Mapping mental calculation systems with electrocorticography.
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ABSTRACT: We investigated intracranially-recorded gamma activity during calculation tasks to better understand the cortical dynamics of calculation.We studied 11 patients with focal epilepsy (age range: 9-28years) who underwent measurement of calculation- and naming-related gamma-augmentation during extraoperative electrocorticography (ECoG). The patients were instructed to overtly verbalize a one-word answer in response to auditorily-delivered calculation and naming questions. The assigned calculation tasks were addition and subtraction involving integers between 1 and 17.Out of the 1001 analyzed cortical electrode sites, 63 showed gamma-augmentation at 50-120Hz elicited by both tasks, 88 specifically during naming, and 7 specifically during calculation. Common gamma-augmentation mainly took place in the Rolandic regions. Calculation-specific gamma-augmentation, involving the period between the question-offset and response-onset, was noted in the middle-temporal, inferior-parietal, inferior post-central, middle-frontal, and premotor regions of the left hemisphere. Calculation-specific gamma-augmentation in the middle-temporal, inferior-parietal, and inferior post-central regions peaked around the question offset, while that in the frontal lobe peaked after the question offset and before the response onset. This study failed to detect a significant difference in calculation-specific gamma amplitude between easy trials and difficult ones requiring multi-digit operations.Auditorily-delivered stimuli can elicit calculation-specific gamma-augmentation in multiple regions of the left hemisphere including the parietal region. However, the additive diagnostic value of measurement of gamma-augmentation related to a simple calculation task appears modest.Further studies are warranted to determine the functional significance of calculation-specific gamma-augmentation in each site, and to establish the optimal protocol for mapping mental calculation.
SUBMITTER: Ueda K
PROVIDER: S-EPMC4225188 | biostudies-literature | 2015 Jan
REPOSITORIES: biostudies-literature
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