2009; Saxe et al. 2006).
Thus, the immature new neurons are assumed to be more easily excitable
than older cells, biasing the input towards the more plastic
subpopulation of cells (Marin-Burgin et al. 2012).
The hypothesis is that this mechanism allows flexible adaptation and
learning of new information in previously established contexts.
Non-specific stimuli would increase precursor cell proliferation to
increase a pool of cells that can be recruited if cognitive demand
arises (for detailed discussion see: Fabel et al. 2009).
The
finding that exercise would have this effect on proliferation raised
the question, whether other non-specific stimuli would also lead to an
increased availability of potentially recruitable cells. Presumably, the
intrinsic stimulus during physical activity essentially consists of
proprioception and vision. Likewise, there are numerous reports on links
between the vestibular system and hippocampal function [(Brandt et al. 2005); see Ref. Smith et al. (2010)
for review] even though effects on adult neurogenesis have not yet been
specifically addressed. In order to identify relevant sensory stimuli
independent of locomotion, we here focused on auditory input as a
potential signal to affect adult hippocampal neurogenesis.
Noise
trauma with inner ear hair cell loss has led to a reduction of
precursor cell proliferation in the hippocampus of rats (Kraus et al. 2010).
A potential positive regulatory effect of sound on the early steps of
adult hippocampal neurogenesis, however, has not yet been explored. We
asked how different types of auditory stimuli would affect the baseline
regulation of adult hippocampal neurogenesis (Fig. 1a).
Regulation of adult hippocampal neurogenesis in dependency of auditory stimuli. a
We used two different approaches to address both proliferation and
survival/differentiation by injection of BrdU either 24 h before daily
sounds exposure or after ...
We
used ambient noise in the animal facility (animal house noise) as
baseline and exposed our mice to four different conditions: (1) white
noise as unstructured auditory stimulus; (2) mouse pup calls as
structured stimulus that is for mice common and relevant; (3) Mozart
piano music as a structured stimulus, unknown and presumably irrelevant
to mice; and (4) silence.
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