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 [4] and unitary EPSPs [5] (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 [6].  The functional role of these oscillations remains a subject of debate, but a plausible hypothesis is that they represent a top-down attentional mechanism [7].




  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]