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R A McCarthy

Publications and source records attributed to R A McCarthy.

At least 37 records · Page 2Linked to original sources
PubMed1994

Disorders of semantic memory.

It is now established that selective disorders of semantic memory may arise after focal cerebral lesions. Debate and dissension remain on three principal issues: category specificity, the status of modality-dependent knowledge, and the stability and sufficiency of stored information. Theories of category specificity have focused on the frequently reported dissociation between living things and man-made objects. However, other dimensions need theoretical integration. Impairments can be both finer-grain and broader in range. A second variable of importance is stimulus modality. Reciprocal interactive dissociations between vision and language and between animals and objects will be described. These indicate that the derivation of semantic information is constrained by input modality: we appear to have evolved separable databases for the visual and the verbal world. Thirdly, an orthogonal distinction has been drawn between degradation disorders, where representations are insufficient for comprehension, and access deficits, in which representations have become unstable. These issues may have their parallel in the acquisition of knowledge by the developing child.

Adolescent↗
PubMed1994

Multiple meaning systems in the brain: a case for visual semantics.

In this study we report our investigations of a category specific visual associative agnosia. The patient D.R.S.'s spoken language skills were excellent. Although he could name objects from their description, he was unable to name them by sight nor was he able to mime their use. On visual-visual matching tasks his performance was impaired and affected by semantic proximity. In two tasks his knowledge of visual objects was demonstrated to be significantly more impaired than his knowledge of visual living things. It is argued that these findings support a multiple knowledge base hypothesis.

Agnosia↗
PubMed1993

Midazolam-induced amnesia: implications for the implicit/explicit memory distinction.

In order to examine how the distinction between implicit and explicit memory might relate to theories regarding the organization of memory, two types of memory tests were administered in conjunction with the amnesia-inducing benzodiazepine midazolam. Performance on an implicit task (perceptual facilitation in identifying degraded pictures and words) was relatively unimpaired by midazolam, whereas performance on an explicit task (recognition memory) was severely impaired. Interpreting the results in both the implicit/explicit framework and an independent stage analysis suggests that the terms implicit and explicit may reflect something about the nature of the memory representation and need not be reserved solely to describe classes of memory tasks.

Adolescent↗
PubMed1993

Comparison of the sedative and amnesic effects of midazolam and propofol.

We have compared the sedative and amnesic effects of midazolam and propofol in 35 volunteers. Sedation was measured by simple reaction time immediately before and after a bolus injection and 1 h after the commencement of a subsequent continuous infusion. Memory was measured three times using two memory tests: perceptual facilitation provided an implicit memory measure and recognition provided an explicit memory measure. Propofol and midazolam had similar sedative effects both immediately after bolus doses and after 1-h continuous infusions of the drugs. In contrast, midazolam had a more profound amnesic effect than propofol on the recognition memory test. The drugs had little effect on performance with the implicit memory test. Performance on the memory tests was unrelated to sedation.

Adolescent↗
PubMed1993

Autobiographical amnesia resulting from bilateral paramedian thalamic infarction. A case study in cognitive neurobiology.

A patient with a chronic amnesic state resulting from bilateral paramedian thalamic infarction showed a pattern of retrograde amnesia not previously reported. Personally relevant autobiographical memory was profoundly impaired, whereas knowledge of famous people and public events was relatively spared. Furthermore, knowledge of famous people, including the ability to make accurate temporal judgements, was less affected than knowledge of public events. In addition, we have documented a severe and systematic distortion of personal memory. These findings are not compatible with current accounts of retrograde amnesia based either upon the type of information stored (e.g. episodic versus semantic memory), or upon simple storage versus access models. We propose an explanation based upon an interactive cognitive model in which the patient shows a disorder at the 'thematic retrieval framework' level of memory organization due to a disconnection of frontal and medial temporal memory systems.

Aged↗
PubMed1992

Actors but not scripts: the dissociation of people and events in retrograde amnesia.

We describe our further investigations of the retrograde amnesia in a single case. R.F.R. became globally amnesic following an attack of Herpes Simplex Encephalitis. He could generate and recognize superordinate level information about the vast majority of proper names including the names of people but he was very impaired at giving information about what had "happened" to these same individuals. He could also provide detailed information about family friends but he could not recall salient major personal episodes in which these same individuals had been involved. Knowledge of people appears to be represented in a different way to that of events, even when a singular event has provided the main or only opportunity for learning about the individual.

Amnesia, Retrograde↗
PubMed1991

Collagen I, laminin, and tenascin: ultrastructure and correlation with avian neural crest formation.

