State-of-the-art in measuring brain signals of cognition

Useful information about the anatomical distribution of brain systems involved in cognition has been obtained by measuring regional blood flow, as well as glucose and oxygen uptake, with radioactive isotopes and tomographic reconstruction procedures. However, critical information about the split-second timing of neurocognitive processes has been unobtainable with these procedures. Electroencephalograms (EEGs) have the requisite temporal resolution but have been unsatisfactory in terms of spatial resolution. The engineering problem is one of untangling the spatially confounded information recorded at the scalp in order to relate the signals to their unique anatomical generating sites. One fruitful approach which is currently being pursued is to further develop EEG and magnetoencephalogram methods without sole reliance on computing equivalent dipole sources. This requires, first, simultaneously sampling the fields at the scalp from a large number of loci. Second, methods of spatial deconvolution are under development at several laboratories that attempt to compensate for the distortion of the fields as they pass through the tissues intervening between the brain and scalp