The ecological validity of tests of executive function

Ninety-two mixed etiology neurological patients and 216 control participants were assessed on a range of neuropsychological tests, including 10 neuropsychological measures of executive function derived from 6 different tests. People who knew the patients well (relatives or carers) completed a questionnaire about the patient's dysexecutive problems in everyday life, and this paper reports the extent to which the tests predicted the patients' everyday life problems. All of the tests were significantly predictive of at least some of the behavioral and cognitive deficits reported by patients' carers. However, factor analysis of the patients' dysexecutive symptoms suggested a fractionation of the dysexecutive syndrome, with neuropsychological tests loading differentially on 3 underlying cognitive factors (Inhibition, Intentionality, and Executive Memory), supporting the conclusions that different tests measure different cognitive processes, and that there may be limits to the fractionation of the executive system.

Assessment after extremely severe head injury in a case of life or death: further support for McMillan

This paper is a sequel to that of McMillan (1997) and describes further assessment of an extremely severely head injured patient. A combination of direct observations, structured interviews with staff, simple cognitive tests and questions with yes/no answers were used to assess communication and cognitive function in an extremely severely head injured patient with minimal ability to respond. Results confirmed the finding of McMillan and showed that the patient could understand and respond consistently to simple commands, could answer simple autobiographical questions consistently and clearly expressed her wish to live. The results of this study and that of McMillan confirm that valid assessment of minimally responsive patients is possible and that a number of different approaches are appropriate.

External cueing systems in the rehabilitation of executive impairments of action

The use of a mnemonic cueing system (NeuroPage) and a paper and pencil checklist in the rehabilitation of executive problems in a 50-year-old woman are described. Following a CVA 7 years earlier, the patient, despite intact general intellectual and memory functioning, had specific executive impairments of attention, planning, realizing intended actions, and also exhibited behavioral routines similar in form to obsessive-compulsive rituals. In a series of ABAB single-case experimental designs, the efficacy of 2 external cueing systems in prompting appropriately timed action is demonstrated. It is argued that the combination of external control and increased sustained attention to action were critical to the success of NeuroPage with this patient. Furthermore it is hypothesized that the checklist was effective in facilitating the patient's ability to foresee and recognize the consequences of her actions, which in turn had an impact on the probability of her changing those same actions.

Genetic heterogeneity in familial hyperinsulinism

Familial hyperinsulinism (HI) is a disorder characterized by dysregulation of insulin secretion and profound hypoglycemia. Mutations in both the Kir6.2 and sulfonylurea receptor (SUR1) genes have been associated with the autosomal recessive form of this disorder. In this study, the spectrum and frequency of SUR1 mutations in HI and their significance to clinical manifestations of the disease were investigated by screening 45 HI probands of various ethnic origins for mutations in the SUR1 gene. Single-strand conformation polymorphism (SSCP) and nucleotide sequence analyses of genomic DNA revealed a total of 17 novel and three previously described mutations in SUR1 . The novel mutations comprised one nonsense and 10 missense mutations, two deletions, three mutations in consensus splice-site sequences and an in-frame insertion of six nucleotides. One mutation occurred in the first nucleotide binding domain (NBF-1) of the SUR1 molecule and another eight mutations were located in the second nucleotide binding domain (NBF-2), including two at highly conserved amino acid residues within the Walker A sequence motif. The majority of the remaining mutations was distributed throughout the three putative transmembrane domains of the SUR1 protein. With the exception of the 3993-9G-->A mutation, which was detected on 4.5% (4/88) disease chromosomes, allelic frequencies for the identified mutations varied between 1.1 and 2.3% for HI chromosomes, indicating that each mutation was rare within the patient cohort. The clinical manifestations of HI in those patients homozygous for mutations in the SUR1 gene are described. In contrast with the allelic homogeneity of HI previously described in Ashkenazi Jewish patients, these findings suggest that a large degree of allelic heterogeneity at the SUR1 locus exists in non-Ashkenazi HI patients. These data have important implications for genetic counseling and prenatal diagnosis of HI, and also provide a basis to further elucidate the molecular mechanisms underlying the pathophysiology of this disease.

Recovery of cognitive functions following nonprogressive brain injury

It has recently become clear that the adult human brain is capable of more plasticity than previously thought. Investigations into the natural history of change following brain injury demonstrate that partial recovery of function can and does occur. Furthermore, there is increasing evidence that intervention through re-training or provision of compensatory memory aids can result in improved cognitive functioning.

