Autism and brain growth

[John H.]

The article did seem surprising so I had a quick look (see below). The
preponderance of evidence is towards increased brain size, particularly
prior to 6 years, and this is not accounted for by enlarged ventricles,
though these are present. I wonder if the increased size prevents midbrain
afferents finding their targets in some neocortical regions, hence the loss
of size in later years may reflect loss of tissue because of lack of
sufficient innervation(note loss of white matter in autistics with age
below). Also wonder if the increased size of some regions relates in some
way to the savant like abilities in autistics. No, I do not equate savant
with genius, actually I think these are very different things, but perhaps
the sheer enlargement of cortical surface areas allows some of those
extraordinary skills to emerge in spite of loss of executive functions. Or
given the recent work of Alan Synder, where he can induce savant like
abilities by suppressing some neocortical regions in normal individuals,
perhaps executive functions inhibit savant like abilities. Eg. In some cases
of traumatic brain injury, during the recovery phase individuals may
demonstrate savant like abilities but these fade through recovery (haven't
checked that reference but concordant with Synder's little games).

Certainly a neurodevelopmental disorder and a fascinating one. Research last
year at the opposite end of the spectrum indicated microencephaly is
associated with a particular gene mutation, that may provide a clue.

17/07/03 4:01am

Effects of age on brain volume and head circumference in autism.
  Aylward EH    Field K Sparks BF ),   Singh N Neurology 2002 Jul 59:175-83

 Neurology ) . Volume 59  . Issue Abstract
OBJECTIVE: To determine whether brain volume, as assessed on MRI scans,
differs between individuals with autism and control subjects, and whether
such differences are affected by age. BACKGROUND: Previous studies have
found increased brain weight, head circumference, and MRI brain volume in
children with autism. However, studies of brain size in adults with autism
have yielded conflicting results. The authors hypothesize that enlargement
of the brain may be a feature of brain development during early childhood in
autism that normalizes with maturational processes. METHODS: The authors
measured total brain volumes from 1.5-mm coronal MRI scans in 67
non-mentally retarded children and adults with autism and 83 healthy
community volunteers, ranging in age from 8 to 46 years. Head circumference
was also measured. Groups did not differ on age, sex, verbal IQ, or
socioeconomic status. RESULTS: Brain volumes were significantly larger for
children with autism 12 years old and younger compared with normally
developing children, when controlling for height. Brain volumes for
individuals older than age 12 did not differ between the autism and control
groups. Head circumference was increased in both younger and older groups of
subjects with autism, suggesting that those subjects older than age 12 had
increased brain volumes as children. CONCLUSIONS: Brain development in
autism follows an abnormal pattern, with accelerated growth in early life
that results in brain enlargement in childhood. Brain volume in adolescents
and adults with autism is, however, normal, and appears to be due to a
slight decrease in brain volume for these individuals at the same time that
normal children are experiencing a slight increase.





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17/07/03 4:02am

Brain volume in autism.
  Hardan AY ,   Mallikarjuhn M ),   Keshavan MS J Child Neurol 2001 Jun
16:421-4

BROWSE: J Child Neurol  Volume 16 . Issue 6

Abstract
Increased brain size has been observed in individuals with autism with a
wide range of cognitive functioning. The purpose of this investigation was
to obtain measurements of the brain volume in a sample of nonmentally
retarded autistic individuals. Magnetic resonance imaging scans from 16
nonmentally retarded individuals with autism and 19 male volunteer
comparison subjects were obtained and the following structures were
measured: third, fourth, and lateral ventricles and intracranial and
cerebral volumes. Mean cerebral and third ventricle volumes in the autistic
subjects were significantly greater than in the controls when adjusted for
intracranial volume. No other significant results were found. Our finding of
increased brain volume in autism is consistent with previous reports in the
literature. Additional longitudinal neuroimaging and, more importantly,
neuropathologic studies are warranted to provide a better understanding of
the complexities underlying increased brain size in autism.

MeSH



--
17/07/03 4:05am

International Journal of Developmental Neuroscience Structural and
functional magnetic resonance imaging of autism
Heather Cody Kevin Pelphrey and Joseph Piven

....

