This image shows ensemble spike activity of 13 motor cortical neurons recorded simultaneously during presentation of 5 sequential stimuli to be memorized. The spikes from each of the 13 neurons in the ensemble are plotted with a different color, with each line representing one trial. Trials using 8 different sequences are shown, randomly intermixed. The serial position of each sequence element is encoded in the ensemble activity, as can be seen in the change in the predominant colors going from left to right. For more information, see the article by Carpenter et al. (pages 4912–4933).