Simultaneous VmD estimations of excitatory and inhibitory background conductances.

<p>A. The raw traces show sample intracellular recordings from three neurones recorded in the same slice, and showing a great peak-to-peak voltage activity in L2. Estimation of background inhibition and excitation (see methods) required calculation of mean and variance of membrane potential at two levels of injected current (not shown). The histograms show the frequency distributions of membrane fluctuations at the two levels of injected current (geen being closer to resting potential and blue slightly more depolarized) in sample neurones from each layer. The solid lines on the graphs show the potential fluctuations constrained to a Gaussian function and in each case the goodness of fit (R²) was close to unity. B. Comparison of average data for background synaptic conductances estimated in the three layers of the EC. Background excitation (E_Bg) was highest in L3 and approximately 40% higher than that in L2 or L5. Inhibition (I_Bg) was greatest in L2 followed by L3 and L5. The resultant ratios showed a predominance of inhibition in a ll three layers, but in L2 this was this was almost double that seen in the other layers. C. The variance associated with the conductances (which is suggested to reflect the level of temporal synchrony in presynaptic inputs) was dramatically higher for both inhibition and excitation in L2 than in either of the deeper layers.