Increased distractibility in schizophrenic patients. Electrophysiologic and behavioral evidence

The inability of schizophrenics to filter irrelevant information has often been implicated in the psychopathology of schizophrenia. Despite numerous attempts at characterizing the behavior of schizophrenics in the presence of distractors, evidence of increased distractibility has been equivocal due to the difficulty of assessing simultaneously the behavioral and neurophysiological effects of distracting stimuli. We report the results of an experiment in which event-related potential and performance measures were used to assess distractibility during reaction time tasks under different distracting conditions. The results supported the view of an increased distractibility in schizophrenic patients. Event-related potential data suggested that in schizophrenic patients, a reduced amount of processing resources is allocated to process external stimuli and attention is abnormally apportioned to task-irrelevant vs task-relevant stimuli.

The cerebellum: 3. Anatomic-MR correlation in the coronal plane

Thin (5-mm) coronal high-field (1.5-T) MR images of four human brain specimens and 14 normal volunteers were correlated with myelin-stained microtomic sections of the specimen cerebella. The primary white-matter tracts innervating several hemispheric (posterior quadrangular, superior, and inferior semilunar, gracile, biventer, tonsil) and vermian (declive, folium, tuber) lobules are oriented perpendicularly to the coronal plane of section and are shown well on proton-density-weighted (long TR/short TE) and T2-weighted (long TR/long TE) spin-echo images, which provide excellent contrast between gray and white matter. Several of the surface sulci and fissures of the cerebellar hemispheres (including the superior posterior, horizontal, secondary, and posterolateral fissures) also course perpendicular to the coronal plane and are depicted well on T1-weighted (short TR/short TE) and T2-weighted images, which maximize contrast between CSF and parenchyma. The opportunity for side-to-side comparison of the hemispheres is a distinct advantage of the coronal view. Nevertheless, more obliquely oriented surfaces (preculminate, primary, inferior posterior, inferior anterior, and intrabiventral fissures) and deep hemispheric structures (primary white-matter tracts to central, anterior quadrangular, and floccular lobules) may be obscured by volume-averaging in the coronal plane; moreover, much of the finer anatomy of the vermis is depicted poorly. The constant surface and deep anatomy of the cerebellum revealed on coronal images in normal volunteers encourages detailed mapping. MR imaging in the coronal plane should be especially useful in identifying, localizing, and quantifying normal and abnormal morphologic differences between the cerebellar hemispheres.

The cerebellum in sagittal plane--anatomic-MR correlation: 2. The cerebellar hemispheres

Thin (5-mm) sagittal high-field (1.5-T) MR images of the cerebellar hemispheres display (1) the superior, middle, and inferior cerebellar peduncles; (2) the primary white-matter branches to the hemispheric lobules including the central, anterior, and posterior quadrangular, superior and inferior semilunar, gracile, biventer, tonsil, and flocculus; and (3) several finer secondary white-matter branches to individual folia within the lobules. Surface features of the hemispheres including the deeper fissures (e.g., horizontal, posterolateral, inferior posterior, and inferior anterior) and shallower sulci are best delineated on T1-weighted (short TR/short TE) and T2-weighted (long TR/long TE) sequences, which provide greatest contrast between CSF and parenchyma. Correlations of MR studies of three brain specimens and 11 normal volunteers with microtone sections of the anatomic specimens provides criteria for identifying confidently these structures on routine clinical MR. MR should be useful in identifying, localizing, and quantifying cerebellar disease in patients with clinical deficits.