We have investigated the distribution of type I collagen, tenascin, and laminin in younger chick embryos than have previously been studied in detail. The initial appearance of type I collagen, but not tenascin and laminin, is exactly correlated with the beginning of neural crest migration, suggesting a role for collagen I in the migration. Light microscopy of whole mounts of 2-day-old chick embryos reveals that type I collagen is expressed in a rostral to caudal gradient; it localizes to the notochord sheath before accumulating around the neural tube and somites. Collagen I and tenascin also associate with central somite cells. Surprisingly, no extracellular matrix can be detected among the early sclerotomal cells, which suggests that little or no cell migration is involved in this epithelial-mesenchymal transformation. Electron microscopy using peroxidase antiperoxidase reveals that tenascin is present in nonstriated, 10 nm wide fibrils and in interstitial bodies, both of which have previously been reported to contain fibronectin. However, collagen I only occurs in the 10 nm fibrils and larger striated fibrils. This is the first ultrastructural study to assign tenascin to fibrils and interstitial bodies and to describe its appearance and disappearance from embryonic basement membranes. The discussion emphasizes the possible importance of type I collagen in neural crest cell migration and compares the ultrastructural associations of the ECM molecules present at this early embryonic stage.

Animals↗
PubMed1988

Evidence for modality-specific meaning systems in the brain.

Patients with cerebral lesions offer a unique opportunity to investigate the organization of meaning systems in the brain. Clinical neurologists have long been aware that knowledge of particular classes or categories of information may be selectively impaired in some cases and selectively spared in others. For example knowledge of letters, colours, objects, or people may be lost as a consequence of damage to the left hemisphere of the brain. Recently there has been quantitative evidence for even more specific impairment and preservation of particular classes of knowledge. More recently the evidence for knowledge of living things as compared with inanimate objects is particularly striking. Such observations have suggested that our semantic knowledge base is categorical in its organization. In this preliminary report, we describe a patient whose semantic knowledge deficit was not only category specific, but also modality specific. Although his knowledge of the visual world was almost entirely normal, his knowledge of living things (but not objects!) was gravely impaired when assessed in the verbal domain. These findings call into question the widely accepted view that the brain has a single all-purpose meaning store.

Brain↗
PubMed1988

The fractionation of retrograde amnesia.

This single case study describes our investigations of the retrograde memory deficit of a patient who became severely and selectively amnesic after an encephalitic illness. On clinical assessment his retrograde deficit for both personal and public events appeared to encompass his entire adult life. However, he retained knowledge of words introduced into the vocabulary during the retrograde period. The experimental investigation documented his inability to recall, recognize, and place in temporal order the names and faces of famous people for all time periods sampled. By contrast, his recall of either a famous face or a famous name was significantly facilitated by the verbal cue of the person's first name and initial of the surname (i.e., Margaret T...). His performance on a test of "familiarity" that required him to select the famous name or the famous face from two distractors (unknown) was within normal limits. It is argued that names and faces of famous people are represented in more than one system: both in a vocabulary-like fact memory system that is preserved and also in a congnitively mediated schemata that in this case is functionally inoperative.

Amnesia↗
PubMed1987

Laminin is structurally conserved in the sea urchin basal lamina.

The extracellular matrix is involved in the regulation of differentiation and morphogenesis. Here we report the identification of a sea urchin embryonic extracellular matrix protein by means of a monoclonal antibody BL1 (Mab BL1) and the isolation of the protein from basal lamina preparations. In paraffin sections of fixed embryos, the antibody can be detected on the basal surfaces of cells after the blastula stage. Immunoprecipitation from embryo lysates and salt extracts of metabolically labeled basal lamina preparations demonstrates that the basal lamina antigen is a large mol. wt protein of approximate mol. wt 10 which consists of disulfide-linked subunits of mol. wts 480 000 and 260 000. Electron microscopic images show that the Mab BL1 basal lamina antigen is structurally related to the vertebrate extracellular matrix protein laminin.

Journal Article↗
PubMed1987

Categories of knowledge. Further fractionations and an attempted integration.

In this study we investigated the category specificity of the comprehension impairments of Y.O.T., a patient with a severe global dysphasia. Using matching to sample techniques it was possible to demonstrate selective impairments and selective preservations not only of broad categories of semantic knowledge but also of particular subsets of such categories. Specifically, Y.O.T.'s comprehension of 'objects' was, in general, significantly more impaired than for foods or living things. Within the broad class of objects she was significantly more impaired in the comprehension of small manipulable objects than large man-made objects. Within her proper noun vocabulary there was a significant dissociation between her good comprehension of proper nouns having a unique and well-known referent (e.g., Churchill) and common proper nouns without such a referent (e.g., Jones). Her error responses were not consistent, semantic similarity and significant rate effects were observed, and it was therefore considered that her category specific comprehension deficits were primarily ones of access to a full semantic representation. We attempt to give a principled account of the increasing number of seemingly arbitrary instances of fine-grain categorical impairments of semantic knowledge. We have suggested that different weighting values from multiple sensory channels will be important in the acquisition of different categories of knowledge and that such differential weightings could be the basis of the categorical organization of systems in the brain subserving semantic knowledge.

Aphasia↗
PubMed1987

The double dissociation of short-term memory for lists and sentences. Evidence from aphasia.

