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Biomedical subjects

C Frith

Publications and source records attributed to C Frith.

At least 37 records · Page 2Linked to original sources
PubMed1996

Neuropsychology of schizophrenia, what are the implications of intellectual and experiential abnormalities for the neurobiology of schizophrenia?

The diagnosis of schizophrenia is largely based on reports of bizarre experiences such as having alien thoughts inserted into one's mind. Many patients with this diagnosis show a marked intellectual decline and particular problems with tasks involving certain kinds of memory or requiring mental flexibility. Similar patterns of performance can be seen in patients with damage in the prefrontal cortex. However, patients with schizophrenia show a very varied pattern of impairments relating to their current mental state. Chronic patients with negative features, such as poverty of speech, are most likely to show poor test performance, while the presence of severe hallucinations and delusions need not be associated with any impairment. A cognitive approach suggests that hallucinations and delusions result from the patient attributing his own actions to an external agency. This error is due to an inability to distinguish between external events and perceptual changes caused by his own actions. The basis of this failure could be a functional disconnection between frontal brain areas concerned with action and posterior areas concerned with perception.

Brain↗
PubMed1995

A functional neuroanatomy of hallucinations in schizophrenia.

Hallucinations, perceptions in the absence of external stimuli, are prominent among the core symptoms of schizophrenia. The neural correlates of these brief, involuntary experiences are not well understood, and have not been imaged selectively. We have used new positron emission tomography (PET) methods to study the brain state associated with the occurrence of hallucinations in six schizophrenic patients. Here we present a group study of five patients with classic auditory verbal hallucinations despite medication, demonstrating activations in subcortical nuclei (thalamic, striatal), limbic structures (especially hippocampus), and paralimbic regions (parahippocampal and cingulate gyri, as well as orbitofrontal cortex). We also present a case study of a unique, drug-naive patient with visual as well as auditory verbal hallucinations, demonstrating activations in visual and auditory/linguistic association cortices as part of a distributed cortical-subcortical network. Activity in deep brain structures, identified with group analysis, may generate or modulate hallucinations, and the particular neocortical regions entrained in individual patients may affect their specific perceptual content. The interaction of these distributed neural systems provides a biological basis for the bizarre reports of schizophrenic patients.

Adult↗
PubMed1995

The functional anatomy of recovery from auditory agnosia. A PET study of sound categorization in a neurological patient and normal controls.

H2(15)O-PET was used to investigate the functional anatomy of recovery in a patient (J.B.) with bilateral perisylvian strokes and auditory agnosia, who partially regained the ability to recognize environmental sounds, but remained clinically word-deaf. The patient and a group of six normal volunteers were scanned in the following three conditions: (i) passive listening to environmental sounds; (ii) categorization of environmental sounds; (iii) at rest. In normal subjects, passive listening as compared with rest was associated with significant activations in the auditory cortices and posterior thalami, and in the inferior parietal lobe and anterior insula/frontal opercular region on the right. In J.B., activations were observed in the spared auditory cortex and inferior parietal lobe of the right hemisphere and in regions adjacent to the perisylvian lesion in the left hemisphere (anterior insula/frontal opercular region, middle temporal gyrus and inferior parietal lobe). The recovered function, as measured by categorization of sounds compared with passive listening, in J.B. was associated with bilateral activation of a distributed network comprising (pre)frontal, middle temporal and inferior parietal cortices, as well as the right cerebellum and the right caudate nucleus. In addition, there was a left-sided activation of the anterior cingulate gyrus. In normal subjects, the same categorization task led to activation of a network comprising (pre)frontal, middle temporal and inferior parietal cortices in the left hemisphere only. These results suggest that bilateral activation (with recruitment of areas homologous to those known to be responsible for normal function), the engagement of peri-infarct regions, and the involvement of a more widespread neocortical network, are mechanisms of functional reorganization after injury that may enable recovery from, or compensation for, cognitive deficits.