The cerebellum in sagittal plane--anatomic-MR correlation: 1. The vermis

Correlation of thin (5-mm) sagittal high-field (1.5-T) MR images of three brain specimens and 11 normal volunteers with microtome sections of the human cerebellar vermis and hemispheres demonstrates that proton-density-weighted (long TR/short TE) and T2-weighted (long TR/long TE) spin-echo pulse sequences provide the greatest contrast between gray and white matter. These images also can display (1) the corpus medullare and primary white-matter branches to the vermian lobules, including the lingula, centralis, culmen, declive, folium, tuber, pyramis, uvula, and nodulus; and (2) several finer secondary branches to individual folia within the lobules. Surface features of the vermis including the deeper fissures (e.g., preculminate, primary, horizontal, and prepyramidal) and shallower sulci are best delineated by T1-weighted (short TR/short TE) and T2-weighted images, which provide greatest contrast between CSF and parenchyma. Given that the width of the normal vermis varied from 6 to 12 mm in our volunteers, the acquisition of thin slices (less than or equal to 5 mm) was required to minimize volume averaging of the cerebellar hemispheres with the vermis on a midline sagittal MR section. Knowledge of the detailed normal anatomy of the cerebellar vermis on sagittal MR images can assist in the identification of various pathologic alterations.

Brainstem and middle latency auditory evoked potentials in autism and developmental language disorder

Brainstem auditory evoked potentials (BAEP) and middle latency responses (MLR) were studied in 8 nonretarded subjects with infantile autism (mean age = 23.3, SD = 2.8), 8 subjects with receptive developmental language disorder (mean age = 16.3, SD = 1.4), and normal control subjects matched to each group for age, gender, and Performance IQ. Click stimuli were delivered monaurally to the left and the right ear and binaurally for both the BAEPs (70-dB HL, 7/sec) and the MLRs (60-dB HL, 13/sec). Amplitudes and latencies (Waves I to VI), interwave latencies (III-V, I-V, and I-III), and Wave I/V amplitude ratio of the BAEPs were determined for each group. For the MLR study, Wave Na, Pa, and Nb latencies, and Wave Na-Pa and Pa-Nb amplitudes were calculated. There were no consistent differences in the BAEP and MLR characteristics of the control and the experimental groups. These results suggest that the abnormal cognitive processes indexed by the cognitive and attention-related event-related potential components in infantile autism and receptive developmental language disorder are not due to abnormal sensory processing in the brainstem and in areas central to the brainstem whose activity generates the BAEPs and MLRs.

Reduced cerebellar hemisphere size and its relationship to vermal hypoplasia in autism

Cerebellar hemisphere size was calculated in 10 autistic and 8 normal control subjects by summing the cross-sectional areas of cerebellar hemisphere tissue measured on paramidline sagittal magnetic resonance images. The areas of two cerebellar vermal regions (lobules I through V and lobules VI through VII) were also measured using the midsagittal image. Our cumulative slice area measure of cerebellar hemisphere size was significantly smaller in the autistic subjects than in the control group. The cumulative slice area correlated positively with the area of vermal lobules VI through VII only in the autistic subjects. Our results indicated that the decreased size of the cerebellar hemispheres and vermal lobules VI through VII was associated with autism.

Pathophysiologic findings in nonretarded autism and receptive developmental language disorder

In nonretarded autistic, receptive developmental language disordered, and normal subject groups, we recorded in auditory and visual target detection tasks two neurophysiological components of the event-related brain potential, Nc and P3b. Existent research shows that, in normals, Nc and P3b appear early in development, are associated with attention and memory processes, and are endogenous which means that they are triggered by internal, consciously initiated attentional and cognitive mechanisms and that they can be triggered even by the omission of sensory stimulation so long as it has meaning or importance for the subject. In this report, Nc and P3b were recorded in response to auditory and visual stimulation and to the omission of auditory and visual stimulation. Consistent with the hypothesis that non-retarded autism involves abnormal attentional and cognitive responses to important information, P3b was found to be smaller than normal and Nc was small and often absent in the nonretarded autistic group even under the condition when no auditory language or sensory processing was required. Receptive developmental language disorder has been linked with difficulties in processing sequences of auditory stimuli, and in this study P3b was found to be somewhat enlarged in this group even under the conditions when P3b was elicited by stimuli separated by 1 sec and also when P3b was elicited by the omission of stimulation.