Brain size in that study was measured as a covariate for cerebellar size,
where robust increases in mid-sagittal brain area were noted in autistic
individuals in contrast to two normal comparison groups, after taking
gender, cognitive ability, age and socioeconomic status (SES) into account.
Subsequently, Piven et al. (1996) ( \l "bib89") reported enlargement of
brain volume in 22 autistic males compared to 36 non-autistic males of
comparable age and cognitive ability. Lateral ventricular volume was also
noted to be enlarged, but this did not account for the observation of brain
volume enlargement as cortical brain tissue volume was also noted to be
significantly enlarged. Subsequently, this same group of investigators
employed a semi-automated technique to divide the brain into cortical lobes
based on the method of Talairach and Tournoux (1988) ( \l "bib111") in a
larger, overlapping sample of 35 autistic individuals (age range 12-29
years) and 36 controls (age range 13-28 years). The total brain volume in
the male autistic individuals was found to be significantly larger than male
controls, however, the sample of autistic females was too small to make any
definitive comments. Analyses using the Talairach coordinate system
suggested significant enlargements in the temporal, parietal, and occipital
lobes in the autistic subjects compared to controls, whereas no differences
were detected in the frontal lobe. These findings suggested that the pattern
of brain enlargement was regional and not global.

Postmortem studies support findings of megalencephaly (increased brain
weight) in autism (Bailey et al., 1993 ( \l "bib11")). Further documentation
of increased head size associated with autism come from head circumference
studies ( Bailey ( \l "bib12"); Lainhart ( \l "bib65") and Stevenson ( \l
"bib109")) showing that approximately 20% of autistic individuals have head
circumferences above the 98th percentile (i.e. macrocephaly). In a
retrospective chart review study of autistic individuals with macrocephaly,
Lainhart et al. (1997) ( \l "bib65") found evidence suggesting that while
enlarged head size is often present at birth, macrocephaly is not present
until the first few years of life. Other studies have found results
consistent with this finding ( Stevenson ( \l "bib109") and Courchesne ( \l
"bib26")). Thus, the timing of the enlargement, which clearly encompasses
the early postnatal period, is most consistent with an underlying mechanism
that involves a decrease in the normal course of elimination of neuronal
processes during early development (e.g. a decrease in the rate of dendritic
pruning) ( Huttenlocher, 1990 ( \l "bib59")).
...

Segmentation of the brain volumes into gray and white tissue in the
Courchesne et al. (2001) ( \l "bib26") study revealed that the 2-4-year-old
autistic subjects also had increased gray and white tissue volumes in the
cerebrum that were not present in the older autistic subjects (5-16-year
old). Their data suggested that cortical white matter volume increased
linearly with age, a finding similar to that of Giedd et al. (2001) ( \l
"bib36"), but that the rate of increase was smaller in the autistic group
than in normal controls. Also similar to the findings by Giedd et al. (2001)
( \l "bib36"), cortical gray tissue volumes were found to peak in early
childhood for autistic and control subjects, although the autistic group had
a decrease in gray tissue volume between 2 and 9 years while the normal
controls continued to show an increase. By middle childhood, gray tissue
volumes began to decrease for both groups, with the autism cases showing
smaller gray tissue volumes than the normal controls.


"Emma Chase VanCott" <7elc at qlink.queensu.ca> wrote in message
news:bf3j6i$ifl$2 at knot.queensu.ca...
> In sci.med.psychobiology John H. <john at faraway.com> wrote:
> : Interesting because of recent research showing that schizophrenia is a
> : neurodevelopmental disorder and schizophrenics showed delayed
> : lateralisation.
> : http://news.bbc.co.uk/2/hi/health/3067149.stm
>
> : Autism linked to brain growth
>
>
> : Autism may be linked to unusually rapid brain growth during the first
year
> : of life, say researchers.
> : They found that children with a small head at birth,
>
> Brain, or head growth.
>
> Huge difference.
>
> Maybe they just have oversized ventricles, with a small brain, which still
> makes their head "large".
>
> Small head at birth is not surprising. Autism is a "developmental
> disorder".
>
> Emma
>