Biomedical subjects

C L Isaac

Publications and source records attributed to C L Isaac.

14 recordsLinked to original sources

PubMed2005

Prose recall and amnesia: more implications for the episodic buffer.

Baddeley and Wilson [Baddeley, A. D., & Wilson, F. B. (2002). Prose recall and amnesia: implications for the structure of working memory. Neuropsychologia 40, 1737-1743.] have argued that their finding of a positive association between amnesics' immediate prose recall scores and their scores on measures of executive function and fluid intelligence supports the view that an episodic buffer exists. However, the pattern of data from amnesics tested in our laboratory presented some problems for this conceptualisation of the episodic buffer.

Adult↗

PubMed2004

Associative recognition in a patient with selective hippocampal lesions and relatively normal item recognition.

Previous work (Mayes et al., Hippocampus 12:325-340, 2002) found that patient YR, who suffered a selective bilateral lesion to the hippocampus in 1986, showed relatively preserved verbal and visual item recognition memory in the face of clearly impaired verbal and visual recall. In this study, we found that YR's Yes/No as well as forced-choice recognition of both intra-item associations and associations between items of the same kind was as well preserved as her item recognition memory. In contrast, YR was clearly impaired, and more so than she was on the above kinds of recognition, at recognition of associations between different kinds of information. Thus, her recognition memory for associations between objects and their locations, words and their temporal positions, abstract visual items or words and their temporal order, animal pictures and names of professions, faces and voices, faces and spoken names, words and definitions, and pictures and sounds, was clearly impaired. Several of the different information associative recognition tests at which YR was impaired could be compared with related item or inter-item association recognition tests of similar difficulty that she performed relatively normally around the same time. It is suggested that YR's familiarity memory for items, intra-item associations, and associations between items of the same kind was mediated by her intact medial temporal lobe cortices and was preserved, whereas her hippocampally mediated recall/recollection of these kinds of information was impaired. It is also suggested that the components of associations between different kinds of information are represented in distinct neocortical regions and that initially they only converge for memory processing within the hippocampus. No familiarity memory may exist in normal subjects for such associations, and, if so, YR's often chance recognition occurred because of her severe recall/recollection deficit. Conflicting data and views are discussed, and the way in which recall as well as item and associative recognition need to be systematically explored in patients with apparently selective hippocampal lesions, in order to resolve existing conflicts, is outlined.

Aged↗

PubMed2004

Visual paired comparison performance is impaired in a patient with selective hippocampal lesions and relatively intact item recognition.

In this study, we have examined visual recognition memory in a patient, YR, with discrete hippocampal damage who has shown normal or nearly normal item recognition over a large number of tests. We directly compared her performance as measured using a visual paired comparison task (VPC) with her performance on delayed matching to sample (DMS) tasks. We also investigated the effect of retention interval between familiarisation and test. YR shows good visual recognition with the DMS task up to 10 s after the familiarisation period, but only shows recognition with the VPC task for the shortest retention interval (0 s). Our results are consistent with the view that hippocampal damage disrupts recollection and recall, but not item familiarity memory.

Brain Damage, Chronic↗

PubMed2002

Under what conditions is recognition spared relative to recall after selective hippocampal damage in humans?

The claim that recognition memory is spared relative to recall after focal hippocampal damage has been disputed in the literature. We examined this claim by investigating object and object-location recall and recognition memory in a patient, YR, who has adult-onset selective hippocampal damage. Our aim was to identify the conditions under which recognition was spared relative to recall in this patient. She showed unimpaired forced-choice object recognition but clearly impaired recall, even when her control subjects found the object recognition task to be numerically harder than the object recall task. However, on two other recognition tests, YR's performance was not relatively spared. First, she was clearly impaired at an equivalently difficult yes/no object recognition task, but only when targets and foils were very similar. Second, YR was clearly impaired at forced-choice recognition of object-location associations. This impairment was also unrelated to difficulty because this task was no more difficult than the forced-choice object recognition task for control subjects. The clear impairment of yes/no, but not of forced-choice, object recognition after focal hippocampal damage, when targets and foils are very similar, is predicted by the neural network-based Complementary Learning Systems model of recognition. This model postulates that recognition is mediated by hippocampally dependent recollection and cortically dependent familiarity; thus hippocampal damage should not impair item familiarity. The model postulates that familiarity is ineffective when very similar targets and foils are shown one at a time and subjects have to identify which items are old (yes/no recognition). In contrast, familiarity is effective in discriminating which of similar targets and foils, seen together, is old (forced-choice recognition). Independent evidence from the remember/know procedure also indicates that YR's familiarity is normal. The Complementary Learning Systems model can also accommodate the clear impairment of forced-choice object-location recognition memory if it incorporates the view that the most complete convergence of spatial and object information, represented in different cortical regions, occurs in the hippocampus.