We document the sentence and list repetition skills of 3 aphasic patients. Cases 1 and 2 were classified as span-impaired conduction aphasics and Case 3 was classified as a span-preserved transcortical sensory aphasic. We found that repetition by the span-impaired cases was facilitated by increasing the 'meaningfulness' of lists, whereas this had no effect on the performance of the span-preserved case. The patients' ability to repeat sentences was contrasted with their ability to repeat three words contained in the sentences, and a double dissociation was obtained: the span-impaired cases were better at repeating sentences than in repeating three word lists whereas the span-preserved case showed the opposite pattern of difficulty. The repetition of sentences containing a known and unknown vocabulary was tested in the span-preserved case. His repetition of sentences containing words which he still knew was significantly better than his ability to repeat sentences containing a vocabulary of words which he had 'forgotten' as a consequence of his aphasia. The patients' ability to repeat complete, incomplete, and nonsense sentences was contrasted: overall the span-impaired patients were somewhat better at repeating complete sentences than incomplete sentences. Finally we examined the patients' ability both to comprehend and repeat word strings in an abbreviated 'naming from description' task: the span-impaired patients were able to comprehend three word strings, but unable to repeat them, the span-preserved case was able to repeat but not comprehend. On the basis of these double dissociations we conclude that the evidence indicates two dissociable short-term memory systems, one a relatively passive phonological store subserving list repetition, the other a dynamic, anticipatory, and integrative memory system which underpins sentence repetition.

Adult↗
PubMed1987

Understanding: a function of short-term memory?

We describe our investigations of the sentence comprehension abilities of 2 patients with a severe impairment in their auditory verbal short-term memory (conduction aphasia). Both were capable of comprehending a range of sentences, even when adequate comprehension was dependent upon the processing of order-dependent syntactic information rather than the utilization of semantic knowledge. Thus they performed satisfactorily on tests using plausibly reversible subject and object constituents with either active or passive verb phrases or prepositional phrases. Both, however, were impaired on sentences which departed from normal conversational conventions in terms of their reference to the order of event occurrence, or to the subject and object of an array. They were also very poor at performing comparative judgements, even when these involved a simple intrinsic attribute such as colour. These findings are discussed in terms of the role of auditory verbal short-term memory in backing up and back-tracking over spoken information when conditions preclude the immediate understanding of auditory-verbal information.

Adult↗
PubMed1986

Visual associative agnosia: a clinico-anatomical study of a single case.

A single case study of a patient with visual associative agnosia is described. The patient had well preserved language, spatial, visual, and perceptual abilities but nevertheless was impaired in recognising visually presented common objects. It is argued that his deficit cannot be accounted for in terms of a disconnection syndrome. Behavioural and anatomical (MRI scan) evidence for focal unilateral dysfunction is presented. It is concluded that the left hemisphere plays a crucial role in recognising the meaning of common objects.

Aged↗
PubMed1983

Serum effects on the in vitro differentiation of sea urchin micromeres.

When micromeres isolated from the 16-cell stage of Strongylocentrotus purpuratus are cultured in sea water containing 3.5% horse serum, they produce spicules at approximately the same time as in normal development. The serum requirement of the micromeres has been investigated by adding serum at varying intervals after isolation or by pulsing the cells with serum at specific times during their in vitro development. The optimum time of serum addition for spicule formation is 36 h after fertilization (AF). Further delay in the addition of serum results in a reduction in the number of spicules formed in culture and a delay in the time at which they appear. A 1-h pulse of serum at 36 h AF is sufficient to initiate a response in some of the micromere aggregates. A 12-h pulse at 36 h AF produces the maximum number of spicules per culture. The critical period for serum addition, 36-48 h AF, corresponds to the time in the normal embryo at which the syncytial primary mesenchyme ring is formed. Electron micrographs of cultured cells demonstrate that micromeres cultured without serum until 48 h AF fail to form pseudopodial extensions and remain as rosette-like clusters of cells. If serum is present, extensive pseudopodial networks form which resemble the primary ring syncytium. These results suggest that serum acts to stimulate fused pseudopodial networks in cultures of micromeres and that the resulting syncytium is necessary for spicule formation.

Animals↗
PubMed1983

Protein composition of the hyaline layer of sea urchin embryos and reaggregating cells.

The protein composition of the sea urchin embryo hyaline layer has been studied by 125I surface labeling. The electrophoretic patterns of iodinated proteins indicate that the composition of the hyaline layer is species and stage-specific. Dissociation of iodinated embryos removes some labeled proteins of apparent molecular weights of 290,000, 175,000, 145,000, 110,000, 70,000, and 50,000. The electrophoretic pattern of labeled proteins found in the intact embryo is reestablished on the surface of aggregates following reaggregation. The possible function of these proteins with respect to cell adhesion, cell-sorting behavior and morphogenesis is discussed.

Age Factors↗
PubMed1983

The enhancement of reaggregation of sea urchin blastula cells by exogenous proteins.

The ability of exogenous proteins to enhance the reaggregation of aggregation-deficient butanol extracted cells has been studied using blastula cells of the sea urchin Arbacia punctulata. Butanol extracts, calcium- and magnesium-free sea-water dissociation supernatant, human plasma fibronectin and bovine serum albumin enhance reaggregation in a concentration dependent manner. Electrophoretic analysis and autoradiography of 125I surface labeled dissociated cells indicate that while butanol extracts a large number of proteins, few iodinated proteins are present in the butanol extract. The non-specificity of proteins to promote reaggregation and the probable cellular location of the butanol extracted proteins are discussed.

Animals↗