Agnosia↗
PubMed1994

Effect of bleomycin-induced fibrosis on pulmonary metabolism of selected xenobiotics.

Few studies are available characterizing the effects of fibrosis on pulmonary disposition of drugs or environmental pollutants. Two model substrates, p-nitroanisole and carbofuran, were selected to evaluate the effect of bleomycin-induced fibrosis on pulmonary disposition and metabolism using the isolated perfused lung and in vitro enzyme preparations. The rate of p-nitroanisole oxidation in the isolated perfused lung was significantly lower in fibrotic (k = 0.0334 min-1) than in control (k = 0.0493 min-1) lungs. However, there was no difference in the amount of p-nitrophenol formed between control (38 +/- 4 micrograms) and fibrotic (47 +/- 7 micrograms) lungs. Carbofuran clearance was similar in control (t1/2 = 91 min, ke = 0.008 min-1) and fibrotic (t1/2 = 75 min, ke = 0.009 min-1) lungs and was consistent with a one-compartment model. The Km value for p-nitrophenol formation in microsomes (0.185 +/- 0.095 mM) from control lungs was similar to fibrotic lungs (0.054 +/- 0.014 mM); however, Vmax was significantly higher in healthy (34.6 +/- 6.3 pmoles/min per mg microsomal protein) than in fibrotic (11.16 +/- 3.19 pmoles/min per mg microsomal protein) lungs. In vitro carbofuran studies indicated limited metabolism of carbofuran in both healthy and fibrotic microsomal enzyme preparations (< 5% of the administered dose). Lower p-nitroanisole metabolism in fibrotic lungs was consistent with lower levels of cytochrome P-450 2B1/B2 measured in bleomycin-treated lungs. Results suggest that individuals with bleomycin-induced pulmonary fibrosis may be at greater risk when exposed to certain toxic environmental chemicals or drugs that require detoxification by pulmonary microsomal enzymes.

Animals↗
PubMed1993

Hypothesis: the bradyphrenia of parkinsonism is a nosological entity.

Reaction time was studied in 103 subjects with idiopathic parkinsonism and 144 without. Central processing time, as measured by the response to a warning, had a component which could be explained by the presence or absence of parkinsonism, but not by the ageing process, a mental test score, or consumption of exogenous substances. Depression did not influence the efficiency of response. Cigarette smoking and anti-parkinsonian medication were associated with greater efficiency.

Adult↗
PubMed1991

Positron emission tomography studies of frontal lobe function: relevance to psychiatric disease.

The frontal lobes in man include about one-third of the total cortical area of the cerebrum, a considerably greater proportion than in other primates. It is likely that the frontal lobes subserve the most complex of cognitive functions including will and consciousness. During the performance of willed actions (spontaneous selection of actions without help from external cues) an increase of activity can be observed in dorsolateral prefrontal cortex. Critically, there is no increased activity in this location when the same actions are performed routinely. Such observations, which systematically use positron emission tomography (PET) in conjunction with specific cognitive activations, should make it possible (a) to specify more precisely the cognitive components comprising 'frontal' attributes such as willed behaviour and planning, (b) to relate these components to particular frontal lobe areas, and (c) to show how these frontal lobe areas interact with other parts of the brain. Psychotic patients typically show abnormalities of willed behaviour (e.g. poverty of speech and action) and consciousness (e.g. hallucinations, delusions of control). PET studies of frontal lobe function in patients with these signs and symptoms should not only provide information about the pathophysiology of these disorders, but also increase our knowledge of the brain systems underlying the most complex human faculties.

Attention↗
PubMed1985

Relationships between esophageal speech proficiency and surgical, biographical, and social factors.

The relationship between judged esophageal speech proficiency and detailed medical/surgical, biographical, and social factors was investigated among a large sample of alaryngeal speakers. The data suggested that more extensive surgery such as radical neck dissection did not lessen the subjects' ability to learn esophageal speech. Surprisingly, subjects who had undergone radical neck surgery had better voices in many cases than those who had undergone only a simple laryngectomy. Educational level, socioeconomic status, length of time spent in speech therapy, and the number of years since surgery did not statistically influence speech results. However, those subjects still gainfully employed did achieve esophageal speech more often than those who were unemployed, particularly with reference to female subjects.

