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) [1] (Fig. 1).  In primate motor cortex STAs of membrane potentials exhibit features representing post-spike unitary potentials as well as synchrony effects [2] (Fig. 2).  CCH's also documented the synaptic connections between motor cortex neurons whose activity was modulated during wrist movements [3].  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 [4] (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 [5].  The functional role of these oscillations remains a subject of debate, but a plausible hypothesis is that they represent a top-down attentional mechanism [6].




  1. Fetz EE, Toyama K, and Smith W. Synaptic interactions between cortical neurons, in CEREBRAL CORTEX, VOL IX ALTERED CORTICAL STATES, A. Peters, and E.G. Jones, eds. Plenum Press, New York, 1-47, 1991. [PDF]
  2. Matsumura M, Chen D-F, Sawaguchi T, Kubota K, and Fetz EE, Synaptic interactions  between primate precentral cortex neurons revealed by spike-triggered averaging of intracellular membrane potentials in vivo, Journal of Neuroscience, 16: 7757-7767, 1996. [PDF]
  3. Smith, WS and Fetz EE, Synaptic interactions between movement-related motor cortex neurons in behaving monkeys, Journal of Neurophysiology, 102: 1026-1039, 2009.  PMCID: PMC2724363. [PDF]
  4. Fetz EE, and Gustafsson B, Relation between shapes of postsynaptic potentials and changes in firing probability of cat motoneurons. Journal of Physiology 341:387-410, 1983. [PDF]
  5. Cope TC, Fetz EE, and Matsumura M, Cross-correlation assessment of the synaptic strength of single Ia fibre connections with lumbar motoneurones in the cat, J. Physiol 390:161-188, 1987. [PDF]
  6. Murthy VN, and Fetz EE, Synchronization of neurons during local field potential oscillations in sensorimotor cortex of awake monkeys, Journal of Neurophysiology, 76: 3968-3982, 1996. [PDF]
  7. Fetz EE, Volitional control of cortical oscillations and synchrony, Neuron, 77, 216-218, 2013. [PDF]



Figure 1. Synaptic interactions measured with STA and CCHs [1]

Figure 2. Interactions between cortical neurons produce post-spike and synchrony potentials [2].

Figure 3. Relation between unitary EPSPs and resulting correlograms in motoneurons [4]