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AIST TODAYNo.16 Spring 2005 [ PDF:17.6MB ]

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A new view on the mechanism for generating evoked fields

I analyzed not-averaged neuromagnetic responses to repetitive sounds. It was found that ongoing oscillations around 6 Hz are relevant for generating the auditory evoked fields. Namely, phases of the oscillation were locked, their magnitudes were increased and magnetic fields were often reduced to an equivalent current dipole in the auditory cortex at around the timings of N100m, but the phases were unlocked and the fields were seldom reduced to a dipole at the other timings. These lines of evidence suggest there exist several oscillators within the cortex whose phases are locked at around the timings of N100m, but otherwise unlocked.
Fig.1
 Fig.2
Fig.1 Auditory evoked field. Vertical bar:onset and 100 fT/cm. Horizontal bar: 100 ms.
Fig.2 Raw data after passed the band-pass filter in 20 consecutive trials. Scales are the same as in Fig.1.

Fig.3
Fig.3
(a): One of the traces in Fig.2.
(b): Magnetic field above the right cortex at the timing shown by a triangle in (a), and the estimated dipole.
(c): Magnitude (20 nAm step) and goodness-of-fit (10 % step) of the estimated dipole vs. time (50 ms step).

Relational Information

AIST Today Vol.5 , No.1 (2005-No.16) 15

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