Visual memory processes in high-functioning individuals with autism

High-functioning autistic individuals were compared with age-matched normal control subjects on a visual recognition memory task. In order to evaluate the effects of "meaning" and "delay" on the visual memory of autistic individuals, meaningful (pictures) and meaningless (nonsense shapes) stimuli were presented visually in no delay and 1-minute delay intervals to both groups. It was concluded that autistic subjects perform particularly poorly on meaningless material, but they are able to utilize meaning to aid their visual memory. Contrary to expectations, 1-minute delay intervals did not differentially affect the visual memory performance of autistic individuals compared to control subjects. The results do not support the idea of a simple parallel between autism and mediotemporal lobe amnesias. The visual memory performance of the autistic subjects was discussed in the light of the possibility of a subtle involvement of the mediotemporal brain structures and inflexible cognitive strategies poorly suited to encode novel information.

A study of intellectual abilities in high-functioning people with autism

This research extends previous research regarding the intellectual functioning of autistic individuals on standardized measures of intelligence (Wechsler Adult Intelligence Scale-Revised and the Wechsler Intelligence Scale for Children-Revised). In Study I 33 individuals with autism who closely fit the DSM-III criteria were studied. Clear evidence was found that differentiates these individuals' verbal intellectual processes from their visual-motor intellectual abilities. Principal components analysis was used to examine the interrelationship among the various intellectual abilities which such tests of intelligence measure. In Study II the intellectual abilities of a group of autistic 8- to 12-year-olds were compared to age-matched groups of children with receptive developmental language disorder, dysthymic disorder, or oppositional disorder. The intellectual abilities of autistic children were significantly different from the other groups of children.

Hypoplasia of cerebellar vermal lobules VI and VII in autism

Autism is a neurologic disorder that severely impairs social, language, and cognitive development. Whether autism involves maldevelopment of neuroanatomical structures is not known. The size of the cerebellar vermis in patients with autism was measured on magnetic resonance scans and compared with its size in controls. The neocerebellar vermal lobules VI and VII were found to be significantly smaller in the patients. This appeared to be a result of developmental hypoplasia rather than shrinkage or deterioration after full development had been achieved. In contrast, the adjacent vermal lobules I to V, which are ontogenetically, developmentally, and anatomically distinct from lobules VI and VII, were found to be of normal size. Maldevelopment of the vermal neocerebellum had occurred in both retarded and nonretarded patients with autism. This localized maldevelopment may serve as a temporal marker to identify the events that damage the brain in autism, as well as other neural structures that may be concomitantly damaged. Our findings suggest that in patients with autism, neocerebellar abnormality may directly impair cognitive functions that some investigators have attributed to the neocerebellum; may indirectly affect, through its connections to the brain stem, hypothalamus, and thalamus, the development and functioning of one or more systems involved in cognitive, sensory, autonomic, and motor activities; or may occur concomitantly with damage to other neural sites whose dysfunction directly underlies the cognitive deficits in autism.

Abnormal neuroanatomy in a nonretarded person with autism. Unusual findings with magnetic resonance imaging

Recent studies of infantile autism using computed tomographic scanning emphasized the importance of studying cases of classic autism (Kanner's syndrome) without complicating conditions such as mental retardation. Computed tomographic scan studies of such patients reported no evidence of anatomical abnormalities of cerebral hemispheres or of subcortical structures, which are defined by landmarks such as the lateral ventricles and lentiform nuclei. Examination of the cerebellum was not mentioned. The most recent postmortem neuropathologic study reported significant cerebellar abnormality, but the study was of a severely retarded autistic individual. Using magnetic resonance imaging, we have found in vivo evidence of a significant and unusual cerebellar malformation in a person with the classic form of autism uncomplicated by mental retardation (current nonverbal IQ = 112), epilepsy, history of drug use, postnatal trauma, or disease. The finding showed hypoplasia of the declive, folium, and tuber in posterior vermis, but not of the anterior vermis, and hypoplasia of only the medial aspect of each cerebellar hemisphere. The right posterior cerebral hemisphere also showed pathologic findings.

