Performance measures of 16- to 86-year-old males and females on the auditory verbal learning test

This study reports Auditory Verbal Learning Test (AVLT) data for 153 adults in age groups spanning seven decades, with approximately equal numbers of males and females and matched for intelligence, education, and occupation. Overall performance deteriorated with increased age, females performing better than males. Older subjects recalled fewer words, were more susceptible to information overload during input, showed diminished retrieval efficiency, and had a decline in memory for the source of items. In contrast, rate of learning, forgetting over 20-min, monitoring of recall, and interference effects remained stable across the age range.

Genetic covariation between event-related potential (ERP) and behavioral non-ERP measures of working-memory, processing speed, and IQ

The aim of this study was to identify genetic covariants for fundamental measures of brain function (event-related potentials (ERPs): P300 latency and slow wave amplitude recorded in a working-memory task) and more complex cognitive measures (behavioral non-ERP measures: working-memory performance, information processing speed, IQ). Data were collected from 252 monozygotic and 297 dizygotic twin pairs aged 16. Multivariate modeling identified two independent genetic factors associated with processing speed that also influenced working-memory performance (one reflected the duration of neural activity required to evaluate target information, the other reflected more general cognitive and speed-related abilities). However, the allocation of neural resources, as assessed by ERP slow wave amplitude measures, was not associated with the other cognitive measures investigated. Thus, of the ERP measures examined, P300 latency, but not slow wave amplitude, may be an informative measure to include (i.e., with working-memory performance) in future multivariate linkage and association analyses of cognitive function.

Slow binocular rivalry in bipolar disorder

BACKGROUND

The rate of binocular rivalry has been reported to be slower in subjects with bipolar disorder than in controls when tested with drifting, vertical and horizontal gratings of high spatial frequency.

METHOD

Here we assess the rate of binocular rivalry with stationary, vertical and horizontal gratings of low spatial frequency in 30 subjects with bipolar disorder, 30 age- and sex-matched controls, 18 subjects with schizophrenia and 18 subjects with major depression. Along with rivalry rate, the predominance of each of the rivaling images was assessed, as was the distribution of normalized rivalry intervals.

RESULTS

The bipolar group demonstrated significantly slower rivalry than the control, schizophrenia and major depression groups. The schizophrenia and major depression groups did not differ significantly from the control group. Predominance values did not differ according to diagnosis and the distribution of normalized rivalry intervals was well described by a gamma function in all groups.

CONCLUSIONS

The results provide further evidence that binocular rivalry is slow in bipolar disorder and demonstrate that rivalry predominance and the distribution of normalized rivalry intervals are not abnormal in bipolar disorder. It is also shown by comparison with previous work, that high strength stimuli more effectively distinguish bipolar from control subjects than low strength stimuli. The data on schizophrenia and major depression suggest the need for large-scale specificity trials. Further study is also required to assess genetic and pathophysiological factors as well as the potential effects of state, medication, and clinical and biological subtypes.

The n-back as a dual-task: P300 morphology under divided attention

The n-back task was hypothesized to be a dual task, permitting the imposition of parametrically increasing attentional and working memory demands, while keeping constant the demands of an embedded matching subtask. Visual targets were presented for 200 ms every 2.2 s at pseudorandomly varying positions on a computer screen. Participants were required to remember the most recent 0, 1, 2, or 3 positions and responded with a choice button push to whether the current target position matched the position presented n items previously. P300 peak latency was constant across n-back tasks, reflecting constant perceptual and cognitive demands of the matching subtask. P300 peak amplitude decreased with increasing memory load, reflecting reallocation of attention and processing capacity away from the matching subtask to working memory activity. These data support a dual-task nature of the n-back, which should be considered when employing this paradigm.

Genetic influence on the variance in P3 amplitude and latency

The P3(00) event-related potential (ERP) component is widely used as a measure of cognitive functioning and provides a sensitive electrophysiological index of the attentional and working memory demands of a task. This study investigated what proportion of the variance in the amplitude and latency of the P3, elicited in a delayed response working memory task, could be attributed to genetic factors. In 335 adolescent twin pairs and 48 siblings, the amplitude and latency of the P3 were examined at frontal, central, and parietal sites. Additive genetic factors accounted for 48% to 61% of the variance in P3 amplitude. Approximately one-third of the genetic variation at frontal sites was mediated by a common genetic factor that also influenced the genetic variation at parietal and central sites. Familial resemblance in P3 latency was due to genetic influence that accounted for 44% to 50% of the variance. Genetic covariance in P3 latency across sites was substantial, with a large part of the variance found at parietal, central, and frontal sites attributed to a common genetic factor. The findings provide further evidence that the P3 is a promising phenotype of neural activity of the brain and has the potential to be used in linkage and association analysis in the search for quantitative trait loci (QTLs) influencing cognition.

Genetic covariance among measures of information processing speed, working memory, and IQ

The genetic relationship between lower (information processing speed), intermediate (working memory), and higher levels (complex cognitive processes as indexed by IQ) of mental ability was studied in a classical twin design comprising 166 monozygotic and 190 dizygotic twin pairs. Processing speed was measured by a choice reaction time (RT) task (2-, 4-, and 8-choice), working memory by a visual-spatial delayed response task, and IQ by the Multidimensional Aptitude Battery. Multivariate analysis, adjusted for test-retest reliability, showed the presence of a genetic factor influencing all variables and a genetic factor influencing 4- and 8-choice RTs, working memory, and IQ. There were also genetic factors specific to 8-choice RT, working memory, and IQ. The results confirmed a strong relationship between choice RT and IQ (phenotypic correlations: -0.31 to -0.53 in females, -0.32 to -0.56 in males; genotypic correlations: -0.45 to -0.70) and a weaker but significant association between working memory and IQ (phenotypic: 0.26 in females, 0.13 in males; genotypic: 0.34). A significant part of the genetic variance (43%) in IQ was not related to either choice RT or delayed response performance, and may represent higher order cognitive processes.

