Pallidal neuron activity during sequential arm movements.

1. We examined the activity of neurons in the globus pallidus (GP) while monkeys (n = 2) performed sequential pointing movements under two task conditions: visually guided (TRACK task) and remembered (REM task). 2. Almost two-thirds of the task-related neurons in GP (155/236) were considered task dependent because they displayed exclusive or enhanced (greater than +/- 50%) changes in activity for one of the two task conditions. 3. More than 65% of the task-dependent neurons were termed REM neurons because they either displayed changes in activity that occurred only during the REM task or displayed changes that were more pronounced (greater than +/- 50%) during the REM task than during the TRACK task. 4. Nearly half of the REM neurons in GP displayed changes in activity that were limited to a single phase of the REM task (i.e., phase specific). Phase-specific neurons varied in the extent to which their activity depended on the particular sequence of movements performed. Some displayed a change in activity for all of the eight different movement sequences. Others displayed a change in activity during only one of the eight different sequences (i.e., phase and sequence specific). 5. We speculate that an ensemble of GP neurons with phase-specific responses could be used to encode the detailed spatio-temporal characteristics of a sequential movement. In this way, GP neurons would provide part of the neural substrate that solves the "serial order of motor behavior problem".