P300 ASYMMETRIES IN FOCAL BRAIN-LESIONS ARE REFERENCE DEPENDENT

In 6 patients with lesions of frontal, parietal and temporal lobe, in 4 patients affected by primary progressive aphasia (PPA) and in 56 age -matched controls, event-related potentials (ERPs) to an auditory odd- ball paradigm were recorded with the linked earlobe reference (LER) an d with a computer calculated average reference (AR), excluding the two linked earlobe derivations. Latencies, amplitudes and scalp distribut ion of the earlier ERP components (P1, N1, P2, N2) were within normal limits for both LER and AR recordings. P300 scalp distribution in pati ents was normal when LER was used. When P300 was recorded using AR, th e scalp distribution was statistically different from normal distribut ions in all patients. A negativity, instead of the positive P300 obser ved in controls, was recorded in patients from leads corresponding to the affected hemisphere.