COMPARISON OF EEG TIME SERIES FROM RAT OLFACTORY SYSTEM WITH MODEL COMPOSED OF NONLINEAR COUPLED OSCILLATORS

Abstract

The so-called “spontaneous,” background, or “basal” time series of electroencephalographic (EEG) data from rat olfactory cortex are compared with those generated by a model of the ol-factory system, denoted KIII, composed of nonlinear coupled second order ODEs with feedback delay. Each ODE (KO) represents a neural mass having either excitatory or inhibitory output to the ODEs to which it connects. Connected mutually inhibitory or mutually excitatory pairs represent populations of similar neurons interacting to form one structure (KI set). A connected set (KII set) of excitatory and inhibitory KI sets (KIe and KIi) represents the activity of a gross structure in the olfactory system (the olfactory bulb—OB, anterior olfactory nucleus—AON, and prepyriform cortex—PPC or PC). The set of KII sets connected with dispersion-delay feedback pathways (KIII set) form a model of the first central stage of olfactory perceptual processing upon olfactory stimulation, with transition on receptor input from a self-sustained basal state of activity to an induced burst. Both basal and stimulated states are studied using amplitude histograms, power spectra, attractor reconstruction, visual inspection of traces, and correlation. A comparison shows that the two systems are similar, having broad spectra, correlation functions that rapidly go to zero, and gaussian amplitude histograms. Activity is nearly periodic and higher amplitude in the excited state and aperiodic, lower amplitude in the basal state with close to 1/f falloff. Cross spectra between OB and PPC show wide frequency bands of coherent high frequency activity in both the model and rat. The excited state nearly periodic frequencies differ between the KIII model and rat (30–60 Hz in KIII, 50–100 Hz in rat EEG), because the KIII model was developed for the cat and the rabbit, which have lower frequencies than the rat. These benchmarks may be used to evaluate the physiological validity of the output produced by a proposed model, as all components of the system and its connectivity were derived from or evaluated by physiological data.