Biomedical subjects
P Fenwick
Publications and source records attributed to P Fenwick.
The contingent negative variation in a Go/No Go avoidance task: relationships with personality and subjective state.
Howard et al. (1982) reported an association in mentally abnormal offenders between psychometric impulsiveness and the degree of differentiation in the contingent negative variation (CNV) recorded at the vertex between Go and No Go conditions in a Go/No Go signalled avoidance task. The present study aimed to investigate whether this finding extended to two samples of young, healthy volunteers using a variety of impulsiveness-related measures. As well as examining the Go/No Go CNV recorded from the vertex, the present study investigated the Go/No Go CNV recorded bilaterally at central (C3 and C4: Experiment 1) and temporal (T3 and T4: Experiment 2) electrode derivations. The study also investigated relationships between the Go/No Go CNV and subjective state. including stress and arousal as measured by a mood-adjective checklist, as well as several task-related state measures. The Go CNV recorded at the vertex was found to relate to a variety of impulsiveness-related measures, in particular to Eysenck's Impulsivity, Venturesomeness and Psychoticism. The Go/No Go CNV recorded at temporal sites was more closely related to measures of Emotionality. While the Go CNV appears to be an electrocortical index of a neuropsychological system mediating subjective stress, the No Go CNV appears to index subjective arousal. Results are interpreted in terms of orthogonal 'primary' and 'secondary' appraisal processes (Folkman et al., 1979), and their implications for Gray's (1982) neuropsychological theory of anxiety and Tucker and Williamson's (1984) neural control systems model of human self-regulation are outlined.
Kinetics of Nippostrongylus brasiliensis infection in the zinc-deficient rat.
The role of zinc (Zn) in the immunological expulsion of the nematode Nippostrongylus brasiliensis (Nb) from the small intestine of the rat was investigated. Three groups of 28 rats each were fed a basal diet providing either 3 mg Zn/kg for the zinc-deficient group (-Zn) or 40 mg Zn/kg for ad libitum-fed and pair-fed controls. After 6 wk each group was divided into two equal subgroups and infected with either 1000 or 4000 infective Nb larvae/rat. The -Zn rats showed significant reductions (P less than 0.001) in food intake, weight gain and food conversion efficiency when compared to the rats fed ad libitum but not when compared to the pair-fed controls. Plasma zinc concentration in the -Zn rats (0.50 microgram/ml) was significantly lower than in both ad libitum-fed (1.33 micrograms/ml) and pair-fed (1.45 micrograms/ml) controls (P less than 0.001). The recovery of worms from the rats 3, 7 and 12 d postinfection was similar for the corresponding day and dose of infection in all groups. Expulsion was almost complete in all groups by 12 d post-infection. There were no significant differences in size and fecundity of worms recovered from the different groups of rats on 7 d postinfection. However, over the whole period of infection, the -Zn rats excreted significantly more parasite eggs than did controls (P less than 0.001). These results indicate that although zinc deficiency affected growth performance of the rats, it did not affect the establishment or expulsion of Nb. Impairment of the immune response of the zinc-deficient rat was manifested only by a significant increase in the number of parasite eggs excreted in feces.
The nature and management of aggression in epilepsy.
Minor episodes of aggressive behavior are relatively common in some populations of patients with epilepsy. However, they are probably no more common than in populations who are socially disadvantaged or who have brain damage. The confusion that commonly follows seizures can lead to apparently aggressive behavior. Rarely, the seizure itself may lead to directed aggression; very rarely does it lead to murderous attacks. Although post-ictal psychotic aggression is usually not severe, when it is driven by prominent delusions and hallucinations, it can result in self-destructive acts or serious violence. Clearly, however, it is quite unfair to globally classify epileptics as aggressive, and the time has come to abandon this stereotype.
Hypoglycaemia in patients with insulin dependent diabetes.
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The inverse problem: a medical perspective.
The techniques of magnetoencephalography (MEG) have advanced considerably recently with several major installations now being built or planned. In this paper, the present status of MEG within clinical medicine is evaluated and compared with that of other large diagnostic instruments. Deficiencies in present instruments and procedures are discussed. It is argued that in the future methods must be found of investigating sub-cortical structures which are relevant in the majority of clinically significant conditions. Some important possible lines of enquiry are indicated.
Metrizamide and the EEG: three case reports and a review.
Three patients are described who developed cerebral complications and an EEG abnormality for several days after metrizamide myelography. Clinically, the patients showed a fluctuating confusional state with dysphasia and retrograde amnesia, while their EEGs were dominated by runs of slow wave activity interspersed with frequent spikes. The runs appeared either continuously or in paroxysmal bursts. The clinical symptoms and the EEG are compatible with complex partial status epilepticus and are similar to the symptomatology of ten patients described in the literature. This rare clinical entity should be distinguished from a more common complication of metrizamide--non-specific slow wave abnormality of variable degree in the EEG with or without clinical signs. Clinical manifestations may include transient aphasia and weakness of the limbs with pyramidal signs.
