Sensitivity of the WAIS-R Verbal-Performance IQ difference and intersubtest scatter to traumatic brain injury. Wechsler Adult Intelligence Scale-Revised.

The Wechsler Adult Intelligence Scale-Revised (WAIS-R) Verbal IQ-Performance IQ (VIQ-PIQ) discrepancy and a number of indices of intersubtest scatter were examined in 25 subjects with a history of traumatic brain injury (TBI) and magnetic resonance imaging (MRI) evidence of structural brain abnormality. Abnormal VIQ-PIQ differences and scatter index values were identified by referring to published normal base rates. Only 16% of the subjects were identified as abnormal on any one of these WAIS-R measures, which suggests these measures are largely insensitive to the presence of structural brain abnormality in TBI.

The P300 ERP component: an index of cognitive dysfunction in depression?

A number of measures of brain function have suggested that depression is associated with cerebral hypoactivity. This study examines the late components of the event-related potential (ERP), in particular the P300 component, in depression. The P300 component is thought to index the updating of neurocognitive models which are concerned with the prediction of future events. Cognitive theories of depression include the proposition that depression may be characterized by abnormalities in the prediction of future events. The P300 component may therefore provide one neurophysiological index of cognitive dysfunction in depression. Twenty-seven subjects (14 medicated, 13 drug-free) fulfilling DSM-III criteria for Major Depression were compared to 27 age- and sex-matched normal controls. The amplitudes and latencies of N100, P200, N200 and P300 ERP components, reaction time and task accuracy were recorded during a standard auditory discrimination task. No significant differences were found in any ERP component measure or in reaction-time between the groups. Depressed subjects performed the experimental task significantly less accurately than normal controls, but this was not reflected in the ERPs.

Normal latency of the P300 event-related potential in mild-to-moderate Alzheimer's disease and depression.

A two-tone-discrimination task was used to elicit the P300 component of event-related (brain) potentials (ERPs) from patients with presumed Alzheimer's dementia of mild or moderate severity, depressed patients of older age, and cognitively normal individuals. Although the average P300 latency of the Alzheimer patients was greater than that of the depressed patients, which in turn was greater than that of older aged normals, none of the group differences in latency were statistically significant. Moreover, when latency was examined on an individual basis, less than one-quarter of the Alzheimer patients had an abnormally delayed P300 for their age. Reaction times and the percentage of correct behavioral responses to the tones did distinguish the Alzheimer from the normal group; on both measures the patients' scores were significantly worse. It was concluded that the performance of a simple tone discrimination task requiring a button-press response does not sufficiently tax those cognitive functions impaired in the earlier stages of Alzheimer's dementia to result in abnormally slowed cognitive processing of the kind reflected in P300 latency.

Neuropsychological assessment and brain imaging technologies in evaluation of the sequelae of blunt head injury.

A 43 year old man with a traumatic amnesic syndrome experienced only a brief, if any, loss of consciousness following an injury to the head. Four years after this injury, his results on standard psychometric assessment were normal. Long-latency evoked response potentials results were normal, and the neurological examination and computed tomography scans were unhelpful in explaining his amnesic symptoms. He had no history of alcohol abuse, yet his neuropsychological profile was that of a Korsakoff-like amnesia with frontal lobe features. Magnetic-resonance images demonstrated evidence of extensive frontal lobe damage, while cerebral blood flow studies provided additional evidence of bilateral frontal lobe dysfunction. The case highlights the need for those giving opinions in medico-legal head trauma cases to go beyond a reliance on routine indicators, such as duration of coma, results of standard psychometric assessment and computed tomography scans, to more specialised neuropsychological evaluations and magnetic-resonance imaging scans.

Augmentation of auditory evoked potentials in somatization disorder.

Sensory input regulation was examined in terms of augmenting/reducing of auditory evoked potentials in 10 patients with somatization disorder (8 males and 2 females) and 10 age- and sex-matched normal controls. The slope of P1-N1 amplitude change as a function of stimulus intensity was greater in patients compared with controls, suggesting an enhanced central nervous system response to sensory input. Taken together with previous findings of a failure to habituate to incoming stimuli in a similar group of patients, and evidence obtained in somatizers of both over-responding to background stimuli in a simple tone-discrimination task and enhanced parietal activation during selective attention, this finding suggests disturbances in the processes of attention and in the regulation of afferent stimuli in somatization disorder, and may help explain the multiple and chronic complaints characteristic of patients with the disorder.

Regional cerebral blood flow measurements in the diagnosis of dementia.

