By Sheba Khan
Summer 2010

Dr. Horacio Rotstein has mastered many sciences, two of which include biology and math. Dr. Rotstein studies oscillations in the brain at the cellular, molecular, and network level. Particularly, he focuses on the dynamics of the brain, how learning occurs, and how memories are stored and retrieved using rhythmic oscillations. These rhythms are found in the hippocampus and entorhinal cortex (EC). Frequency bands of the brain’s rhythmic oscillations are recorded using an electroencephalogram (EEG). These rhythms have been found to be connected to many different cognitive and behavioral tasks, including memory, learning, and spatial navigation. Dr. Rotstein uses the reduction of dimensions technique to produce nonlinear, multi-scale biological models that describe the oscillatory patterns found in the brain.

Test animals are induced to have an epileptic attack, and the bioelectrical response produced is compared to the model using various wave analysis methods. In epileptic patients, the cells become hyper-excited just as the person goes into shock.
Dr. Rotstein studies why this occurs, and what sort of oscillatory patterns epileptic attacks disrupt. In the models, there is no difference between, or damage, to the individual cells. Though the cells found in this region have the potential to be hyper-excited, conditions are adjusted such that they do not. This rules out a problem at the sub-cellular level; the problem, then, takes place at the level of interactions between cells or between networks of cells. With the use of biophysical, biological and mathematical modeling, the impact of these rhythms is studied at the sub-cellular, cellular, and network levels, and it is here that the impacts of Dr. Rotstein’s research becomes readily apparent. By understanding and correctly representing the normal behavior of cells as well as their excited behavior with mathematical models, Dr. Rotstein is able to extract what the variation is at the different previously named levels. By understanding how a healthy brain generates rhythms, the brains that do not function properly can be studied, and ultimately assessed for treatment.

At the cellular level, Dr. Rotstein focuses on the stellate cells (SC), a type of neuron, which exhibits mixed-mode oscillations that produce interspersed spikes. The corresponding model of this phenomenon uses the minimum frequency of the SC, which mimics the mixed-mode oscillatory patterns. By studying the underlying structure of this model, as well as others like it, the patterns at the subcellular, cellular, and network levels allow for the determination of how SCs process and integrate information. Understanding the natural mixed-mode oscillatory patterns enables researchers to forecast the way the brain can generate other patterns and rhythms. Dr. Rotstein’s research of these behaviors can be extended to human navigation issues, as well as the role these waves play on epileptic patients.