The recovery functions of auditory event-related potentials during split-second discriminations

We examined the recovery cycles of auditory event-related potentials (ERPs) in a high-speed auditory discrimination task and in passive conditions. Each trial contained 3 tones cued by a warning flash. In passive conditions, auditory ERPs consisted mainly of N1 (108 msec) and P2 (213 msec) components superimposed on a small CNV. The N1 and P2 were comparable in amplitude and both had prolonged refractory periods. In discriminative reaction time (DRT) conditions the same tones cued or inhibited press responses and elicited additional endogenous components (principally the Nd and P3). ERPs in DRT conditions were superimposed upon a prominent CNV that began after the warning cue and lasted throughout the signal delivery period. The N1 was larger in active than passive conditions and showed less marked refractory effects, while the P2 was smaller and showed more marked refractoriness. Differences between active and passive conditions could be explained by the presence of an endogenous negative potential (the Nd) with a short refractory period that was superimposed upon the N1 and P2. The P3 was recorded only in active conditions. At short ISIs (0.5 sec), P3 amplitudes were reduced and P3 latencies lengthened in parallel with prolongations in reaction time due to so-called psychological refractory period (PRP) effects. Both P3 recovery and the PRP reflected central mechanisms since they were observed at short ISIs when stimuli cueing different responses succeeded one another. N1 and P3 amplitudes diminished over the course of the experiment in both active and passive conditions. The decrease (amounting to about 30% of initial amplitudes) did not appear due to reductions in vigilance, since it was not accompanied by changes in reaction time or response accuracy, or by changes in other endogenous components (CNV or Nd). Short-term N1 habituation was unaffected by long-term amplitude reductions suggesting that independent mechanisms were responsible for the two phenomena.

Functioning of the brain-stem auditory pathway in non-retarded autistic individuals

Functioning of auditory brain-stem pathways was examined in non-retarded autistic individuals (14-28 years of age). Functioning was assessed by recording ERPs (event-related brain potentials) generated by these auditory pathways. These ERPs were evoked by click stimuli and occurred within the first 8 msec following the onset of the click. To assess the ability of these early auditory pathways to process sensory stimuli of varying characteristics, we systematically varied click intensity, rate of stimulation, ear of stimulation, and polarity of clicks. The results show that non-retarded autistic individuals have normal functioning of the brain-stem auditory pathways which generate these ERPs: every autistic subject had normal ERPs. So, disorder in auditory brain-stem pathways which generate these ERPs is not necessary for autism to occur. The dysfunctioning neural systems directly responsible for autism in non-retarded individuals must be sought elsewhere. Ten of the autistic subjects in this study, whom we found to have normal auditory brain-stem ERPs, had previously been found to have abnormalities in longer latency cognitive ERP components (Courchesne et al. 1984, 1985). We conclude, therefore, that those abnormalities in longer latency components are not the downstream consequences of abnormalities in the structures generating the auditory brain-stem ERPs recorded in the present study.

Event-related brain potential correlates of the processing of novel visual and auditory information in autism

Event-related brain potentials (ERPs) elicited by visual and auditory stimuli were recorded from nonretarded individuals with autism (ages 13-25 years) and age-matched normal controls. In "no-task" conditions, subjects simply looked at or listened to these stimuli; only one difference was found between subject groups. Several ERP differences between groups were found in "task" conditions; subjects pressed a button at the occurrence of target stimuli intermixed with unexpected, novel stimuli and also with expected, nonnovel stimuli. Visual ERP abnormalities in the autistic group differed from auditory abnormalities. Results suggest that (1) nonretarded autistic individuals may have a limited capacity to process novel information--they are neither hypersensitive to novel information nor misperceive it as nonnovel and insignificant; (2) classification of simple visual information may be less impaired than auditory; and (3) with one exception, visual and auditory ERP abnormalities do not seem to reflect maturational delay.

Neuropsychological correlates of information-processing by children with Down syndrome

Nine children with Down syndrome were compared to two groups of nonretarded children, one similar in CA, the other a chronologically younger group of similar MA. The event-related brain potential (ERP) and reaction time (RT) results indicated that children with Down syndrome process some types of auditory information more slowly than do MA- or CA-matched nonretarded children. They were found to differ from nonretarded children in the scalp distribution of amplitudes of certain ERP components. Finally, the speed of processing and amplitude differences that were found could not be explained on the basis that children with Down syndrome are simply maturationally delayed in their cognitive abilities. The possible relation of these neuropsychological (ERPs) and performance (RT) differences to pathological changes in the hippocampus were discussed.

