Brain structure
Neuroimaging techniques such as magnetic resonance imaging
(MRI) have identified a number of morphological abnormalities
in the brains of children with ADHD. While ADHD is
associated with reduced global brain volume (Castellanos et al.
2002), specific regional abnormalities have also been identified,
namely reduced grey matter in regions forming part of
frontostriatal circuits (Nakao et al. 2011). In addition, atypical
white matter volume in numerous neural tracts suggests
impaired communication between some of these implicated brain regions (Nagel et al. 2011). Other abnormalities identified
include cortical thinning (Batty et al. 2010) and some suggest
that cortical development may be delayed in children with
ADHD, who reach peak levels of cortical thickness approximately
3 years later than typically developing controls (Shaw
et al. 2007). The pathogenesis of ADHD is therefore likely to
be the result of complex structural abnormalities involving a
number of brain regions and connecting circuitry (Cortese
2012). At least some of these structural abnormalities are likely
to have a genetic basis; as evidenced by structural abnormalities
observed in unaffected siblings of children with ADHD
(Durston et al. 2004). However, associations between adverse
institutional rearing and reduced cortical thickness are also
apparent (McLaughlin et al. 2013), highlighting the role of environmental
experience on brain development.