Genetic influence on ERP slow wave measures of working memory

Individual differences in the variance of event-related potential (ERP) slow wave (SW) measures were examined. SW was recorded at prefrontal and parietal sites during memory and sensory trials of a delayed-response task in 391 adolescent twin pairs. Familial resemblance was identified and there was a strong suggestion of genetic influence. A common genetic factor influencing memory and sensory SW was identified at the prefrontal site (accounting for an estimated 35%-37% of the reliable variance) and at the parietal site (51%-52% of the reliable variance). Remaining reliable variance was influenced by unique environmental factors. Measurement error accounted for 24% to 30% of the total variance of each variable. The results show genetic independence for recording site, but not trial type, and suggest that the genetic factors identified relate more directly to brain structures, as defined by the cognitive functions they support, than to the cognitive networks that link them.

Concussion in contact sports: reliable change indices of impairment and recovery

This paper reports a follow-up study to an article on the sensitivity of three tests of speed of information processing to impairment after concussion (Hinton-Bayre, Geffen, & McFarland, 1997). Group analyses showed that practice effects can obscure the effects of concussion on information processing, thereby making the assessment of functional impairment and recovery after injury unreliable. A Reliable Change Index (RCI) was used to assess individual variations following concussion. It was found that 16 of the 20 concussed professional rugby league players were impaired 1-3 days following injury. It was also demonstrated that 7 players still displayed cognitive deficits at 1-2 weeks, before returning to preseason levels at 3-5 weeks. The RCI permits comparisons between different tests, players, and repeated assessments, thereby providing a quantitative basis for decisions regarding return to play.

Event related potentials during covert orientation of visual attention: effects of cue validity and directionality

Covert orientation of attention was studied in 30 adults who fixated warning cues and pressed a button at target onset. Directional cues (arrows) indicated the most probable (p = 0.8) side of target occurrence. Subjects responded fastest when validly cued, slowest to invalidly cued targets, and at an intermediate rate when the cue (a cross) was not directional. Directional cues took longer to evaluate (increased N1 and P2 latencies) and produced more focussed attention and greater response preparation (enhanced CNV and P3 amplitude) than non-directional cues. These findings indicate that the expectancy of a target can be manipulated by a spatial cue at three levels, sensory, attention, and response preparation, and lead to changes in the sensory perceptual processing of the target. Validly cued targets produced an increase in P1 amplitude reflecting attention enhanced sensory processing whereas invalidly cued targets increased N1 and P3 amplitudes reflecting the re-orientation of attention, and further processing and updating of information required of low probability stimuli respectively. P3 latency to invalidly cued targets was also delayed reflecting the additional processes required to shift attention to a new location. The P3 latency validity effect was smaller than that found for response time suggesting response execution may also be affected by spatial attention.

Interhemispheric control of manual motor activity

The interhemispheric control of manual motor processes is reviewed, focusing on the clinical evidence from patients with commissurotomies and with agenesis of the corpus callosum. There is little evidence for a role of the corpus callosum in transferring explicit motor commands. Rather, the corpus callosum seems important for transferring lateralised information (such as verbal or visuospatial activity) of the pre-motor variety. Also, the corpus callosum may become very significant when movement begins: there appears to be a transcallosal passage of corollary motor signals and feedback sensory signals that are used to control asychronous bimanual movements and to inhibit the opposite hemisphere from interfering when a simple unimanual movement is required.

Auditory verbal learning test components as measures of the severity of closed-head injury

Auditory verbal learning and memory was assessed in 18 patients with moderate-severe closed-head injury (CHI). Compared to a matched control group, performance of the CHI subjects on all measures of the Auditory Verbal Learning Test (AVLT) was significantly worse. Discriminant function analysis correctly classified 90% of subjects as CHI or control using the three most reliable measures of the AVLT. Retention of the learning list following the distractor trial varied with severity of injury as indexed by duration of post-traumatic amnesia (PTA). The more severe the injury (longer PTA), the fewer words were recalled after interference (r = -0.72). Susceptibility of verbal memory to retroactive interference is sensitive to the presence and severity of CHI.

Test-retest reliability of a new form of the auditory verbal learning test (AVLT)

The equivalence between the original form (Form 1) of the Auditory Verbal Learning Test (AVLT), and a new form (Form 4) was examined in 51 normal adult subjects (20-67 years) of average estimated intelligence who were assessed in two separate sessions. Performance on the new form was equivalent to that on the original and most measures on the two tests showed significant positive correlations. Test-retest reliability of AVLT scores between sessions was also assessed, both globally and separately for Form 1 followed by Form 4 and for the reverse order. The most reliable measures on the AVLT were the total number of words learned over the five learning trials, (r =.77), and performance on the retention trial of the learning list following the presentation and performance of the distractor list (r =.70). These measures are sufficiently robust for use in clinical serial assessments.

Event-related potentials associated with covert orientation of visual attention in Parkinson's disease

Event-related potentials (ERPs) were measured in a group of patients with idiopathic Parkinson's disease and compared with a matched control group during a task involving covert orientation of visual attention. Central warning cues directed attention to the probable location of a lateralized signal that required a button-press response. Parkinson patients had enhanced post-cue P1 (at Oz) and P2 (at Cz) amplitudes, delayed N1 (at Oz) latencies, and diminished CNV amplitudes. Post-target amplitudes were similar to controls, except for an enhanced P1 to invalidly cued targets, and delayed N1 and P3 target latencies. These results indicate that Parkinson patients, in addition to their motor deficits, process spatial cues more effortfully and slowly, have impaired response preparation, and process imperative stimuli more slowly.