Autism: processing of novel auditory information assessed by event-related brain potentials

Event-related brain potentials (ERPs) of 13-21-year-old autistic subjects and age-matched controls were elicited by auditory stimuli in a variation of orienting response paradigms. Unexpected, novel sounds (bizarre concoctions of human, mechanical and computer sounds) were randomly inserted as probes in a sequence of expected, non-novel sounds (the word 'me'). In order to help ensure that both subject groups were attending to this stream of information, each subject was required to press a button to a specified target sound (the word 'you') also randomly inserted in the sequence of expected non-novel sounds. The ERP results showed that in both groups, unexpected, novel probes and also targets evoked a different neurophysiological response than did expected, non-novel sounds. This suggests that the autistic group did not misperceive novel information as non-novel and were able to make simple classification decisions as accurately as normal controls. However, in the autistic group, there may be less 'processing' of the novel probes and of targets: compared to the control group, the autistic group had smaller amplitudes of two long-latency components to novels and smaller P3b amplitudes to targets. The two components to novels were termed A/Pcz/300 (A = auditory; P = positive; cz = electrode site of maximum amplitude; 300 = latency in msec) and A/Ncz/800. In another sequence of sounds, subjects simply listened to frequently presented 'me' sounds (90%) and infrequently presented 'you' sounds (10%). In this no-task condition, no differences between autistic and normal control subjects were found.

Event-related brain potentials to human faces in infants

Event-related brain potentials (ERPs) in response to tachistoscopically presented photographs of 2 human faces were recorded for 4--7-month-old infants. For each infant 1 face was chosen to be presented frequently (p = .88, a low-information event) and the other infrequently (p = .12, a high-information event). Both types of events elicited in our infants a long-latency negative ERP wave (ca. 700 msec), termed Nc, and a long-latency positive wave (ca. 1,360 msec), termed Pc. We found that the discrepant, infrequently presented face elicited Nc waves which were higher in amplitude and longer in latency than those elicited by the frequent face. These differences suggest that our infants were able to remember the frequently presented face from trial to trial and to discriminate it from the discrepant face. The discrepant event elicited Pc waves which were insignificantly higher in amplitude than those elicited by frequent events. In adults and children, discrepant events have been found by numerous researchers to elicit positive P3 waves (latency ca. 300--800 msec). In our study, however, such waves could not be discerned. So, of all of the ERP waves which have been related to cognitive processes, the wave which is maturationally the earliest to appear is the Nc wave, which has been related to the perception of attention-getting events or events of interest to the subject. Our findings suggest that ERP responses could provide a sensitive means for investigating infant cognitive development since they do not depend upon an integrated motor-response system.

Recovery cycles of event-related potentials in multiple detection tasks

We examined the recovery cycle of the P3 in two different experiments, one in which subjects detected near-threshold (NT) tones and the other in which they detected suprathreshold (ST) tones presented in rapid sucession. In both experiments P3 amplitudes and latencies were decremented at ISIs of 300 msec but fully recovered by 900 msec. The N1 and P2 components elicited by ST tones showed a much more prolonged (> 7.0 sec recovery cycle. These results reveal that the P3 has a recovery cycle which closely resembles that of human decision processes, a recovery cycle far shorter than those of exogenous ERP components previously examined. Sequential changes in P3 amplitude between trials were also investigated. In both experiments P3 amplitudes were largest following signal-absent trials. This suggests that subjects may have modified their expectancies about tone delivery on a trial-by-trial basis. In these experiments the P3 wave was distinguished from the resolution of the CNV on several grounds, including differences in scalp distribution, intra-trial kinetics, effect of previous tone sequences, and distributions among the subjects. These results support the position that P3 is a neurophysiological event distinct from modulations of the CNV. Differences in the amplitude and habituation of P3s produced in the NT and ST experiments suggest that the P3 may be related to decisions which require 'controlled' stimulus processing.

