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-evok ed potentials (mEP) in bimanual and unimanual movements with single-unit ac tivity recorded concurrently. The mEP was often different during bimanual a nd unimanual movements (a "bimanual-related" effect), but, unlike the singl e units, the size of the mEP in both MI and SMA was always greater during b imanual movements than during unimanual movements. This increase primarily reflected an increase in the late positive peak of the mEP, a result that m ay reflect greater overall cortical activation during bimanual movements. I n addition, analysis of the mEP revealed differences between MI and SMA not seen in the single-unit activity. mEP in MI had greater contralateral pref erence than in SMA. Also, SMA mEP was more correlated to the single-unit ac tivity than in MI. This greater correlation was also more apparent in the l ate peaks of the mEP than in the early peaks and may reflect a greater infl uence of recurrent activation in SMA than in MI. Our results further reinfo rce the idea that unimanual and bimanual movements are represented differen tly 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-outpu t relations of different cortical areas.