Exp Brain Res (1993) 95:51-64 Experimental BrainResearch 9 Springer-Verlag 1993 Primate basal ganglia activity in a precued reaching task: preparation for movement Dieter Jaeger, Sid Gilman, J. Wayne Aldridge Department of Neurology,Neuroscience Lab. Bldg., Universityof Michigan, 1103 E. Huron, Ann Arbor, MI 48104, USA Received: 21 July 1992/Accepted: 27 February 1993 Abstract. Single cell activity was recorded from the pri- mate putamen, caudate nucleus, and globus pallidus dur- ing a precued reaching movement task. Two monkeys were trained to touch one of several target knobs mount- ed in front of them after an LED was lighted on the correct target. A precue was presented prior to this target "go cue" by a randomly varied delay interval, giving the animals partial or complete advance information about the target for the movement task. The purpose of this design was to examine neuronal activity in the major structures of the basal ganglia during the preparation phase of limb movements when varying amounts of ad- vance information were provided to the animals. The re- action times were shortest with complete precues, inter- mediate with partial precues, and longest with precues containing no information, demonstrating that the ani- mals used precue information to prepare partly or com- pletely for the reaching movement before the target go cue was given. Changes in activity were seen in the basal ganglia during the preparatory period in 30% of neurons in putamen, 31% in caudate nucleus, and 27% in globus pallidus. Preparatory changes were stronger and more closely linked to the time of movement initiation in puta- men than in caudate nucleus. Although the amount of information contained in the precues had no significant effect on preparatory activity preceding the target go cue, a directional selectivity during this period was observed for a subset of neurons with preparatory changes (15% in putamen, 11% in caudate nucleus, 14% in globus pal- lidus) when the precue contained information about the upcoming direction of movement. A smaller subset of neurons showed selectivity for the preparation of move- ment amplitude. A larger number of preparatory changes showed selectivity for the direction or amplitude of movement following the target go cue than in the delay period before the cue. The intensity of preparatory changes in activity in many cases depended on the length of the delay interval preceding the target go cue. Even following the target go cue, the intensity of the preparato- Correspondence to: J. WayneAldridge ry changes in activity continued to be significantly influ- enced by the length of the preceding delay interval for 11% of changes in putamen, 8% in caudate nucleus, and 18% in globus pallidus. This finding suggests that preparatory activity in the basal ganglia takes part in a process termed motor readiness. Behaviorally, this pro- cess was seen as a shortening of reaction time regardless of precue information for trials in which the delay inter- val was long and the animals showed an increased readi- ness to move. Preparatory activity in putamen following the target go cue was most intense in trials with a short delay interval, in which motor readiness had not achieved its maximum level prior to the go cue. The re- sults of this study indicate that the basal ganglia are in- volved in multiple aspects of preparatory processing for limb movement. Preparatory processing is therefore un- likely to be divided anatomically along the functional lines examined in this study. In the basal ganglia, preparatory processing reflects both preparation for target selection and control of timing the onset of move- ment (motor readiness). These characteristics can be inte- grated in a functional scheme in which the basal ganglia are predominantly responsible for the automated execu- tion of well-trained behavior. Key words: Basal ganglia - Motor control - Precue Single unit - Monkey Introduction In learned motor tasks, the basal ganglia participate in processing events during preparation for movement (Soltysik 1975; Neafsey et al. 1978; Alexander 1987; Schultz and Romo 1988; Alexander and Crutcher 1990a,b). The activity of single neurons in the striatum is modulated prior to the onset of movement, both in movements triggered by sensory "go cues" (Alexander and Crutcher 1990a) and in self-initiated movements