Fig. 3.
Functional connectivity. (A) Synaptic boutons found between pairs of neurons after analysis of high-magnification confocal images and classified according to the functional connectivity of the neuronal pairs. C, connected; A, autapses; U, unconnected. (B) Example of functional connectivity between layer V pyramidal neurons. The presynaptic action potential train (Top) elicited synaptic responses in the first postsynaptic neuron (Middle) but not in the second (Bottom). The postsynaptic traces represent an average of 30 individual trials. (C) Correlation between EPSP amplitudes and the numbers of boutons in connected pairs. Amplitudes of unitary EPSPs (first EPSP in a train) are plotted against the number of boutons, as identified by confocal microscopy. The correlation coefficient is 0.77, and the slope of the linear fit is 0.41 ± 0.12 mV per bouton. (D) Negative correlation between the CV of EPSP amplitudes and the number of boutons. The CV was calculated as SD divided by the mean of EPSP amplitudes from at least 30 individual responses. The continuous line represents a fit to the inverse square function, which is predicted from models of CV analysis of quantal synaptic transmission.