Motor cortical encoding of serial order in a context-recall task

The neural encoding of serial order was studied in the motor cortex of monk eys performing a context-recall memory scanning task. Up to five visual sti muli were presented successively on a circle (List presentation phase), and then one of them (test stimulus) changed color; the monkeys had to make a single motor response toward the stimulus that immediately followed the tes t stimulus in the List. Correct performance in this task depends on memoriz ation of the serial order of the stimuli during their presentation. It was found that changes in neural activity during the list presentation phase re flected the serial order of the stimuli; the effect on cell activity of the serial order of stimuli during their presentation was at Least as strong a s the effect of motor direction on cell activity during the execution of th e mot or response. This establishes the serial order of stimuli in a motor task as an important determinant of motor cortical activity during stimulus presentation and in the absence of changes in peripheral motor events, in contrast to the commonly held view of the motor cortex as just an "upper mo tor neuron."