3d digitizer

Eleven healthy subjects were included in the study (right handed, male, 28 ± 5 (mean ± std) years old). Each subject gave informed written consent prior to the experiments. Subjects with a history of neurological trauma or psychiatric disorders, or who were unable to keep their head still, were excluded.
Prior to the actual experiment, electrical stimulation was applied to each subject's left thumb through electrodes with a 5 Hz electrical stimulator (Neurometer CPT, Neurotron, Baltimore, MD) to determine current levels that elicited subjective ratings of 3/10 (innocuous) and 7/10 (noxious) from each subject. The electrical stimulus was increased from baseline (0.7 mA) by 0.05 mA increments, while the subjects were expected to specify when the electrical stimulus reaches to a pain level of 3 (innocuous) and 7 (noxious) on a 0 to 10 scale. These current values were used in the actual experiment.
During the actual experiment, randomized innocuous and noxious electrical stimuli at 5 Hz were applied by a neurometer (Neurotron Inc. Baltimore, MD). Each stimulus lasted 5 seconds, followed by a 25 second rest. Each run lasted 12.5 minutes and consisted of 12 innocuous and 12 noxious stimuli which were randomly ordered (Figure 7, panel C).
Following the NIRS acquisition, the 3D positions of the sources and detectors were obtained using a 3D digitizer (Polhemus Inc., VT).

The simultaneous MEG and EEG data were collected at the BioMag Laboratory of the Helsinki University Central Hospital. The measurements were performed in an electrically and magnetically shielded room (ETS-Lindgren Euroshield, Eura, Finland) with Vectorview™ 306-channel MEG system (Elekta Neuromag, Elekta Oy, Helsinki, Finland) equipped with a compatible EEG system. The MEG system had 102 triple-sensor elements, each comprising two orthogonal planar gradiometers and one magnetometer. A 64-channel EEG electrode cap was used. The reference electrode was placed on the nose tip and the ground electrode was on the right cheek. Blinks, as well as vertical and horizontal eye movements, were measured with four electrodes attached above and below the left eye and close to the external eye corners on both sides. Four head position indicator coils were placed on top of the EEG cap. Their positions were determined with respect to the nasion and preauricular points by an Isotrak 3D digitizer (Polhemus, Colchester, VT, USA). MEG and EEG data were recorded with a sample rate of 600 Hz.
During the measurement, subjects were comfortably seated and watched a silenced movie with subtitles. The stimuli were presented with Presentation software (Neurobehavioral Systems, Ltd.). The sound was delivered through a pair of pneumatic headphones at individually adjusted loudness.

MEG data were acquired using a 306 channel (204 planar gradiometers and 102 magnetometers) Neuromag Vectorview system (Elekta AB, Stockholm) in a sound-attenuated and magnetically shielded room. Data were sampled at 1000 Hz with an online band-pass filter of 0.03–333 Hz. Five Head Position Indicator (HPI) coils were attached firmly to the EEG cap to track the head movements of the participant. The locations of the HPI coils as well as the EEG electrodes were recorded with a Polhemus 3D digitizer. We also measured three anatomical landmark points (nasion, left and right preauricular points) and additional points on the head to indicate head shape and enable matching to each individual's structural MRI scan.

MEG signals were recorded using a 306-channel Neuromag Vectorview MEG system (Elekta, Helsinki, Finland). Anatomical images were obtained using a 3.0 T MRI scanner (Achieve, Philips N.V., Eindhoven, the Netherlands) for analysis and interpretation of MEG data (TE, 60 ms; TR, 100 ms; voxel size, 1.5 × 1.5 × 1.5 mm³). Magnetic fields were recorded continuously at a sampling rate of 1000 Hz with a bandpass filter of 0.1–330 Hz. Before each recording, four head-position indicator (HPI) coils attached to the scalp and a 3D digitizer (FastTrack, Polhemus, VT, USA) were used to measure anatomical landmarks (nasion, and left and right auricular points) of the head, the HPI positions, and approximately 200 head-surface points^{34 (link)}. During the recording, participants were positioned in a quiet magnetically shielded room with their head inside the helmet-shaped sensor array. During each run, continuous HPI (cHPI) measurement was performed using the four HPI coils.