Galanin-containing fibers innervate substance P-containing neurons in the pedunculopontine tegmental nucleus in humans

Galanin is a putative peptide transmitter distributed widely in the central nervous system. Galanin shows potent inhibitory effects on neuronal activity and learning behaviors induced or mediated by acetylcholine. Here, we demonstrate that in humans there are abundant galanin-containing fibers in the pedunculopontine tegmental nucleus, the lateral dorsal tegmental nucleus and the oral pontine reticular nucleus. These neurons contain both acetylcholine and substance P (SP). Using a double-immunostaining method, we show that galanin-containing terminals from pericellular baskets around many SP-positive neurons in these nuclei. Our results suggest galanin may influence brain functions via inputs to the ascending mesopontine acetylcholine-containing nuclei.

Loss of C1 and C3 epinephrine-synthesizing neurons in the medulla oblongata in Parkinson's disease

We used immunohistochemical analysis to determine whether medulla oblongata neurons containing phenylethanolamine N-methyltransferase (PNMT) are affected in patients who died with idiopathic Parkinson's disease (n = 7) compared with age-matched control subjects who died with nonneurological diseases (n = 8). Transverse sections (50 microns) of medulla were prepared either for conventional neuropathological examination or for the immunohistochemical demonstration of PNMT. Immunopositive neurons at approximately 30 rostrocaudal levels, evenly spaced throughout the whole medulla, were mapped and cells in each section were counted with a camera lucida system linked to a computer. In the ventrolateral medulla, from the level of the obex to 11 mm rostral to the obex where the C1 group of neurons is located, there were 7,631 +/- 844 PNMT-positive neurons in control brains and 3,604 +/- 1,051 in brains affected by Parkinson's disease (47% of control). Many PNMT-positive neurons contained Lewy bodies. We observed a previously undescribed midline (C3) group of PNMT-positive neurons in normal brains, and this group was also severely affected (12% of control) in parkinsonian brains. Neither the C2 group nor the small PNMT-positive neurons in the nucleus tractus solitarii were significantly reduced in numbers but there was a reduction in the numbers of melanin-pigmented cells in both the ventrolateral (50% of control) and the dorsomedial (79% of control) region. Our results demonstrate a selective loss of C1 and C3 PNMT-positive neurons, providing the first quantitative evidence for damage to these presumed brainstem sympathetic premotor neurons in Parkinson's disease. These changes may underlie some of the autonomic symptoms occurring in this condition.

Age-related loss of dorsal vagal neurons in Parkinson's disease

Older patients who die with Parkinson's disease (PD) have fewer pigmented neurons in the locus coeruleus and fewer substance P-containing neurons in mesopontine tegmental nuclei. We analyzed two other medullary nuclei, the dorsal vagal nucleus and the hypoglossal nucleus, in eight PD patients and six normal controls by counting neurons in serial Nissl stained sections to determine the relationship between age at death and cell loss in these nuclei. PD-related neurodegenerative changes (Lewy bodies and neuronal loss) were present only in the dorsal vagal nucleus (13,637 +/- 1,323 neurons in PD, 24,885 +/- 1,157 in normal controls). Cells in the intermediate rostrocaudal part of the nucleus were most severely affected. There was a significant correlation between loss of vagal neurons and age at death in PD patients. No age-related cell loss was present in the dorsal vagal nucleus of normal brains, or in the hypoglossal nucleus in either PD or normal brains. These results confirm that age-related cell death depends on whether or not there is coexistent PD.

The case for graduate schools of medicine in Australia

The present length of the medical curriculum in Australia is, with one exception, six years. It is argued that the time is ripe for the development of some four-year graduate schools from among the existing ten medical schools. Selection from a pool of university graduates would permit a greater degree of self-selection of motivated students able to perform well in tertiary studies. At present admission to medicine occurs mainly direct from secondary school. It is argued that graduate students entering medicine would be more broadly educated, more mature and more self-directed in their studies and career selection. The curricula of such graduate schools could foster better integration of scientific knowledge and clinical practice. Such graduate schools would be concordant with current priorities of national policies on higher education.

The Flinders experiment in medical education revisited

OBJECTIVE

The undergraduate medical curriculum of the Flinders University of South Australia is reviewed and evaluated against American recommendations for the basic education of doctors practising in the 21st century.

DATA SOURCES

Two previous articles in The Medical Journal of Australia describing earlier versions of the Flinders curriculum and the report on General Professional Education for the Physician of the Association of American Medical Colleges.

DATA SYNTHESIS

The Flinders curriculum attempts to fully integrate the teaching of medical science and clinical disciplines. The earliest version of the curriculum emphasised horizontal integration of normal structure and function of body systems, followed by abnormalities of these systems, and finally clinical practice. The second version introduced vertical integration of basic science and clinical medicine within a body system. The present version attempts to balance the demands of horizontal and vertical integration. An important feature of all versions is the large proportion of time allowed for elective studies in most years of the course.

CONCLUSIONS

The Flinders curriculum has been able to adapt to the changing needs of medical education because its organisation is relatively free from the constraints of departmental rivalry over resources.

Substance P-containing neurons in the mesopontine tegmentum are severely affected in Parkinson's disease

Substance P immunoreactive (SP+) neurons were analysed quantitatively in serial sections of the mesopontine tegmentum in 6 patients with idiopathic Parkinson's disease and 5 age-matched normal controls. In the tegmentum of the Parkinson's disease brains many SP+ neurons contained swollen, twisted neuronal processes as well as Lewy bodies. There were significant reductions in the total number of SP+ neurons in the pedunculopontine tegmental nucleus (loss 43%), in the laterodorsal tegmental nucleus (loss 28%), in the oral pontine reticular nucleus (loss 41%) and in the median raphe nucleus (loss 76%). It was the large SP+ (greater than 20 microns) neurons that were particularly affected. In our control group we did not document a significant relationship between age at death and number of SP+ neurons in these tegmental nuclei or between age at death and number of pigmented neurons in the locus coeruleus. In contrast, in patients with Parkinson's disease, there was a strong inverse relationship between age at death and numbers of SP+ and pigmented neurons. Our findings suggest an interaction between the pathophysiological mechanisms initiated by Parkinson's disease and other processes related to ageing. Since tegmental SP+ neurons are affected by the primary pathological processes underlying Parkinson's disease as severely as catecholamine-synthesizing neurons are affected, theories of pathogenesis and therapeutic strategies in Parkinson's disease will need to take into account the involvement of these SP+ neurons.

