Parkinson’s disease (PD) is a neurodegenerative disease characterized by a loss of voluntary movement control and cognitive impairment. It emerges from impairment in the basal ganglia, a part of the brain that plays an important role in movement control (Berg, 2003, p.63). General descriptions of Parkinson’s disease have stated that it is not associated with language deterioration. However, Parkinson’s disease identifies as subcortical dementia. This means that motor deficits come before intellectual and language deficits. It is essential to note that although motor impairments appear first, PD patients often show language impairments due to the basal ganglia being involved in language domains such as semantics, pragmatics, and phonology (STM Digest, 2015). Although it is known that different impairments eventually occur in patients with PD, many are not aware that over the past few decades, several studies examined a significant relationship between cognitive, motor, and language deficiencies concerning the symptoms involved.
Connecting Parkinson’s Disease Deficits to Dysarthria
The speech of people with Parkinson’s disease is often affected by dysarthria. Dysarthria is a motor speech disorder that causes difficult or unclear articulation of speech that is otherwise linguistically normal (Saldert, etc. al, 2014, p.710). Dysarthria that derives from PD impacts intelligibility in conversational interaction. Moreover, dysarthria in PD patients occurs when the muscles used to talk, such as the tongue, lips, and throat, are weak due to brain damage. The impact that dysarthria and degeneration of cognition loss have on PD causes difficulties in the use of language with word-retrieval as well as pragmatic problems. In Saldert’s and other’s study, it is suggested that in PD patients with dysarthria, there is a connection between cognitive decline and the decline of language production.
In this study, conversations involving at least one person with PD and dysarthria were recorded. The results of these instances connected the difficulty in pragmatic use involving the relation of the use of words to a qualitative analysis based on the principles of the conversation recorded (Saldert, etc.al, 2014, p. 710). The findings of this study show that the interaction of these subjects may be influenced by semantic and pragmatic problems. During the recordings, researchers observed that the subjects with PD and dysarthria had more difficulty in pragmatic problems (Saldert, etc. al, 2014, p. 711). These problems included adapting to known social rules, and being introduced to a new topic. Furthermore, there was noticeable atypical wording in the patients with PD. These cases can be perceived as a type of semantic-paraphasia, which is replacing an intended word with a related or unrelated word that is associated with cognitive decline. This study had a significantly higher mean of the frequency of the word finding difficulty in the PD subjects (Saldert, etc. al, 2014, p. 718). The motor deficits associated with dysarthria in subjects with PD that lead to unclear speech, contribute to this research in highlighting that the pragmatic and semantic language problems and the cognitive aspect of word-retrieval difficulties that occurred were all heavily affected.
Deficits in Parkinson’s Disease Related to Word-Finding Difficulty
In a study conducted by Smith and colleagues, the evidence provided suggests that speech, cognitive, and language changes are synonymous in patients with PD. Cognitive impairment is a common symptom in Parkinson’s disease and is seen through memory aspects such as word-finding difficulty (WFD). At the time of diagnosis, about one-third of patients already have a mild cognitive impairment. Comparatively, all language skills are eventually impacted by PD. However, semantics is one of the most affected language skill used in word-finding; this because there is a breakdown between the meaning of a word and the entry into an individual's mental lexicon. A person, who suffers from word-finding difficulty, may express their inability to retrieve the word that he or she wants to use. WFD connects speech, language, and cognitive skills because of the frequent reports of symptoms regarding that specific deficit and deterioration of language skill performance task when there is an increased cognitive load (Smith, 2018, p. 1691).
Evaluating Linguistic Markers in Word-Finding Difficulty to Cognitive Function
The purpose of the study was to compare the relationship between the linguistic markers found in a linguistic analysis that focused on pauses in speech, to word-finding difficulty (WFD) symptoms, and cognitive function in patients with Parkinson’s disease. The study included 53 patients with Parkinson’s disease and healthy patients acted as a control. Language sample analyses were conducted with a 90-second time limit and the total quantity of speech output and rates were also controlled. The researchers then gave the participants a questionnaire regarding the language sample to determine the word-finding difficulty. In regard to the questionnaires, 75% of the patients with PD reported having word-finding difficulty. Compared with the control, subjects with PD produced significantly fewer words per minute and also had a lower percentage of well-formed sentences. In like manner, it was found that pausing before verbs occurred more frequently in the participants that have Parkinson's rather than those who do not. The lack of linguistic markers such as pauses and WFD are easily distinguished between patients with PD and those who are the healthy control. The results of this study state that “pauses before verbs and grammatical markers may index early cognitive symptoms such as WFD that may interfere with functional communication (Smith, 2018, p. 1691).” This suggests that language and communication skills are compatible with cognitive deficits such as word-finding difficulty.
