Does Dopamine Depletion Trigger a Spreader Lexical-Semantic Activation in Parkinson’s Disease? Evidence from a Study Based on Word Fluency Tasks

Abstract

It has been hypothesised that, in Parkinson's disease (PD), dopamine might modulate spreading activation of lexical-semantic representations. We aimed to investigate this hypothesis in individuals with PD without dementia by assessing word frequency and typicality in verbal fluency tasks. We predicted that the average values of both of these parameters would be lower in PD patients with respect to healthy controls (HC). We administered letter-cued and category-cued fluency tasks to early PD patients in two experimental conditions: the tasks were administered both after 12–18 hours of dopaminergic stimulation withdrawal (“OFF” condition) and after the first daily dose of dopaminergic therapy (“ON” condition). HC were also given the two tasks in two conditions with the same intersession delay as PD patients but without taking drugs. Results showed that in both OFF and ON treatment conditions PD patients did not differ from HC in word frequency or typicality. Moreover, in the PD group, no significant difference was found between the experimental conditions. Our results show that semantic spreading was not altered in the PD sample examined; this suggests that in early PD the functioning of the semantic system is relatively independent from the activity of dopamine brain networks.

Dopamine-Related Reduction of Semantic Spreading Activation in Patients With Parkinson’s Disease

“…In this regard, the analysis of the dynamic change of lexical frequency instead of the overall word frequency of all responses (which did not differ between groups or medication conditions in our study) might be a more sensitive measure of semantic activation underlying word search and retrieval. Other studies, which included lexical frequency in their analysis of semantic or phonemic VF, also reported no difference between PD groups and controls regarding the overall word frequency in semantic and phonemic VF (Herrera et al, 2012 ; Zabberoni et al, 2017 ; Wagner et al, 2020 ). One study, however, observed an increased mean word frequency of verbs produced by the PD group, which was not attributed to altered semantic activation but rather disrupted coupling between motor abilities and cognition (Herrera et al, 2012 ).…”

“…An increase of lexical frequency in this context is rather reminiscent of lexical simplification of language due to the substitution of single words by highly frequent alternatives as observed in conditions with speech impairment (e.g., Bird et al, 2000 ; Cuetos et al, 2002 ; Boukrina et al, 2015 ; Faroqi-Shah and Milman, 2018 ; Tiedt et al, 2021 ). However, another study, which analyzed the dynamic change of lexical frequency during VF by means of the median split analysis in a PD group (ON and OFF medication) and healthy controls did not yield significant differences between either medication conditions or participant groups with respect to the change (i.e., decrease) of word frequency during VF tasks (Zabberoni et al, 2017 ). A possible explanation could be a longer duration of each individual VF task in our study (2 min as compared to one).…”

“…Manipulations of word frequency have been shown to unfold consistent effects in studies of language processing, i.e., often used words are faster and more easily produced and recognized than infrequent words (Oldfield and Wingfield, 1965 ; Forster and Chambers, 1973 ; Allen et al, 1992 ; Jescheniak and Levelt, 1994 ; Morrison and Ellis, 1995 ; Gerhand and Barry, 1999 ; Brysbaert et al, 2000 ; Bonin and Fayol, 2002 ). Furthermore, the analysis of VF word output with respect to lexical frequency has demonstrated a characteristic dynamic change with a decrease of word frequency throughout task performance in both semantic and phonemic VF (Crowe, 1998 ; Juhasz et al, 2012 ; Zabberoni et al, 2017 ). With respect to the semantic spreading activation theory and lexico-semantic retrieval, lower-frequency words can be interpreted as being represented in more remote nodes within conceptual networks.…”

Cognitive change after subthalamic deep brain stimulation for Parkinson’s disease – a systematic meta-regressive analysis

“…Late-stage PD patients in an off-medication condition were able to outperform healthy controls at verbal fluency when producing verbs but were otherwise poorer than control and their own on-medication performance on all other measures of verbal fluency (phonemic and categorical (Herrera et al, 2012)). By comparison, early PD patients have demonstrated comparable verbal fluency performance to healthy controls both on- and off-medication, with little difference between phonemic or categorical fluency (Zabberoni et al, 2017).…”