GENETIC INFLUENCES ON
BRAIN PLASTICITY
It follows from what is known
about the neurobiology of neuronal development
and synaptic plasticity that
variations in some of the genes that
control basic steps in the process are
likely to emerge as clinically determinants
of recovery from acquired injuries.
At this point, one leading candidate
for this type of gene is brain
derived neurotrophic factor (BDNF).
BDNF is expressed by neurons in
response to neuronal activity, and it
plays a role in NMDA-dependent LTP
and in hippocampal plasticity and memory
formation. Egan et al. [2003]
reported that individuals with the val66-
met polymorphism of BDNF had poor
episodic memory and low levels of hippocampal
N-acetyl aspartate (NAA)
measured with MR spectroscopy, as
well as a defect depolarization induced
secretion of BDNF when the variant
was transfected into normal neurons in
vitro. A follow-up report showed that
these individuals also had differences in
the anatomy of the hippocampus and
frontal lobes compared to individuals
with val66val [Pezawas et al., 2004].
Kleim et al. [2006] used a motor training
task involving the fingers to show
that individuals with val66met had significantly
lower training dependent
increases in the amplitude of motor
evoked potentials and reduced motor
map reorganization in cerebral cortex.
A recent study also showed that individuals
with the met allele had impaired
responses to median nerve paired associative
stimulation and a probe of cortical
plasticity using tDCS and TMS
[Cheeran et al., 2008]. This information
strengthens the link between the basic
science model of neuronal plasticity
presented above and clinical plasticity,
but there is limited information about
this mutation in children or adults with
brain injuries.