Brain Diseases↗

PubMed2002

Relative sparing of item recognition memory in a patient with adult-onset damage limited to the hippocampus.

There is disagreement about whether selective hippocampal lesions in humans cause clear item recognition as well as recall deficits. Whereas Reed and Squire (Behav Neurosci 1997;111:667-775) found that patients with adult-onset relatively selective hippocampal lesions showed clear item recognition deficits, Vargha-Khadem et al. (Science 1997;277: 376-380, Soc Neurosci Abstr 1998;24:1523) found that 3 patients who suffered selective hippocampal damage in early childhood showed clear recall deficits, but had relatively normal item recognition. Manns and Squire (Hippocampus 1999;9:495-499) argued, however, that item recognition may have been spared in these patients because the early onset of their pathology allowed compensatory mechanisms to develop. Therefore, to determine whether early lesion onset is critical for the relative sparing of item recognition and to determine whether its occurrence is influenced by task factors, we extensively examined item recognition in patient Y.R., who has pathology of adult-onset restricted to the hippocampus. Like the developmental cases, she showed clear free recall deficits on 34 tests, but her item recognition on 43 tests was relatively spared, and markedly less disrupted than her recall. Her item recognition performance relative to that of her controls was not significantly influenced by whether tests tapped visual or verbal materials, had a yes/no or forced-choice format, contained few or many items, had one or several foils per target item, used short or very long delays, or were difficult or easy for normal subjects. Interestingly, YR's bilateral hippocampal destruction was greater than at least 2 of the 3 patients of Manns and Squire (Hippocampus 1999;9:495-499). The possible reasons why item recognition differs across patients with relatively selective hippocampal damage of adult-onset and how the reasons that are truly critical can be best identified are discussed.

Age of Onset↗

PubMed2002

Differential involvement of the hippocampus and temporal lobe cortices in rapid and slow learning of new semantic information.

The present study examined the rapid and slow acquisition of new semantic information by two patients with differing brain pathology. A partial double dissociation was found between the patterns of new learning shown by these two patients. Rapid acquisition was impaired in a patient (YR) who had relatively selective hippocampal damage, but it was unimpaired in another patient (JL) who, according to structural MRI, had an intact hippocampus but damage to anterolateral temporal cortex accompanied by epileptic seizures. Slow acquisition was impaired in both patients, but was impaired to a much greater extent in JL. The dissociation suggests that the mechanisms underlying rapid and slow acquisition of new semantic information are at least partially separable. The findings indicate that rapid acquisition of semantic, as well as episodic information, is critically dependent on the hippocampus. However, they suggest that hippocampal processing is less important for the gradual acquisition of semantic information through repeated exposure, although it is probably necessary for normal levels of such learning to be achieved.

Adult↗

PubMed2000

A comparison of egocentric and allocentric spatial memory in a patient with selective hippocampal damage.

The spatial memory of a single patient (YR) was investigated. This patient, who had relatively selective bilateral hippocampal damage, showed the pattern of impaired recall but preserved item recognition on standardised memory tests that has been suggested by Aggleton and Shaw [Aggleton JP, Shaw C. Amnesia and recognition memory: a reanalysis of psychometric data. Neuropsychologia 1996;34:51-62] to be a consequence of Papez circuit lesions. YR was tested on three recall tests and one recognition test for visuospatial information. The initial recall test assessed visuospatial memory over very short unfilled delays and YR was not significantly impaired. This test was then modified to test recall of allocentric and egocentric spatial information separately after filled delays of between 5 and 60 s. YR was found to be more impaired at recalling allocentric than egocentric information after a 60 s interval with a tendency for the impairment to increase up to this delay. Recognition of allocentric spatial information was also assessed after delays of 5 and 60 s. YR was impaired after the 60 s delay. The results suggest that the human hippocampus has a greater involvement in allocentric than egocentric spatial memory, and that this most likely concerns the consolidation of allocentric information into long-term memory rather than the initial encoding of allocentric spatial information. The findings also suggest that YR's item recognition/free recall deficit pattern reflects a problem retrieving or storing certain kinds of associative information.

