Robert J. Strandburg

Midlatency auditory evoked responses: differential effects of a cholinergic agonist and antagonist

The effects of a cholinergic antagonist (scopolamine) and agonist (physostigmine) on the auditory middle latency evoked responses (MLRs) were studied in 7 normal male volunteers. Scalp recordings were made from a central (Cz) electrode referenced to linked ear lobes on one channel and to a non-cephalic, sternovertebral reference on a second channel. Three components were statistically analyzed for changes in latency and amplitude: Pa, with peak positivity in the 25-40 msec latency range, Nb, with peak negativity 40-50 msec, and P1, with peak positivity 50-65 msec. Control recordings included responses to click rates of 1, 5, 8 and 10/sec; as has been previously reported, P1 showed a marked decrease and disappeared at the faster rates of stimulation whereas Pa showed no change in amplitude. Intravenous injections of scopolamine resulted in a rapid and complete disappearance of P1 and a slight increase in Pa; concurrently, the subjects reported feeling drowsy but were awake with eyes open through the recordings. Subsequent injections of physostigmine resulted in a rapid reversal of the scopolamine effects so that the subjects became alert, Pa decreased, and P1 reappeared and increased to control amplitudes. Rapid click rates caused P1 to diminish, as in the control period, indicating a common P1 recovery cycle in both the control and physostigmine conditions. These data are discussed in terms of the hypothesis that the P1 generator system is comprised of a cholinergic brain-stem-thalamic component of the ascending reticular activating system.

Continuous-processing-related event-related potentials in children with attention deficit hyperactivity disorder

Visual information processing in children with attention deficit hyperactivity disorder (ADHD) was studied using event-related potentials recorded during two versions of the Continuous Performance Task (CPT). ADHD children made more errors, and had longer reaction times than normal children on both the single- and dual-target CPT. Event-related potential waveforms were normal in the ADHD children with reference to early processing stages, i.e., contingent negative variation, P1-N1 laterality, and processing negativities, suggesting that ADHD children did not differ in their level of preparedness or their ability to mobilize resources for target identification and categorization. With respect to later processing, P3 amplitude was reduced in the ADHD group, whereas P3 latency was longer than normal. ADHD children had a diminished late frontal negative component, suggestive of reduced involvement in postdecisional processing.

Event-related potential correlates of linguistic information processing in schizophrenics.

Event-related potentials (ERPs) were recorded from adult schizophrenics and age- and education-matched normal controls during performance of an idiom recognition task involving judgments of the meaningfulness of idiomatic, literal, and nonsense phrases. Schizophrenics produced more errors and had prolonged reaction times while attempting to correctly differentiate meaningful from meaningless phrases. An ERP correlate of that deficit was a larger than normal N400 to idioms and literals, with no difference in N400 amplitude to nonsense phrases. This result was interpreted as evidence that the influence of the linguistic context provided by the first word of two-word idiomatic and literal phrases is reduced in schizophrenia. Schizophrenics also showed reduced amplitude P300.

Event-related potentials in high-functioning adult autistics: Linguistic and nonlinguistic visual information processing tasks

Event-related potentials (ERPs) were recorded from high-functioning adult autistics and age- and IQ-matched normal controls during performance of two non-linguistic information processing tasks, the Continuous Performance Task (CPT) and Span of Apprehension (SPAN), and an Idiom Recognition Task (IRT) involving idiomatic, literal and nonsense phrases. The autistics exhibited behavioral deficits only when attempting to identify idiomatic phrases. The ERP correlate of that deficit was greatly reduced N400 to idioms. In addition, autistics produced larger N1 amplitudes in all tasks, and larger P3s in the IRT and CPT.

Event-related potential concomitants of information processing dysfunction in schizophrenic children ☆

ERPs were recorded from 10 schizophrenic and 13 normal children during the performance of the Span of Apprehension task (Span). This task involves the discrimination of a randomly placed target letter among distractors, and it has been shown to discriminate between normal and schizophrenic individuals. The EEG was recorded at 7 scalp loci, and ERPs were averaged over a 1500 msec interval initiated by a warning tone which preceded the visual Span stimuli by 500 msec. Stimulus arrays were grouped into 4 levels of difficulty. The data from both subject groups were combined in a single principal components analysis (separate PCAs exhibited few differences between groups) generating 8 rotated factors which were readily interpreted in terms of conventional ERP components. Factor scores for the two groups were examined using Analysis of Variance. The schizophrenic children produced a small CNV which was slow to develop and resolve as well as diminished amplitudes for the N1, P3 and slow wave components. This suggests that these children are impaired in their ability to regulate processes involved in the mobilization and direction of attention and the discrimination of target stimuli. Significantly, the schizophrenic children did not show progressive increases in N1 and SW amplitudes in response to increases in information processing demand (array difficulty) as was the case in the normal children. ERP components of the schizophrenic children were most aberrant at frontal leads, but midline and lateralized deficits were also seen at vertex and posterior recording sites.

