Biology subjects

Matchin, W.

Publications and source records attributed to Matchin, W..

3 recordsLinked to original sources

bioRxiv2020

Neuroanatomical dissociations of syntax and semantics revealed by lesion-symptom mapping

Theories of language organization in the brain commonly posit that different regions underlie distinct linguistic mechanisms. However, such theories have been criticized on the grounds that many neuroimaging studies of language processing find similar effects across regions. Moreover, condition by region interaction effects, which provide the strongest evidence of functional differentiation between regions, have rarely been offered in support of these theories. Here we address this by using lesion-symptom mapping in three large, partially-overlapping groups of aphasia patients with left hemisphere brain damage due to stroke (N=121, N=92, N= 218). We identified multiple measure by region interaction effects, associating damage to the posterior middle temporal gyrus with syntactic comprehension deficits, damage to posterior inferior frontal gyrus with expressive agrammatism, and damage to inferior angular gyrus with semantic category word fluency deficits. Our results are inconsistent with recent hypotheses that regions of the language network are undifferentiated with respect to high-level linguistic processing.

neuroscience↗

bioRxiv2020

Syntax-sensitive regions of Broca's area and the posterior temporal lobe are differentially recruited by production and perception

Neuroimaging studies of syntactic processing typically result in similar activation profiles in Brocas area and the posterior temporal lobe (PTL). However, substantial functional dissociations between these regions have been demonstrated with respect to lesion-symptom mapping in aphasia. To account for this, Matchin & Hickok (2020) proposed that both regions play a role in syntactic processing, broadly construed, but attribute distinct functions to these regions with respect to production and comprehension. Here we report an fMRI study designed to test this hypothesis by contrasting the subvocal articulation and comprehension of structured jabberwocky phrases (syntactic), sequences of real words (lexical), and sequences of pseudowords (phonological). We defined two sets of language-selective regions of interest (ROIs) in individual subjects for Brocas area and the PTL using the contrasts [syntactic > lexical] and [syntactic > phonological]. We found robust significant interactions of comprehension and production between these two regions at the syntactic level, for both sets of language-selective ROIs. This suggests a core difference in the function of these regions: language-selective subregions of Brocas area play a role in syntax driven by the demands of production, whereas language-selective subregions of the PTL play a role in syntax driven by the demands of comprehension.

neuroscience↗

bioRxiv2020

Agrammatism and paragrammatism: a cortical double dissociation revealed by lesion-symptom mapping

The fundamental distinction of grammatical deficits in aphasia, agrammatism and paragrammatism, was made over a century ago. However, the extent to which the agrammatism/paragrammatism distinction exists independently of differences in speech fluency has not clearly been investigated. Despite much research on agrammatism, the lesion correlates of paragrammatism are essentially unknown. Lesion-symptom mapping was used to investigate the degree to which the lesion correlates of agrammatism and paragrammatism overlap or dissociate. Four expert raters assessed videos of 53 right-handed patients with aphasia following chronic left hemisphere stroke retelling the Cinderella story. Consensus discussion determined each subjects classification with respect to grammatical deficits as Agrammatic, Paragrammatic, Both, or No Grammatical Deficit. Each subjects lesion was manually drawn on a high-resolution MRI and warped to standard space for group analyses. Lesion-symptom mapping analyses were performed in NiiStat including lesion volume as a covariate. Secondary analyses included speech rate (words per minute) as an additional covariate. Region of interest analyses identified a double dissociation between these syndromes: damage to Brocas area was significantly associated with agrammatism, p = 0.001 (but not paragrammatism, p = 0.930), while damage to the left posterior superior and middle temporal gyri was significantly associated with paragrammatism, p < 0.001 (but not agrammatism, p = 0.873). The same results obtained when regressing out the effect of speech rate, and non-overlapping lesion distributions between the syndromes were confirmed by uncorrected whole brain analyses. Our results support a fundamental distinction between agrammatism and paragrammatism.

neuroscience↗