The anatomical basis of articulatory and phonological processes: A VLSM study in a cohort of aphasic patients

Introduction: Phonological impairment and articulatory programming impairment may co-occur in aphasic patients and previous research does not offer a clear-cut picture of their anatomical counterparts. Methods: In this study we aimed at disentangling the neuroanatomical foundation of the phonological and articulatory component in a large cohort of aphasic patients. We analyzed speech sampling at the Aachen Aphasia Test (AAT) and we employed voxel-based lesion-symptom mapping (VLSM) to correlate the behavioral performance with the underlying neuroanatomical basis. Results: Predominant phonological impairment is associated with lesions localized in the areas assigned to the phonological network (dorsal superior temporal gyrus, mid-to-posterior superior temporal gyrus). Predominant articulatory impairment is underpinned by damage at the posterior inferior frontal gyrus, premotor cortex and anterior insula. Discussion: In general, our results are in line with Hickok and Poeppel’s (2004; 2008) model of phonological processing and also support a peculiar role played by the anterior insula in articulatory planning (Dronkers & Ogar, 2004). References: Hickok, G. et al. Nature (2007) 8:393-402; Hickok, G., et al. Cognition (2004) 92: 67-99; Dronkers, N. et al. Brain(2004)127:1461-1462

Neural dynamics of reading morphologically complex words

Despite considerable research interest, it is still an open issue as to how morphologically complex words such as “car+s” are represented and processed in the brain. We studied the neural correlates of the processing of inflected nouns in the morphologically rich Finnish language. Previous behavioral studies in Finnish have yielded a robust inflectional processing cost, i.e., inflected words are harder to recognize than otherwise matched morphologically simple words. Theoretically this effect could stem either from decomposition of inflected words into a stem and a suffix at input level and/or from subsequent recombination at the semantic–syntactic level to arrive at an interpretation of the word. To shed light on this issue, we used magnetoencephalography to reveal the time course and localization of neural effects of morphological structure and frequency of written words. Ten subjects silently read high- and low-frequency Finnish words in inflected and monomorphemic form. Morphological complexity was accompanied by stronger and longerlasting activation of the left superior temporal cortex from 200 ms onwards. Earlier effects of morphology were not found, supporting the view that the well-established behavioral processing cost for inflected words stems from the semantic–syntactic level rather than from early decomposition. Since the effect of morphology was detected throughout the range of word frequencies employed, the majority of inflected Finnish words appears to be represented in decomposed form and only very high-frequency inflected words may acquire full-form representations

Disentangling phonological and articulatory processing: A neuroanatomical study in aphasia

Phonological and articulatory programming impairments may co-occur in aphasic patients and previous research does not offer a clear-cut picture of their anatomical counterparts. Hickok and Poeppel (2007) put forward a seminal model of speech processes. The ventral stream (mostly bilateral) would be involved in speech recognition and phonological-lexical processing, whereas the dorsal stream (largely lateralized to the left hemisphere) would map phonological representations onto articulatory motor patterns. In this study we analyzed repetition errors for single words and spontaneous speech ratings on the Italian version of the Aachen Aphasia Test. Through a VLSM procedure we aimed at discriminating the neuroanatomical substrates of the phonological and articulatory impairment (and of their normal functional processing). We also estimated functional connectivity networks related to articulation and phonology using seed-to-voxel connectivity analysis with resting state fMRI data. Results indicate that repetition deficit of single words is associated with lesions in a network of left perisylvian areas including the central operculum, the Heschl's gyrus, the angular gyrus, and the supramarginal gyrus (posterior part). Articulatory impairment is associated with lesions in a number of areas in the left dorsal stream, such as the insula (anterior portion), the pars opercularis of the inferior frontal gyrus, the central operculum and the precentral gyrus. On the contrary, phonological impairment is underpinned by lesions of the Heschl's gyrus, and of the posterior portion of the superior temporal and supramarginal gyri. Anatomo-clinical correlative results partly support Hickok and Poeppel's functional model of phonological and articulatory processing