Paper IV is a model study of a population of layer 5 pyramidal neurons. The validity of methods used to interpret linear (laminar) multielectrode recordings is investigated. The modeling of the layer 5 population is based on a NEURON simulation of a biologically realistic cell template from Mainen and Sejnowski, and the extracellular potential is computed by electrostatic forward modeling.
The population has somas restricted to a cylindrical volume with both diameter and height 0,4 mm, and is activated by various synaptic input patterns. In response to the synaptic stimuli, some of the neurons fire one AP while most of the neurons have no AP firing activity. To achieve LFP and MUA amplitudes comparable to those seen in experiments, a total of 40 spiking cells and 1000 non-spiking cells had to be used. Hence, a very small fraction of the cells produced spikes.
The extracellular potential is computed at positions along the center axis of the population, and the experimental procedure of filtering the signal into the LFP and MUA bands is followed. The CSD is then computed from the LFP by using the standard CSD method as well as the iCSD methods. The results are compared to the real CSD.
Similarly, the relationship between the MUA and the population firing rate is investigated.