This study recorded the activity of neurons in the (i) supplementary motor area (SMA), (ii) pre-SMA (the motor area immediately rostral to the SMA), (iii) premotor cortex (PMC) and (iv) primary motor cortex (MI), while the monkey performed a conditional sequential motor task that ensures sequencing of multiple movements to the same manipulandum. This paradigm was chosen in order to prevent the participation of spatial cues in prompting the correct motor sequence. Three different movements (turn-push-pull) were performed under two task conditions: (i) internally determined (I): the monkey had to generate a pre-determined sequence from memory and without visual guidance; (ii) externally triggered (E): the correct sequence of movements was performed by following lights illuminated one after the other. Neuronal activity during the following periods were analyzed: instruction (300 ms following the onset of the auditory instruction signal); delay (interval between the end of the instruction period or the termination of the previous movement and the movement trigger); premovement (interval between the trigger signal and the movement onset); movement (interval between the mechanically-sensed movement onset and the completion of the movement) and reward (500 ms period centered at the time of reward delivery). Pre-SMA neurons were generally more active during the delay and premovement as compared to the movement, instruction and reward periods. Activity in the pre-SMA was more related to E during the pre-movement period, but exhibited a preferential relationship to I in the movement period. SMA neurons were more active when the sequential motor task was internally generated. By contrast, PMC neurons were more active when the sequence was visually guided. Such preferential activity was rarely found in MI neurons.
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