The Xenon-133 regional cerebral blood flow technique (rCBF) was used to assess cortical perfusion in a group of 15 elderly patients (mean age = 79.1, SD = 8.7) with a probable diagnosis of Dementia of the Alzheimer type (DAT). Nine had mild DAT and six were in the moderate stages of DAT. These patients were compared with 15 age and sex matched normal elderly controls (mean age = 75.1, SD = 5.6). RCBF was measured in each patient and control at rest with eyes closed. The DAT patients had significantly lower mean global CBF than normal controls (t = -4.63, p less than 0.0001). In addition, a further 15 normal elderly subjects aged 60 to 92 were assessed and combined with the original 15 to allow calculation of a normal range of rCBF for elderly individuals. Seventy-three per cent of the DAT patients fell below the lower limit of the normal range (39.3 - 59.3 ISI units). These results show the possible usefulness of rCBF as an aid in the diagnosis of early DAT.

A modified selective attention auditory event-related potential paradigm suitable for the clinical setting.

Auditory event-related potentials (ERPs) were recorded without practice sessions using a selective attention ERP paradigm modified from Hillyard et al. (1973) in 20 normal individuals who varied across wide ranges of age and educational background. The results concur with previous findings concerning the effects of selective attention on both the earlier and later phases of the ERP waveform. Attended stimuli elicited a larger N1 deflection compared with unattended stimuli. Processing negativity was also elicited by attended stimuli, but not by unattended stimuli. Mismatch negativity (N2) was evident in waveforms to signals as compared with standards, and a late positivity (P3) followed N2 only in waveforms to attended signals. This paradigm may be appropriate for evaluating suspected attentional dysfunctions in clinical populations.

The P300 event-related potential and regional cerebral blood flow in patients with Alzheimer's disease.

A number of studies have reported that an abnormal delay in the latency of the P300 event-related potential (ERP) is characteristic of the majority of patients with a dementing process. Another body of research suggests regional cerebral blood flow (rCBF) is significantly reduced in Alzheimer's disease (AD). No previous study has compared the effectiveness of these 2 measures in identifying the same patients with AD. Furthermore, most of the studies on which the above findings are based examined patients in the moderate to severe stages of the disorder. In this study we examined P300 latency and rCBF in 10 patients with mild to moderate Alzheimer's disease, and compared their responses with those of normal subjects of similar age. The P300 component was not evident in 2 of the patients: the remaining 8 had a latency within normal limits for their age. On the other hand, 8 of the patients had abnormally reduced rCBF. These results suggest rCBF measures may be useful for identifying AD in its early stages.

The relationship between reaction time and latency of the P300 event-related potential in normal subjects and Alzheimer's disease.

The latency of the P300 event-related potential is though to reflect the time it takes to conclude that a task-relevant stimulus has been presented, i.e. it is an index of cognitive processing time. Reaction time (RT) also reflects cognitive processing time, but additionally reflects the time taken physically to respond to the stimulus. If serial models of information processing are correct, then the P300 latency must be less than RT, and a positive correlation between the 2 measures is to be expected. We examined these hypotheses in 100 normal subjects aged from 18 to 92 years. The P300 component elicited via a 2-tone discrimination task, and RT to the task-relevant tones was measured simultaneously. The resulting correlation between these measures was weak (r = 0.26, p greater than 0.05), and there were instances in which RT preceded the P300 latency. These results are consistent with parallel rather than serial models of information processing. Fifteen patients with Alzheimer's disease were also examined. Three had an abnormally delayed P300 latency, and 7 had abnormally delayed RTs compared with age-matched controls. Simultaneous measurement of the P300 latency and RT may thus help resolve whether dysfunction is evident in neuronal networks concerned with stimulus evaluation or in those concerned with response execution.

Selective attention and auditory event-related potentials in somatization disorder.

Janet suggested a disorder of attention was fundamental to hysteria. This idea was investigated in this study by examining mismatch negativity (MMN), which depends upon a subtraction of cortical potentials evoked by background stimuli from those evoked by target stimuli. Ten patients with somatization disorder (SMD) were compared with ten normal individuals. MMN was smaller in somatizers, particularly at the central recording site. One interpretation of this observation is that somatizers respond more similarly than normals to "relevant" and "irrelevant" stimuli. This finding of an impairment in attentional processing in somatization disorder suggests a subtle neurophysiological disturbance.

The P300 event related potential component in the diagnosis of dementia.

Several studies have suggested that delays in the latency of the P300 ERP component are highly sensitive and specific to dementia and that ERP measurements may become a useful clinical tool in aiding diagnosis. This study examines the sensitivity of P300 measurements to dementia and addresses several methodological issues that limit previous research. Twenty-four patients with dementia diagnosed according to ICD-10 criteria were compared with 100 normal controls, 31 of whom were older than 60. An auditory oddball paradigm was employed to elicit the P300. Mean P300 latency did not differ significantly between the two groups. When individual subjects were examined only 13% of patients with dementia fell outside the two standard error band of the regression of P300 latency on age derived from controls. Thus, this study has not demonstrated clinically useful abnormalities of the P300 component in dementia.

An investigation of patients presenting with multiple physical complaints using the illness behaviour questionnaire.

