Positive Event-related Potentials Research Articles

Effects of focused selective attention tasks on event-related potentials in autistic and normal individuals

Event-related potentials (ERPs) and behavioral responses were recorded from autistic and normal subjects under two focused selective attention conditions. In each condition, subjects were presented with an identical stimulus paradigm - a random sequence of 50 msec sounds and flashes occurring at interstimulus intervals ranging between 0.5 and 1.5 sec. The sequence consisted of rare auditory (12.5%), rare visual (12.5%), standard auditory (37.5%) and standard visual (37.5%) stimuli. In the focal auditory condition, subjects pressed a button to the rare auditory target, and a in a focal visual condition, they pressed a button to the rare visual stimuli. When normal subjects detected target stimuli in a given attended modality, all stimuli in the attended modality produced enhanced negative ERP responses at frontal electrode sites (i.e., auditory Nde, Ndl, and Nc; visual N270 and Nc) and enhanced positive ERP responses at posterior electrode sites (i.e., P3b and visual P400). In the autistic subjects, in contrast, all auditory and visual attention-related negativities recorded in the auditory and visual focused attention tasks were not in evidence. P3b was significantly diminished in size. The results suggest that abnormalities in the neurophysiological mechanisms of selective attention may underlie the cognitive deficits in autism. The present report and its companion papers are the first reports of the neurophysiological correlates of selective attention in autism.

Potentiels evoques cerebraux et reconnaissance consciente et non consciente des visages: Application a l'etude de la prosopagnosie

Twelve normal subjects and a prosopagnosic patient were tested in a classification task of a random display of well-known among unknown faces. Each face was presented several times. Event-related potentials (ERP) and reaction time (RT) were studied as a function of face repetition and familiarity. For normal subjects, the greater the repetition level, the more positive ERPs were on both hemispheres: between 250 and 600 msec. Moreover, the familiarity of faces modified ERPs between 350 and 600 msec. In contrast for the patient, the greater the repetition, the more negative the ERPs were. This "negative effect" was maximum on right parieto-temporal leads and was longer for unrecognized well-known than for unknown faces. These results support a differential processing of faces as a function of their memory representations for both normal subjects and patients. They further demonstrate the existence of covert face recognition processes in prosopagnosia.

Abnormal P300 Responses in Schizophrenic Children

The auditory information processing abilities of psychotic children were examined using an “oddball” P300 protocol. Event related potentials (ERPs) were recorded from nine children (age range 10-13 years) diagnosed as having schizophrenia or schizotypal personality disorder, nine age-matched normal children, and nine younger normal children (age range 6-8 years). In all three groups, a positive ERP component in the 300-400-msec range was obtained. Statistical analyses of the ERPs indicated that this component differed across task conditions in both groups of normal children but not in the group of psychotic children.

Effects of visual field, stimulus degradation, and level of practice on event-related potentials of the brain.

ABSTRACTThe present study reports the results of an experiment in which subjects were instructed to indicate whether letter‐pairs that were randomly presented in the center and peripheral (left and right) visual fields were semantically same or different. Letter‐pairs could be either intact or perceptually degraded, and all subjects participated in 3 consecutive sessions of the experiment. The results showed that event‐related‐potential (ERP) components were strongly affected by the visual field of presentation of stimuli. Center field stimuli elicited late positive components (P630, SW) of larger amplitude than peripheral field stimuli, at all electrode locations. At lateral electrode sites, N200 components were always larger (more negative), and late positive components were consistently smaller (less positive) to contralaterally than ipsilaterally presented stimuli. However, the contralateral negativity of N200 was much larger over the right than left regions of the scalp, while positive ERP components showed a more symmetrical distribution of the contra‐ vs. ipsilateral stimulation effect. These results are discussed in relationship to cognitive aspects of information processing, as well as the neural origin of endogenous ERP components.

Reaching-related potentials in caudate nucleus and cerebellum of rats

Electrical correlates of the lateralized reaching reaction was studied in rats with implanted electrodes. Averaged event-related potentials (ERPs) in the cerebellar dentate nucleus consisted of a negative wave coinciding with reach onset and followed 70 msec later by a positive deflection. The most prominent component of the more variable caudate ERPs was a negative wave culminating 60--120 msec after reach onset. The positive and negative ERP deflections corresponded to inhibitory and excitatory reactions respectively, at the single neuron level.

Multiple Positive ERP Components in Visual Discrimination Tasks

Publisher Summary This chapter discusses multiple positive event-related potential (ERP) components in visual discrimination tasks. The evidence that the ERPs elicited during task-oriented paradigms consist of several late positive components has steadily accumulated. These components have been reported to occur within the latency range of from 200 to 600 msec. Psychological constructs for these components have varied from frequency sensitivity for the earlier of these peaks, to utilization of feedback information and response selection for the longest latency positivities reported. The most oft-used criterion for judging the uniqueness of a given peak has been scalp distribution. The visual identification and measurement of distinct peaks leads to problems, since components interact both spatially and temporally at the scalp. The factor analytic technique has been used in certain cases to disentangle these overlapping components, with the time courses of the resultant loading functions allowing the investigator to associate factors with visually identified ERP components.