The effect of sex and task difficulty of EEG alpha activity in association with arithmetic.

The effects of arithmetic task difficulty and sex of subject on parietal alpha activity (8-13 Hz) and alpha asymmetry (RH-LH/LH + RH) were investigated using a series of eyes closed self-generated tasks. Sixteen right-handed subjects (8 males, 8 females) were asked to carry out sets of successive addition and multiplication tasks divided into three levels of difficulty. In comparison to a simple counting task, more difficult tasks showed lower alpha power. All tasks except the counting condition and the successive addition of 3's task (right hemisphere only) were associated with below-baseline levels of alpha activity. When laterality ratios were considered, all addition tasks and the easy multiplication task were found to be relatively left lateralized in relation to baseline and spatial task values. A sex by task interaction, however, was detected. Males exhibited relative left hemisphere activation for the more difficult addition task and the multiplication task of medium difficulty. Females, on the other hand, showed relative left lateralization for the easy tasks and one of the more difficult addition tasks. When the harder arithmetic tasks were repeated, females showed an increase in relative left hemisphere activation for one of the more difficult multiplication tasks. Males computed the problem sets significantly faster than females. These data suggest that the effects of difficulty may interact with ability such that ability may determine the maximum level of relative hemisphere activation achieved within a given difficulty range. While no absolute differences in asymmetry were found between the sexes, females tended to show greater asymmetry differences between spatial and arithmetic tasks. Finally, no significant relationship was found between the degree of alpha asymmetry and performance measures.