A nonsense mutation in the inward rectifier potassium channel gene, Kir6.2, is associated with familial hyperinsulinism

ATP-sensitive potassium (K[ATP]) channels are an essential component of glucose-dependent insulin secretion in pancreatic islet beta-cells. These channels comprise the sulfonylurea receptor (SUR1) and Kir6.2, a member of the inward rectifier K+ channel family. Mutations in the SUR1 subunit are associated with familial hyperinsulinism (HI) (MIM:256450), an inherited disorder characterized by hyperinsulinism in the neonate. Since the Kir6.2 gene maps to human chromosome 11p15.1 (1,2), which also encompasses a locus for HI, we screened the Kir6.2 gene for the presence of mutations in 78 HI probands by single-strand conformation polymorphism (SSCP) and nucleotide sequence analyses. A nonsense mutation, Tyr-->Stop at codon 12 (designated Y12X) was observed in the homozygous state in a single proband. 86Rb+ efflux measurements and single-channel recordings of COS-1 cells co-expressing SUR1 and either wild-type or Y12X mutant Kir6.2 proteins confirmed that K(ATP) channel activity was abolished by this nonsense mutation. The identification of an HI patient homozygous for the Kir6.2/Y12X allele affords an opportunity to observe clinical features associated with mutations resulting in an absence of Kir6.2. These data provide evidence that mutations in the Kir6.2 subunit of the islet beta-cell K(ATP) channel are associated with the HI phenotype and also suggest that the majority of HI cases are not attributable to mutations in the coding region of the Kir6.2 gene.

Cognitive rehabilitation: how it is and how it might be

This paper suggests there are, at present, four main kinds of cognitive rehabilitation programs for brain injured people. The first attempts to rehabilitate cognitive deficits through drills and exercises. The second uses theoretical models from cognitive psychology to identify deficits in order to remediate them. The third is primarily a patient-driven approach that uses a combination of learning theory, cognitive psychology, and neuropsychology to identify and remediate cognitive difficulties. The fourth is the holistic approach that has, as its basic philosophy, a belief that cognitive functions cannot be divorced from emotion, motivation, or other noncognitive functions, and consequently all aspects of functioning should be addressed in rehabilitation programs. Despite some overlap between these approaches, there are major differences. The two main arguments offered in this paper are (1) that the first two approaches do not lead to good clinical rehabilitation practice; and (2) that a synthesis of the second two approaches would result in the best cognitive rehabilitation model.

Knowing where and knowing what: a double dissociation

We report a double dissociation between visuo-spatial abilities and semantic knowledge (knowledge of the names and attributes of objects and people), in two brain-injured people with longstanding stable impairments, using a wide range of tests to explore the extent of the dissociation, MU, who has bilateral lesions of occipito-parietal cortex, shows severe spatial disorientation with relatively well-preserved semantic knowledge. He is contrasted with JBR, who has bilateral temporal lobe damage and shows severe semantic problems and no impairment on visuo-spatial tasks. Our findings thus demonstrate a double dissociation between the performance of semantic and spatial tasks by MU and JBR. This pattern is consistent with Ungerleider and Mishkin's (1982) neurophysiological hypothesis of separable cortical visual pathways; one which is specialised for spatial perception and follows a dorsal route from occipital to parietal lobes, and the other following a more ventral route from occipital to temporal lobes, whose target is semantic information needed in specifying what an object is.

Evaluation of NeuroPage: a new memory aid

This report describes NeuroPage, a simple and portable paging system, developed in California by the engineer father of a son with head injury working together with a neuropsychologist. Using an ABA single case experimental design, the efficacy of NeuroPage was evaluated with 15 neurologically impaired subjects all of whom had significant everyday memory problems because of organic memory impairment or because of problems with planning and organisation consequent on frontal lobe damage. Data were analysed with an odds ratio test which takes into account different underlying success rates for each target and calculates an average improvement factor. This test showed a significant improvement between the baseline and the treatment phases for each subject (P<0.05).

Assessment of the dysexecutive syndrome in schizophrenia

BACKGROUND

Cognitive neuropsychological theories hypothesize a role for frontal lobe executive deficits in the aetiology of schizophrenic symptoms. The study examined the performance of a schizophrenic group on the Behavioural Assessment of the Dysexecutive Syndrome (BADS; Wilson et al. 1996), a test battery which assesses the 'everyday' difficulties associated with the dysexecutive syndrome. Performance of the schizophrenics was contrasted with that of brain injured and healthy volunteer groups.

