Allegra 3t scanner

All participants completed a scanning session of approximately 75 minutes, comprised of structural, diffusion tensor imaging (DTI), and functional (fMRI) sequences during the episodic memory paradigm.^{48 (link),49 (link)} DTI data were acquired on a Siemens 3T Allegra scanner using echo-planar imaging (EPI) sequences (matrix= 128×128×34, FOV 200, slice thickness 3mm) consisting of seven transaxial images collected in 6 gradient directions at a b-value of 850 with one b=0 weighted image. Structural scans acquired during these sessions included axial T2 weighted images (39 contiguous 3mm slices, TR = 6440 ms, TE = 73 ms, 256 × 256 matrix, FOV = 200mm, flip angle = 150°) and a sagittal 3-D MPRAGE sequence (224 contiguous 0.78 mm slices, TR = 1680ms, TE = 2.48ms, 256×256 matrix, FOV = 200mm, flip angle = 8°).

We used fMRI data from 18 subjects (localizer data from Turk-Browne et al., 2012 (link)), who viewed sequences of face and scene images in alternating blocks, while performing male/female and indoor/outdoor judgment tasks, respectively. Each subject completed one functional run that contained 12 blocks (6 involving faces and 6 involving scenes). Each block contained 12 images from one category and lasted for 18 s, followed by blank fixation period of 12 s between blocks.
Data were acquired using a Siemens 3T Allegra scanner, with a T2*-weighted EPI sequence: volumes = 224, slices = 26, TR = 1500 ms, TE = 28 ms, matrix = 64, field of view = 224 mm, flip angle = 64°, and thickness = 5 mm (3.5 x 3.5 x 5 mm voxels). Data were preprocessed prior to FCMA with corrections for head motion and slice-time acquisition, spatial smoothing (5 mm), and high-pass temporal filtering (128 s period). Brains were anatomically aligned to MNI space using standard linear registration methods (Jenkinson et al., 2002 (link)) and masked to remove non-brain voxels. After alignment, every brain contained 34,470 voxels.

Participants were 65 healthy adults (36 males; age range: 17 – 49 years; mean ± SD of age: 30.5 ± 9.2 years) pooled from two fMRI studies. Written informed consent, approved by the Institutional Review Board of the National Institute on Drug Abuse, was obtained from each participant prior to study enrollment. All participants had no major medical conditions, no history of neurological or psychiatric disorders, no history of substance abuse, and were not on medication that would affect neurotransmitter levels or cortical inhibition and excitation during the study participation. The 35 participants in Cohort 1 and the 30 participants in Cohort 2 both underwent a high-resolution anatomical scan and n-back WM fMRI scans on a Siemens 3T Allegra scanner (Cohort 1) or Trio scanner (Cohort 2) (Hu et al., 2013 (link); Liang et al., 2015 ). In addition, the 30 participants from Cohort 2 also received single-voxel proton MRS scans for GABA and glutamate quantification at the PCC/PCu prior to the WM fMRI scan.