Balancing the 2 Hemispheres in Simple Calculation: Evidence From Direct Cortical Electrostimulation.
How do the parietal lobes contribute to simple calculation? Clinical and neuroimaging methods, which are based mainly on correlational evidence, have provided contrasting results so far. Here we used direct cortical electrostimulation during brain surgery to causally infer the role of the left and right parietal lobes in simple calculation. Stimulation provoked errors for addition and multiplication in different parietal areas on both hemispheres. Crucially, an innovative qualitative error analysis unveiled the functional contrast of the 2 parietal lobes. Right or left stimulation led to different types of substitution errors in multiplication, unveiling the function of the more active hemisphere. While inhibition of the left hemisphere led mainly to approximation errors, right hemisphere inhibition enhanced retrieval within a stored repertory. These results highlight the respective roles of each hemisphere in the network: rote retrieval of possible solutions by the left parietal areas and approximation to the correct solution by the right hemisphere. The bilateral orchestration between these functions guarantees precise calculation.
Neuroscience Department and Centre for Cognitive Neuroscience, University of Padova, 35128 Padova, Italy.|IRCCS San Camillo Hospital Foundation, Neuropsychology Unit, 30126 Lido-Venice, Italy.
C
C
Semenza
Basque Center on Cognition, Brain and Language , 20009Donostia, Spain.
E
E
Salillas
Neuroscience Department and Centre for Cognitive Neuroscience, University of Padova, 35128Padova, Italy.
S
S
De Pallegrin
Department of Neurosurgery, University Hospital of Padova, 35128 Padova, Italy.
A
A
Della Puppa
D000328:Adult; D000368:Aged; D001931:Brain Mapping / Q000379:methods; D001932:Brain Neoplasms / Q000503:physiopathology / Q000601:surgery; D002540:Cerebral Cortex / Q000503:physiopathology* / Q000601:surgery; D005260:Female; D007839:Functional Laterality / Q000502:physiology*; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D008297:Male; D008875:Middle Aged
approximation; brain mapping; exact calculation; hemispheric complementarity; parietal lobe