16 Introduction to Autism Spectrum Disorders
associated with profoundly disabled intellectual capacity [82]. In Figure 1.8, we
have illustrated the corpus callosum in the normal brain. A recent review of
normal versus ASD brain structural analyses by brain imaging has shown that
total brain volume and amygdala overgrowth were increased in ASD brains,
while corpus callosum and cerebellum volume were found to be decreased in
ASD brains [83].
Let us take this a little further and realize that the human brain contains an
unknown number of compartments to perceive and respond to environmental
challenges. This starts when the fetus is the size of a little green pea. Then,
hundreds or perhaps thousands of different compartments arise from a single
progenitor cell that repeatedly divides and then differentiates into second lay
ers of progenitor cells, each destined to become one or more compartments of
our wonderful brain. If any chemical takes away a few of these secondary pro
genitor cells, then there will be fewer or smaller compartments. When certain
cell types disappear from a fetal brain at early stages of development, the vac
uum created by the untimely death and degeneration of selected neurons
invites replacement by another type of neuron. The growth and migration rate
of each type of neuron is different and these new neurons may divide slightly
faster than the ones that died due to environmental factors (we will describe
the mechanism in Chapter 5 and provide recent evidence from our laboratory).
Therefore, when certain neurons grow faster, the brain enlarges and the num
ber of those filler neurons swell. Keep in mind that an autistic child’s brain
is generally 30% bigger than that of a typical child. Thus, the brain matter may
be more densely packed, meaning many more neurons are squeezed into an
ASD‐affected child’s skull than into that of a typically developing child. We
repeat that a typical human brain possesses 130 billion neurons and 1,500,000,
000,000,000,000,000,000 synapses. A 30% increase in size means that about
130 billion neurons, and perhaps 100 to 10,000 times more synapses, are pre
sent, which can make the child highly sensitive to sound, touch, pressure, and
light (or make the child totally unresponsive to those stimuli if connections are
scrambled). This translates into a sensory overload with perhaps one excep
tion, the paucity of olfaction, or sense of smell. In a significant number of ASD
children, the sense of smell is reduced, suggesting the early death of olfactory
neurons during the developmental pathways (this concept is further discussed
in Chapter 3).
One example of this sensory overload was provided in 2012 when ABC
News published a video of a young woman who felt trapped by autism but
who also, with extensive support from family and others, began to express
herself in a remarkable way at age 11 through a computer keyboard. Pushed
to communicate by keyboard in order to get privileges she wanted, Carly
Fleishmann proved not only that she could communicate but also that
she was an exceptionally gifted thinker and writer. “Autism has locked me
inside a body I cannot control,” she explained (https://www.youtube.com/