Linking Parkinson’s Disease Deficits to Trail Making Test and Dual-Task Performance
According to researchers at Harvard University, “Executive function and self-regulation skills are the mental processes that enable us to plan, focus attention, remember instructions, and juggle multiple tasks successfully (2018)”. This exemplifies that executive function is an umbrella term for cognitive based skills that associates with mental control of behavior. The skills required for proper executive function correlate with each other, and in order to successfully apply these skills they need to operate together. The impact on daily activities people with Parkinson’s disease have is detected by their executive function deficits.
Evaluating Verbal Fluency, Cognitive, and Cognitive-Motor Skills
Barbosa and colleagues studied the performance of PD patients and a control group related to executive function. In addition to the executive function being studied, the language skills of semantic and phonemic verbal fluency were also examined in order to investigate the relationships between them.
The researchers evaluated forty people with PD and forty controls with the Trail Making Test (TMT), which tested the executive function. The Trail Making Test is a neuropsychological test that measures visual attention and task switching. This test is considered as a cognitive test because it isolates the cognitive impact added by alternating the letter sequence. According to the authors, part A of the TMT consists of connecting a trail to match numbers in sequence, and part B focuses on number and letters alternating in (2017, p. 2). The sequence of this test suggests that part A evaluates the time that the subject spends on the task and how it reflects their motor performance. In addition to this, part B measures cognitive flexibility, task switching, response to inhibition and working memory. These tests evaluate cognitive-motor, dual-task performance. The results of performing two tasks simultaneously when diagnosed with PD exemplify the impairment the person faces. The impairment is manifested by increased errors or reaction times compared to individually performed tasks. Under these conditions, the researchers observed that after the TMT, people with PD needed more time to complete parts A and B than the controls (Barbosa, et al., 2017, p. 3).
Patients with Parkinson’s disease often have difficulties in movement performance. The evidence in the research suggests the motor deficits are also prominent during a dual-task. The movement problem became more obvious when the subjects had to combine motor movements with cognitive thinking. Correspondingly, there is an implication between cognitive thought and motor development.
In addition to the TMT, verbal fluency test was also given to test executive function in people with PD. Verbal fluency tests are considered a cognitive-motor test because the motor system participates in mental processing. These tests are involved in articulatory coordination, response inhibition, and phonological processing. The researchers instructed the participants to say as many words as possible in sixty seconds. In the phonemic test, words must begin with a given letter. In a semantic test, words that the subjects state must belong to the same category. As a result of this test, it was concluded that subjects with PD said fewer words in the phonemic and semantic verbal fluency tests. The researchers also observed that people with PD usually relied on semantic cues to aid in their lexical search.
The research conducted in this study further emphasizes the idea that the cognitive, executive function deficits in patients with Parkinson’s disease relate to their verbal fluency skills such as phonation and semantics. There was a strong correlation between the phonemic verbal fluency test and part B of the trail marking test (Barbosa, et al., 2017, p. 4). This suggests that dual-task performance, such as the motor requirement in tracing the trail and the fluency required in speaking, is important in both tasks. Likewise, both of these tasks are associated with the cognitive components of the other two tasks that included following the sequence in part B of the TMT and recalling the words in the phonemic test. These results further explain cognitive and cognitive-motor executive function tasks influence verbal fluency.
Conclusion and Critique
Parkinson’s disease is often described as having a range of cognitive and motor dysfunctions. Over the past few decades, several studies have examined a significant relationship between cognitive, motor, and language deficiencies such as semantics and pragmatics. Not only are these aspects associated with PD, but they are also connected to each other.
The information in each study provided organized information that clearly discussed the results. Each study explained the connection to either the cognitive, motor or language skill discussed in a consistent manner that related back to the main idea that the experiment was researching. The associations that the studies made aided in creating new ideas that could further an investigation in an additional type of therapy that could be used to manage symptoms.
The use of music may aid in the reduction of Parkinson’s disease symptoms. The damage of nerve cells causes the dopamine levels to drop, leading to the symptoms in PD. Certain types of music can stimulate dopamine production, which leads to a theory that music can reduce symptoms. Many individuals with PD have problems with consecutive movement. The rhythm created in music may organize simple movements and be used as a therapy in managing symptoms. Furthermore, PD patients can use music as a way to increase breath support and help with their articulation. Patients that “sing” and sustain syllables for longer of periods of time as well as tapping a rhythm can aid clarifying of the patient’s prosody of speech. There are endless reasons why music should be researched as a way to contend the symptoms of Parkinson’s disease.