Abstract
Processing of nouns and action verbs can be differentially compromised following lesions to posterior and anterior/motor brain regions, respectively. However, little is known about how these deficits progress in the course of neurodegeneration. To address this issue, we assessed productive lexical skills in a patient with posterior cortical atrophy (PCA) at two different stages of his pathology. On both occasions, he underwent a structural brain imaging protocol and completed semantic fluency tasks requiring retrieval of animals (nouns) and actions (verbs). Imaging results were compared with those of controls via voxel-based morphometry (VBM), whereas fluency performance was compared to age-matched norms through Crawford’s t-tests. In the first assessment, the patient exhibited atrophy of more posterior regions supporting multimodal semantics (medial temporal and lingual gyri), together with a selective deficit in noun fluency. Then, by the second assessment, the patient’s atrophy had progressed mainly toward fronto-motor regions (rolandic operculum, inferior and superior frontal gyri) and subcortical motor hubs (cerebellum, thalamus), and his fluency impairments had extended to action verbs. These results offer unprecedented evidence of the specificity of the pathways related to noun and action-verb impairments in the course of neurodegeneration, highlighting the latter’s critical dependence on damage to regions supporting motor functions, as opposed to multimodal semantic processes.
Highlights
Abundant neuropsychological evidence supports a dissociation between nouns and verbs – action verbs (Damasio and Tranel, 1993; Bookheimer, 2002; Chiarello et al, 2002; Cappa and Perani, 2003; Vigliocco et al, 2011)
Fluency Results The patient’s semantic fluency performance on Eval-1 revealed a dissociation between noun and action-verb processing (Figure 1B). He retrieved only two words in the noun condition, exhibiting a significant impairment relative to age-matched norms (Z = −3.2; t = −3.2; p = 0.002). He produced 13 action verbs, which indicated low but normal performance in verb fluency compared to controls (Z = −1.4; t = −1.4; p = 0.18)
The present study aimed to assess the dissociation between noun and action-verb production in a longitudinal lesion model showing earlier atrophy of posterior regions (Eval-1) and later compromise of fronto-motor regions (Eval-2)
Summary
Abundant neuropsychological evidence supports a dissociation between nouns and verbs – action verbs (Damasio and Tranel, 1993; Bookheimer, 2002; Chiarello et al, 2002; Cappa and Perani, 2003; Vigliocco et al, 2011). Far from being a random anatomo-clinical coincidence, this pattern has been sensibly interpreted from an embodied cognition framework (García and Ibáñez, 2016a, 2018; Birba et al, 2017) This account highlights that nouns denote individuated, atemporal entities (such as objects or animals), typically identified by the collection of their sensory (e.g., visual, spatial, color, tactile) properties (Black and Chiat, 2003). We present the case of a right-handed, 73-year-old man with PCA who reported no previous history of psychiatric or neurological disorders He completed high school education, entered law school, and dropped out a few years later. An initial brain MRI showed no evidence of neoplastic, vascular or inflammatory disease, but it revealed atrophy in the posterior parietal cortex, the post-central gyrus, and the superior parietal lobule
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