"Say no to plagiarism. Get a tailor-made essay on "Why violent video games should not be banned"? Get an original essay We can think of our brain as a complicated electrical circuit composed of billions of neurons and trillions of synapses (gaps between one neuron and another). Each neuron can be considered as a component of this complex circuit. The reflexes to reasoning and emotions depend on the processing of these circuits 'healthy excitatory depends on the precision of these circuits. And many of the psychiatric disorders such as depression can be the result of improper excitability. Transcranial direct current stimulation (tDCS) is also a technique used to modulate cortical excitability showed an optimistic result. The technique is implemented by placing two electrodes on the scalp and applying a potential difference, which results in an electricity field in the brain as shown in figure 1. There are other brain stimulation techniques such as transcranial electrical stimulation. (TES) and transcranial magnetic stimulation (TMS), but the difference between these techniques and tDCS is that in the latter the static field range does not create neuronal action potential, but simply modulates excitability. For this reason, tDCS is also called neuromodulatory intervention. tDCS is managed by injecting constant direct current (low amplitude) through electrodes placed on the scalp. The longer the duration of the stimulation, the greater the effect of the stimulation. The amplitude of the injected current will also increase the stimulation effect. tDSC can cause two changes in the brain; depolarization and hyperpolarization. The changes (depolarization and hyperpolarization) depend on the type of stimulation performed. Positive stimulation (anodal tDCS), which increases the excitability of neurons, causes depolarization, and negative stimulation (cathodal tDCS), which results in a decrease in the excitability of neurons, causes hyperpolarization. There are many factors that influence the efficiency of the tDCS technique such as stimulation duration, amplitude of the injected current etc. However, you have to be very careful about the magnitude of the current because there are limits to the amount of current the brain can function with. From an application perspective, the location and size of the electrode also matter a lot. Other studies imply that electrodes with a smaller area cause deep stimulation while larger electrodes induce superficial stimulation. Since the effect of stimulation is a function of current density, it is important to study the factors that influence the distribution within the brain and much work has been done in the past to study this influence. To study the current density distribution, we first need a mathematical formulation of this electrical model. In 1968 Rush & Driscoll [6] formulated an analytical expression for the potential within a 3-layer (spherical) head model. An important inference from this study is that the magnitude of current density within the brain has a direct influence on the effect of tDCS. However, the magnitude of current density is not the only factor that decides the performance of tDCS. There are other factors such as the size of the electrode, the location and distance between the electrodes, etc. In 2007 Nitsche studied the effect of electrode size on current distribution and concluded that more focal stimulation could be achieved by using smaller electrodes. In contrast, increasing the electrode area gives less focal stimulation, i.e. one"