METHODS

Matched groups of 31 schizophrenic patients, 35 patients with brain injuries and 26 healthy volunteers were administered the BADS. Patients were also given tests of general intelligence and memory. Patients and their relatives/carers also completed a questionnaire rating day-to-day failures of executive functioning.

RESULTS

Schizophrenic and brain-injured patients showed impairment on the BADS, compared to healthy controls. There were no significant differences between the two patient groups. Significant impairment was found in a subgroup of 16 schizophrenics who showed otherwise intact general intellectual functioning, suggesting the existence of a specific executive deficit. Among the schizophrenic patient group there was evidence of a dissociation between executive and memory impairments. A significant correlation existed between performance on the BADS and relatives ratings of executive problems for the brain injured group, but not for the schizophrenic group.

CONCLUSIONS

The BADS is a useful tool for identifying executive deficits in people with a diagnosis of schizophrenia, especially those who are otherwise generally intellectually intact. This is particularly important in the context of rehabilitation and community transition programmes.

Understanding strategies for treating HIV

A great deal has been learned over the past 1 to 2 years about treatment of HIV infection. Viral load testing now provides a reliable method of assessing the effectiveness of any treatment regimen. And it is now clear that triple combinations of drugs (typically two nucleoside analogues and one protease inhibitor) are producing excellent reductions in viral load with concomitant elevations in CD4+ counts. This new triple-approach drug regimen has demonstrated clear advantage in delaying disease progression in persons in very early or late stages of the disease.

Semantic memory impairments following non-progressive brain injury: a study of four cases

Four brain-injured subjects with semantic memory impairments are described. Two had sustained traumatic head injury and two had herpes simplex virus encephalitis. The study seeks to determine (a) whether subjects with non-progressive brain injury and impaired semantic memory perform similarly to patients with progressive disorders on a semantic memory battery and (b) whether the anatomical lesions of the present group of subjects are similar to those seen in patients with progressive disorders. Results suggests that scores on the semantic memory battery are broadly similar for patients with progressive and non-progressive disorders information from magnetic resonance imaging scans supports other findings that the crucial area involved in semantic memory lies in the left temporal neocortex.

Pasteurella multocida toxin activates the inositol triphosphate signaling pathway in Xenopus oocytes via G(q)alpha-coupled phospholipase C-beta1

Pasteurella multocida toxin (PMT) has been hypothesized to cause activation of a GTP-binding protein (G-protein)-coupled phosphatidylinositol-specific phospholipase C (PLC) in intact cells. We used voltage-clamped Xenopus oocytes to test for direct PMT-mediated stimulation of PLC by monitoring the endogenous Ca2+-dependent C1- current. Injection of PMT induced an inward, two-component Cl- current, similar to that evoked by injection of IP3 through intracellular Ca2+ mobilization and Ca2+ influx through voltage-gated Ca2+ channels. These PMT-induced currents were blocked by specific inhibitors of Ca2+ and Cl- channels, removal of extracellular Ca2+, or chelation of intracellular Ca2+. Specific antibodies directed against an N-terminal, but not a C-terminal, peptide of PMT inhibited the toxin-induced currents, implicating that the N terminus of PMT is important for toxin activity. Injection with specific antibodies against PLCbeta1, PLCbeta2, PLCbeta3, or PLCgamma1 identified PLCbeta1 as the primary mediator of the PMT-induced Cl- currents. Injection with guanosine 5'-O-(2-(thio)diphosphate), antibodies to the common GTP-binding region of G-protein alpha subunits, or antibodies to different regions of G-protein beta subunits established the involvement of a G-protein alpha subunit in PMT-activation of PLCbeta1. Injection with specific antibodies against the alpha-subunits of G(q/11), G(s/olf), G(i/o/t/z), or G(i-1/i-2/i-3) isoforms confirmed the involvement of Gq/11alpha. Preinjection of oocytes with pertussis toxin enhanced the PMT response. Overexpression of G(q)alpha in oocytes could enhance the PMT response by 30-fold to more than 300-fold, whereas introduction of antisense G(q)alpha cRNA reduced the response by 7-fold. The effects of various specific antibodies on the PMT response were reproduced in oocytes overexpressing G(q)alpha.

