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Event-related brain potentials (ERPs) were used to investigate thetime course of memory processes following the presentation of faces. Following a phase in which subjects were asked to memorise faces presented on a computer screen (study phase) they had to distinguish the previously presented faces from others new to the experiment (test phase). We found that in a time period from 250-350 ms after onset of stimulus presentation ERPs show higher negativity for both repeated and novel faces in the test phase compared to the study phase. This situation dependent effect is most pronounced in occipito-temporal regions. We conclude that memory retrieval for faces is a sequential process: The early part of this process constitutes preparation for the retrieval of stored information, and a later part of the process comprises the discrimination between repeated and novel faces.

We assessed serial event-related potentials (ERPs) as well as neuropsychological and clinical test findings in a group of multiple sclerosis (MS) patients (n = 14) treated with interferon beta-1b (INF-beta-1b) compared to normal controls (n = 14). All investigations were done within 1 week before INF-beta-1b therapy was started and 12 months later. An auditory oddball paradigm was employed. No significant differences in the N100, P200, N200 or P300 latencies between patients and control group were found, but 3 out of 14 MS patients developed abnormal P300 latencies (more than 2 standard errors from the mean) after 1 year of INF-beta-1b therapy. This was not reflected by the respective neurological impairment as assessed by the Expanded Disability Status Scale score. ERPs might be a useful tool in clinical studies in order to evaluate drug effects on cognition, but for a final statement, the analysis of ERPs in a larger group of patients is required., (Copyright 2000 S. Karger AG, Basel)

Brain potentials were recorded from 15 healthy young subjects during the performance of a word recognition task. During the study phase, subjects had to intentionally memorise a series of words. These words were presented again together with the same number of new words in a following test phase where the instruction was to discriminate between repeated words and new words. We compared event-related potentials (ERPs) evoked by correctly identified repeated words (hits) and ERPs evoked by incorrectly classified new words (false alarms). Although both types of words were thought to be repeated the ERPs indicated differences between these two conditions starting at about 450 ms after the stimulus onset. These differences were mostly pronounced over frontal scalp locations but occurred also over parietal scalp locations (false alarms produced significantly more negative going ERPs than hits). We interpret that frontal and parietal brain areas show greater activation during false recognition because of a more intensive search for item representations.

First, we recorded brain potentials from 15 healthy young subjects during the performance of a word/non-word discrimination task. During continuous visual presentation, some of the meaningful words were repeated after 86-94 s. We found a significant decrease of response time associated with the classification of repeated words which is an index for priming, an unconscious brain process. However, event-related potentials (ERPs) did not differ significantly between first and second presentations. Second, we recorded brain potentials during a following recognition test. Some of the meaningful words which were presented only once during the semantic discrimination task were repeated and had to be discriminated from randomly interspersed new words. We compared ERPs produced by incorrectly classified repeated words (misses) with ERPs produced by correctly classified new words (correct rejections). We found early ERP differences between 250 and 400 ms and later differences starting at about 500 ms after the stimulus onset. The early effect occurred over parietal scalp locations and the later effect over frontal, parietal and occipital scalp locations. This is evidence for unconscious brain activity related to the processing of missed repeated words. We suggest that the later frontal effect we found is due to an enhanced effort of the retrieval of item representations during word recognition and that the earlier parietal effect reflects partial recognition.

In a recognition memory experiment we recorded event-related brain potentials (ERPs) following the presentation of faces. We compared correctly classified repetitions of faces (hits) with new faces classified as repeated (false alarms). Stimulus-related averaging yielded significantly more negative ERPs to false alarms between 750 and 900 ms after onset of stimulus presentation. With response-related averaging we found significantly more negative ERPs to false alarms within the last 100 ms before movement onset. The differential activity was distributed over central and frontal regions and was still present in the period after the response. We interpret the phenomenon as an electrophysiological manifestation of false recognition as described by Schacter et al. (Schacter, D.L., Norman, K.A. and Koutstaal, W., The cognitive neuroscience of constructive memory, Annu. Rev. Psychol., 49 (1998) 289-318). False recognition could be the result of a preliminary decision based on illusionary familiarity and be associated with post-retrieval processing.