Selective attention frequency-specifically enhances processing within the mirror-symmetric tonotopic areas of the human primary auditory cortex
The question of how one is able to select, out of the wealth of all possible ones, the task-relevant stimuli for more advanced scrutiny is one of the most fundamental research questions in cognitive neuroscience. While a number of studies have stressed that selective attention involves only secondary auditory cortical areas, there are converging lines of evidence suggesting that processing of attended stimulus features could also be enhanced at the level of human primary auditory cortex. There is neuroimaging evidence showing that the mirror-symmetric tonotopic maps of primary auditory cortex can be mapped with ultra high-field functional magnetic resonance imaging, however, localization of sound-frequency specific selective attention effects to specific parts of these tonotopic fields has been to date lacking.
Da Costa et al. (2013) addressed this question by combining, in human volunteers, 7-Tesla functional magnetic resonance imaging of the tonotopic primary auditory cortex areas with mapping of selective attention effects within these areas. The mirror-symmetric tonotopic maps were first localized on an individual basis in six healthy volunteers using multiple sound frequencies. Subsequently, the subjects were to alternate, once every 30 seconds, their focus of attention between low-frequency 250-Hz and high-frequency 4000-Hz stimulus streams. The authors observed that selective attention to the low-frequency sounds specifically enhanced responses of voxels that were most selective to the 250-Hz sounds and, vice versa, attention to high-frequency sounds specifically enhanced responses in voxels most selectively responded to 4000-Hz sounds.
The findings of this study very nicely demonstrate that selective attention indeed works at the level of primary auditory cortex, by “tuning” processing of stimuli to those occuring within the attended frequency channel, analogously to a radio being tuned on a specific frequency channel. The study also demonstrates how ultra-high field 7-Tesla functional magnetic resonance imaging can be utilized to map, and assess selective attention effects within, even the gradients of the mirror-symmetric tonotopic fields of the human auditory cortex core areas with very high accuracy.
Reference: Da Costa S, van der Zwaag W, Clarke S, Saenz M. Tuning in to sound: frequency-selective attentional filter in human primary auditory cortex. Journal of Neuroscience (2013) 33: 1858-1863. http://dx.doi.org/10.1523/JNEUROSCI.4405-12.2013