A brain computer interface (BCI) is a system aimed to provide the brain with an additional channel of communication and control, which does not depend on the normal output pathways. This dissertation is focused on the study of signal processing techniques to address two issues of current BCI methodologies. These issues are related to spatial filtering techniques and approaches for capturing temporal behavior of electrical brain signals recorded through two different modalities: Electroencephalography (EEG) and electrocorticography (ECoG). Concerning to spatial filtering, a non-supervised algorithm based on the steepest descent method to adapt spatial filter’s coefficients for preprocessing ECoG signals is proposed.