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Brain lesions and IQ: recovery versus decline depends on age of onset

Julie Duval1, Claude M J Braun, Isabelle Montour-Proulx

  • 1Université du Québec à Montréal, Département de psychologie, Montréal, Québec, Canada.

Journal of Child Neurology
|June 10, 2008
PubMed

Insights

Early brain lesions correlate with lower IQ outcomes, while later lesions show better recovery. This study refutes the Kennard principle regarding IQ in brain-lesioned individuals across a wide age range.

Area of Science:

  • Neuroscience
  • Developmental Psychology
  • Clinical Neurology

Background:

  • Existing research links early brain lesions to poorer intellectual quotient (IQ) outcomes.
  • Previous studies were limited to pediatric populations and did not account for key influencing factors.

Purpose of the Study:

  • To investigate the impact of age at lesion onset on IQ changes in both children and adults with unilateral focal brain lesions.
  • To determine if the Kennard principle, which suggests younger brains have better recovery, applies to IQ outcomes.

Main Methods:

  • Analysis of 725 cases with unilateral focal brain lesions (ages 0-84) from clinical records and literature.
  • Inclusion of 240 cases with repeated IQ testing.
  • Multiple regression analyses to assess the influence of age at lesion onset, controlling for lesion side, site, volume, and etiology.

Main Results:

  • Early-onset lesions were significantly associated with lower post-lesion IQ and a decline in IQ over time.
  • Later-onset lesions were linked to better post-lesion IQ scores and greater IQ recovery.
  • The findings contradict the established Kennard principle concerning IQ outcomes.

Conclusions:

  • Age at onset is a critical factor influencing IQ changes following brain lesions.
  • The study provides evidence against the universal applicability of the Kennard principle for IQ in brain-lesioned individuals.
  • Understanding the timing of brain injury is crucial for predicting long-term cognitive outcomes.

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