A theoretical computer model of cellular modification associated with olfactory learning in the rat piriform cortex

Abstract

Learning-associated cellular modifications were previously studied experimentally in the rat piriform cortex after operand conditioning. The results showed a 19% reduction in the level of the action potential after-hyperpolarization (AHP) in trained rats, while the spike trains indicated decreased adaptation during long depolarization. Paradoxically, this reduced AHP amplitude was associated with a level of depression in the EPSP amplitude, which was significantly higher in trained rats than in the control groups, the pseudo-trained and naive rats. Our goal in the present study is to analyze and explain through computational techniques the effect of increased EPSP depression after learning. We apply three different models to simulate the exact reduction in the AHP amplitude: (1) ‘‘ Conductance change:’’ Controlled by decreasing g kCa by 40 %. (2) ‘‘ Moving:’’ Shifting the location of the dendritic segment that exhibits active conductances, including AHP conductance, distally from the soma, while decreasing g kCa by only 15%. (3) ‘‘ Shrinkage:’’ Decreasing the length of the AHP dendritic segment, while increasing g kCa by 9%. Moving the synaptic input distally from the soma enhances EPSP depression by the AHP conductance. Hence, the learning process could be simulated by a “jump” from the control curve to any other curve, representing decreased AHP amplitude. At the same time, the enhanced EPSP depression requires an additional shift of the EPSP input to more distal locations.