64 channel mr compatible eeg system

EEG recordings were conducted with a 64‐channel MR‐compatible EEG system (Brain Products, Gilching, Germany; 0.1–250 Hz hardware band‐pass filter, ±16.38 mV recording range at a 0.5 μV resolution and 5 kHz sampling rate) and an EEG cap with ring‐type sintered silver chloride electrodes with iron‐free copper leads (EasyCap, Herrsching, Germany). Sixty‐one scalp electrodes were arranged based on the international 10–20 system with FCz as reference and ground electrode at AFz. In addition, two electrocardiogram (ECG) electrodes and one vertical electro‐oculogram (EOG) were recorded. An abrasive electrolyte gel (Abralyt 2000, Easycap, Herrsching, Germany) served to keep the impedances of all electrodes below 5 kΩ. The EEG‐sampling was synchronized to the gradient‐switching clock of the MR scanner, to ensure time‐invariant sampling of the image acquisition artifact (SyncBox, Brain Products, Gilching, Germany) (Anami et al., 2003 (link); Freyer et al., 2009 (link)).

The participants were required to maintain a regular schedule for 2 weeks before the electroencephalography (EEG)‐fMRI experiment that was monitored by actigraphy and recorded in a sleep diary.
The experimental data were collected on an MRI scanner (3 T Prisma; Siemens Healthineers, Erlangen, Germany) at the Center of MRI Research, Peking University. Within 1 week after a 2‐week period of sleep monitoring, each subject underwent an fMRI adaptation session. The subjects were asked to wear an EEG cap (64‐channel, MR‐compatible EEG system; Brain Products, Munich, Germany) lying in the MRI scanner. The adaptation session included a 6‐min T1‐weighted scan and a 20‐min BOLD‐fMRI scan. Within 1 week after the adaptation scan, simultaneous EEG‐fMRI data were acquired at the participant's usual bedtime when the participant had been instructed to sleep. It is worth noting that no sleep deprivation was involved.

Participants were asked to follow a regular sleep schedule for 2 weeks before MRI data collection, and their habitual sleep patterns were monitored through actigraphy and sleep diaries.
An adaptation session to our MR scanner (3T Prisma Scanner, Siemens Healthineers, Erlangen, Germany) was conducted at the Center for MRI Research, Peking University, within a week after the 2‐week sleep schedule was maintained. Participants were asked to lie in the scanner wearing an EEG cap (64‐channel MR‐compatible EEG system, Brain Products, Munich, Germany) and underwent 6 min of T1‐weighted scanning and 30 min of BOLD fMRI scanning. Within a week after the adaptation session, simultaneous EEG‐fMRI recordings were conducted at the participants’ usual bedtime. Notably, no sleep deprivation was involved, and natural sleep under normal homeostatic sleep pressure was investigated in this study.