Induction of human myeloblastic ML-1 cell G1 arrest by suppression of K+ channel activity

Our previous studies have shown that a voltage-gated K+ channel is highly expressed in proliferating human myeloblastic ML-1 cells and is suppressed in the early stages of 12-O-tetradecanoylphorbol-13-acetate-induced ML-1 cell differentiation. In the present study, we report that inhibition of the K+ channel activity by 4-aminopyridine (4-AP) suppressed ML-1 cell proliferation, as measured by DNA synthesis. Cell cycle mapping indicated that ML-1 cells were arrested in G1 phase after 24-h treatment with 4-AP. Blockade of ML-1 cells at the G1/S boundary of the cell cycle with aphidicolin revealed that ML-1 cells past the G1 checkpoint were capable of entering S phase and synthesizing DNA independently of the channel blockade. ML-1 cell differentiation, measured by CD14 marker protein expression, revealed that the effect of 4-AP was to cause growth arrest and that it did not cause differentiation. Dephosphorylation of retinoblastoma protein accompanied inhibition of ML-1 cell proliferation and suggested that suppression of K+ channel activity by 4-AP is associated with retinoblastoma protein-mediated G1 arrest in ML-1 cells. Moreover, we found that ML-1 cell volume increased 35 +/- 7% after 4-AP treatment, which could be an early event triggering inhibition of ML-1 cell proliferation. These findings suggest that a 4-AP-sensitive K+ channel may play an important role in the transduction of mitogenic signals in ML-1 cells.

Cognitive functioning of adult survivors of cerebral hypoxia

What should clinical neuropsychologists look out for when asked to assess someone with hypoxic brain damage? To determine whether there are typical cognitive profiles of hypoxic patients, all referrals for a neuropsychological assessment made to the author over a period of 16 years were scanned to identify those with a primary diagnosis of cerebral hypoxia as recorded in the hospital notes. From a total sample of 567 patients, 18 (3.17%) had sustained primary cerebral hypoxia from a variety of causes including carbon monoxide poisoning, cardiac arrest, anaesthetic accident, respiratory failure following a pulmonary embolus, hanging and drowning. Not surprisingly, in view of the different degrees of brain damage, the cognitive functioning of the 18 patients was variable, with the greatest number showing deficits of memory and executive functioning (n = 6). Three presented with an amnesic syndrome; two with memory, executive and visuospatial deficits; and three with visuospatial or visuoperceptual problems without severe memory impairments. The remaining four patients were very severely impaired intellectually (VSI), with widespread cognitive deficits precluding the use of neuropsychological assessment procedures designed for adults.

Mutations in the sulonylurea receptor gene are associated with familial hyperinsulinism in Ashkenazi Jews

Familial hyperinsulinism (HI) is a disorder of pancreatic beta-cell function characterized by persistent hyperinsulinism despite severe hypoglycemia. To define the molecular genetic basis of HI in Ashkenazi Jews, 25 probands were screened for mutations in the sulfonylurea receptor (SUR1) gene by single-strand conformation polymorphism (SSCP) analysis of genomic DNA and subsequent nucleotide sequence analyses. Two common mutations were identified: (I) a novel in-frame deletion of three nucleotides (nt) in exon 34, resulting in deletion of the codon for F1388 (delta F1388) and (II) a previously described g-->a transition at position-9 of the 3' splice site of intron 32 (designated 3992-9g-->a). Together, these mutations are associated with 88% of the HI chromosomes of the patients studied. 86Rb+ efflux measurements of COSm6 cells co-expressing Kir6.2 and either wild-type or delta F1388 SUR1 revealed that the F1388 mutation abolished ATP-sensitive potassium channel (KATP) activity in intact cells. Extended haplotype analyses indicated that the delta F1388 mutation was associated with a single specific haplotype whereas the 3992-9g-->a mutation was primarily associated with a single haplotype but also occurred in the context of several other different haplotypes. These data suggest that HI in Ashkenazi Jews is predominantly associated with mutations in the SUR1 gene and provide evidence for the existence of at least two founder HI chromosomes in this population.

