title: Dual-echo fMRI can detect activations in inferior temporal lobe during intelligible speech comprehension.
abstract: The neural basis of speech comprehension has been investigated intensively during the past few decades. Incoming auditory signals are analysed for speech-like patterns and meaningful information can be extracted by mapping these sounds onto stored semantic representations. Investigation into the neural basis of speech comprehension has largely focused on the temporal lobe, in particular the superior and posterior regions. The ventral anterior temporal lobe (vATL), which includes the inferior temporal gyrus (ITG) and temporal fusiform gyrus (TFG) is consistently omitted in fMRI studies. In contrast, PET studies have shown the involvement of these ventral temporal regions. One crucial factor is the signal loss experienced using conventional echo planar imaging (EPI) for fMRI, at tissue interfaces such as the vATL. One method to overcome this signal loss is to employ a dual-echo EPI technique. The aim of this study was to use intelligible and unintelligible (spectrally rotated) sentences to determine if the vATL could be detected during a passive speech comprehension task using a dual-echo acquisition. A whole brain analysis for an intelligibility contrast showed bilateral superior temporal lobe activations and a cluster of activation within the left vATL. Converging evidence implicates the same ventral temporal regions during semantic processing tasks, which include language processing. The specific role of the ventral temporal region during intelligible speech processing cannot be determined from this data alone, but the converging evidence from PET, MEG, TMS and neuropsychology strongly suggest that it contains the stored semantic representations, which are activated by the speech decoding process.
authors.affiliation: Neuroscience and Aphasia Research Unit, School of Psychological Sciences, University of Manchester, Zochonis Building, Brunswick Street, Manchester M13 9PL, UK. Electronic address: ajay.halai@manchester.ac.uk.
authors.forename: Ajay D
authors.initials: AD
authors.lastname: Halai
authors.affiliation: Centre for Imaging Sciences, Institute of Population Health, University of Manchester, Stopford Building, Oxford Road, Manchester M13 9PL, UK.
authors.forename: Laura M
authors.initials: LM
authors.lastname: Parkes
authors.affiliation: Neuroscience and Aphasia Research Unit, School of Psychological Sciences, University of Manchester, Zochonis Building, Brunswick Street, Manchester M13 9PL, UK.
authors.forename: Stephen R
authors.initials: SR
authors.lastname: Welbourne
mesh_terms: D000328:Adult; D001931:Brain Mapping / Q000379:methods*; D032882:Comprehension / Q000502:physiology*; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D012815:Signal Processing, Computer-Assisted; D013067:Speech Perception / Q000502:physiology*; D013702:Temporal Lobe / Q000502:physiology*; D055815:Young Adult
keywords: Dual gradient-echo; Inferior temporal lobe; Intelligible speech; Magnetic susceptibility