Automatic and intentional number processing both rely on intact right parietal cortex: a combined FMRI and...

Area of Science:

• Cognitive Neuroscience
• Neurobiology

Background:

• Performance improvement with practice often involves a shift towards automatic processing.
• The neural mechanisms underlying automatic versus intentional processing are debated, with conflicting evidence regarding shared or distinct brain regions.
• Previous correlational studies have yielded inconclusive results on the neural basis of automatic and intentional processing.

Purpose of the Study:

• To causally investigate the role of left and right parietal cortex in automatic and intentional numerical processing using transcranial magnetic stimulation (TMS).
• To determine if automatic and intentional numerical processing rely on the same or different neural mechanisms within the parietal cortex.
• To examine hemispheric lateralization in parietal cortex function for numerical tasks.

Main Methods:

• Utilized transcranial magnetic stimulation (TMS) to temporarily disrupt activity in the left and right parietal cortex.
• Assessed the impact of TMS on automatic numerical processing via the size congruity effect.
• Assessed the impact of TMS on intentional numerical processing via the numerical distance effect.

Main Results:

• Disruption of the right parietal cortex significantly impaired performance in both automatic and intentional numerical processing.
• Disruption of the left parietal cortex or sham stimulation did not affect performance in either processing type.
• Demonstrated a functional hemispheric asymmetry within the parietal cortex for numerical processing.

Conclusions:

• The right parietal cortex plays a causal role in both automatic and intentional numerical processing.
• Automatic and intentional numerical processing appear to rely on the same underlying hemispheric lateralization within the parietal cortex.
• These findings provide causal evidence for the functional relevance of the right parietal lobe in numerical cognition.