Human brain activation during passive listening to sounds from different locations: An fMRI and MEG study

Abstract

Recent animal and human studies indicate the existence of a neural pathway for sound localization, which is similar to the "where" pathway of the visual system and distinct from the sound identification pathway. This study sought to highlight this pathway using a passive listening protocol. We employed fMRI to study cortical areas, activated during the processing of sounds coming from different locations, and MEG to disclose the temporal dynamics of these areas. In addition, the hypothesis of different activation levels in the right and in the left hemispheres, due to hemispheric specialization of the human brain, was investigated. The fMRI results indicate that the processing of sound, coming from different locations, activates a complex neuronal circuit, similar to the sound localization system described in monkeys known as the auditory "where" pathway. This system includes Heschl's gyrus, the superior temporal gyrus, the supramarginal gyrus, and the inferior and middle frontal lobe. The MEG analysis allowed assessment of the timing of this circuit: the activation of Heschl's gyrus was observed 139 ms after the auditory stimulus, the peak latency of the source located in the superior temporal gyrus was at 156 ms, and the inferior parietal lobule and the supramarginal gyrus peaked at 162 ms. Both hemispheres were found to be involved in the processing of sounds coming from different locations, but a stronger activation was observed in the right hemisphere.

A Rate Code for Sound Azimuth in Monkey Auditory Cortex: Implications for Human Neuroimaging Studies

“…Although lesions that include auditory cortex can impair sound localization in both animals and humans (Sanchez-Longo and Forster, 1958;Jenkins and Masterton, 1982;Thompson and Cortez, 1983;Hefner and Heffner, 1986;Zatorre and Penhune, 2001;Smith et al, 2004;King et al, 2007), human neuroimaging studies have had mixed success at identifying differential patterns of activation as a function of sound location. For monaural sounds, activation is stronger in the contralateral than in the ipsilateral primary auditory cortex (Woldorff et al, 1999;Petkov et al, 2004;Krumbholz et al, 2005a), but no contralateral preference has been found for more realistic binaural stimuli (Woldorff et al, 1999;Brunetti et al, 2005;Krumbholz et al, 2005b;Zimmer and Macaluso, 2005;Zimmer et al, 2006). Similar mixed results have occurred for other metrics of spatial sensitivity: one study found that, when stimuli were presented from a larger range of space, the area of activation in primary auditory cortex was larger (Brunetti et al, 2005), and one study using a similar strategy did not (Zatorre et al, 2002).…”

“…For monaural sounds, activation is stronger in the contralateral than in the ipsilateral primary auditory cortex (Woldorff et al, 1999;Petkov et al, 2004;Krumbholz et al, 2005a), but no contralateral preference has been found for more realistic binaural stimuli (Woldorff et al, 1999;Brunetti et al, 2005;Krumbholz et al, 2005b;Zimmer and Macaluso, 2005;Zimmer et al, 2006). Similar mixed results have occurred for other metrics of spatial sensitivity: one study found that, when stimuli were presented from a larger range of space, the area of activation in primary auditory cortex was larger (Brunetti et al, 2005), and one study using a similar strategy did not (Zatorre et al, 2002).…”

“…The size of this bias, on the order of 8 -15%, provides an account for why it has been difficult to observe a contralateral bias in the level of activation in human primary auditory cortex with imaging studies (Woldorff et al, 1999;Zatorre et al, 2002;Petkov et al, 2004;Brunetti et al, 2005;Krumbholz et al, 2005a,b;Zimmer and Macaluso, 2005;Zimmer et al, 2006): the modest size of the effect may be pushing the limits of the sensitivity of imaging methods. This is a valuable insight because it reassures that the difficulty in identifying a contralateral bias in human auditory cortex is to be expected from primate single-unit data, and does not necessarily consti- Figure 7.…”

Neuronal representations of distance in human auditory cortex

“…Only relatively broad anatomical divisions, such as that between the anterior "what" vs. posterior "where" (8)(9)(10)(11)(12)(13) pathways, have been shown in human neuroimaging studies. The posterior auditory "where" pathway, which encompasses nonprimary auditory cortex areas including the planum temporale (PT) and posterior superior temporal gyrus (STG), is strongly activated by horizontal sound direction changes (12,(14)(15)(16) and movement (17,18). However, although human (19,20) (and nonhuman primate, refs.…”

From where to what: a neuroanatomically based evolutionary model of the emergence of speech in humans

“…EEG studies using source-localization also identified the pSTG-Spt region of the ADS as the sound localization processing center ( Tata & Ward, 2005a; Tata & Ward, 2005b). A combined fMRI and MEG study corroborated the role of the ADS with audiospatial processing by demonstrating that changes in sound location resulted in activation spreading from Heschl’s gyrus posteriorly along the pSTG and terminating in the IPL ( Brunetti et al , 2005). In another MEG study, the IPL and frontal lobe were shown active during maintenance of sound locations in working memory ( Lutzenberger et al , 2002).…”