How much do they tell us to move?

A previous study revealed that neuronal activity in primary motor cortex (M I) and supplementary motor area (SMA) of the monkey depends both on which a rm(s) moved and on the direction of movement. At the level of single cells, no differences were found between the areas in the information conveyed ab out each correlate. We constructed pseudosimultaneous response vectors and applied a decoding algorithm to quantify differences at a population level. We found that, on average, samples of 20 MI units carried less information about both movement type and direction than SMA units in a time window of 500 ms across the movement onset; a more detailed temporal analysis has rev ealed that SMA precedes M1 in motor planning and execution and that along t he trial M1 cells carry as much information about direction as SMA cells. ( C) 2001 Elsevier Science B.V. All rights reserved.