Local field potentials related to bimanual movements in the primary and supplementary motor cortices

We recorded local field potentials (LFP) in primary (MI) and supplementary (SMA) motor areas of rhesus monkey cortex in order to compare movement-evoked potentials (mEP) in bimanual and unimanual movements with single-unit activity recorded concurrently. The mEP was often different during bimanual and unimanual movements (a "bimanual-related" effect), but, unlike the single units, the size of the mEP in both MI and SMA was always greater during bimanual movements than during unimanual movements. This increase primarily reflected an increase in the late positive peak of the mEP, a result that may reflect greater overall cortical activation during bimanual movements. In addition, analysis of the mEP revealed differences between MI and SMA not seen in the single-unit activity. mEP in MI had greater contralateral preference than in SMA. Also, SMA mEP was more correlated to the single-unit activity than in MI. This greater correlation was also more apparent in the late peaks of the mEP than in the early peaks and may reflect a greater influence of recurrent activation in SMA than in MI. Our results further reinforce the idea that unimanual and bimanual movements are represented differently both in MI and in SMA and also show that a complex relationship between spikes of individual neurons and LFP may reflect the different input-output relations of different cortical areas.