**4. Problems related to use of EEG mapping**

One of the major problems of the brain maps is that similarity of brain mapping to classical neuroimaging techniques (CT, MRI or PET scans) is illusory. In classical neuroimaging techniques there is a direct and close correspondence between the image and the affected structure. On the contrary, in the case of topographic changes in electrical activity, there is a more complex relationship to function and cerebral pathology.

Cerebral maps could be easily misinterpreted. In fact, the selection of what to map is at the discretion of the user, there aren't clear standards and interpretation is strongly subjective.

Maps do not distinguish between cerebral potentials and artefacts or between the feature of interest and a superimposed activity with different topography. Consequently, it is essential that users analyse with attention the trace recorded before plotting cerebral maps.

Another problem of quantitative EEG analysis is to determine the best method of deriving the signal to be analysed. Common reference derivation seems be the obvious choice. However asymmetrical activity involving ears reference is particularly open to misinterpretation so that asymmetries in alpha activity may be shown as reversed [15]. A paradox of EEG mapping is that when a focal activity occurs at

or near the reference, the deflections produced are greatest on channels recording from the most distant electrodes [16]. This effect is particularly liable to misinterpretation in spectral maps: thus focal temporal delta activity may be misallocated to the contralateral central region [17].
