Cortical BOLD responses grow nonlinearly with sound intensity, steepening at high levels

Evidence

Throughout all investigated stages of the auditory system, except for ipsilateral stimuli in IC bilaterally and in left MGB, neural activation as reflected by the fMRI BOLD response was significantly and positively related to physical sound intensity. Specifically, at cortical level, changes in sound pressure level were reflected by nonlinear (quadratic) increases of activation magnitude, with steeper slopes at the highest sound levels. — Dijk, Pim van, Physiology, Psychoacoustics and…, 2610

Throughout all investigated stages of the auditory system, except for ipsilateral stimuli in IC bilaterally and in left MGB, neural activation as reflected by the fMRI BOLD response was significantly and positively related to physical sound intensity. Specifically, at cortical level, changes in sound pressure level were reflected by nonlinear (quadratic) increases of activation magnitude, with steeper slopes at the highest sound levels. While this is in agreement with some previous findings (Hart et al. 2002 , 2003 ), other studies reported a more or less linear increase of BOLD signal strength with sound intensity (Hall et al. 2001 ; Langers et al. 2007 ; Röhl and Uppenkamp 2012 ) and still others found indications of response saturation at the highest levels (Mohr et al. 1999 ). To what extent these differences can be explained in terms of the use of different types of stimuli, dynamic ranges, fMRI paradigms or other factors (e.g., perceived loudness) is an interesting topic by itself, but this is not the scope of the present study. As opposed to AC, activation in the investigated subcortical structures increased predominantly linearly with increasing sound pressure level, which is in line with previous findings (Röhl and Uppenkamp 2012 ). — Dijk, Pim van, Physiology, Psychoacoustics and…, 2641

Throughout all investigated stages of the auditory system, except for ipsilateral stimuli in IC bilaterally and in left MGB, neural activation as reflected by the fMRI BOLD response was significantly and positively related to physical sound intensity. Specifically, at cortical level, changes in sound pressure level were reflected by nonlinear (quadratic) increases of activation magnitude, with steeper slopes at the highest sound levels. While this is in agreement with some previous findings (Hart et al. 2002 , 2003 ), other studies reported a more or less linear increase of BOLD signal strength with sound intensity (Hall et al. 2001 ; Langers et al. 2007 ; Röhl and Uppenkamp 2012 ) and still others found indications of response saturation at the highest levels (Mohr et al. 1999 ). To what extent these differences can be explained in terms of the use of different types of stimuli, dynamic ranges, fMRI paradigms or other factors (e.g., perceived loudness) is an interesting topic by itself, but this is not the scope of the present study. … As opposed to AC, activation in the investigated subcortical structures increased predominantly linearly with increasing sound pressure level, which is in line with previous findings (Röhl and Uppenkamp 2012 ). — Dijk, Pim van, Physiology, Psychoacoustics and…, 2641

Categorization

• QUESTION: The dispute between quadratic, linear, and saturating intensity functions across studies is flagged by the authors as open — worth chasing what stimulus/dynamic-range factors explain it.
• corroborated: 3 independent passages support this claim — Dijk, Pim van, Physiology, Psychoacoustics and…, 2610; Dijk, Pim van, Physiology, Psychoacoustics and…, 2641