Synaptic interactions between neurons
The synaptic interactions between neurons can be documented by spike-triggered averages (STA) of intracellular membrane potentials and by cross-correlation histograms (CCH)  (Fig. 1). In primate motor cortex STAs of membrane potentials exhibit features representing post-spike unitary potentials as well as synchrony effects  (Fig. 2). CCH's also documented the synaptic connections between motor cortex neurons whose activity was modulated during wrist movements . The relationship between these two measures was documented directly by determining the effects that excitatory postsynaptic potentials had on the firing rate of spinal motoneurons, for both compound and unitary EPSPs  (Fig. 3).
Motor cortex neurons can exhibit widespread oscillatory interactions. These oscillatory episodes are evident in the local field potentials, to which many neurons are entrained . The functional role of these oscillations remains a subject of debate, but a plausible hypothesis is that they represent a top-down attentional mechanism .
Figure 1. Synaptic interactions measured with STA and CCHs 
Figure 2. Interactions between cortical neurons produce post-spike and synchrony potentials .
Figure 3. Relation between unitary EPSPs and resulting correlograms in motoneurons