Cytoarchitecture of serotonin-synthesizing neurons in the pontine tegmentum of the human brain

We have employed immunohistochemical and morphometric procedures to study serotonin-synthesizing (PH8-immunoreactive) neurons in the pontine reticular formation of the adult human. PH8-immunoreactive neurons were found in three cytoarchitectural regions: the median raphe nucleus (MnR), oral pontine reticular nucleus (PnO), and supralemniscal region (group B9). On the basis of cell size, morphology, and position, it was possible to distinguish distinct subgroups within the MnR (dorsal, midline, and paramedian cell clusters) and within the PnO (dorsal and central cell clusters), whereas within the B9 there were no distinct cell clusters. We have estimated that there are approximately 125,000 PH8-immunoreactive neurons in the human pontine tegmentum; 64,400 in the MnR, 30,700 in PnO and 29,000 in B9. The large numbers of serotonin-synthesizing neurons in the human pontine tegmentum contrasts with their relative paucity in nonprimate species such as rats and cats. Nonhuman primates also have large numbers of pontine serotonergic neurons but the morphology of these neurons and their spatial arrangement is significantly different in humans. These results are discussed with respect to the possible projections and functions of these neurons in humans.

Distribution, morphology and number of monoamine-synthesizing and substance P-containing neurons in the human dorsal raphe nucleus

The distribution, morphology and number of serotonin-, catecholamine- and substance P-containing neurons in the human dorsal raphe nucleus were studied. Parallel series of sections were prepared from 10 human brainstems obtained at autopsy from patients without neurological disease aged between 42 and 88 years. The neurons were identified using immunohistochemistry with antibodies raised against phenylalanine hydroxylase (tryptophan hydroxylase-containing, serotonin neurons), tyrosine hydroxylase (catecholamine neurons) and substance P. A reference series of Nissl-stained sections was also prepared and data published separately were used to delineate the subnuclear divisions of the dorsal raphe nucleus and to establish the total number of neurons in each subnucleus. The following principal findings emerged. (1) Serotonin-synthesizing neurons are present in all regions of the dorsal raphe nucleus and their total number is 165,000 +/- 34,000. The same types of neurons as those seen in Nissl material characterize each of the five subnuclei (caudal, dorsal, ventral, ventrolateral and interfascicular). (2) Substance P-containing neurons mostly occupy the rostral part of the nucleus and their number is 74,600 +/- 17,600. (3) Catecholamine cells are only found in the rostral part of the dorsal raphe nucleus and their number is 5600 +/- 3400. (4) In the ventral and interfascicular subnuclei the combined number of serotonin-synthesizing and substance P-containing neurons exceeds the total number of Nissl-stained neurons suggesting that serotonin and substance P co-exist in a substantial part of the cell population of the dorsal raphe nucleus. This is further supported by the highly similar morphology and size of these neurons. It is concluded that there are demonstrable chemical differences between the various subregions of the human dorsal raphe nucleus. These differences are in harmony with the results of hodological studies in animals, which have demonstrated differential projection pathways emerging from this nucleus.

Galanin immunoreactive neurons in the human hypothalamus: colocalization with vasopressin-containing neurons

Galanin (GA) is a recently described neuropeptide that has been demonstrated to be widely distributed in the hypothalamus of experimental animals. So far there is no immunohistochemical description of GA in the human hypothalamus and, in particular, no studies of the colocalization of this neuropeptide with other transmitter candidates in the human hypothalamus. We have now investigated this question immunohistochemically by using human brains fixed by vascular perfusion within 24 hours of death. Nerve cell bodies and fibers stained for GA were observed throughout the hypothalamus. Major populations of GA-ir cell bodies were found in the suprachiasmatic, intermediate, supraoptic, paraventricular, arcuate, tuberomammillary, and supramammillary nuclei. Scattered positive neurons were found in the periventricular preoptic area, the posterior hypothalamic nucleus, the lateral hypothalamic area, and zona incerta. A few positive cells were located in the dorsomedial and ventromedial hypothalamic nuclei. The number of GA-ir neurons estimated from three brains was 11,100 +/- 2,400 for the intermediate nucleus, 57,800 +/- 9,100 for the supraoptic nucleus and 47,400 +/- 13,900 for the paraventricular nucleus. GA-ir fibers were widely distributed in the hypothalamus. They were more dense in the periventricular and medial hypothalamic zones, whereas the lateral tuberal nuclei and the dorsolateral part of the supraoptic nucleus contained sparse positive fibers. The mammillary complex contained almost no GA-ir fibers. In the ventromedial tuberal region, GA-ir axons formed bundles travelling down in the infundibular stem. In the median eminence the vascular plexus was wrapped by GA-ir fiber networks. The coexistence of GA with arginine vasopressin (AVP), oxytocin (OXY), and tyrosine hydroxylase (TH) was examined in the supraoptic, paraventricular, and suprachiasmatic nuclei in adjacent paraffin sections. Neurons containing both GA and AVP were very common in the supraoptic nucleus and also occurred in the paraventricular and suprachiasmatic nuclei. The supraoptic and paraventricular nuclei also contained some neurons immunoreactive for both GA and OXY. Neurons positive for GA and TH were rare. The topographic distribution of GA-ir neuronal structures in the hypothalamus and the colocalization of GA, principally with AVP and to a lesser extent with OXY, in some hypothalamic nuclei constitute anatomical evidence that this neuropeptide may be involved in the regulation of endocrine, autonomic, and behavioural homeostatic responses.

