THE EFFECT OF REFERENCE-ELECTRODE CHOICE ON THE SPATIAL-RESOLUTION OFTOPOGRAPHICAL POTENTIAL MAPS IN THE DISCRIMINATION OF DEEP CEREBRAL SOURCES

Although scalp potential distributions do not uniquely determine the l ocation and configuration of neural generators, they are important bec ause they provide the necessary conditions that any hypothesized sourc es must satisfy and suggest a basis for testing alternate source hypot heses. One problem that could confound the correct interpretation of s calp potentials is the choice of reference electrode. Changing the ref erence may make activity patterns and waveform components appear and d isappear (Pascual-Marqui et al. (1988) Int. J. Neurosci., 43: 237-249) . The cortical imaging technique (CIT), a method for approximating pot ential fields on the cortical surface, was used to test the effects of the choice of reference electrode on these fields. Simulated and empi rical evoked potential scalp-recorded referential data were mathematic ally analyzed for the case in which the reference (linked-ears) was ar bitrarily assumed to be at zero potential, and the case in which the r eference was the 'average' electrode, the arithmetic mean of all of th e scalp-recorded voltages in the referential montage. The results for the two references were similar. This is encouraging because potential measurements relative to a point at infinity (zero potential) are nev er available and the assumption that any actual reference used for a r ecording is at zero potential is therefore suspect.