Power spectral density potential fluctuations

When eyes are closed the sine-wave-shaped large-amplitude alpha rhythm appears in the scalp potentials, of which frequency fluctuates within a frequency range 8-13 Hz, and this almost periodic waveform is clearly seen in the spontaneous electroencephalogram. The instantaneous frequency is defined from the interval between consecutive zerocrossing points. Its power spectral density is found to be of 1// in a certain range of the Fourier frequency. It is another example of 1// fluctuations of biological rhythm phenomena. When a subject is in a... 

Figure 11.2 (a.) Measured power spectral density of the voltage fluctuations V, and P reg a platinum disk electrode (area I0 cm ) In I M KCI solution with potassium ferri/ferrocyanide (I0 M) at the potential + 115 mV versus SCE. Curve (a) = bare platinum curve (b) = platinum covered with a gel layer (b) Calculated phase-sensitive detection ol V, Vi and P, in the same experimental conditions as in (a). Reprinted with permission from Ref. [20], Copyright 1993, AlP Publishing EEC. 

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