# The Influence of Electrode Impedance on the Parameters of Visual Evoked Potentials
## 4 Discussion  
The presented research confirmed the generally known fact that the electrode impedance decreases with increasing frequency. However, during the tests, an increase in impedance with the subsequent use of the same electrode and also an increase in VEP parameters (i.e., latency and amplitude) were observed. The entire cycle of VEP potential registrations lasted almost two years, which could have affected the obtained values of amplitude and latency. Since the VEP parameters depend on several factors, this author attempted to eliminate most of them. In clinical practice, the accuracy of the analysis and the interpretation of the obtained results of brain potential examinations depends on the experience and skill of the clinician. When preparing the analysis of the brain potential parameters, it is necessary to take into account a number of factors affecting these parameters, the most important of which are the interindividual differences observed in the same age group of patients and the intrapersonal variability of the range of parameter values [9]. The analysis of interindividual variability mainly takes into account the patient's age and health status, as well as gender [9,16]. According to [26], the evoked potentials are stable from about 5 years of age to 60 years of age. The mean peak latency only slows by about one millisecond per decade from the age of 5 until the age of 60. The amplitude and speed of VEPs remain stable until about age 28, after which time the amplitudes begin to attenuate. In the case of gender, the VEP showed a shorter mean latency but a higher mean amplitude for females than males. The age-dependent increase in mean latency was observed in the female group but not in the male group. In contrast, intrapersonal variability in the parameters is not necessarily due to pathological changes and is often observed in healthy individuals [8]. The reasons for this variability may be due to body temperature, blood pressure, the pH of blood, and bodily fluids. Therefore, all registrations of visual evoked potentials used for the analyses were carried out in a one healthy volunteer, i.e., the author of the paper. To confirm the subject's good health before starting the VEP recording, his author was tested for demyelinating diseases, diabetes, basic retinal disease, and glaucoma. All these diseases affect visual function, especially retinal disease. In the case of Friedrich's Ataxia, delayed latency and increased amplitude of the VEP are the most frequent electrophysiological alterations in this pathology [27]. The results of these tests confirmed the absence of these diseases. To be sure, these tests were repeated after a year. Moreover, the values of the parameters of some brain potentials, e.g., VEP, depend on the parameters of the stimulating stimulus [5,6]. Hence, all VEP registrations prepared for these studies took place for the same value of stimulation parameters due to the dependence of the VEP waveform, amplitudes, and peak times on the parameters of the stimulus. The VEP examinations had the same start time, because the amplitude of brain potentials is influenced not only by the patient's health, age, gender, inter-individual differences, and antiepileptic and psychotropic drugs. Measurement conditions (i.e., recording times) are also important, because sleepiness and stress affect the VEP amplitude. Sleepiness causes a slowdown in neuronal activity and therefore a decrease in amplitude, while stress increases the amplitude and additionally affects the following latencies: P300, N100, and N400. Another factor affecting changes in brain potential values discussed in papers [8,9,13,15,18] is electrode selection. The main criteria for selecting reusable electrodes for recording brain potentials are the patient's age and the type of examination [1, 2, 3, 4, 5, 6, 9].