The Illness Behaviour Questionnaire was used to determine whether three groups of patients who had presented with multiple symptoms in different treatment settings (Briquet's syndrome, post-viral fatigue syndrome, and a heterogeneous general practice group) could be differentiated from one another and from a mixed group of psychiatric patients on the basis of their abnormal illness behaviour. All groups completed a version of the Perley and Guze diagnostic criteria for Briquet's syndrome. The three groups presenting with multiple symptoms were more similar to each other than to the psychiatric patients. The results suggest that patients presenting with multiple symptoms include similar populations of patients who are poorly distinguished using current schemes of classification.

Evoked response potentials and regional cerebral blood flow in somatization disorder.

Somatization disorder (SMD) is a chronic condition characterized by multiple complaints which are not due to any apparent organic illness but frequently involve pain. This study employs computer-aided imaging technologies to examine brain function in thousandths of a second (event-related brain potentials) and over a number of minutes (regional cerebral blood flow). Fourteen patients with SMD and 14 normal controls were investigated. Results from both studies suggest that patients with SMD have a dysfunction in the processes of attention, compared to normal controls.

Magnetoencephalography: locating the source of P300 via magnetic field recording.

A description is given of the theory and instrumentation involved in measuring magnetic fields of the brain. The magnetic counterpart of event-related potentials are capable of locating more accurately the generators of these electrical signals. Preliminary results of the first application of magnetoencephalography in Australia are presented. These localize the generator of the auditory P300 event-related potential component to the temporal cortex.

The differential diagnosis of dementia using P300 latency.

The P300 component was elicited by an auditory oddball paradigm in 55 normal adults from a wide age range: 19 patients with dementia, 17 patients with depression, and 15 patients with schizophrenia. Normal P300 latency at a given age was predicted by using an age regression equation that had been calculated on the basis of the entire normal sample. Using this procedure, an abnormal delay in latency (greater than 2 SD) was found in approximately 80% of the dementia patients. However, when normal latency was predicted with a slightly greater degree of reliability according to separate equations for adults younger and older than 63 years, an abnormal delay in P300 was found to be less sensitive and specific to dementia. Suggestions for enhancing the diagnostic utility of the P300 component are proposed.

Images of the brain in psychiatry.

In psychiatry, the use of computer-based techniques for constructing images of the brain is relatively recent. Nevertheless, findings that have resulted from their use thus far might provide us with a new perspective in the understanding of mental illness. They raise the possibility that many of the disorders, previously understood primarily in terms of psychosocial factors, are associated with specific abnormalities of brain structure and/or function. Although terms such as NMR, BEAM, RCBF, SPECT and PET are increasingly found in medical and psychiatric journals, few people understand in simple terms the principles on which these techniques are based. In this article the techniques used for constructing images of brain structure and function are explained, and an overview of the findings in psychiatric disorders is presented.

Psychometrics and event-related potentials in the diagnosis of dementia.

This study attempted to increase the reliability of predicting the normal latency of the P3 component in elderly adults. It was hypothesized this would allow a more accurate distinction to be made between normal adults (n = 20) and patients with dementia (n = 19) on the basis of observed P3 latencies. Two models for predicting latency were assessed. The first, which used age alone as a predictor, explained 18% of the normal variation in latency and misclassified 40% of the patients. The second model, which incorporated scores on psychometric tests, explained 74% of latency variation and misclassified 20% of the patients. Scores on the Similarities subtest of the WAIS and the Rey Auditory Verbal Learning Test, however, correctly identified 92% of the patients. This finding casts doubt on the justification of the P3 latency measures to diagnose dementia.

P300 and the effects of aging: relevance to the diagnosis of dementia.

A tone discrimination task was used to elicit the P300 component of event related potentials in 55 normal subjects aged between 15 and 89 years. The age/latency relationship in the total sample was significant, but contrary to the reports of some others was statistically better described at CZ by a linear and not a curvilinear age regression function. Adults over 45 had steeper age regression slopes and larger age/latency correlations frontally and centrally than younger adults, but there was no difference in amplitude between these groups. The effect of age on latency seemed slightly more pronounced frontally in older adults, and there was significantly more latency variability in this group. Overall, the age/latency relationship in adults was statistically best described by separate linear age regression functions for adults less than or equal to 45 and greater than 45. It is suggested that latency variability may account for some of the discrepancy in the age/P300 literature, and the clinical implications of this are discussed.

The prediction of normal P3 latency and the diagnosis of dementia.

The relationship between age and the latency of the P3 (auditory evoked response potential) component was best described in 55 normals aged 15-89 by separate linear regression equations for those younger and those older than 63. Twelve out of 19 patients with dementia had P3 latencies at FZ and CZ which were delayed by more than two standard errors from the normal latency for their age predicted using the above equations, and were thus correctly identified. However, an equation calculated across the entire adult age range provided a better patient identification rate. The potential usefulness of P3 measures in clarifying the nature of cognitive impairment in dementia is discussed.