Neuropathology of immunohistochemically identified brainstem neurons in Parkinson's disease

Regional loss of immunohistochemically identified neurons in serial sections through the brainstem of 4 patients with idiopathic Parkinson's disease was compared with equivalent sections from 4 age-matched control subjects. In the Parkinson brains, the catecholamine cell groups of the midbrain, pons, and medulla showed variable neuropathological changes. All dopaminergic nuclei were variably affected, but were most severely affected in the caudal, central substantia nigra. The pontine noradrenergic locus ceruleus showed variable degrees of degeneration. There was also a substantial loss of substance P-containing neurons in the pedunculopontine tegmental nucleus. However, the most severely affected cell group in the pons was the serotonin-synthesizing neurons in the median raphe. In the medulla, substantial neuronal loss was found in several diverse cell groups including the adrenaline-synthesizing and neuropeptide Y-containing neurons in the rostral ventrolateral medulla, the serotonin-synthesizing neurons in the raphe obscurus nucleus, the substance P-containing neurons in the lateral reticular formation, as well as the substance P-containing neurons in the dorsal motor vagal nucleus. Lewy bodies were present in immunohistochemically identified neurons in many of these regions, indicating that they were affected directly by the disease process. These widespread but region- and transmitter-specific changes help account for the diversity of motor, cognitive, and autonomic manifestations of Parkinson's disease.

Loss of brainstem serotonin- and substance P-containing neurons in Parkinson's disease

Using postmortem immunohistochemical analysis, we have identified degeneration of several different neuronal cell groups in the brainstem of patients dying with idiopathic Parkinson's disease. We report the first chemically identified loss of presumed serotonin neurons in the median raphe nucleus of the pons and of substance P-containing preganglionic neurons in the dorsal motor vagal nucleus. This evidence is concordant with other evidence that the primary neuropathological process is not confined either to a single pathway or to neurons containing a particular transmitter. Rather it appears that Parkinson's disease affects several classes of neurons in localized areas of the brainstem.

Substance P-containing neurons in the pontomesencephalic tegmentum of the human brain

We have employed immunohistochemical and computerized morphometric procedures to study substance P-containing neurons in the tegmentum of adult humans. An estimated 192,500 +/- 40,500 substance P-containing neurons were found in three main cytoarchitectural regions: the mesencephalic reticular formation, the central gray, and the pontine reticular formation. The morphology of the immunoreactive neurons varied according to the region in which they were found. On the basis of size alone two types of substance P-containing neurons, large and small, were readily distinguishable by eye and measurement. Within each of the three main regions it was possible to distinguish distinct subgroups using cell size, morphology and position. Large neurons were concentrated in the caudal midbrain (pedunculopontine tegmental nuclei), in the oral pontine reticular nucleus and in the lateral dorsal tegmental nucleus. In contrast, small neurons were concentrated in the rostral mesencephalic reticular formation (cuniform nuclei). Both small and large neurons were found in the midbrain and pontine raphe nuclei. In addition, small neurons were concentrated in discrete midline regions (the periaqueductal gray, the tegmental nuclei of the pontine central gray, and the interpeduncular nucleus). The findings suggest that the majority of neurons in the brainstem tegmental nuclei previously identified as cholinergic also contain substance P in humans.

Covert orientation of visual attention in Parkinson's disease: an impairment in the maintenance of attention

Covert orientation of attention was studied in a group of patients with idiopathic Parkinson's disease and compared to a matched control group using a cued reaction time task which measured disengagement, covert movement and engagement of attention. Parkinson patients had an increased response latency and disengaged from attended locations more readily than controls. This impairment in the maintenance of attention in Parkinson's disease was comparable to that produced in a previous study by pharmacological blockade of brain catecholamines in normal subjects. It is suggested that an impairment in the maintenance of oriented attention may underlie some of the cognitive deficits reported in Parkinson's disease.

Catecholamines and the covert orientation of attention in humans

The role of brain catecholamines in covert orienting was tested in normal subjects using a cued reaction time paradigm which measures the directional engagement, disengagement and movement of attention. Droperidol and clonidine were administered intravenously to suppress central dopamine and noradrenaline transmission. Both drugs produced reductions in the cost of invalid cueing without change in the benefit of valid cueing suggesting that both noradrenaline and dopamine are involved in facilitating the disengagement of attention. These results are relevant to the slowed disengagement observed with parietal lesions in monkeys and humans since this region of the cortex associated with visuospatial analysis receives a dense innervation by both dopamine and noradrenaline projections in primates.

Tyrosine hydroxylase-containing neurons in the supraoptic and paraventricular nuclei of the adult human

We have studied the distribution of tyrosine hydroxylase-containing neurons in the paraventricular nucleus (PVN) and supraoptic nucleus (SON) of the adult human hypothalamus. Large numbers of these neurons were seen in these hypothalamic nuclei; approximately 40% of all the cells within the SON and PVN were immunoreactive for tyrosine hydroxylase (TH-ir). Most of these cells were magnocellular. Their distribution was compared to that of arginine-vasopressin-immunoreactive (AVP-ir) cells. In the SON a greater proportion of magnocellular TH-ir cells was found caudally compared to AVP-ir cells. In the PVN the magnocellular TH-ir cells were larger in mean diameter compared to AVP-ir cells. In double-immunofluorescence experiments some TH-ir cells contained oxytocin immunoreactivity but none contained AVP-ir. In the adult human a large number of PVN and SON magnocellular cells appear to synthesize a catecholamine. A subclass of these neurons also synthesize oxytocin but most cells are distinct from the classically described neurosecretory neurons.

