Figure 2. DCM and the Neural Mass Model.

A Neural mass model used to represent regions in auditory cortex. Three cell subpopulations contribute to the ongoing dynamics. These include spiny stellate cells in granular layer IV, pyramidal cells and inhibitory interneurons in extra granular layers (II & III and V & VI). Intrinsic connections link dynamics between subpopulations in each source. Dynamic states include currents, g, and membrane potentials v. Extrinsic connections enter at specific cell layers. B Functions controlling ongoing dynamics and their parameterisation. Left: Excitatory synaptic kernel, which is convolved with the input firing to produce a depolarising change in membrane potential. The function is parameterised by its height H_e and time constant. H_e is allowed to mediate the effects of isoflurane. Increases in H_e produce different responses, as per the arrow. Right: Inhibitory synaptic kernel, which is convolved with the input firing to produce a hyperpolarising change in membrane potential. The function is parameterised by its height H_i and rate constant κ_i. Both can mediate the effect of isoflurane. Increases in these parameters produce different responses as per the arrow. C Three competing hypotheses regarding extrinsic connectivity in hierarchical auditory cortex, embodied by model 1, with forward connections from A1 to PAF and backward connections from PAF to A1 (M1:FB). The reverse architecture is constructed for model 2 (M2: BF). Model 3 contains lateral connections between the regions (M3: LL).