Event-related brain potentials (ERP) were used to study cognitive processes such as short- and long-term memory, spatial attention and visual search, mental rotation, mental arithmetic, and language comprehension. ERP studies of normal subjects were intended to reveal the brain mechanisms underlying cognition. Studies of patients with neuropsychiatric disorders were intended to provide information on the physiological sources of these cognitive processes while allowing us to characterize better the patients' information processing deficits. Data analysis continues on studies of temporal lobectomy patients, Turner's patients, and the maturation of cognitive processes. ERP studies of dementia are continuing for patients with Alzheimer's disease while data collection has been completed for patients with HlV disease and progressive supranuclear palsy. The results from the HIV and PSP studies indicate that, in the earliest stages of subcortical disease, processing at the cortical level is more affected than processing at the subcortical level (i.e., resembling a cortical dementia). This pattern reverses as the subcortical disease progresses. Studies of the mechanisms underlying and affecting attentional processes continue. Data collection was completed recently in two studies, one on how normal controls visually search a spatial array for items previously stored in short-term memory and one on the effects of on attention in patients with chronic fatigue syndrome and normal controls. Studies with Daniel Ruchkin have been aimed at understanding a newly emerging class of ERP components known as slow waves. Completed studies have investigated the processes of mental arithmetic, mental rotation, and short-term memory. Data collection is nearly complete in an experiment on the differences between rehearsal processes for verbal and spatial material. Studies with Wolfgang Miltner have been aimed at providing additional data on the neural sources of ERP components. Completed studies have provided a comparison of the ERP components elicited by auditory and somatosensory stimuli using large electrode montages. A new experiment was recently finished so that the neural source localization program, BESA, can be applied to the data. Patient and control data have been used to validate the predictions of Johnson's model of the variables controlling P300 amplitude. These data revealed that, contrary to the widely accepted notion, the P300 is a modality-dependent component whose amplitude represents the sum of a number of distinct neural generators which we are attempting to characterize and localize.
