Fannie Chan

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Information Transfer Between Hemispheres in
Normal Children

• Fannie Chan
• Christine Law
• Lau Sau Yin
• Suanne Ma
• November 12, 2002

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Corpus Callosum

• The role of Corpus Callosum
• A larger set of axons conveying information
  between the two hemispheres.

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Development of Corpus Callosum

• Not completely formed at birth.
• Last systems to begin and complete myelination.
• Mature very slowly over the first decade of life.

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Growth of corpus callosum
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Two Behavioral Test

• Young children
• little communication between hemispheres
• similar to split-brain patients
• Two Behavioural Test
• Comparison of fabric samples with the same hand
  vs the opposite hand
• Identification of a designed finger with the same
  hand vs the opposite hand

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Test 1 Comparison of Fabric Sample

• Hypothesis
• 3-year-olds children show more frequent errors in
  the crossed condition than in the uncrossed
• 5-year-olds children show less if any difference
  between crossed and uncrossed errors.

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Subject

• Fifteen 3-year-old and fifteen 5-year-old
  right-handed girls were tested
• Half of each age group was black and half white
• They were drawn form a working-class day-care
  center and an upper-middle class private school.

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Procedure

• There were four sets of different pillow linen,
  denim, rayon, rough wool
• The experimenter rubbed one of the fabrics over
  the fingers of one hand and then used either the
  identical fabric or a different one to stimulate
  the same(uncrossed condition) or the opposite
  hand(crossed condition) The child was required to
  respond only that the fabric was the same or not
  the same

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Result
There was no significant difference in uncrossed
errors between the left and right hands for
either age group. The difference between the age
groups in crossed errors relative to total errors
was significant t(28) 4.31, P .0002
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We conclude that 3-year-olds have more difficulty
comparing tactile information between the two
hemispheres than within a hemisphere and that
this difference is reduced by the age of 5
11
Alternative hypothesis unrelated to
inter-hemispheric communication
It might be hypothesized that matching between
different skin sites was intrinsically harder
than at the same site, requiring some memory or
schema-forming ability mastered by age 5 but not
by age 3. Therefore, a subset of subjects with a
variant of the original procedure is tested.
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Alternative hypothesis unrelated to
inter-hemispheric communication
Four 3-year-olds were re-tested with the same
procedure except ? in the uncrossed condition,
the sample fabric was presented to the volar
surface of the forearm of the same side ? in
the crossed condition, the sample is presented to
the forearm and the test fabric to the opposite
forearm.
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Alternative hypothesis unrelated to
inter-hemispheric communication
Results Essentially as before. Conclusion The
difference in skin sites stimulated does not
account for the difference in performance between
age 5 and age 3 children.
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Evaluating the reliability of the test
Seven of the 3-year-olds who were available for
re-testing by the same experimenter within 1
month of the first test.
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Evaluating the reliability of the test
Results although some change in the absolute
scores was indicated, rank order correlation
showed the relative standing within the group to
be well preserved. Conclusion the measure
seems stable.
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Improvement of the test
further standardizing ? the type of tactile
stimulus ? its locus on the hand ? pressure ?
duration ? the inter-stimulus interval
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Evaluation
? Sample size too small
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The ability to identify or localize a designated
finger

• One hand is touched and the other hand is used to
  point to the spot touched
• Involve the ability to transfer information from
  one hemisphere to the other
• Corpus callosum and other forebrain commissures
  are late to myelinate, we might infer that the
  ability to transfer tactile information from one
  hemisphere to the other changes significantly
  with age

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Procedure of Test

• Sample size 108 children
• Age 4 years 9 months and 10 years 1 month
• Sex Both
• Background upper middle class, with no known
  neurological or behavioural problems

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Method
The examiner lightly touched one of ten points on
the fingers (proximal, middle, distal phalanx of
each finger, excluding the thumb, distal index
finger and proximal little finger
The child to touch that spot with the thumb of
the same hand (uncrossed localization)
or
The child to touch the homologous spot on the
opposite hand with the opposite thumb (crossed
localization)
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Result

• More crossed than uncrossed errors were found
• The younger the child, the more the crossed error
• older child showed developmental improvement in
  interhemispheric transfer of information
• progressive myelination
• maturation of the forebrain commissure neurons

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Criticism
Get it right the first time?
Why only 10 points?
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Discussion

• Further studies on more age groups.
• How to improve the growth of corpus callosum?
• Nutrition
• Training
• Sex difference
• Females have larger corpus callosum!

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The End