......................................................................

NJIT Mathematical Biology Seminar

Tuesday, November 14, 2006, 4:00pm
Cullimore Hall 611
New Jersey Institute of Technology

......................................................................

Mechanistic aspects of the creation of theta rhythmic activity in the hippocampus: A modeling study

Horacio Rotstein

Department of Mathematical Sciences
NJIT

Field potential oscillations at theta frequencies (8-12 Hz) in the hippocampal formation have been correlated with various brain functions and behavioral states, including representation of visuospatial information, REM sleep, active exploration, and memory formation and retrieval. Recently, Gillies et al. [1] have experimentally shown the existence of oscillatory activity in the theta frequency range in slices of the hippocampal area CA1 when phasic excitation is blocked. Two different types of inhibitory neurons are involved in the mechanism of generating these rhythms: fast spiking interneurons (I) and oriens lacunosum-moleculare (O) cells. They differ in their ionic currents and in their inhibitory decay times. We present a biophysically plausible mathematical model that reproduces experimental findings. This model focuses on the activity of the O and I cells. Each cell is modeled as a single compartment and includes the standard Hodgkin-Huxley currents. In addition, we include a hyperpolarization activated inward current (Ih) in the O cells. Blockade of Ih has been shown to destroy the rhythmicity both experimentally and in simulations. Following experimental evidence, we model the O cells with longer lasting inhibitory postsynaptic potentials in comparison with the I cells. We propose a mechanism by which coherent theta oscillations are created due to the interaction of the I and O cells. Using numerical and analytical techniques we demonstrate the effect that the I cells exert on the O cells, as a consequence of the presence of Ih, and the O-I network effects which are due to the fast and slow inhibition.