Age Factors↗
PubMed1984

Muscarinic cholinergic receptors in a rat phaeochromocytoma cell line.

The high affinity binding of the muscarinic ligand 3H-N-methylscopolamine (3H-NMS) to intact cells of the rat pheochromocytoma cell line PC12 was studied. A single class of saturable binding sites was observed with a density of about 5000 sites per cell, and a pharmacological profile consistent with muscarinic receptors. The inhibition of 3H-NMS binding by the antagonist pirenzepine was of low affinity suggesting PC12 muscarinic receptors may be similar to those found on rat sympathetic nerve terminals.

Animals↗
PubMed1976

Dose-response hyperplasia and neoplasia from feeding N-2-fluorenylacetamide (2-FAA) to BALB/c mice for varying time intervals.

Hyperplasia induced by N-2-fluorenylacetamide requires the continuous presence of the chemical for its maintenance. Feeding the chemical at levels of 8 to 86 ppm results in a dose-response related urinary bladder hyperplasia and, after 9 to 12 months, in bladder neoplasia at the higher dose levels. Neoplasia of the lungs, liver, parotid gland, lacrimal gland, harderian gland, and submaxillary gland was also observed. Measurement of oncogenic viruses revealed no synergism with 2-FAA and no relationship between virus counts and neoplasia. Calcareous pericarditis was observed and most general toxicological effects occurred in the liver. A pronounced sex difference in response was observed with the males giving greater responses than the females in all instances.

2-Acetylaminofluorene↗
PubMedDate not supplied

Chemical carcinogens. A review and analysis of the literature of selected chemicals and the establishment of the Gene-Tox Carcinogen Data Base. A report of the U.S. Environmental Protection Agency Gene-Tox Program.

The literature on 506 selected chemicals has been evaluated for evidence that these chemicals induce tumors in experimental animals and this assessment comprises the Gene-Tox Carcinogen Data Base. Three major sources of information were used to create this evaluated data base: all 185 chemicals determined by the International Agency for Research on Cancer to have Sufficient evidence of carcinogenic activity in experimental animals, 28 selected chemicals bioassayed for carcinogenic activity by the National Toxicology Program/National Cancer Institute and found to induce tumors in mice and rats, and 293 selected chemicals which had been evaluated in genetic toxicology and related bioassays as determined from previous Gene-Tox reports. The literature data on the 239 chemicals were analyzed by the Gene-Tox Carcinogenesis Panel in an organized, rational and consistent manner. Criteria were established to assess individual studies employing single chemicals and 4 categories of response were developed: Positive, Negative, Inconclusive (Equivocal) and Inconclusive. After evaluating each of the individual studies on the 293 chemicals, the Panel placed each of the 506 chemicals in an overall classification category based on the strength of the evidence indicating the presence or absence of carcinogenic effects. An 8-category decision scheme was established using a modified version of the International Agency for Research on Cancer approach. This scheme included two categories of Positive (Sufficient and Limited), two categories of Negative (Sufficient and Limited), a category of Equivocal (the evidence of carcinogenicity from well-conducted and well-reported lifetime studies had uncertain significance and was neither clearly positive nor negative), and three categories of Inadequate (the evidence of carcinogenicity was insufficient to make a decision, however, the data suggested a positive or negative indication). Of the 506 chemicals in the Gene-Tox Carcinogen Data Base, 252 were evaluated as Sufficient Positive, 99 as Limited Positive, 40 as Sufficient Negative, 21 as Limited Negative, 1 as Equivocal, 13 as Inadequate with the data suggesting a positive indication, 32 as Inadequate with the data suggesting a negative indication, and 48 Inadequate with the data not suggesting any indication of activity. This data base was analyzed and examined according to chemical class, using a 29 chemical class scheme.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