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Related Experiment Videos

Hemispheric lateralization of number comparison.

Michael Andres1, Xavier Seron, Etienne Olivier

  • 1Unité de Neurosciences Cognitives, Faculté de Psychologie, Université Catholique de Louvain, B-1348 Louvain-la-Neuve, Belgium. michael.andres@psp.ucl.ac.be

Brain Research. Cognitive Brain Research
|July 12, 2005
PubMed
Summary

Disrupting the left posterior parietal cortex (PPC) impaired precise number comparisons. Approximate number comparisons, however, required both PPCs, as bilateral disruption slowed reaction times.

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Area of Science:

  • Neuroscience
  • Cognitive Psychology
  • Neuroimaging

Background:

  • The posterior parietal cortex (PPC) is implicated in numerical cognition.
  • The distinct roles of the left and right PPC in number comparison remain unclear.

Purpose of the Study:

  • To elucidate the specific contributions of the left and right PPC to number comparison using transcranial magnetic stimulation (TMS).

Main Methods:

  • Subjects performed a number comparison task (digit vs. 5).
  • Single-pulse TMS was applied unilaterally or bilaterally over the PPC at various time points.
  • Sham TMS served as a control to isolate TMS effects on reaction time (RT).

Main Results:

  • Disrupting the left PPC alone or both PPCs simultaneously significantly increased RTs for digits close to 5.

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  • Comparing digits far from 5 was unaffected by unilateral PPC disruption but slowed by bilateral PPC disruption.
  • These effects were consistent across different TMS timing delays.

    • Conclusions:

    • Precise numerical coding relies on the integrity of the left PPC, evidenced by deficits in discriminating close numerical values after its disruption.
    • Approximate numerical comparisons involve both left and right PPCs, as bilateral disruption was necessary to impair performance on digits far from 5.