Disentangling language production impairments in Parkinson’s Disease

Abstract

Parkinson’s Disease (PD) is a neurodegenerative disorder characterized by cardinal motor symptoms, including resting tremor, rigidity and bradykinesia, and cognitive impairments, such as deficits in executive function, attention and short-term memory. Beyond these issues, patients frequently report morphosyntax, lexical-semantic and word finding difficulties but the underlying nature of these deficits is not well understood. Verbal fluency is often used as a neuropsychological test to assess production impairments in PD, however, due to its time constraints, it puts extra demands on motor and executive functions, making it a less sensitive task to tap into language specific processes. Moreover, individuals with PD show a bigger impairment for action words with a high motor content (e.g., motor-related words like ‘walk’) than for other words, suggesting their production difficulties cannot be fully explained by motor and executive function impairments. Silent pauses in continuous speech, i.e., a period of non-speech within or between words that could coincide with inhalation, have been suggested to reflect cognitive mechanisms underlying language production. Pauses are often located at syntactic boundaries (e.g., “she pets the dog [pause] of her friend”), but can also occur at non-syntactic boundaries (e.g., “she pets the [pause] dog”), such as within phrases. More pauses and/or longer pauses might suggest either a conceptually driven word retrieval problem or a cognitive-linguistic planning problem, and therefore offer a more language specific measure of production impairment. In our current ongoing experiment, we assessed language production impairment by comparing performance between individuals with PD and matched controls on three language production tasks differing in cognitive demands: 1) a speeded reading task, where participants read aloud as many words on a list as possible in one minute, a relatively simple task that can be performed using grapheme to phoneme conversion, serving as a measure of motor speech; 2) a category fluency task, where participants produced as many words as possible from one semantic category in one minute, serving as a measure of conceptually driven word production with higher executive demands; and 3) a picture description task, where participants described line drawings of people performing actions with no time constrains. Our interest in this last task lies particularly in the pausing patterns (i.e., location, duration and frequency), as this could indicate impairments in conceptually driven word retrieval and/or syntactic planning. Longer and/or more pauses at non-syntactic boundaries will be indicative of lexical retrieval deficits, and at syntactic boundaries will suggest impairment at the syntactic planning level. Moreover, we will correlate results from the picture description task with performance on word reading and category fluency, which will allow to disentangle between motor and executive function impairments, respectively, and language specific deficits. Our findings could give a clearer perspective into the underlying mechanisms that are impaired in individuals with PD. Moreover, it could shed a light into whether including pausing as a linguistic marker in semi-spontaneous speech could contribute to improved diagnosis and treatment in PD.