Planning and Control of Sequential Rapid Aiming in Adults With Parkinson’s Disease A. L. Smiley-Oyen K. A. Lowry Motor Control and Learning Research Laboratory Department of Health and Human Performance Iowa State University, Ames ABSTRACT. Eight people with Parkinson’s disease (PD), 8 age- matched older adults, and 8 young adults executed 3-dimensional rapid aiming movements to 1, 3, 5, and 7 targets. Reaction time, flight time, and time after peak velocity to the 1st target indicated that both neurologically healthy groups implemented a plan on the basis of anticipation of upcoming targets, whereas the PD group did not. One suggested reason for the PD group’s deficiency in anticipatory control is the greater variability in their initial force impulse. Although the PD group scaled peak velocity and time to peak velocity similarly to the other groups, their coefficients of variation were greater, making consistent prediction of the move- ment outcome difficult and thus making it less advantageous to plan too far in advance. A 2nd finding was that the PD group exhibited increased slowing in time after peak velocity in the final segments of the longest sequence, whereas the other 2 groups did not. The increased slowing could be the result of a different move- ment strategy, increased difficulty modulating the agonist and antagonist muscle groups later in the sequence, or both. The authors conclude that people with PD use more segmented plan- ning and control strategies than do neurologically healthy older and young adults when executing movement sequences and that the locus of increased bradykinesia in longer sequences is in the deceleration phase of movement. Key words: anticipation, basal ganglia, motor planning, sequence, variability t is well established that people with Parkinson’s disease (PD) exhibit difficulties with movement sequencing in such tasks as handwriting (Phillips, Chiu, Bradshaw, & Iansek, 1995; Teulings, Contreras-Vidal, Stelmach, & Adler, 1997), buttoning (Rocca, Maraganore, McDonnell, & Schaid, 1998; Soliveri, Brown, Jahanshahi, & Marsden, 1992), keyboarding (Freund, 1989; Longstreth, Nelson, Linde, & Munoz, 1992), and even finger tapping (Camicioli, Grossmann, Spencer, Hudnell, & Anger, 2001; Harrington, Haaland, & Her- manowicz, 1998). People with PD move more slowly when performing a movement sequence than when performing dis- crete movements, and they exhibit longer pause times between elements of the sequence (Agostino, Berardelli, Formica, Accornero, & Manfredi, 1992; Benecke, Rothwell, Dick, Day, & Marsden, 1987; Harrington & Haaland, 1991; Weiss, Stelmach, & Hefter, 1997). They also exhibit an increase in bradykinesia, that is, movement slowness, in the later segments of a sequence (Agostino et al., 1992; Agostino et al., 1994; Harrington & Haaland). One reason that execution of movement sequences may be different in PD is that they are planned differently. One can measure planning on the basis of changes in reaction time (RT, i.e., the time required to preprogram the move- ment); as the number of elements in a rapidly executed series of discrete movements increases, so does RT. Investigators have concluded that as this type of sequence increases in number of elements, the movement is more complex; and therefore more neurological and psychological processing time is required before the movement is initiated (Christina, 1992; Fischman, 1984; Garcia-Colera & Semjen, 1987; Gor- don & Meyer, 1987; Henry & Rogers, 1960; Lajoie & Franks, 1997; Sidaway, 1991; Sidaway, Christina, & Shea, 1988; Smiley-Oyen & Worringham, 2001; Sternberg, Mon- sell, Knoll, & Wright, 1978). A longer RT for longer sequences indicates that young adults plan a movement sequence in an integrative fashion, taking into account many segments, not just the first one or two segments. People with PD exhibit increased preprogramming time comparable with that of age-matched controls for two- and Correspondence address: A. L. Smiley-Oyen, 244 Forker Build- ing, Department of Health and Human Performance, Iowa State University, Ames, IA 50011, USA. E-mail address: asmiley @iastate.edu 103 I Journal of Motor Behavior, 2007, Vol. 39, No. 2, 103–114 Copyright © 2007 Heldref Publications J. P. Kerr Voxel Research Ames, Iowa