Katrien Colman

The impact of executive functions on verb production in patients with Parkinson's disease

A growing number of studies suggest that language problems in Parkinsons disease (PD) are a result of executive dysfunction. To test this hypothesis we compared Dutch verb production in sentence context in a group of 28 PD patients with a control group consisting of 28 healthy participants matched for age, gender and education. All subjects were assessed on both verb production in sentence context as well as on cognitive functions relevant for sentence processing. PD patients scored lower than healthy controls on the verb production ability-scale and showed a response pattern in which performance was worse (1) in base than in derived position; (2) in present than in past tense; (3) for intransitive than in transitive verbs. For the PD group the score on the verb production ability-scale correlated significantly with set-switching and working memory. These results provide support for previous research suggesting that executive dysfunctions underlie the performance of the PD patients on verb production. It is furthermore suggested that because of failing automaticity, PD patients rely more on the cortically represented executive functions. Unfortunately, due to the disturbed intimate relation between the basal ganglia and the frontal cortex, these executive functions are also dysfunctional.

Sentence comprehension and its association with executive functions in patients with Parkinson's disease.

Coexistent impairments in executive functions and language comprehension in patients with Parkinsons disease (PD) have been repeatedly observed. In this study, the aim was to provide insights into the interaction between linguistic representation and processing and executive functioning. Therefore, sentence comprehension and executive functions were assessed in 28 Dutch-speaking PD patients and 28 healthy control subjects. Three aspects of the sentence materials were varied: (1) phrase structure complexity, (2) sentence length, and (3) picture congruence. PD patients with mild-to-moderate disease severity showed decreased sentence comprehension compared to healthy control subjects. The difficulties encountered by PD patients were not limited to one aspect of the sentence materials. The same pattern of results was present in healthy control subjects. Deficits in set-switching were specifically associated with the comprehension of passive sentences. Generally, our study confirms that there does not appear to be a language faculty encapsulated from the influence of executive functions.

What is measured with verbal fluency tests in Parkinson's disease patients at different stages of the disease?

Verbal fluency tests (VFT) are often used to assess executive functioning in Parkinson’s disease (PD). Various cognitive functions may, however, impair performance on VFT. Furthermore, since PD is a progressive neurodegenerative disease, it is also not clear whether deficits on VFT reflect impairments in the same cognitive functions throughout the different disease stages. This study will investigate what is measured with VFT in PD, in particular at different disease stages. Eighty-eight PD patients and 65 healthy participants, matched for age, gender, and education, were included. All were assessed with semantic and phonemic VFT and tests assessing executive functions, memory, and psychomotor speed. Mild and moderate PD patients did not differ in the number of words generated on both VFT. However, mild and moderate PD patients differed significantly with regard to the size of the largest cluster and the number of intra-dimensional shifts on phonemic VFT. Furthermore, at the mild disease stages, psychomotor speed predicted the performance on both VFT; whereas at the moderate stages of the disease, cognitive flexibility and psychomotor speed predicted the performance on both VFT. In conclusion, different cognitive functions underlie the performances of PD patients at different stages of the disease on semantic and phonemic VFT. Impairments in VFT, therefore, do not necessarily represent a specific deficit of executive functioning in patients with PD but should rather be interpreted in the context of disease severity and dysfunctions in other domains of cognition.

