Article

The auditory evoked sustained field: origin and frequency dependence

Wilhelms-University of Münster, Institute of Experimental Audiology, Centre of Biomagnetism, Germany.
Electroencephalography and Clinical Neurophysiology 02/1994; 90(1):82-90. DOI: 10.1016/0013-4694(94)90115-5
Source: PubMed

ABSTRACT A sound lasting for several seconds is known to elicit a baseline shift in electrical and magnetic records. We have studied the dependence of the magnetic field distribution of this "per-stimulatory" sustained field (SF) on tone frequency. Tone bursts of 2 sec duration and 60 dB nHL intensity were presented to 11 subjects at varying interstimulus intervals between 5 and 7 sec. The carrier frequencies of 250, 1000 and 4000 Hz varied randomly from trial to trial. The field distributions obtained are consistent with the view that the auditory evoked sustained field activity originates in the supratemporal cortex. Differences in the locations of equivalent current dipoles of the SF from those of the M100 wave of the slow auditory evoked field are consistent across subjects. The SF source locations corresponding to stimulus frequencies over an extended frequency range are arranged in a tonotopic manner and support the idea that the sources of the M100 and the SF are current dipole sheets located on the superior surface of the primary auditory cortex.

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    • "Electroencephalographic (EEG) and magnetoencephalographic (MEG) data allow the effective location of current dipoles to be reconstructed, typically one for each hemisphere. A number of studies reported that the dipole's depth below the scalp and its coordinate along the rostrocaudal axis increased with stimulus frequency, and its orientation varied due to gyral morphology (Romani et al. 1982; Pantev et al. 1988; Kuriki and Murase 1989; Cansino et al. 1994; Pantev et al. 1994; Huotilainen et al. 1995; Verkindt et al. 1995; Gabriel et al. 2004; Weisz, Wienbruch, et al. 2004; Wienbruch et al. 2006; Ozaki and Hashimoto 2007). These findings confirm that human auditory cortex is organized tonotopically, with an effective low-to-high-frequency gradient extending in the (antero)lateral-to-(postero)medial direction along HG. "
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    • "g selec - tivity to richer and more complex stimuli ( Kaas & Hackett , 2000 ; Rauschecker , 1998 ; Rauschecker & Tian , 2004 ; Rauschecker et al . , 1995 ) . These results from animal models are supported by measurements in humans : Tonotopic organization has been ver - ified intracortically ( Howard et al . , 1996 ) and with MEG mea - surements ( Pantev et al . , 1988 , 1994 ) , which also indicate the existence of amplitopic maps ( Pantev , Hoke , Lehnertz , & Lu¨tkenhoner , 1989 ) . Also , fMRI results indicate that the fre - quency of amplitude modulation ( i . e . , the inverse of ISI ) is a feature represented spatially , with primary auditory cortex re - sponding preferentially to sounds amplitude - m"
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