Distribution of monoamine-synthesizing neurons in the human medulla oblongata

We have employed immunohistochemical and morphometric procedures to study the distribution of monoamine-synthesizing neurons in the medulla oblongata of the adult human, utilizing antibodies to tyrosine hydroxylase (TH), phenylethanolamine N-methyltransferase (PNMT), and phenylalanine hydroxylase (PH8). In the human brain, the antigen with which PH8 reacts occurs within neurons that presumably synthesize serotonin (Haan et al., '87). Neurons containing these antigens were mapped and counted in successive coronal sections with the aid of a computer-assisted procedure. The results indicate that monoamine-synthesizing neurons are distributed in the human brain in patterns broadly similar to those described for other species. TH-immunoreactive cells extended caudorostrally for approximately 32 mm commencing at the spinomedullary junction and ending 8 mm caudal to the pontomedullary junction. In coronal sections these TH-immunoreactive neurons were seen in the lateral medulla dorsal to the inferior olive extending in a continuous band to the dorsomedial medulla. Above the obex the majority of these cells apparently synthesize adrenaline since many PNMT-immunoreactive cells were also found in this region. There were few or no PNMT-immunoreactive cells caudal to the obex, indicating that the TH-immunoreactive cells in this region synthesize either noradrenaline or dopamine. Approximately 65% of these TH-immunoreactive neurons contained melanin pigment, whereas few or no PNMT-immunoreactive cells contained melanin pigment. PH8-immunoreactive cells extended throughout the rostrocaudal extent of the medulla oblongata (approximately 40 mm). In coronal sections the majority were found in the medullary raphe nuclei. However, many cells throughout the rostrocaudal extent of the medulla were found laterally intermingled with catecholamine-synthesizing neurons. Occasional neurons in the lateral medulla appeared to contain both PH8- and TH-immunoreactivity.

The distribution of neuropeptide Y-like immunoreactive neurons in the human medulla oblongata

We have described the distribution of neuropeptide Y-like immunoreactive neurons in the medulla oblongata of the adult human. The majority of neuropeptide Y-like immunoreactive cells were found in four regions of the medulla: the ventrolateral reticular formation, the dorsomedial medulla, the secondary sensory nuclei and the rostral raphe nuclei. The morphology of neuropeptide Y-like immunoreactive cells varied in each of these regions. In the ventrolateral reticular formation, the labelled neurons were round and pigmented caudal to the obex but elongated and non-pigmented rostral to the obex; in the dorsomedial medulla, they were triangular and pigmented caudal to but not rostral to the obex; in the secondary sensory nuclei, they were multipolar, non-pigmented and significantly smaller than in the other areas; in the rostral raphe nuclei, they were bipolar and non-pigmented. Colocalization studies revealed that many neuropeptide Y-like immunoreactive cells also synthesize monoamines, consistent with conclusions based on a quantitative comparison of their distributions. Neuropeptide Y-like immunoreactivity was present in about 25% of presumed noradrenaline-synthesizing cells in the caudal ventrolateral medulla (corresponding to the A1 region); about 50% of adrenaline- and 70% of presumed serotonin-synthesizing cells in the rostral ventrolateral medulla (C1 and B2-3 regions); 90-100% of presumed noradrenaline-synthesizing cells in the dorsomedial medulla at and above the obex (A2 region); about 50% of adrenaline-synthesizing cells in the rostral dorsomedial medulla (C2 region); about 5% of presumed serotonin-synthesizing cells in the rostral raphe nuclei (B2-3 region). The largest of these groups was the presumed serotonin-synthesizing cells that contained neuropeptide Y-like immunoreactivity in the rostral ventrolateral medulla. This is the first report of such a cell group in the medulla of any mammal, and emphasizes the neuroanatomical differences between humans and other species.

Event-related potentials in autistic and healthy children on an auditory choice reaction time task

Event-related potentials (ERPs) were recorded from midline (Fz, Cz, Pz) and lateral sites (F3, F4, P3, P4) in autistic children (n = 7) and age-matched controls (n = 9) on an auditory choice reaction time task. Subjects were asked to press a button to an infrequent target (500 Hz, P = 0.14) and to ignore higher pitched infrequent (2000 Hz, P = 0.14) and frequent (1000 Hz) non-targets. Autistic subjects made twice as many errors of omission as controls and showed a higher criterion (beta) for targets. Maximum ERP peak amplitudes showed a more varied scalp distribution in the autistic group. N1 latencies were consistently shorter in the autistic group and in 3 subjects the target P3 latencies were markedly longer than for the controls. Compared to controls, the N1 amplitude of the autistic response was larger to the rare stimuli (particularly to non-targets). The amplitude of the P3 component was smaller in the autistic group (particularly to the target). The stimuli were also presented in a passive condition requiring no response. After subtraction of the waveform obtained in the passive condition from that obtained in the active condition or subtraction of the waveform elicited by the rare non-target from that elicited by the target, N1 target amplitude was larger in control than in autistic children. Autistic subjects showed more early negativity to the rare non-target at left frontal and a larger P3 to the target at right parietal sites. ERPs of autistic children are more responsive to stimulus features (e.g. high/rare non-target tone) and less responsive to their associations or meaningfulness (e.g. target P3). Attention-related ERPs of autistic children show signs of precocious (right dominance for P3) and delayed development (P3 not maximal at parietal sites).

Distribution of substance P-like immunoreactive neurons in the human medulla oblongata: co-localization with monoamine-synthesizing neurons

