Topography of evoked brain activity during mental arithmetic and language tasks: sex differences

We studied visual information processing using two different tasks in a gro up of 10 female and 10 male healthy, right-handed adults. Subjects solved a rithmetic tasks shown sequentially on a computer monitor, and they also com pared words presented as anagrams. The experimental design allowed us to co mpare the effects of reading or actively processing a given stimulus. Task difficulty was varied in three steps ('easy', 'medium', 'hard') after an in dependent group of 81 young adults had judged the stimulus material accordi ng to difficulty by answering questionnaires. Brain activity was recorded f rom an array of 30 electrodes extending from the inion to 5% anterior of F- 2. For each subject mean potentials were averaged off-line after screening the EEG for artifacts. Components were determined quantitatively as epochs of stable topography resulting in 10 independent components occurring withi n 1200 ms after stimulus onset. Significant effects were seen with field strength and scalp topography: sim ply reading the stimuli yielded significantly smaller amplitudes than when the subjects actively processed the same stimuli. Females had consistently larger global field power than males, and they also displayed different sca lp field topography of various components. In addition, processing anagrams was accompanied by larger field strength than mental arithmetic. The scalp field distributions were also affected by sex, task type and difficulty in dicating the activation of different neuronal assemblies during visual info rmation processing of males and females. Many effects were seen at short la tencies in the order of 70-120 ms indicating very early selective processin g of visual stimuli where specific differences were introduced by sex and t ask parameters. (C) 1999 Elsevier Science Ltd. All rights reserved.