Brain Mapping↗

PubMed2000

Factor analysis of three standardized tests of memory in a clinical population.

OBJECTIVES: The aim of this study was to determine the factor structure of three standardized memory tests: Wechsler Memory Scale-Revised (WMS-R), Warrington Recognition Memory Test (WRMT), Doors and People Test (D&P). We investigated whether these different standardized tests of memory are consistent in their evaluation of memory function, and the extent to which these tests discriminate between different memory functions (e.g. recall/recognition and verbal/non-verbal memory). DESIGN: Fifty patients with selective memory impairment were tested on the WMS-R, WRMT and D&P. METHODS: Age-scaled scores from selective measures of these tests (WMS-R-verbal, WMS-R-visual, WMS-R-delay, WRMT-words, WRMT-faces, D&P-people, D&P-doors, D&P-shapes, D&P-names) were used as input to a factor analysis. RESULTS: Maximum likelihood factor analysis yielded a three-factor solution consistent with a theoretically motivated fractionation of memory function into recall and recognition components. Recognition performance, but not recall performance, showed dissociation into visual and verbal components. CONCLUSIONS: The WMS-R, WRMT and D&P are highly consistent in their assessment of memory function. The results of the factor analysis are consistent with a theoretically motivated fractionation of recall and recognition memory. They are also partially consistent with a dissociation between visual and verbal memory function.

Adolescent↗

PubMed1999

Rate of forgetting in amnesia: I. Recall and recognition of prose.

Three experiments explored the rate at which amnesic participants' free recall, cued recall, and recognition of prose declined over short filled delays. In Experiment 1, after performance had been matched to that of controls at 15s, amnesics showed accelerated forgetting over delays of up to 10 min in a free-recall condition, whereas recognition performance declined normally over delays of up to 1 hr. This pattern of results was replicated in Experiment 2, which showed that amnesic rate of forgetting on a test of cued recall was influenced by level of cuing. Experiment 3 showed that excessive sensitivity to interference was unlikely to be the cause of the amnesic patients' accelerated forgetting rate, which is instead explained in terms of storage deficit accounts of amnesia.

Adult↗

PubMed1999

Rate of forgetting in amnesia: II. Recall and recognition of word lists at different levels of organization.

Amnesic rate of decline of free recall, cued recall, and recognition of word lists with different levels of organization was investigated in 2 experiments. In Experiment 1, it was found that amnesic free recall of semantically related word lists declined at an accelerated rate, whereas free recall of lists of unrelated words declined at a normal rate. Cued recall and recognition performance of both kinds of word lists appeared to decline at a normal rate. In Experiment 2, the results of the free-recall and recognition conditions were replicated using an improved experimental design. The observed amnesic forgetting pattern is interpreted as arising from an impairment in consolidation of long-term memory for complex associations between 2 or more items and their study context that is caused by extended hippocampal system lesions.

Adult↗

PubMed1998

Face processing impairments after encephalitis: amygdala damage and recognition of fear.

Face processing and facial emotion recognition were investigated in five post-encephalitic people of average or above-average intelligence. Four of these people (JC, YW, RB and SE) had extensive damage in the region of the amygdala. A fifth post-encephalitic person with predominantly hippocampal damage and relative sparing of the amygdala (RS) participated, allowing us to contrast the effects of temporal lobe damage including and excluding the amygdala region. The findings showed impaired recognition of fear following bilateral temporal lobe damage when this included the amygdala. For JC, this was part of a constellation of deficits on face processing tasks, with impaired recognition of several emotions. SE, YW and RB, however, showed relatively circumscribed deficits. Although they all had some problems in recognizing or naming famous faces, and had poor memory for faces on the Warrington Recognition Memory Test, none showed a significant impairment on the Benton Test of Facial Recognition, indicating relatively good perception of the face's physical structure. In a test of recognition of basic emotions (happiness, surprise, fear, sadness, disgust and anger), SE, YW and RB achieved normal levels of performance in comparison to our control group for all emotions except fear. Their results contrast with those of RS, with relative sparing of the amygdala region and unimpaired recognition of emotion, pointing clearly toward the importance of the amygdala in the recognition of fear.

