GARCIA adolfo Martin
congresos y reuniones científicas
The road less traveled: Alternative pathways for action-verb processing in Parkinson?s disease
La Havana
Congreso; 18th World Congress of the International Organization of Psychophysiology; 2016
Institución organizadora:
International Organization of Psychophysiology
Introduction: Relative to other lexical units, action verbs distinctively involve activations along motor brain networks. In movement disorders, damage to the latter is associated with difficulties to access such words. However, patients are not fully incapable of processing them, as their performance is far from floor level. Action-verb processing may then rely on less efficient, non-motor semantic circuits. To test this hypothesis, we separately measured behavioral performance and neurofunctional correlates during lexical processing tasks in Parkinson?s disease (PD) patients and healthy controls. Methods: The sample comprised 17 pre-demented PD patients and 15 socio-demographically matched controls presenting no history of psychiatric or neurological disease. Participants listened to action verbs and nouns as they underwent fMRI scanning. We selected seeds known to be differentially engaged by processing of action- (putamen, primary motor area) and non-action (posterior superior temporal lobe) stimuli. For each participant, we extracted the BOLD signal time-course from the voxels within each seed region. Functional connectivity maps were obtained by correlating these data to every voxel in the brain using Pearson?s correlation coefficient. The ensuing maps were then recalculated by reference to their z scores. We performed a randomize analysis (5000 permutation) with a mass cluster based correction (p < .05 FWE corrected) with a 2.5 threshold, and made non-parametric permutation inferences on neuroimaging data. Results: FMRI data revealed that they recruited different networks only for action-related words. During noun processing, activity in all seeds was similar between groups. However, for action-verb processing, analysis of the motor seed revealed greater activations in posterior and anterior regions for patients (p = .03) and controls (p = .05), respectively. Analysis of the putamen seed showed greater reduced functional connectivity in patients for both lexical categories (p = .005 for verbs, and p = .03 for nouns). Discussion: Our results suggest that PD patients, unlike controls, process action-verbs via temporal networks implicated in amodal semantics and post-lexical imagery. Such regions would afford alternative (though, arguably, less efficient) pathways to process word meaning when putative embodied mechanisms are disturbed (in this case, motor networks). Moreover, differences in putamen connectivity for both action verbs and nouns points to a distinct association between the patients? distinctive physiopathology and lexical-level processing at large. These results offer new insights into non-embodied routes for high-order processing, while revealing neurofunctional aspects of relevant compensatory mechanisms in neuropathology. [Work partially supported by CONICET, CONICYT/FONDECYT Regular (1130920), COLCIENCIAS (1115-545-31374 and 1115-569-33858), FONCyT-PICT 2012-0412, FONCyT-PICT 2012-1309, FONDAP 15150012, and INECO Foundation].