The raphe nuclei also contained SP-like immunoreactivity (up to 30%) while few monoamine-synthesizing neurons in the lateral and dorsomedial medulla contained SP-like immunoreactivity (approximately 5% of presumed serotonin-, noradrenaline-, and adren- the adult human. The majority of SP-like immunoreactive neurons were found in four main regions: the lateral medulla, the dorsomedial medulla, the spinal trigeminal nucleus, and the raphe nuclei. The morphology of immunoreactive cells varied according to the region in which they were found. In contrast to previous studies, we found large numbers (90,000) of SP-like immunoreactive neurons throughout the adult human medulla oblongata. The distribution of these SP-like immunoreactive neurons appears to be significantly different from those described in the rat and cat. These results were compared to the distributions of monoamine-synthesizing and neuropeptide Y (NPY)-like immunoreactive neurons in the human medulla previously reported (Halliday et al.: Neuroscience, in press, 1988a; J. Comp. Neurol., in press, 1988b). Colocalization studies revealed that many presumed serotonin-synthesizing neurons in the raphe nuclei also contained SP-like immunoreactivity (up to 30%) while few monoamine-synthesizing neurons in the lateral and dorsomedial medulla contained SP-like immunoreactivity (approximately 5% of presumed serotonin-, noradrenaline-, and adrenaline-synthesizing neurons). The distributions of SP- and NPY-like immunoreactive neurons were similar, although SP-like immunoreactive neurons were concentrated in the lateral regions of the same structures. We have found that the distributions of monoamine-synthesizing, NPY-, and SP-like immunoreactive neurons significantly overlap, particularly in the lateral medulla of the adult human. There is a large increase in the number of these cells in this region compared to other species, emphasizing the neuroanatomical differences between humans and other species.

Catecholamines and attention. I: Animal and clinical studies

One important function of the catecholamine innervation of the cerebral cortex may be the control of attention. Of particular interest are the catecholamine projections to the cerebral cortex from the reticular formation, namely the dopamine neurons of the ventral tegmentum of the midbrain and the noradrenergic neurons of the locus coeruleus in the upper pons. Animal studies implicate noradrenaline and dopamine in a wide range of attention-related behaviours involving search and exploratory activity, distractibility, response rate, discriminability and the switching of attention. Most human studies come from the clinical literature relating to schizophrenia, Parkinson's disease and attention deficit disorder. An association has been claimed in each of these conditions between abnormal catecholamine activity (in particular dopamine) and attentional dysfunction. In particular, difficulty with the attachment of appropriate responses to environmental stimuli, akin to those observed in animals with lesions to central dopamine pathways, indicates a role for dopamine in response selection processes. Overall, the animal and human studies reviewed indicate a role for central noradrenaline and dopamine in the early and late processing of information, respectively.

Catecholamines and attention. II: Pharmacological studies in normal humans

Part I of this review [17] found evidence from animal and clinical studies of a role for catecholamines in the control of attention. This part of the review examines the results of a systematic study of the acute effects of a number of catecholamine active drugs on measures of attention in normal adults. The results are interpreted within the context of a general capacity model of information processing in which level of arousal determines the capacity to process stimulus information and level of activation the capacity for processing response demands. Whilst the dopamine antagonist, droperidol, and the alpha agonist, clonidine, had similar effects on behavioural indices of processing capacity and reports of the degree of effort required to carry out processing, they differentially affected subjective state and measures of activation and arousal. These differences provide some support for the hypothesis that central noradrenaline and dopamine modulate the capacity for early and late processing of information, respectively, in humans.

Role of monoamine pathways in the control of attention: effects of droperidol and methylphenidate in normal adult humans

Methylphenidate (0.65 mg/kg), droperidol (15 micrograms/kg) or placebo were administered to normal adult males undertaking a dichotic auditory attention task. Performance following placebo, as measured by the ability of subjects to detect nominated target words and discriminate them from phonemically distracting words, was superior when attention was focused on one ear than when divided between the ears. Following droperidol, target detection and discrimination were reduced for both divided and focused attention and in the latter case responses were also slowed. However, these effects were small compared to the striking withdrawn behaviour of the subjects, who reported an unwillingness to attend to external events. Methylphenidate reversed all of these effects when administered following droperidol. Administered alone, methylphenidate had no effect on dichotic measures of attention but had marked effects on spontaneous behaviour, when most subjects reported a substantial increase in both the field and distractibility of attention. These results are interpreted as implicating central dopaminergic pathways in the regulation of attention without precluding a role for other neurotransmitter systems including ascending noradrenaline and serotonin pathways to cerebral cortex. The disparity between these objective and subjective assessments of the effects of the drugs on attention is discussed in terms of the degree of mental effort voluntarily brought to bear by subjects in the selective allocation of their attentional capacity.

Role of monoamine pathways in attention and effort: effects of clonidine and methylphenidate in normal adult humans

Methylphenidate (0.65 mg/kg), clonidine (200 micrograms) or placebo were administered to normal adult males undertaking a dichotic monitoring task in which they were required to detect nominated target words and discriminate them from phonemic distractors. Following placebo, performance was better when attention was focused than when divided. Following clonidine, subjects were poorer and slower at discriminating targets during both divided and focused attention and subjectively were withdrawn and reported difficulties with concentration. Methylphenidate had no effect on target discrimination or response time but raised the rate of response and had marked effects on spontaneous behaviour in which an increased attention capacity was generally reported. The effects on attention of the pharmacological agents employed in this study are attributed to their effects on central monoamines. The disparity noted between objective and subjective assessments of attention is discussed in terms of the voluntary allocation of effort.

Phentolamine increases neuronal binding and retrograde transport of dopamine beta-hydroxylase antibodies

When 125I-labelled antibodies against dopamine beta-hydroxylase (DBH) were injected into the anterior eye chamber of guinea-pigs they bound to sympathetic nerve terminals, were internalized into the axons and retrogradely transported to the ipsilateral superior cervical ganglion (SCG). This process was demonstrated to depend on specific binding sites since neutralized antibodies were not taken up and transported. The alpha-receptor antagonist phentolamine caused a 2.5-fold increase in binding in the iris and a 2.1-fold increase in accumulation of [125I]anti-DBH in the SCG. The results demonstrate that retrograde axonal transport of synaptic vesicle components is coupled to their turnover in nerve terminals.

