Balancing the 2 Hemispheres in Simple Calculation: Evidence From Direct Cortical Electrostimulation

Area of Science:

• Neuroscience
• Cognitive Psychology
• Neurosurgery

Background:

• The precise roles of the parietal lobes in simple calculation remain unclear, with conflicting evidence from correlational studies.
• Previous research using clinical and neuroimaging methods has not definitively established hemispheric contributions to mathematical processing.

Purpose of the Study:

• To causally investigate the contribution of the left and right parietal lobes to simple calculation using direct cortical electrostimulation.
• To differentiate the specific functions of each parietal lobe during mathematical tasks.

Main Methods:

• Direct cortical electrostimulation was applied during brain surgery to patients performing simple calculations.
• A novel qualitative error analysis was employed to categorize errors induced by stimulation.

Main Results:

• Stimulation of both left and right parietal areas induced calculation errors (addition and multiplication).
• Inhibiting the left hemisphere primarily resulted in approximation errors.
• Inhibiting the right hemisphere led to enhanced retrieval errors from a stored repertoire.

Conclusions:

• The left parietal lobe is crucial for the rote retrieval of potential solutions in calculation.
• The right parietal lobe plays a key role in approximating the correct answer.
• Precise calculation relies on the coordinated interaction between the approximation function of the right hemisphere and the retrieval function of the left hemisphere.