Dexterity with numbers: rTMS over left angular gyrus disrupts finger gnosis and number processing

Area of Science:

• Cognitive Neuroscience
• Neurobiology of Number Processing
• Neuroscience of Body Schema

Background:

• Gerstmann's syndrome links finger agnosia and acalculia, suggesting a neuro-cognitive relationship between fingers and calculation.
• Previous research often utilized special populations (neurological patients, children) to explore this connection.
• The precise neural basis for the relationship between body representation and numerical cognition remains an active area of investigation.

Purpose of the Study:

• To investigate the neuro-cognitive relationship between finger representation and numerical processing in healthy adults.
• To determine if disrupting the left angular gyrus affects tasks involving finger schemas and number magnitude.
• To test Gerstmann's original anatomical hypothesis regarding the angular gyrus's role in these functions.

Main Methods:

• Participants performed tactile-to-key-press finger tasks and numerical magnitude/parity matching tasks.
• Repetitive transcranial magnetic stimulation (rTMS) was applied over the posterior parietal lobe (left and right hemispheres).
• Task performance was assessed during rTMS to identify causal effects of neural disruption.

Main Results:

• rTMS over the left angular gyrus significantly disrupted performance on both finger schema access tasks and number magnitude processing.
• Disruption was observed in the same group of participants for both finger and numerical tasks.
• No significant disruption was noted for parity matching tasks or when rTMS was applied to the right hemisphere.

Conclusions:

• The findings support Gerstmann's hypothesis by demonstrating that the left angular gyrus is crucial for both finger representation and number magnitude processing.
• This study confirms a shared neural substrate for numerical cognition and body knowledge (specifically finger schema) in skilled adults.
• The results highlight the importance of the left angular gyrus in integrating somatosensory and numerical information.