Dopamine beta-hydroxylase in health and disease

DBH is a copper-containing oxygenase that catalyzes the hydroxylation of the beta carbon of a wide variety of phenylethylamine derivatives using molecular oxygen ascorbate as cofactors. It is a glycoprotein with a molecular weight of 290,000 and consists of four identical subunits, each with a single copper atom and 5% carbohydrate by weight. The enzyme is a constituent of catecholamine storage vesicles in chromaffin cell and adrenergic neurons in the peripheral and central nervous system where it functions to synthesize noradrenaline from dopamine. Although endogenous inhibitors have been isolated, they have not been demonstrated to have a physiological function, and the kinetics of the enzyme in vitro and in vivo suggest that the enzyme is not a rate limiting step in catecholamine synthesis under normal conditions. DBH exists in both a soluble form within vesicles and as a constituent of their membranes with its active site directed inward. The significance of the partition of the enzyme into soluble and membrane forms is not understood, although the soluble form has a fivefold greater homospecific activity. DBH has been one of the most intensively investigated enzymes in neurochemistry for several reasons. It is a readily assayable constitutent of catecholamine storage vesicles and, as such, provides a convenient biochemical marker for subcellular fractionation work and studies of the cellular regulation of catecholamine synthesis, storage, and release. The adrenal medulla is a rich source of the enzyme for purification, and the purified enzyme is highly antigenic, thereby enabling the use of several immunological techniques to study the cellular dynamics of the enzyme and the organelles in which it is located. These include radioimmunoassay, immunohistochemistry, and cytochemistry. This review firstly summarizes the present state of knowledge concerning the molecular properties of DBH. It then describes the tissue, cellular, and subcellular localization of the enzyme and its physiological regulation. The remainder of the review concentrates on those aspects of research on DBH in which the authors have participated that have led to general advances such as the development of the concept of homospecific activity, the introduction of immunohistochemistry for the localization of enzymes involved in transmitter metabolism, the release of macromolecules from synaptic vesicles during the process of exocytosis, the use of antibodies to DBH administered in vivo to study the fate of synaptic vesicle membranes and to produce specific immunological lesions of noradrenergic nerves in the peripheral and central nervous system, the genetic, environmental, and physiological determinants of serum DBH activity as an index of sympathetic function in animals and man, and the question of its diagnostic value in disease.

Immune lesions of central noradrenergic neurons produced by antibodies to dopamine-beta-hydroxylase

(1) Intraventricular injection of antibodies to dopamine-beta-hydroxylase (DBH) caused degeneration of central noradrenergic nerve terminals in rats and guinea-pigs. In rats it was necessary to infuse exogenous complement in the form of guinea-pig serum together with the anti-DBH, whereas in guinea-pigs the anti-DBH was effective on its own. Control animals were infused with equivalent amounts of non-immune serum and complement and showed no signs of degeneration other than in the region of the needle tract. (2) There was a loss of varicosities in most terminal fields of the noradrenergic projections and swollen distorted axons were seen in both ascending and descending noradrenergic pathways. Noradrenergic cell bodies in the locus coeruleus and subcoeruleus appeared unaffected. No histochemical changes were observed in dopaminergic neurons. (3) The ultrastructural changes in degenerating axons that were first identifided by fluorescence histochemistry included swelling, vacuolation, accumulation of dense cored vesicles, lysosome-like bodies and smooth membranous sacs. The surrounding neuropil appeared normal. (4) There was a significant depletion of noradrenaline in all regions of the rat brain ranging from 20% in the hypothalamus to 80% in the neocortex. Dopamine concentrations were unaffected. (5) These observations provide a new approach to the production of selective lesions in specific neurotransmitter pathways that could be extended to non-adrenergic neurones. They may also be useful as a model for the study of autoimmune diseases of the nervous system.

Noradrenergic transmission in isolated guinea-pig intestine following in vivo administration of antibodies to dopamine beta-hydroxylase

The effectiveness of transmission from noradrenergic nerves supplying the guinea-pig ileum was evaluated in normal preparations and in preparations taken from animals injected 18 h to 4 days previously with antiserum to dopamine beta-hydroxylase. Degeneration of the nerves following the antiserum was monitored histochemically in the same preparations. A decline in the effectiveness of transmission, which paralleled the degeneration of the nerves, was observed. The earliest effects were detected at 18 h and the greatest effect was found at 2-4 days following the administration of antiserum. Binding of the antibodies has been detected as early as 6 h after injection. It is therefore concluded that binding of the antibodies to the nerves, per se, does not significantly compromise transmission, and that histochemical evidence of degeneration can be used to indicate the onset of functional deterioration of noradrenergic nerves following their exposure to antibodies to dopamine beta-hydroxylase.

Involvement of complement in degeneration of sympathetic nerves after administration of antiserum to dopamine beta-hydroxylase

The involvement of complement in the degeneration of noradrenergic nerves in the guinea-pig iris produced by administration of antibody to dopamine beta-hydroxylase (DBH) in vivo was investigated histochemically. When 500 microliter of antiserum to DBH was injected systemically, no evidence of degeneration was observed in the iris although the noradrenergic supply of the myenteric plexus of the ileum degenerated within 2 days. However, injection of 20 microliter of complement (C) into the anterior chamber of one eye within 2 days of the systemic administration of anti-DBH produced a degeneration of 50--90% of noradrenergic terminals in the iris, the nerves of the iris of the contralateral uninjected eye being unaffected. Electron microscopy confirmed the presence of degenerating nerve terminals in the iris. The extent of degeneration produced by addition of C decreased when C was injected at increasing intervals after the antiserum. Intraocular injection of 5 microliter of anti-DBH together with 20 microliter of C caused a substantial degeneration of noradrenergic nerves in the iris. In contrast, intraocular injection of the Fab'2 fragment of anti-DBH (which did not bind C, but still bound DBH in vitro and in vivo) failed to cause degeneration in the presence of 20 microliter of C. The degeneration of guinea-pig sympathetic nerves caused by antibodies to DBH thus appears to be due to a complement mediated lysis of sympathetic axon membranes. The relative susceptibilities of the noradrenergic fibres in different tissues probably depend on the local concentrations of anti-DBH and C.