Aged↗

PubMed1995

Assessment of familiarity and recollection in the false fame paradigm using a modified process dissociation procedure.

A modified way of administering the process dissociation procedure to the false fame paradigm is described. Multidimensional signal detection theory (SDT) is used to correct for recollection as well as familiarity false alarms, and two experiments are reported that compare this method of false alarm correction with the hybrid procedure preferred by Jacoby et al. (1993). In experiment 1, it is shown that recollection and familiarity are lost at the same rate in normal subjects over a delay of 1 d when an SDT analysis is used. Analysis with the hybrid procedure fails to find any forgetting over the 1-d delay. In experiment 2, amnesics are shown to have preserved familiarity in the face of impaired recollection for names when the results are analyzed by either method. An additional analysis showed that the amnesics' familiarity was normal even for relatively novel surnames. The SDT analysis also revealed that the amnesics, relative to controls, showed a conservative recollection and a liberal familiarity response bias. The results indicate that it is important to correct for recollection as well as familiarity false alarms.

Adult↗

PubMed1982

RNA polymerase-associated interactions near template promoter sequences of defective interfering particles of vesicular stomatitis virus.

Methylation protection studies suggested that the NS protein component of the RNA polymerase of vesicular stomatitis virus contacts the RNA templates of defective interfering (DI) particles at the sequence 3'...GUCUAUUUUUAUUUUUGGUG...5',17 to 37 nucleotides downstream from the site of initiation of in vitro transcription. The data indicated that vesicular stomatitis virus and DI particle RNAs contain different polymerase binding sequences and that NS may function as a transcription initiator protein for template recognition at both sequences. These results are thus compatible with the hypothesis that differences in the rate of defective and nondefective viral particle replication and autointerference are due to higher-affinity binding sites for polymerase at the 3' end of DI particle RNAs. In addition, a unique DI particle (DI-LT2) RNA that contains a transcriptionally inactive vesicular stomatitis virus leader gene 72 to 118 nucleotides from its 3' end showed interactions with the viral polymerase similar to those reported previously for the 3'-terminal vesicular stomatitis virus leader gene (Keene et al., Proc. Natl. Acad. Sci, U.S.A. 78:6191--6195, 1981). The interaction of polymerase with the internal leader gene of DI-LT2 RNA suggested that the lack of leader RNA and mRNA production by this particle is not due to the inability of polymerase to bind to internal sites along the template. Instead, the initiation of transcription is more likely influenced by the position of the polymerase binding site relative to the 3' end or by requisite interactions between the catalytic polymerase component (L) and the proposed initiator protein (NS).

Base Sequence↗

PubMed1981

Transfer RNAs associated with vesicular stomatitis virus.

The predominant RNAs in purified VSV particles are 42S and 4S in size. The 4S RNA is host transfer RNA that did not incorporate detectable radiolabel during VSV infection and was detected by in vitro labelling. Surprisingly, when BHK cells were prelabelled for 30 to 54 h before infection, the incorporation of [3H]uridine and [32P]orthophosphate into virus tRNAs remained very low and virus tRNAs were found to have a 5- to 15-fold lower specific activity than the total host tRNA, the value depending, in part, upon the period of prelabelling. Two-dimensional gel electrophoresis and partial sequence analysis indicated that the virus tRNAs include most species of host tRNA and no singly predominant species was apparent. Transfer RNAs are packaged by several enveloped viruses, but we have not found 4S RNA in reovirus, which lacks an envelope. We suggest that VSV contains a membrane-associated population of tRNA which has a slower rate of turnover than the total population of cellular tRNA.

Electrophoresis, Polyacrylamide Gel↗