The Krakow Paradigm - fMRI datasets in BIDS format

Participants

Forty-nine participants (mean age, 24.2 ± 3.7 years; 16 males) met the following experiment requirements: no contraindication for MRI scanning; normal or corrected-to-normal vision; no reported physical or psychiatric disorders; drug-free. To ensure sufficient experience in the environment, subjects had to be Krakow residents for at least one year. Subjects lived in Krakow on average 9.1 years (SD 8.1).

Participants were informed about the procedure and goals of the study and they gave written consent. The study was approved by the bioethics commission at the Polish Military Institute of Aviation Medicine and was conducted in accordance with ethical standards described in the Declaration of Helsinki. The study was a part of a larger registered project (ISRCTN 18109340). 

Experimental Task

A novel place recognition task, the Krakow Paradigm, was prepared and generated using E-Prime 2.0 (©Psychology Software Tools). The task comprised of two stages: the training session and the fMRI session. Before the training session, subjects were presented with a map of Krakow city on which a thick red line marked the city “center” area and were asked to familiarize with the borders. 

The trial comprised of the stimulus (4.5 sec duration) and two response screens (each 1.0 sec duration), all separated by the blank screens (each 0.5 sec duration). The stimulus was a photograph taken in the Krakow city (resolution 640 x 428), presenting either characteristic landmarks (e.g. an Old Square) or uncharacteristic outside places (e.g. a playground near an estate community). Photograph was presented centrally on the light-gray background and covered 60% of the screen. On the first response screen, the question “Krakow Center?” occurred with three possible answers (‘yes’, ‘no’, ‘I don’t know’) given by pressing a button on a key-pad with right-hand index, middle, or ring finger respectively. On the second response screen, the question “Have you seen it in real-life?” occurred with two possible answers (‘yes’, ‘no’) given by pressing a button using index or middle finger respectively. For both questions, responses were recorded for 1.5 sec. Between the stimuli, a fixation point (a hash sign) was presented for a varying interval between 2.4 and 6.6 sec every 0.7 sec (on average total trial length = 12 sec). Total scan time was less than 13 minutes.

The training session was conducted to ensure timely responses. It was comprised of 7 trials, different than those used in the fMRI session, and was presented on regular computer screen. The fMRI session included 60 trials and was presented using the VisualSystem HD (NordicNeuroLab, Bergen, Norway) binocular apparatus. 50% of the photos were taken in the “center” and 50% outside of it. Characteristic and uncharacteristic places were counterbalanced across both location possibilities. At the end of the task, a feedback information was given to participants informing them the percentage of correctly classified places. Because participants were instructed to wait until the response screen appeared before making a response, reaction times are not informative and were not reported. The rationale for this procedure was to promote accuracy rather than speed, and to encourage response preparation, i.e. memory retrieval, while looking at a photo.

MRI Data Acquisition

MRI was performed using a 3T scanner (Magnetom Skyra, Siemens) with a 20-channel head/neck coil. High-resolution, whole-brain anatomical images were acquired using a T1-MPRAGE sequence. A total of 176 sagittal slices were obtained (voxel size 1×1×1.1 mm3; TR = 2300 ms, TE = 2.98 ms, flip angle = 9°) for co-registration with the fMRI data. Next, a B0 inhomogeneity gradient fieldmap (magnitude and phase images) was acquired with a dual-echo gradient-echo sequence, matched spatially with fMRI scans (TE1 = 4.92 ms, TE2 = 7.38 ms, TR = 400 ms).

Functional T2*-weighted images were acquired using a whole-brain echo planar (EPI) pulse sequence with the following parameters: 3 mm isotropic voxel; TR = 2070 ms; TE = 30 ms; flip angle = 90°; FOV 224 × 224 mm2; GRAPPA acceleration factor 2; and phase encoding A/P. Due to magnetic saturation effects, the first four volumes (dummy scans) of each session were discarded instantly resulting in 360 volumes acquired for each participant.