300 PROMOTING POTENTIALthose reared in cages with toys, ladders, tunnels, running wheels, and so
on. Th ey found that enriched early experience improved per for mance on
several tests of learning. Further studies revealed changes in cortical thick-
ness, size, and number of synapses, and extent of dendritic branching.
Th ese fi ndings have been replicated and extended in more recent re-
search. Just a few days of motor skill training, or learning to run a maze,
for example, seems to have produced brain structural changes. And it is
now known that cognitive stimulation and exercise increases neurogen-
esis (production of new neurons) in some parts of the brain. Th e Rosen-
zweig team concluded that “suffi ciently rich experience may be necessary
for full growth of species- specifi c brain characteristics and behavioral
potential.”^19
Further studies of institutionalized children have specifi cally exam-
ined outcomes in brain development, with the assumption that it will be
refl ected in cognitive development. For example, the Bucharest Early
Intervention Proj ect found reduced cortical brain activity (as mea sured by
EEG recordings) among institutionalized children compared to never-
institutionalized children. However, activity eventually returned to nor-
mal in children placed in foster care before the age of two years.
Other studies in this vein have found reduced brain metabolism in
parts of the ce re bral cortex of institutionalized children and reductions
in white matter in vari ous brain regions. Th ere have also been reports of
reductions in gray and white matter volumes, and increased amygdala
volumes, in previously institutionalized children (the amygdala being
part of the limbic system mediating cognitive with aff ective brain activ-
ity, as described in chapter 6).^20
Studies on humans have been much extended in recent years with the
advent of fMRI scans. As mentioned in earlier chapters, some of these
have reported experience- dependent changes in brain tissues. Short
periods of specifi c cognitive or skill practice, or general learning or mem-
ory training, even in adults, have all been claimed to have structural
eff ects on brain, such as increased regional volumes. Even short periods
of aerobic exercise— and of dancing in el derly people!— have been shown
to make slight diff erences.
However, as Martin Lövdén and colleagues point out, many of these
studies have serious methodological fl aws, and the eff ects are not usually
This content downloaded from 139.184.14.159 on Tue, 17 Oct 2017 13:58:05 UTChttp://www.ebook3000.com