Electrophysiological signs of split-second decision-making

When young adults detected auditory stimuli at split-second intervals, different components of the event-related brain potentials showed markedly different speeds of recovery. The P3 component (latency 300 to 350 milliseconds) was fully recovered at intervals of less than 1.0 second, while the N1--P2 components (latencies 100 to 180 milliseconds) were markedly attenuated with stimulus repetition even at longer interstimulus intervals. Thus, the N1--P2 recovers much more slowly than a subject's ability to evaluate signals, whereas the P3 appears to be generated at the same high rates as the decision processes with which it is associated.

Evoked potential correlates of human information processing

The late positive component (P3) of the feedback evoked potential was investigated in two tasks: the detection of near-threshold auditory stimuli, and the estimation of 1 s time intervals. When the intensity or probability of the threshold stimuli was varied in the detection task, it became apparent that the feedback P3 was related to the 'contingent probability' of confirming or disconfirming feedback given a particular response. In the time-estimation task the relative probabiliti-s of confirming and disconfirming feedback were altered by changing the time-window wherein a response was judged correct. In these experiments it was found that the feedback P3 component was highly dependent upon the probability of the feedback, and relatively independent of its confirming or disconfirming meaning. With decreasing probability of the feedback stimuli, the P3 component became larger, later, and somewhat more frontal.

Changes in P3 waves with event repetition: long-term effects on scalp distribution and amplitude

Event-related brain potentials to tachistoscopically presented events were recorded from adults 24--36 years of age. Subjects counted the number of target events (P = 0.12) randomly interposed in sequences of background events (either P = 0.88 or P = 0.76). In some sequences, slides bearing the letter A were targets and those bearing the letter B were backgrounds; the reverse was true in the other sequences. Also interposed (P = 0.12) in these sequences of targets and backgrounds were one of two types of non-target events: in some sequences non-targets were slides (termed dims) bearing any one of the letters C to Z and having one-tenth the luminance of the target and background slides, while in the others, they were slides bearing 'novel' patterns, each consisting of a different, quasi-random, unrecognizable color pattern. The scalp amplitude distribution of P3 waves to novels were initially frontal, but, with repeated presentations of novel events, they became parietal. The scalp distributions of P3 waves to targets and dims were both initially parietal and did not change with repeated presentations of target and dim events. P3 amplitudes to targets were unaffected by repeated presentations of target events. However, P3 amplitudes to dims and novels were affected. P3 amplitudes to dims decreased linearly at Fz, Cz and Pz with repetition of dims. P3 amplitudes to novels decreased at Fz and increased at Pz with repetition of novels. An abbreviated analysis of possible effects of sequential event probabilities on P3 amplitudes and latencies to novels, dims and targets was performed and no effects were found. It is suggested that P3 waves may be affected by at least 4 factors: the facility with which events may be categorized by subjects, the importance attached to events (via task instructions, subjective assessment of the contents of events, etc.), a priori category probability, and sequential event structure.

Neurophysiological correlates of cognitive development: changes in long-latency event-related potentials from childhood to adulthood

Event-related brain potentials (ERPs) to tachistoscopically flashed slides were recorded from subjects ranging from 6 to 36 years of age. Subjects counted the number of presentations of target slides (P = 0.12) randomly interposed in sequences of background slides (either P = 0.76 or P = 0.88). Also interposed (P = 0.12) in these sequences of targets and backgrounds were one of two types of slides: those (termed dims) bearing any one of the letters from C to Z or those bearing 'novel' patterns, each consisting of a different, quasi-random, 'unrecognizable' color pattern. Targets and backgrounds elicited N1, P2, N2 and P3 waves in subjects of every age tested, suggesting that the mode of processing such explicitly important events and the neuronal substrate for such processing, is similar in children and adults. However, P3 latencies and reaction times in response to these events decreased with age, suggesting that the speed of such processing increases with age. On the other hand, dims and novels elicited ERPs in young children and adults characterized by different late waves. ERPs in 6--8 year olds were characterized by Nc waves (ca. 410 msec and 30 muV) and Pc waves (ca. 900 msec and 30 muV), while ERPs in adults were characterized by P3 waves (ca. 420 msec and 15 muV. The transition from the childhood to adulthood wave form occured in the mid-teens. It is suggested that these differences in ERP wave forms reflect differences in the way children and adults categorize events.