Auditory tracts identified with combined fMRI and diffusion tractography.
The auditory tracts in the human brain connect the inferior colliculus (IC) and medial geniculate body (MGB) to various components of the auditory cortex (AC). While in non-human primates and in humans, the auditory system is differentiated in core, belt and parabelt areas, the correspondence between these areas and anatomical landmarks on the human superior temporal gyri is not straightforward, and at present not completely understood. However it is not controversial that there is a hierarchical organization of auditory stimuli processing in the auditory system. The aims of this study were to demonstrate that it is possible to non-invasively and robustly identify auditory projections between the auditory thalamus/brainstem and different functional levels of auditory analysis in the cortex of human subjects in vivo combining functional magnetic resonance imaging (fMRI) with diffusion MRI, and to investigate the possibility of differentiating between different components of the auditory pathways (e.g. projections to areas responsible for sound, pitch and melody processing). We hypothesized that the major limitation in the identification of the auditory pathways is the known problem of crossing fibres and addressed this issue acquiring DTI with b-values higher than commonly used and adopting a multi-fibre ball-and-stick analysis model combined with probabilistic tractography. Fourteen healthy subjects were studied. Auditory areas were localized functionally using an established hierarchical pitch processing fMRI paradigm. Together fMRI and diffusion MRI allowed the successful identification of tracts connecting IC with AC in 64 to 86% of hemispheres and left sound areas with homologous areas in the right hemisphere in 86% of hemispheres. The identified tracts corresponded closely with a three-dimensional stereotaxic atlas based on postmortem data. The findings have both neuroscientific and clinical implications for delineation of the human auditory system in vivo.
Neuroradiological Academic Unit, Department of Brain Repair and Rehabilitation, UCL Institute of Neurology, University College London, Queen Square, London WC1N 3BG, UK.
Faiza
F
Javad
Jason D
JD
Warren
Caroline
C
Micallef
John S
JS
Thornton
Xavier
X
Golay
Tarek
T
Yousry
Laura
L
Mancini
D000328:Adult; D001303:Auditory Cortex / Q000033:anatomy & histology* / Q000502:physiology*; D001306:Auditory Pathways / Q000033:anatomy & histology* / Q000502:physiology*; D063132:Connectome / Q000379:methods; D056324:Diffusion Tensor Imaging / Q000379:methods*; D005260:Female; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D007090:Image Interpretation, Computer-Assisted / Q000379:methods; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D064847:Multimodal Imaging / Q000379:methods; D010363:Pattern Recognition, Automated / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
AC; AM; Auditory radiation; Auditory tracts; BOLD; CoG; DSI; DTI; EPI; FDR; HG; Heschl's gyrus; IC; IRN; IndConn; MGB; MNI; MRI; Montreal Neurological Institute; PAS; PET; PP; PT; SD; SN; STG; Tractography; amplitude modulation; auditory cortex; blood oxygenation level dependent; cSD; centre of gravity; constrained spherical deconvolution; diffusion spectrum imaging; diffusion tensor imaging; echo planar imaging; fMRI; false discovery rate; functional magnetic resonance imaging; index of connectivity; inferior colliculus; iterated ripple noise; magnetic resonance imaging; medial geniculate body; persistent angular structure; planum polaris; planum temporalis; positron emission tomography; spherical deconvolution; substantia nigra; superior temporal gyrus