Neurons oscillating

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Oscillatory reactions are a typical class of phenomena, which display unusual features. After the discovery of Belousov-Zhabotinskii (B-Z) reaction, there has been a tremendous flurry of activity [1] and a large number of such reactions have been discovered during recent years. Biochemical reactions [2-10] such as glycolytic oscillations and peroxidase catalysed oxidation of nicotinamide adenosine deoxyhydrogenase (NADH) have also generated considerable interest. The interest in such reactions is stiU sustained in view of their importance in understanding cardiac and neuronal oscillations. In the case of many oscillatory chemical reactions [1], detailed reaction mechanisms have been postulated and verified with the help of numerical computation. This has also been particularly so for B-Z reaction where Field-Koros-Noyes (FKN) mechanism [11] has been invoked. 

Any oscillatory activity is basically caused by a positive action, followed by a delayed feedback. Oscillations in the brain occur at various stages, i.e., in the membrane of the neurons (resulting in membrane potential fluctuations), between neurons (action potentials), and between neuronal populations. The functional activity of the brain is due to the neuronal oscillations and their synchronization, which involves various complex actions including information processing, awareness, motor control, sleep, and many other functions. Neuronal oscillations usually fall in a well-defined frequency band and hence are frequency specific. The frequency specific nature [11,12] of neuronal oscillations makes it possible for the brain to control various cognitive, motor, and stability processes effectively. 

As we have seen so far, the intrinsic membrane potentials of the neurons is the main cause of neuronal oscillations. However, there also exist other mechanisms that can cause oscillations in the neurons. In general, every single neuron can be classified into two major types of oscillators, i.e., relaxation oscillators and conditional oscillators. Relaxation oscillators are spontaneous and oscillate in the absence of inputs, whereas conditional oscillators are those that fire as a consequence of the inputs it receives. 

In the brain, synchronization and oscillation cause and affect each other. Synchronization can occur as a result of the neuronal oscillations, in which case the synchronization is called oscillation-based synchronization. On the other hand, oscillations can occur as a result of synchronization. This happens, for instance, when the occurrence of firing in a neuron predicts the occurrence of firing in the next neuron with some probability. Thus, neuronal oscillations in the brain are related to synchronization. Since oscillations and synchronization in the brain involves more than one neuron, there is no possibility that one can infer whether a single neuron is in synchrony with the others by making single cell recordings. We absolutely need to measure collective field potentials [14,15]. 

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