ELSEVIER Electroencephalography and clinical Neurophysiology 94 (1995) 175-182 o EEG activation patterns during the performance of tasks involving different components of mental calculation Thalla Fernfindez *, Thalla Harmony, Mario Rodrlguez, Jorge Bernal, Juan Silva, Alfonso Reyes, Erzsrbet Marosi ENEP Iztacala Universidad Nacional Autrnoma de Mdxico, Jos~ Clemente Orozco 36-2, Colonia Ciudad de los Deportes, Mexico City, D.F. 03710, Mexico Accepted for publication: 24 September 1994 Abstract In this study we demonstrate the existence of different patterns of EEG activation during the performance of 4 different tasks involving different components of mental calculation in normal subjects. The EEG was recorded in all monopolar leads of the 10/20 system using linked ear lobes as reference. Absolute and relative power were calculated in the delta (1.5-3.5 Hz), theta (3.5-7.5 Hz), alpha (7.5-12.5 Hz) and beta (12.5-19 Hz) bands. The tasks were presented randomly and the EEG segments preceding presentation of the stimulus were considered as the rest corresponding to the task requested by the stimulus. Tasks were of 4 different types, involving number comprehension, recogaition of mathematical symbols, the calculation process and the spatial component. ANOVAs between the rest periods showed no differences in any band. Neither did ANOVAs between tasks. However, other variables (task minus rest), which were calculated as the differences in power between task and rest respectively, showed significant differences between tasks in the delta and beta bands in the frontal lobes. In addition, new variables were calculated as the difference between tasks, since many factors were common across several tasks. These variables correspond to the EEG change due to a specific component of mental calculation. Significant differences were obtained in delta and theta bands in fight posterior areas and in the beta band in frontal areas. We concluded that the EEG differences obse~:ved during different components of mental calculation suggest the participation of different networks. Keywords: Mental calculation; EEG; Frequency analysis; Absolute power; Relative power; EEG activation 1. Introduction Several studies have demonstrated clear differences in EEG spectral parameters between rest and several cogni- tive tasks, and even between different mental tasks (Petsche et al., 1986). Even when strict experimental control of efferent activities, the characteristics of the stimulus and of performance-related factor~ were applied, Gevins et al. (1979) reported differences between spectral variables of the EEG recorded during tasks that involved distinct logi- cal and spatial cognitive operations, such as block rotation, letter substitution and mental arithmetic. In a more recent paper, Keirn and Aunon (1990) were able to distinguish among various mental tasks with a high degree of accu- racy, using spectral EEG parameters. The tasks used were ° Corresponding author. Tel.: (525) 623 1294; Fax: (525) 390 5900. a non-trivial multiplication problem, the rotation of an image, and the mental composition of a letter to a friend. Two features characterize the papers reporting differences in EEG activity between the tasks: (1) several brain re- gions were involved; (2) the tasks used activate different neural systems. In particular, we were interested in the analysis of mental calculation using different tasks which have been related to different aspects of this process. The majority of papers relating EEG activity with mental calcu- lation have used only one type of task: addition or subtrac- tion (Volavka et al., 1967; Kakizaki, 1985; Petsche et al., 1986; Earle, 1988; Inouye et al., 1993), or a sequence of arithmetical operations (Glass, 1964; Beaumont et al., 1978; Etevenon, 1986). The analysis of impairment in the performance of calcu- lation tasks in single case studies (Warrington, 1982; Mc- Closkey et al., 1985), as well as the correlation between specific impairments observed in different arithmetic sub- 0013-4694/95/$09.50 © 1995 Elsevier Science Ireland Ltd. All rights reserved SSDI 0013-4694(94)00262-2 EEG 94025