Separating the forest from the palm trees: Individual variation in a presurgical language mapping task

Background Selecting optimal tasks for language mapping in neurosurgical patients poses challenges that are exacerbated by mismatches in practice between presurgical and intraoperative evaluations. To help align practices, we evaluated a functional MRI version of a semantic association task increasingly used during intra-operative assessment of awake neurosurgery patients. Using a recently proposed consistency mapping approach, we characterise task fMRI activation reliability across individuals, visits, and scan cohorts. Methods FMRI data were acquired during an adapted Pyramids and Palm Trees Task (PPTT) in 15 healthy controls and 54 pre-surgical patients with a glioma. A new implementation of threshold-weighted overlap mapping (TWOM) was used to evaluate: 1. inter-individual variability in task activations among individuals; 2. test–retest variability in controls scanned twice (16 ± weeks apart); 3. between-scanner reliability across two patient cohorts scanned on a 3 T Siemens Prisma (n = 27) or Verio (n = 24) scanner using standard (TR = 3 s, voxel size 3 × 3 × 3 mm) or advanced (TR = 0.93 s, voxel size 2x2x2 mm) fMRI acquisitions, respectively. Results Task-related activations in the core language network were highly consistent between individuals and across test–retest sessions. Several brain regions showed variable activations, reflecting atypical language dominance (confirmed during neurosurgery), or differences in regional involvement during semantic processing. Conclusion The PPTT engaged widespread brain networks including but not limited to regions implicated in semantic processing. Overlap mapping is a powerful way to visualise meaningful variations in neural processing at the individual level, supporting alignment of pre- and intra-operative mapping for any given task.