A practical framework for understanding compensatory behaviour in people with organic memory impairment

This paper describes a framework for understanding compensatory behaviour in people with organic memory impairment. It builds on a theoretical framework proposed by Bäckman and Dixon (1992) who distinguish four steps in the evolution of compensatory behaviour: (a) origins, (b) mechanisms, (c) forms, and (d) consequences. Although this framework is useful in understanding compensation in neurologically impaired adults, other factors need to be taken into account. Using data from a long-term follow-up study it is shown that age, severity of memory impairment, and additional cognitive deficits are important variables in predicting independence and use of compensations several years post-rehabilitation. The paper concludes with a consideration of how the framework might be used in future studies.

The relationship between respiratory exchange ratio, plasma lactate and muscle lactate concentrations in exercising horses using a valved gas collection system

A valved gas collection system for horses was validated, then used to examine the relationship between the respiratory exchange ratio (RER), and plasma and muscle lactate in exercising horses. Four healthy Standardbred horses were trained to breathe through the apparatus while exercising on a treadmill. Comparisons of arterial blood gas tensions were made at 3 work levels for each horse, without (control), and with the gas collection system present. At the highest work level, the arterial oxygen tension (PaO2) was significantly lower (P < 0.05), and the arterial carbon dioxide tension (PaCO2) was significantly higher (P < 0.05), than control levels when the apparatus was present; however arterial oxygen content remained unchanged. The horses completed a standardized incremental treadmill test on 4 occasions to determine the repeatability of measurements of oxygen consumption (VO2), carbon dioxide production (VCO2), inspired minute ventilation (VI), respiratory exchange ratio (RER), ventilatory equivalent for oxygen (VI/VO2), tidal volume (VT), and ventilatory frequency (VF). All gas exchange and respiratory measurements showed good reproducibility with the mean coefficient of variation of the 4 horses ranging from 3.8 to 12%. We examined the relationship between 3 indices of energy metabolism in horses performing treadmill exercise: respiratory exchange ratio (RER), central venous plasma and muscle lactate concentrations. A relationship between RER and plasma lactate concentration was established. To compare muscle and plasma lactate concentrations, the horses completed a discontinuous exercise test without the gas collection apparatus present. Significant relationships (P < 0.05), between plasma lactate concentration and RER, and between plasma and muscle lactate concentration, were described for each horse. The valved gas collection system produced a measurable but tolerable degree of interference to respiration, and provided reproducible measurements of gas exchange and ventilatory measurements. It was concluded that measurements of both gas exchange and blood lactate may be used to indicate increased glycolytic activity within exercising skeletal muscle.

Use of a comprehensive programme of external cueing to enhance procedural memory in a patient with dense amnesia

This case study describes rehabilitation efforts with a 24-year-old woman who exhibited dense amnesia secondary to status epilepticus following a motor vehicle accident. She was 20 months post-injury upon entry into our day treatment programme. The functional severity of her amnesia was reflected in numerous ways, including no recall of what she wore from day to day and an inability to find the toilet after 2 weeks in the programme. A multidisciplinary comprehensive programme of external cueing was established to exploit her preserved procedural memory. Objective measures of functional compliance were gathered over time and contrasted with both standard neuropsychological test scores and early levels of functioning in rehabilitation. Results demonstrated enhanced functioning via utilization of procedural memory. In addition, the patient actually demonstrated increased independent generalization of strategies and techniques over time. Practical treatment implications are reviewed and discussed.

Dense amnesia in a professional musician following herpes simplex virus encephalitis

We describe the memory functioning of C, a professional musician who became amnesic following herpes simplex encephalitis in 1985. Although transient amnesia in a professional musician has previously been described, this is the first reported case of chronic amnesia in a highly talented professional musician. C is unusual in three respects. First, his amnesia is particularly severe. Second, his amnesia includes semantic as well as episodic memory deficits. Third, he believes he has just woken up and his preoccupation with this state of 'just wakening' has persisted for over 9 years. This appears to be the result of a delusion rather than the consequence of his amnesia.

Oxygen cost of ventilation in the resting horse

The purpose of this study was to develop a technique to measure the oxygen cost of ventilation and the values of ventilatory parameters in seven normal horses rebreathing carbon dioxide (CO2). All the horses responded to increased inspiratory levels of CO2 by increasing their tidal volume (VT) and frequency of breathing (Vf). The mean (SE) oxygen cost litre-1 of ventilation, measured at rates of ventilation greater than 200 litres min-1 was 1.7 (0.04) ml litre-1, similar to that of normal human subjects ventilating submaximally. It was concluded that the CO2 rebreathing test is a practical, non-invasive means of measuring the oxygen cost of breathing and the ventilatory response to CO2 in horses.