The invention relates to a method and apparatus for examining and mapping the reactivity of and connections between different cortical areas. In the method an electromagnetic stimulus is induced in the interior parts of the head and the electromagnetic field generated around the skull is measured by electrical means (1). According to the method, the electromagnetic activity of the brain is measured using multichannel equipment, artefacts caused by the stimulus are eliminated from the signal containing the electromagnetic activity, a visualization of the activity changes in the measured signals is formed, and the areas of the head related to said activity generating said electromagnetic field are localized, or alternatively, the maximum of the sensitivity pattern of the multichannel activity measurement system is focused to a desired point