Retest Reliability of Individual P3 Topography Assessed by High Density Electroencephalography Manuel Va ´ zquez-Marrufo 1 *, Javier J. Gonza ´ lez-Rosa 3 , Alejandro Galvao-Carmona 1 , Antonio Hidalgo- Mun ˜ oz 1 , Mo ´ nica Borges 2 , Juan Luis Ruiz Pen ˜a 2 , Guillermo Izquierdo 2 1 Experimental Psychology Department, Faculty of Psychology, University of Seville, Seville, Spain, 2 Multiple Sclerosis Unit, Virgen Macarena Hospital, Seville, Spain, 3 Laboratory for Clinical Neuroscience, Centre of Biomedical Technology (CTB), Technical University of Madrid (UPM), Madrid, Spain Abstract Background: Some controversy remains about the potential applicability of cognitive potentials for evaluating the cerebral activity associated with cognitive capacity. A fundamental requirement is that these neurophysiological parameters show a high level of stability over time. Previous studies have shown that the reliability of diverse parameters of the P3 component (latency and amplitude) ranges between moderate and high. However, few studies have paid attention to the retest reliability of the P3 topography in groups or individuals. Considering that changes in P3 topography have been related to different pathologies and healthy aging, the main objective of this article was to evaluate in a longitudinal study (two sessions) the reliability of P3 topography in a group and at the individual level. Results: The correlation between sessions for P3 topography in the grand average of groups was high (r = 0.977, p,0.001). The within-subject correlation values ranged from 0.626 to 0.981 (mean: 0.888). In the between-subjects topography comparisons, the correlation was always lower for comparisons between different subjects than for within-subjects correlations in the first session but not in the second session. Conclusions: The present study shows that P3 topography is highly reliable for group analysis (comprising the same subjects) in different sessions. The results also confirmed that retest reliability for individual P3 maps is suitable for follow-up studies for a particular subject. Moreover, P3 topography appears to be a specific marker considering that the between- subjects correlations were lower than the within-subject correlations. However, P3 topography appears more similar between subjects in the second session, demonstrating that is modulated by experience. Possible clinical applications of all these results are discussed. Citation: Va ´zquez-Marrufo M, Gonza ´lez-Rosa JJ, Galvao-Carmona A, Hidalgo-Mun ˜ oz A, Borges M, et al. (2013) Retest Reliability of Individual P3 Topography Assessed by High Density Electroencephalography. PLoS ONE 8(5): e62523. doi:10.1371/journal.pone.0062523 Editor: Xi-Nian Zuo, Institute of Psychology, Chinese Academy of Sciences, China Received November 14, 2012; Accepted March 20, 2013; Published May 1, 2013 Copyright: ß 2013 Va ´ zquez-Marrufo et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: Funding came from Ministerio de Economı ´a, Gobierno de Espan ˜ a, SEJ2007-65343, Asociacio ´ n Neuroinvest. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * E-mail: marrufo@us.es Introduction The study of human cognition is one of the biggest challenges in neuroscience. One crucial aspect is to obtain measures that allow it to be studied objectively. It is desirable that such measures be stable over time while the cognitive mechanism is engaged in performing the task. For several decades, multiple studies have been conducted to check the stabilities of different measures of cerebral activity based upon electroencephalography (EEG) and more specifically in the cognitive potentials field (for instance, the P3 component). It is necessary at this point to emphasize that when studying the retest reliability of an ERP there are two factors at play: a) the measurement of the signal may be noisy (for example due to recording artifacts) and b) the signal itself that may vary from one session to the next. Therefore, the identification of traits in this kind of analysis must be cautious. To study the reliability of the P3 parameters, diverse issues have been considered in the design of these tests: (a) which parameters are to be analyzed in the study (latency, amplitude and/or topography); (b) whether the subjects in a group are to be compared with each other or with a comparative group; (c) what cognitive paradigm is to be used (oddball, stroop, etc); (d) whether stability is to be studied in a single session (for example, comparing the first and second halves of the experiment) or whether time should elapse between the repeated measures (days, weeks, months, years). Since the present study is focused on stability among sessions separated by intervals typically employed in longitudinal studies (pharmacological treatments, neuropsycholog- ical rehabilitation programs, etc.), no review of studies focused on intrasession stability will be included (detailed information can be found in [1,2,3]). The results of studies to check stability between two sessions separated by periods of days, months or even years have commonly suggested that the P3 parameters (latency and amplitude) show a moderate to high level of reliability (ranging from 0.40 to 0.99) (see [1,4,5,6]). However, most of these studies analyzed a small number of electrodes and could not examine the reliability of the P3 topography in follow-up studies with high PLOS ONE | www.plosone.org 1 May 2013 | Volume 8 | Issue 5 | e62523