Academic journal article Journal of Medical Speech - Language Pathology

Aberrant Response Preparation in Parkinson's Disease

Academic journal article Journal of Medical Speech - Language Pathology

Aberrant Response Preparation in Parkinson's Disease

Article excerpt

The basal ganglia circuit plays a fundamental role in the preparation of a response. Individuals with Parkinson's disease (PD) are considered to have difficulty with two particular aspects of response preparation, namely, the maintenance of cognitive and motor sets and the ability to adequately switch between cognitive and motor sets. The vast majority of substantiating evidence derives from limb motor control, electrophysiological, and neuropsychological research. These investigations have begun to unfold the characteristics and mechanisms of aberrant response processing in PD. The putative deficits of response preparation are likely tied to the impaired processing of internally versus externally generated cues and are discussed in this larger context. Despite the relevance of response "maintenance" and "switching" to the preparatory aspects of speech, little research has been conducted in this area. However, extant investigations on the preparatory aspects of cognitive and motor responses in PD can provide a theoretical basis for rehabilitation strategies. Clinical implications and management suggestions are highlighted.

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Idiopathic Parkinson's disease (PD) is traditionally viewed as a disorder of motor control that affects the execution of movement. However, there are strong arguments for additional disruption during response preparation. Overarching themes from neuroimaging, movement disorder, and neuropsychological research suggest that prior to movement, individuals with PD have reduced ability to maintain a prepared response or to switch from a prepared response to a novel response. These deficits arise from both motor and cognitive processes. To date, the potential influence of these preparatory deficits on the communicative function of people with PD has been largely ignored, despite the relevance of "maintenance" and "switching" impairments to the preparatory aspects of speech. Many questions remain unanswered regarding the presence or nature of these deficits as they pertain to verbal communication.

The purpose of this article is to summarize the empirical basis for the reported abnormalities of response maintenance and switching in PD. A review of musculoskeletal and neuropsychological studies is presented along with supportive evidence from related fields. This summary is followed by a discussion of the well established difficulty of individuals with PD to perform internally generated versus externally guided behaviors and how this difficulty relates to maintenance and switching anomalies. Finally, recommendations for rehabilitation are offered based on the theoretical and clinical support for these deficits of response preparation.

RESPONSE MAINTENANCE

One of the primary functions of the basal ganglia is to maintain prepared movements prior to action (Morris & Iansek, 1996). Support for this critical role has derived from diverse areas of investigation, including single cell recordings of neural activity in nonhuman primates (Alexander & Crutcher, 1990; Jaeger, Gilman, & Aldridge, 1993; Schulz & Romo, 1992), cerebral blood flow analysis (Deiber, Ibanez, Sadato, & Hallet, 1996; Horwitz, Deiber, Ibanez, Sadato, & Hallet, 2000; Jueptner & Weiller, 1998), functional neuroimaging (Menon, Anagnoson, Glover, & Pfefferbaum, 2000; Postle & D'Esposito, 1999), and human motor performance (Agostino, Berardelli, Formica, Accornero, & Manfredi, 1992). Further evidence stems from investigations of response maintenance in individuals with PD. Keeping a prepared response in an appropriate state of readiness involves the maintenance of motor and cognitive preparations (Stern, Horvitz, Cote, & Mangels, 2005), and both have been shown to be problematic for individuals with PD.

Maintenance of a Motor Set

Studies of limb control have identified deficits of response maintenance in PD. Preparing a response requires the activation and maintenance of the appropriate action schema or motor program (Berardelli, Rothwell, Thompson, & Hallet, 2001; Stuss, Shallice, Alexander, & Picton, 1995). …

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