Language Processing in Parkinson's Disease Patients Without Dementia

One of the major pathophysiological features in Parkinson’s disease, from now on referred to as PD, is the loss of dopaminergic neurons in the substantia nigra, which in turn results in dysfunction of the cortico-striato-cortical circuits (Bartels & Leenders, 2009). In PD the components of the cortico-striato-cortical circuits are not in an optimal interaction, leading to insufficient engagement of for example the frontal and prefrontal lobes. Motor symptoms of tremor, bradykinesia, and rigidity are the clinical hallmark of PD (Wolters & Bosboom, 2007), however, non-motor symptoms are often present (Dubois & Pillon, 1995, 1997). In particular cognitive impairments in the domain of executive functioning have frequently been observed, both in late and also in very early stages of PD (Muslimovic et al., 2005). The term ‘executive functioning’ is used as a blanket term referring to a set of abilities that allow individuals to achieve goal-oriented behavior. These aspects of behavior can be regarded as top-down processes, in contrast to bottom-up processes that only represent stimulus-driven processing. Strauss et al. (2006) defined executive functioning as a collection of processes that are responsible for guiding, directing, and managing cognitive, emotional and behavioral functions, particularly during active, novel problem solving. As PD progresses, more severe cognitive impairments or dementia can occur (Aarsland et al., 2003). The dementia in PD exhibits normal or only slightly decreased performance in gnosis and praxis functions, and is typically characterized by a progressive dysexecutive syndrome with disturbed memory functions and attention (Dubois & Pillon, 1997). In addition, it has repeatedly been shown that language functions in PD patients with dementia are affected. Demented PD patients show reduced verbal fluency, poor confrontation naming abilities, decreased word list generation, and difficulties in wordfinding (Dubois & Pillon, 1997; Pahwa et al., 1998). However, prior to dementia, PD patients also evidence subtle language impairments. The question whether the language system itself is impaired, as for example in aphasia, or whether language performance is disrupted because of non-linguistic executive function disorders in PD is still unanswered. We assume that, intact executive functioning is a prerequisite for normal language functioning. Therefore, language processing deficits in PD will always be associated with executive function deficits. Under this view, the language faculty is not considered to be totally modular in nature, but thought to depend on other cognitive functions, since, for example, comprehending a sentence demands that a listener flexibly guides his/her attention to relevant linguistic information, maintains information in working memory during the

De ziekte van Parkinson en stoornissen in taalverwerking: waar zit de knoop?

De ziekte van Parkinson is na de ziekte van Alzheimer de meest voorkomende progressieve degeneratieve aandoening. Naast de motorische symptomen (namelijk bradykinesie, rigiditeit en rusttremor) die de kern van de klinische diagnose vormen, zijn cognitieve symptomen frequent aanwezig (Muslimović et al., 2005). De focus van het cognitieve onderzoek naar de ziekte van Parkinson is al decennialang gericht op de stoornissen van de executieve functies. Volgens recente ontwikkelingen neemt ook de kennis van de stoornissen van taalverwerking van patiënten met de ziekte van Parkinson toe. Desondanks blijven de precieze onderliggende processen die aan de basis liggen van stoornissen in het begrijpen en produceren van taal tot op heden nog onderwerp van discussie.AbstractParkinson’s disease and dysfunctions in language processing Parkinson’s disease (PD) is one of the most common progressive degenerative neurological diseases in which the dopaminergic afferents to the striatum are lost and striatal output via the direct and indirect pathways is altered. As a result PD patients often demonstrate a co-occurrence of their cardinal motor symptoms with subtle language processing impairments and other cognitive deficits. Indeed, neuropsychological deficits frequently occur in PD, even in early, untreated PD patients (Aarsland et al., 2009). Domains that are typically affected include executive functions, attention, memory, and visuospatial skills (Dubois & Pillon, 1995, 1997; Green et al., 2002; Muslimovic et al., 2005; Pillon, Czernecki & Dubois, 2003). Although the focus of many cognitive studies is on the typically disturbed executive functions deficits, recent work has shown that alterations in linguistic routines are also often present.This paper gives an overview of recent behavioural and functional imaging research on the underlying causes of the language impairments in non-demented PD patients. Two major research questions were put forward. By using behavioral and neuroimaging experiments, it was first investigated whether syntactic sequencing was disturbed in Dutchspeaking patients with PD who were also known to have difficulties in performing sequences of voluntary movements. Secondly, we examined the interaction of executive functioning on language processing in PD patients compared to ageand education-matched healthy control participants.In conclusion, our experimental results showed that PD patients have a disturbance in processing word order and that there does not appear to be a language faculty independent from executive control.