PET and P300 relationships in early Alzheimer's disease

The P300 (P3) wave of the auditory brain event-related potential was investigated in patients with probable Alzheimers disease to determine whether P300 latency discriminated these patients from controls and whether prolonged P300 latency correlated with rates of brain glucose metabolism as measured by Positron Emission Tomography. P300 latency was prolonged by more than 1.5 standard deviations from age expectancy in 14 of 18 patients, but none of 17 controls. In these subjects P300 latency was shown to be inversely correlated with relative metabolic rates of parietal and, to a lesser extent, temporal and frontal association areas, but not with subcortical areas.

Event-Related Potential Correlates of Impaired Attention in Schizophrenic Children

Electrophysiological correlates of focused attention were studied in 13 schizophrenic and 19 age- and gender-matched children. Subjects performed a version of the Continuous Performance Task (CPT) in which a target was designated as any digit from 0 through 9 occurring on two successive stimulus presentations. Signal digits were surrounded by distractor digits which varied in position, value, and number. Event-related potentials (ERPs) elicited by each stimulus of a target pair were recorded from midline and homologous parietal, temporal, and occipital electrode placements. Schizophrenic children made significantly more errors of omission and commission than normal children. The amplitude and time course of the intertrial CNV was the same for both groups. There was a circumscribed amplitude asymmetry, left smaller than right, for the P1/N1 and P2 measures which was greater in normal than in schizophrenic children. The P3 component was significantly larger to the second stimulus of the target pair than to the first for both groups, and larger for the normal than the schizophrenic children to both stimuli.

The Search for the Psychobiological Substrate of Childhood Onset Schizophrenia

This paper describes a program of neurobehavioral research aimed at: (1) isolating core information processing impairments in childhood onset schizophrenia, and (2) identifying structures in the central nervous system which mediate those impairments. Children meeting DSM-III criteria for schizophrenia, mental age matched normals, and younger normals were administered a series of visual information processing tasks. The results of these studies suggest that controlled attentional processes, which normally develop during middle childhood, are impaired in schizophrenic children while more automatic modes of attending are relatively intact. Convergent evidence for this conclusion was provided by event related potentials recorded from 7 scalp loci while children were performing on one of the tasks used in the first project. The schizophrenic children produced a small contingent negative variation (CNV) which was slow to develop and resolve as well as diminished amplitudes for N1, P3, and slow wave components. This suggests that these children are impaired in their ability to regulate the mobilization and direction of attention and to discriminate target stimuli. Event-related potential components of the schizophrenic children tended to be most deviant at frontal leads, but midline and lateralized deficits were also seen at vertex and posterior recording sites. The relationship of these impairments in controlled attentional processes to the phenomenology of childhood onset schizophrenia is discussed.

Reduced attention-related negative potentials in schizophrenic children ☆

ERPs were recorded from normal and schizophrenic children during performance of a reaction time task (RT) followed by a complex visual discrimination, the span of apprehension task (Span), sensitive to vulnerability factors in schizophrenia. Subjects responded rapidly to the onset of the visual arrays in the RT condition and differentially to the presence of 1 of 2 target letters in the Span condition. The EEG was recorded at 19 scalp sites and ERPs included activity 1 sec before through 1 sec after Span array onset. Difference potentials (Span-RT) were computed to remove unvarying exogenous activity, thus isolating endogenous activity associated with the processing demands of the Span task. When RT and Span task ERPs are compared, schizophrenic children produced a significantly smaller than normal increment in endogenous negative activity. This endogenous negativity differed in its topography and time course from the exogenous components (P1, N1 and P2), and most likely reflects attentional effort associated with serial search, pattern recognition and stimulus identification. We believe that the current results support the position that schizophrenics are impaired in their ability to allocate adequate attentional resources for the processing of the Span stimuli. It is important to note that this deficit is apparent quite early in discriminative processing.

Continuous-processing related ERPS in adult schizophrenia : Continuity with childhood onset schizophrenia

BACKGROUND Previous work with schizophrenic children disclosed deficits on two continuous performance tests (CPTs) and ERP indices of reduced attentional resource allocation. METHODS The two CPTs were administered to adult schizophrenics and matched control subjects. The simple CPT required only that the subject respond whenever the target digit was displayed. The complex version required a response whenever any digit was displayed on two successive trials. Event-related potentials (ERPs) were recorded during task performance. RESULTS Schizophrenics had fewer hits on both CPT versions, showed a greater drop in performance from the simple to the complex CPT, and took longer to respond than controls. The processing negativity (Np) showed a greater amplitude increase from nontarget to target in normals than in schizophrenics, and the overlapping P2 component was more negative in normals. P3 latency was longer in schizophrenics, but P3 amplitude did not differ. CONCLUSIONS Group performance and processing negativity effects replicated those from an earlier study of schizophrenic and normal children administered the same versions of the CPT, suggesting similar abnormalities in the allocation and modulation of information processing resources.