# Temporal order of activations and interactions during arithmetic calculations measured by intracranial electrophysiological recordings in the human brain

## TL;DR

This study uses brain recordings to reveal the timing and brain regions involved in performing arithmetic calculations.

## Contribution

The study provides high-resolution insights into the temporal dynamics of brain activity and connectivity during arithmetic tasks.

## Key findings

- High-gamma band activity peaks first in the ventral occipito-temporal cortex during arithmetic tasks.
- Theta frequency connectivity appears earlier than delta frequency connectivity during calculations.
- Functional connectivity evolves into a robust pattern among key brain regions 200–400 ms after operand presentation.

## Abstract

Arithmetic requires complex and fast processes orchestrated within a large-scale network spanning multiple brain regions. However, reports on the network’s temporal dynamics are scarce. Here, we present data from intracranial EEG (iEEG) of 20 subjects (epilepsy surgery candidates) performing a sequential three-operand arithmetic task. Utilizing the high temporal and spatial resolution of iEEG, we analysed changes in high-gamma band (HGB; 52–120 Hz) activity and functional connectivity assessed by phase-locking value (PLV) in the delta (0.1–3 Hz) and theta (3–7 Hz) frequency bands. Strong and transient HGB activations peaked first in the ventral occipito-temporal cortex, followed by a more gradual increase in the lateral parietal, sensorimotor, and frontal cortices, accompanied by deactivations in default mode network areas. The connectivity patterns were more extensive during calculation than number recognition, with the theta PLV peaking ~ 150 ms earlier than the delta PLV. Earliest connectivity appeared, surprisingly, between ventral temporal and frontal regions at ~ 100–200 ms, evolving into a robust pattern among key network nodes at ~ 200–400 ms after the presentation of each operand. The presented results elucidate information flow within the putative arithmetic network during calculation in the human brain, offering high-temporal-resolution insights into its functional architecture.

The online version contains supplementary material available at 10.1038/s41598-026-36122-z.