Investigating the Coupling between Stimulation and Neural Activity: a Dynamic Modeling Approach

The objective of the present study was to build a dynamic model relating changes in neural responses in rat barrel cortex to an electrical whisker stimulation pulse train of varying frequencies. This work is part of a formal mathematical system currently being developed (e.g. [1] and [2]), which links stimulation to the blood oxygen level dependent (BOLD) functional magnetic resonance imaging (fMRI) signal. Neural responses were measured in terms of local field potentials, which were then converted into current source density (CSD) data. Responses were found to be strongly suppressed immediately following the first stimulus pulse, before recovering to a steady state, which was maintained throughout the rest of the stimulation. The amplitude of this steady state decreases as the stimulation frequency increases, as shown in [3]-[6]. The model structure is based on the physiological pathway from the rat sensory organ to the cortex. Dynamic linear second order systems are used to model the excitatory as well as the suppressive components of the neural response. The interactions between components contain nonlinear modulations. The model was evaluated against CSD data from experiments with varying stimulation frequency (1-40 Hz), and shows a plausible fit. The model parameters obtained by optimization for different physiological conditions (anaesthetized or awake) were significantly different. Although this is a descriptive model, it may well have some physiological implications.