MEG data during the presentation of Gabor patterns and word sets

Subjects

MEG was recorded in 7 healthy subjects (5 young right-handed and 1 left-handed and 1 elderly) in the waking state with their eyes open or closed, who were sitting in a comfortable chair. The experimental technique was approved by the ethical commission of the Institute of Higher Nervous Activity and Neurophysiology of RAS (protocol No. 5 dated 02.12.2020).

Equipment

MEG was recorded on a VectorView device (Elekta Neuromag Oy, Finland), which was placed inside a magnetically protected chamber made of multilayer permalloy (AK3b, Vacuumschmelze GmbH, Germany). Before MEG recording, the coordinates of anatomical reference points (left and right preauricular points and nasion) were determined, as well as indicator coils attached to the surface of the scalp of the subject in the upper part of the forehead and behind the auricles. These points were determined using a FASTRAK 3D digitizer (Polhemus, USA). Each subject had a virtual model of the brain and head obtained from an anatomical 3D MRI taken the day before (file: MRI_V1_7.zip).

Registration and pre-processing

The subject's head was covered by a helmet, which is part of a fiberglass Dewar vessel with an array of sensors immersed in liquid helium. The subject sat down in such a way that the surface of the head was as close as possible to the sensors. The magnetic signal was recorded from 102 triplets, each of which consisted of 1 magnetometer and 2 gradiometers at rest with eyes closed and upon presentation of visual and speech stimuli. Recording was performed with a sampling frequency of 1000 Hz in a bandwidth of 0.1–330 Hz and was processed by the MaxFilter program (Elekta Neuromag Oy, Finland), which eliminates artifacts (the tSSS method—spatio-temporal separation of signals). The signal levels were corrected in accordance with the data on the position of the subject's head in relation to the MEG sensors. The position of the head during the experiment was controlled using special inductors.

Visual and verbal stimuli

After recording the background MEG for 3 minutes with closed eyes, the subject opened his eyes on command and observed the fixation point on the projection screen. After 15 seconds, stimulation was started and the subject's responses were received in the form of pressing a button. In response to the 0 degrees and 90 degrees stimuli, the subject had to press the button with the index finger, and to the 45 degrees and 135 degrees inclined stimuli, the adjacent button with the middle finger. Stimuli lasting 100 ms were presented randomly every 3100±100 ms (intervals between stimuli varied randomly). In two series, 42 stimuli of each orientation were presented. Between the series, the subject rested for 2-3 minutes.  Visual stimuli in the form of Gabor contrast gratings (1.9 cycles per angular degree) with dimensions of 5.25 angular degrees and an average brightness of 4 lux were projected onto a screen located at a distance of 95 cm from the subject's eyes using a Panasonic PT-stimulating projector D7700E-K, which is part of the MEG facility. Visual stimulus patterns were generated at http://www.cogsci.nl/pages/gabor-generator with edge parameters: Circular (sharp edge). The samples are contained in the GaborStim.zip file (the names of the sample files correspond to their name in the script file, but do not match their geometric meaning, see table below). The stimulator was programmed using the Presentation software (USA, Neurobehavioral Systems, Inc). Stimulation scripts are contained in the sce.zip file.

Table

Stimulus or response code Type of stimulus or response

STI101_1                          Fixation point
STI101_2                           90 degrees
STI101_4                         135 degrees

STI101_8                             0 degrees
STI101_16                         45 degrees
STI101_32                       First button (index finger)

STI101_64                       Second button (middle finger)

After 2 series of visual stimuli, the subject closed his eyes and was presented with 3 series of speech stimuli for 2 minutes with a break of 1 minute. In each series, recordings of audio files of 8 separate adjectives of the Russian language were presented, which were repeated 5 times in a pseudo-random order. The series began with 3 words, which were not taken into account in further analysis. The subject listened to the words and had to press the button after he understood the meaning of the presented word. After pressing or no response, the next word followed in 2±1 s. The audio files are contained in the words101_343.zip file (the names correspond to the script file).

Data received

The records are contained in files with the name of the type V1m24r, where V1 is the number of the subject, m is the sex (m/f), 24 is the age, and r is the right-handed subject. This dataset can be easily loaded into the Brainstorm program. Spontaneous and evoked MEG can be used for source localization and reconstruction of traveling waves.

Acknowledgments

The reported study was funded by RFBR, project number 20-015-00475.