Publications

Abstract not provided.

Orthographic visual perception (reading) is encoded via a widespread dynamic interaction between different language centers of the brain and visual cortex. In this study, we investigated orthographic visual perception decoding with Magnetoencephalography (MEG), where phrases were visually presented to participants. We compared the decoding performance obtained with sensors within the occipital lobe that obtained with sensors covering the whole head. Two naive machine learning classifiers namely support vector machines (SVM) and linear discriminant analysis (LDA) were used. Experimental results indicated that the decoding performance using only occipital sensors is similar to the performance obtained with all sensors within the task period, which were all above chance level. In addition, temporal analysis by taking short-time windows showed that the occipital sensors were more discriminative near onset compared to later time periods, while using the whole head sensor setup at later time periods performed slightly better than occipital sensors. This finding may indicate a sequential order (from visual cortex to other areas beyond occipital lobe) during visual speech perception.

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We have developed a pulsed optically pumped magnetometer (OPM) array for detecting magnetic field maps originated from an arbitrary current distribution. The presented magnetic source imaging (MSI) system features 24-OPM channels has a data rate of 500 S/s, a sensitivity of 0.8\mathrm {pT/}\sqrt {\mathrm {Hz}} , and a dynamic range of 72 dB. We have employed our pulsed-OPM MSI system for measuring the magnetic field map of a test coil structure. The coils are moved across the array in an indexed fashion to measure the magnetic field over an area larger than the array. The captured magnetic field maps show excellent agreement with the simulation results. Assuming a 2-D current distribution, we have solved the inverse problem using the measured magnetic field maps, and the reconstructed current distribution image is compared with that of the simulation.

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We describe a multichannel magnetoencephalography (MEG) system that uses optically pumped magnetometers (OPMs) to sense the magnetic fields of the human brain. The system consists of an array of 20 OPM channels conforming to the human subject's head, a person-sized magnetic shield containing the array and the human subject, a laser system to drive the OPM array, and various control and data acquisition systems. We conducted two MEG experiments: auditory evoked magnetic field and somatosensory evoked magnetic field, on three healthy male subjects, using both our OPM array and a 306-channel Elekta-Neuromag superconducting quantum interference device (SQUID) MEG system. The described OPM array measures the tangential components of the magnetic field as opposed to the radial component measured by most SQUID-based MEG systems. Herein, we compare the results of the OPM- and SQUID-based MEG systems on the auditory and somatosensory data recorded in the same individuals on both systems.

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We have developed a four-channel optically pumped atomic magnetometer for magnetoencephalography (MEG) that incorporates a passive diffractive optical element (DOE). The DOE allows us to achieve a long, 18-mm gradiometer baseline in a compact footprint on the head. Using gradiometry, the sensitivities of the channels are < 5 fT/Hz1/2, and the 3-dB bandwidths are approximately 90 Hz, which are both sufficient to perform MEG. Additionally, the channels are highly uniform, which offers the possibility of employing standard MEG post-processing techniques. This module will serve as a building block of an array for magnetic source localization.

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