Frequency and Laminar Profile of Feature Specific and nonspecific Neural Activity in Human Visual Cortex Revealed by Interleaved EEG-fMRI

Abstract

The study included 52 right-handed participants (34 female) aged 18–35 years (mean: 24, SD: 4). Data were collected using a Siemens MAGNETOM Prismafit 3T MRI scanner with a 64-channel head coil. Anatomical data were acquired with a T1-weighted MPRAGE sequence at 0.8 mm isotropic resolution. Functional MRI data were recorded using a 3D gradient-EPI sequence with CAIPI acceleration, covering the occipital and parietal lobes, covering primary visual regions (0.9 mm isotropic voxel size; TR of 3.3 seconds; TE of 34 ms). The sequence was adapted to include a 3-second delay after every three consecutive volumes to ensure clean EEG data acquisition during trials. For pRF mapping, the same fMRI protocol was used, but the 3-second delay was omitted since no EEG was recorded. EEG data were simultaneously recorded during the main experiment using a 64-channel MR-compatible system at a 5 kHz sampling rate, with impedances kept below 20 kΩ. Electrode positions were measured via a photogrammetry (3D model) based approach and aligned to anatomical MRI using facial features (only final sensor locations are provided to protect participant’s privacy). Eye-tracking data were also collected but omitted from the analysis due to poor quality. The experimental protocol included the high-resolution T1 scan, followed by four EEG-fMRI blocks for the main experiment and three pRF mapping blocks. Participants performed a visual attention task, detecting wavy "oddball" patterns among regular - left or right oriented - gratings. A trial started 1.2 s prior to stimulus presentation with the fixation indicator changing color which indicated to the participants to avoid blinking. The stimulus was displayed for 1.6 s. After a period of additional 0.6 s the fixation indicator changed color again, indicating to the participants that they could blink now. Oddball trials (1:5 ratio) required a button press and if appropriate, feedback was provided after the 1.6 s stimulus onset period. The pRF mapping comprised moving checkerboard stimuli to localize visual cortex ROIs. Participants responded to fixation dot color changes.