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)\cdot i.$$ A memristor has to exhibit pinched hysteresis loops in the V-I plot with the pinched point at the origin of the coordinates [ 3 ]. Furthermore, the lobe area of the loop decreases with increased frequency and if the frequency goes towards infinity, the pinched hysteresis loop should shrink to a single valued function [ 4 ]. Volkov et al . demonstrated memristive properties in apples [ 5 ] and in the aloe vera plant [ 6 ]. Here, we study the memristive properties of the same objects by using our methods (three electrode system that enables monopolar

, and to attain this field in specific regions of the brain, the electric current should pass through different head layers via skin, fat, skull, meninges, and cortex (part of the brain). In order to model the brain, different layers should be considered, including gray and white matters. The meninges, three layers of protective tissue, cover the outer surface of the central nervous system (brain and spinal cord) and comprise three connective tissue layers viz. (from the innermost to the outermost layer) the pia mater, arachnoid and the dura mater. The meninges also

4 ). Finally, we did some additional measurements on the forehead of one test subject that allow for a direct comparison with the recordings in the sodium chloride solution. Materials and methods All measurements were done at the University of Oslo. Instrumentation The recordings were done by the use of a custom built measurement system (see Fig. 1b and [ 4 ]). The setup contains a DAQ card (NI USB-6356) which is connected to a computer and controlled by a custom made program based on LabVIEW 2018. A three electrode system was used with “M” as the measurement

by the Federal Ministry of Education and Research (BMBF, FKZ 01EZ0911). The custom-made stimulator system was developed in cooperation with the Steinbeis company (STZ1050, Rostock, Germany) and Dr. R. Arndt (Rückmann & Arndt, Berlin, Germany). References 1 Krack P, Hariz MI, Baunez C, Guridi J, Obeso JA. Deep brain stimulation: from neurology to psychiatry? Trends Neurosci. 2010;33:474-84. Krack P Hariz MI Baunez C Guridi J Obeso JA Deep brain stimulation: from neurology to psychiatry? Trends Neurosci 2010 33 474 84 doi

strength (h) are assigned to the edges. Hence, a system of equations, called Maxwell-Grid Equations, has to be solved for the whole calculation domain, where each cell is described by: (1) C e → = − ∂ b → ∂ t                                   C ˜ h → = − ∂ d → ∂ t + j → $$C\overrightarrow{e}=-\frac{\partial \overrightarrow{b}}{\partial t}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \tilde{C}\overrightarrow{h}=-\frac{\partial \overrightarrow{d}}{\partial t}+\overrightarrow{j}$$ (2) S ˜ d → = q                 S b → = 0 $$\tilde{S}\overrightarrow{d}=q\ \ \ \ \ \ \ \ S

j is the prescribed potential at a given electrode, j ; w j is the width of or between an electrode as illustrated in Fig. 2 and h k is the height of skin layer k . Note that we do not solve for the potential distribution in the electrodes, because the potential drop there is negligible [ 3 ]. Analysis Let’s start by exploiting that the current density distributions underneath the m electrodes are near-to constant because of the high resistance to current of the stratum corneum in the considered frequency range [ 3 ]. This allows us to rewrite the