Reduction in external cues and movement sequencing in Parkinson's disease.

Distinct Contribution of the Striatum and Cerebellum to Motor Learning

“…This notion is congruent with a series of studies showing that cerebellar damage impairs the ability to translate a programmed motor sequence into action before the onset of movement (Inhoff & Bisiacchi, 1990;Inhoff et al, 1989;Inhoff & Rafal, 1990). It should be noted that some researchers (Benecke, Rothwell, Dick, Day, & Marsden, 1987;Canavan, Passingham, Marsden, Quinn, Wyke, & Polkey, 1989;Georgiou, Bradshaw, Iansek, Phillips, Mattingley, & Bradshaw, 1994;Harrington & Haaland, 1991;Stelmach, Worringham, & Strand, 1987;Weiss, Stelmach, & Hefter, 1997;see Dominey & Jeannerod, 1997, for a review) have previously investigated the role of the striatum in the sequencing of movements, by examining the performance of patients with PD who were required to switch between two completely different types of motions such as elbow extension and hand squeeze (Benecke et al, 1987), or were asked to shift from one step in the sequence to the next by changing hand postures (Harrington & Haaland, 1991), in situations where patients had explicit knowledge of the sequence of movements they had to perform. By contrast, in this experiment, the notion first proposed by Flourens (1824), Babinski (1899), and Holmes (1939) that damage to the cerebellum produces a ''decomposition of movements'' was further investigated using a new task that did not require switching between separate movements, but instead measured the patients ability to perform a well-articulated sequence of movements in an implicit fashion.…”

“…The fact that patients with PD showed a significant facilitation effect, hence sug-gesting a preserved ability in combining acquired movements into a well-articulated action, may appear to be at variance with the results of recent clinical studies which suggest that PD impairs the smooth transition between two successive movements (Benecke et al, 1987;Canavan et al, 1989;Georgiou et al, 1994;Harrington & Haaland, 1991;Stern, Mayeux, Rosen, & Ilson, 1983;Weiss et al, 1997;see Dominey & Jeannerod, 1997, for a review). Several reasons may explain this apparent divergence of findings.…”

“…Second, the inconsistency may be due to the explicit vs implicit nature of the sequencing of movements that the patients had to execute. In the other studies, patients with PD acquired declarative knowledge of the sequence of movements they had to perform because (1) they were asked either to memorize the sequence (Rafal, Inhoff, Friedman, & Bernstein, 1987;Stelmach et al, 1987) or to practice it before the experimental testing began (Benecke et al, 1987;Georgiou et al, 1994;Georgiou, Bradshaw, Phillips, Bradshaw, & Chiu, 1995;Georgiou, Iansek, Bradshaw, Phillips, Mattingley, & Bradshaw, 1993;Jones, Phillips, Bradshaw, Iansek, & Bradshaw, 1992;Rafal et al, 1987) or (2) they were allowed to refer to a written version of the sequence they had to produce at all times during the experiment (Harrington & Haaland, 1991). In this study, however, the subjects were unaware that the triads in the Practiced condition were made of the consecutive juxtaposition of the simple figures they had practiced in Phase III, nor that the triads in the Unpracticed condition were composed of novel simple figures that they had never traced individually before.…”

“…Third, evidence from animal (Brotchie, Iansek, & Horne, 1991a, 1991b, clinical (Doyon et al, 1997a(Doyon et al, , 1998Georgiou et al, 1994Georgiou et al, , 1995Georgiou et al, , 1993, and neuroimaging investigations (Doyon et al, 1997b(Doyon et al, , 1996bGrafton et al, 1994;Jenkins et al, 1994;Seitz, Roland, Bohm, Greitz, & Stone-Elander, 1990) has demonstrated that the striatum is critically involved in the late phases of learning where automatization of a skill is thought to occur. Consistent with such a notion is the absence of deficit observed in both PD groups that may result from the fact that, in the present study, subjects had not achieved automatization of the task.…”

Cortical interactions underlying the production of speech sounds

“…In particular, as currently defined, the DIVA model is given a string of sounds by the modeler, and the model produces this string in the specified order. Brain structures involved in the selection, initiation, and sequencing of speech movements are not treated in the preceding discussion; these include the anterior cingulate area, supplementary motor area (SMA), basal ganglia, and anterior insula (Buckner, Raichle, Miezin, & Petersen, 1996;DeLong, 1999;DeLong & Wichman, 1993;Dronkers, 1996;Georgiou et al, 1994;Nathaniel-James, Fletcher, & Frith, 1997;Paus, Petrides, Evans, & Meyer, 1993;Rogers, Phillips, Bradshaw, Iansek, & Jones, 1998 …”