Temporal order of activations and interactions during arithmetic calculations measured by intracranial electrophysiological recordings in the human brain
Arithmetic requires complex and fast processes orchestrated within a large-scale network spanning multiple brain regions. However, reports on the networks 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.