Effects of sound level on fMRI activation in human brainstem, thalamic and cortical centers

Abstract

The dependence of fMRI activation on sound level was examined throughout the auditory pathway of normal human listeners using continuous broadband noise, a stimulus widely used in neuroscientific investigations of auditory processing, but largely neglected in neuro-imaging. Several specialized techniques were combined here for the first time to enhance detection of brainstem activation, mitigate scanner noise, and recover temporal resolution lost by the mitigation technique. The main finding was increased activation with increasing level in cochlear nucleus, superior olive, inferior colliculus, medial geniculate body and auditory cortical areas. We suggest that these increases reflect monotonically increasing activity in a preponderance of individual auditory neurons responsive to broadband noise. While the time-course of activation changed with level, the change was subtle and only significant in a part of the cortex. To our knowledge, these are the first fMRI data showing the effects of sound level in subcortical centers or for a non-tonal, non-speech stimulus at any stage of the pathway. The present results add to the body of parametric data in normal human listeners and are fundamental to the design of any fMRI experiment employing continuous noise.

Neural Coding of Sound Intensity and Loudness in the Human Auditory System

“…This is in line with previous studies on sound intensity (Hegerl et al 1994;Jäncke et al 1998;Mohr et al 1999;Hall et al 2001;Bilecen et al 2002;Brechmann et al 2002;Gutschalk et al 2002;Hart et al 2002Hart et al , 2003Lasota et al 2003;Mulert et al 2005;Sigalovsky and Melcher 2006;Langers et al 2007;Ernst et al 2008). Probably due to the comparatively large number of participants in our study and the large examined range of levels and corresponding perceived loudness, it was possible to specify that the volume of activation increases exponentially and the percent signal change from baseline almost linearly with sound pressure level in all examined stages of the auditory pathway.…”

“…Neural activation in the inferior colliculi and the medial geniculate bodies (MGB) was investigated in a similar way but using a small volume correction procedure instead of the false discovery rate method to adjust the p value. The threshold for significance was set to pG0.01 as in Sigalovsky and Melcher (2006). The small volume was defined by spheres of 5 mm radius as in Griffiths et al (2001).…”

“…The detection of neural activation in brainstem or midbrain areas could probably be systematically improved by applying cardiac-gating procedures with prospective or retrospective methods (Glover et al 2000;Griffiths et al 2001;Sigalovsky and Melcher 2006;Harvey et al 2008). However, as the results suggest, this is not generally required, at least not for the inferior colliculus, if the quality of the PSC measurement is being assessed properly.…”

“…Several neuroimaging studies on the neural coding of sound intensity in the human auditory system have commonly shown that neural activation increases as a function of sound intensity in auditory areas (Hegerl et al 1994;Jäncke et al 1998;Mohr et al 1999;Hall et al 2001, Bilecen et al 2002Brechmann et al 2002;Gutschalk et al 2002;Hart et al 2002Hart et al , 2003Lasota et al 2003;Mulert et al 2005;Sigalovsky and Melcher 2006;Langers et al 2007;Ernst et al 2008;Röhl and Uppenkamp 2010;Röhl et al 2011). There is still some dispute, however, over the precise location of intensity coding, e.g., whether it is more related to primary areas like the Heschl's gyrus as described by Hart et al (2002) or more related to secondary auditory areas like the Planum Temporale as described by Gutschalk et al (2002).…”

Human Cortical Activity during Streaming without Spectral Cues Suggests a General Neural Substrate for Auditory Stream Segregation

“…Activation time courses were calculated as a weighted sum of basis functions and converted to percent signal change vs time (Sigalovsky and Melcher, 2006). The time course for a given ROI and subject was calculated as an average over the surface vertices (in the inflated cortical projection) showing significant activation in the "all conditions versus baseline" contrast described above ( p Ͻ 0.001; F statistic, not corrected for multiple comparisons).…”