Language areas of the brain can be mapped in individual participants with functional MRI. We investigated the validity and reliability of four language mapping paradigms that may be appropriate for individuals with acquired aphasia: sentence completion, picture naming, naturalistic comprehension, and narrative comprehension. Five neurologically normal older adults were scanned on each of the four paradigms on four separate occasions. Validity was assessed in terms of whether activation patterns reflected the known typical organization of language regions, that is, lateralization to the left hemisphere, and involvement of the left inferior frontal gyrus and the left middle and/or superior temporal gyri. Reliability (test-retest reproducibility) was quantified in terms of the Dice coefficient of similarity, which measures overlap of activations across time points. We explored the impact of different absolute and relative voxelwise thresholds, a range of cluster size cutoffs, and limitation of analyses to a priori potential language regions. We found that the narrative comprehension and sentence completion paradigms offered the best balance of validity and reliability. However, even with optimal combinations of analysis parameters, there were many scans on which known features of typical language organization were not demonstrated, and test-retest reproducibility was only moderate for realistic parameter choices. These limitations in terms of validity and reliability may constitute significant limitations for many clinical or research applications that depend on identifying language regions in individual participants.

Spoken and written language processing streams converge in the superior temporal sulcus (STS), but the functional and anatomical nature of this convergence is not clear. We used functional MRI to quantify neural responses to spoken and written language, along with unintelligible stimuli in each modality, and employed several strategies to segregate activations on the dorsal and ventral banks of the STS. We found that intelligible and unintelligible inputs in both modalities activated the dorsal bank of the STS. The posterior dorsal bank was able to discriminate between modalities based on distributed patterns of activity, pointing to a role in encoding of phonological and orthographic word forms. The anterior dorsal bank was agnostic to input modality, suggesting that this region represents abstract lexical nodes. In the ventral bank of the STS, responses to unintelligible inputs in both modalities were attenuated, while intelligible inputs continued to drive activation, indicative of higher level semantic and syntactic processing. Our results suggest that the processing of spoken and written language converges on the posterior dorsal bank of the STS, which is the first of a heterogeneous set of language regions within the STS, with distinct functions spanning a broad range of linguistic processes.

Linguistic stimuli that are degraded in various ways have been used in neuroimaging studies to uncover distinct roles for different brain regions involved in processing language. In order to identify brain regions differentially involved in grammatical and lexical processing, we spectrally rotated specific morphemes and manipulated morpheme order to create speech stimuli that were degraded either grammatically or lexically, yet were matched in intelligibility. Twelve healthy participants were scanned with functional MRI as they listened to the grammatically and lexically degraded stimuli, interspersed with clear stimuli in the context of a familiar narrative. Contrary to our expectations, we did not find any brain regions that were selectively sensitive to grammatical or lexical degradation. However, compared to previous studies, there was less signal reduction than anticipated in response to degradation of either type. These findings may reflect increased attention to the degraded stimuli due to the familiar narrative context, since attention to degraded speech has been shown to attenuate the signal decreases typically associated with reduced intelligibility.

Background Aphasia following infarction of Wernicke's area typically resolves to some extent over time. The nature of this recovery process and its time course have not been characterized in detail, especially in the acute/subacute period. Aims The goal of this study was to document recovery after infarction of Wernicke's area in detail in the first 3 months after stroke. Specifically, we aimed to address two questions about language recovery. First, which impaired language domains improve over time, and which do not? Second, what is the time course of recovery? Methods & Procedures We used quantitative analysis of connected speech and a brief aphasia battery to document language recovery in two individuals with aphasia following infarction of the posterior superior temporal gyrus. Speech samples were acquired daily between 2 and 16 days post stroke, and also at 1 month and 3 months. Speech samples were transcribed and coded using the CHAT system, in order to quantify multiple language domains. A brief aphasia battery was also administered at a subset of five time points during the 3 months. Outcomes & Results Both patients showed substantial recovery of language function over this time period. Most, but not all, language domains showed improvements, including fluency, lexical access, phonological retrieval and encoding, and syntactic complexity. The time course of recovery was logarithmic, with the greatest gains taking place early in the course of recovery. Conclusions There is considerable potential for amelioration of language deficits when damage is relatively circumscribed to the posterior superior temporal gyrus. Quantitative analysis of connected speech samples proved to be an effective, albeit time-consuming, approach to tracking day-by-day recovery in the acute/subacute post-stroke period.