The effect of hypoglycaemia on visual function: a clinical and electrophysiological study.
Disturbance of vision commonly accompanies hypoglycaemia. This study was designed to investigate the nature of the visual disturbance, the blood glucose threshold at which the disturbance occurred and the physiological basis. Measurements were made of the corrected visual acuity, colour vision (100 Hue test), visual evoked potentials (VEP), electroencephalography (EEG) frequency analysis and psychometry (digit recall) during stepwise induction of controlled hypoglycaemia produced by an intravenous insulin infusion. Six male volunteers and five insulin-dependent diabetic subjects were studied. During hypoglycaemia corrected visual acuity was unchanged. Colour vision was significantly impaired. Baseline VEP were normal in both groups but significantly prolonged during hypoglycaemia (mean increment 10.8 ms) and increased by greater than 5 ms in nine out of 11 subjects. Quantitative EEG analysis demonstrated slowing with a power density spectral shift from fast alpha to slow alpha, theta and delta which correlated with VEP latency and amplitude changes. The findings have clinical implications. A deterioration in colour vision is likely to impair the ability to read reagent strips by eye. VEP measurements in diabetic patients are likely to be misleading if hypoglycaemia is present; EEG changes are a sensitive index of cortical dysfunction during hypoglycaemia and provide a theoretical basis for developing a portable device to detect early hypoglycaemia.
'Psychic sensitivity', mystical experience, head injury and brain pathology.
The 'psychic' experiences of 17 students (sensitives) from the College of Psychic Studies were compared with those of 17 church-going control subjects, who were matched for age, sex, and approximate intellectual level. At interview, 67 items of information relating to the medical history, family history, 'psychic gifts', head injuries, and mystical experiences were obtained. The shortened WAIS, the Benton Visual Retention Test, with tests of both dominant (Wechsler Logical Memory) and non-dominant temporal lobe function (the Rey-Osterreith Test) were given. The results showed that the sensitive population contained more single or divorced people, and people who had sometime consulted a psychiatrist. They had experienced more head injuries and serious illnesses than the controls. Sixty-six per cent showed evidence of right hemisphere and right temporal lobe dysfunction and, of these, 35 per cent had poor visual memories. There was evidence to suggest that some 'psychic' experiences were associated with brain dysfunction. Despite an increased occurrence of head injury, no clear correlation with the onset of 'psychic' sensitivity was found. Mystical experiences showed a trend towards being related to non-dominant hemisphere dysfunction. Vagueness about the position of the sensitive's 'psychic helper' in physical space was also associated with non-dominant hemisphere dysfunction.
Lucid dreaming: correspondence between dreamed and actual events in one subject during REM sleep.
During lucid dreaming, a subject willed movements of his fingers, toes and feet, remembered tasks, and counted sensory stimuli. Dreamed speech was related to respiration. EMG activity corresponding to dreamed actions was greater in flexor than in extensor limb muscles and was never present in axial muscles.
Can we still recommend meditation?
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Sex hormones, sexual activity and plasma anticonvulsant levels in male epileptics.
Testosterone, LH, FSH, PRL, and sex hormone binding globulin (SHBG) were measured in 72 male epileptic patients on chronic anticonvulsant drug regimes. Sexual activity was estimated and plasma anticonvulsants measured. Total testosterone (TT), LH, FSH, PRL, and SHBG were increased; free testosterone (FT) was decreased. Sexual activity appeared diminished particularly in relation to reduced FT.
Function of the corpus callosum in schizophrenia.
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Audit of care for epileptics in a general practice.
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Coloured pattern displacement and VEP amplitude.
The results of this experiment confirm that evoked potential amplitude is linear with checkerboard pattern displacement. We have also found that this linear relationship holds for red, green and blue patterns. The hypothesis that there would be no significant differences between the amplitude of the evoked potential to colour/'black' stimulation and a white/'black' stimulus of equivalent luminance has been substituted. Differences were found between colours. The mean level for the blue pattern was lower than that for the red and the green patterns. We have further confirmed the relationship between luminance and the latency of the evoked potential. Differences in latency were found between all conditions in this study, suggesting that more accurate methods of measuring luminance are required in studies using colour pattern displacement if latency measurements are the main focus of the study.
Contingent negative variation and evoked potential amplitude as a function of inspired nitrous oxide concentration.
Nine subjects were given to breath 10%, 20%, 30% and 40% nitrous oxide in oxygen. The inhaled gas concentrations were monitored by a mass spectrograph. At each gas concentration the CNV was measured in a standard long S1-S2 CNV paradigm to a click and tone with a mandatory button press at S2. The results confirmed the previous observations of Lader and Morris (1974) that the cortical evoked potential decreases rapidly with increasing concentrations of nitrous oxide. The CNV, however, against prediction remains surprisingly well preserved up to the borders of unconsciousness. In this situation there is little correlation between CNV amplitude and attention, arousal or reaction time.