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Cortical Neuromagnetic Fields Preceding Voluntary Jaw Movements

Oral Health Science Center, Tokyo Dental College, Chiba 261-8502, Japan;
¹ Department of Physiology, Tokyo Dental College, Chiba 261-8502, Japan;
² Department of Oral Physiology, Matsumoto Dental University, Shiojiri, 399-0781, Japan; and
³ Department of Welfare and Information, Teikyo Heisei University, Ichihara 290-0193, Japan;

View larger version (26K): [in a new window]   Figure 1. Simultaneous records of cortical magnetic fields, EEG, and EMG accompanying jaw-closing (left column) and jaw-opening movements (right column) obtained from subject 5. Upper and lower pairs of MEGs were obtained from the left and right fronto-lateral scalp regions, respectively. Upper and lower traces of each pair represent the latitudinal and longitudinal derivatives of the radial magnetic field, respectively. Magnetic flux out of the head is shown upward in this and the following Figs. EEG traces were recorded from Cz, with negativity upward. Upper pairs of EMG traces in left and right columns represent masseter EMG and its integrated record, while lower pairs represent digastric EMG and its integrated record. Each trace represents a record of 100 trials, and starts 2500 ms preceding the onset of the EMG (vertical dotted lines) and terminates 500 ms after it. Horizontal line in each trace indicates a baseline.

View larger version (15K): [in a new window]   Figure 2. Expanded cortical magnetic field accompanying jaw-opening movements in subject 3. Rightmost vertical line indicates the time of onset of digastric EMG. Abbreviations: RF, readiness field; MEF, motor-evoked field; PMF, post-movement field. Horizontal thick straight line indicates the average level of the resting magnetic field; shaded areas above and below show 2 SD of the resting field, respectively. These values were obtained from the resting field for the period of 300 ms at the beginning of the window (leftmost period indicated by bilateral arrow). Dotted line represents regression line to determine the time of RF onset.

View larger version (60K): [in a new window]   Figure 3. Isocontour maps of RFs accompanying jaw-closing movements and locations of ECDs producing the field distribution, obtained from the same subject as shown in Fig. 1 (subject 5). (A) Isocontour maps of RFs on the left (A1) and right hemispheres (A2) at 94 ms prior to the onset of masseter EMG. In this and the following Figs., isocontour maps are drawn at 20 fT steps; red and blue lines indicate outgoing and ingoing fluxes, respectively. Green arrows show the location and direction of ECDs producing the RF distribution; arrowheads indicate the negative pole. (B) Locations of ECDs producing the cortical distribution of RFs at 94 ms prior to the EMG onset, as drawn in A1 and A2. A two-dipole model was fitted by means of time-varying multi-dipole analysis. In B1 and B2, red circles show the locations of ECDs on MRI sagittal planes on the left and right sides, respectively; red bars attached to circles indicate the size and direction of ECDs projected on each sagittal plane (end of bars attached to circles represents the positive pole). Upper and lower traces of B3 show the current source strength on the left (RFleft) and right (RFright) sides, respectively, as a function of time. (C) Locations of ECDs on the left (C1) and right (C2) sides (red circles), respectively, superimposed on the three-dimensionally reconstructed MRI of the subject’s brain. Arrowheads in C1 and C2 indicate the central sulcus.

View larger version (58K): [in a new window]   Figure 4. Isocontour maps of RFs accompanying jaw-opening movements and locations of ECDs producing the field distribution at 83 ms prior to the onset of digastric EMG, obtained from subject 1. The construction of A, B, and C is the same as in Fig. 3. To clarify the ECD location in C1, we rotated the three-dimensional image on the z-axis with approximately 40° against the direct viewing angle from the left.