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Biomedical subjects

K Allan

Publications and source records attributed to K Allan.

At least 19 recordsLinked to original sources
PubMed2004

Does speculum examination have a role in assessing bleeding in early pregnancy?

OBJECTIVES: To assess to what extent a speculum examination after a bimanual examination influences the accuracy of diagnosis and subsequent management of women with bleeding in early pregnancy in an accident and emergency (A&E) department. METHOD: A prospective study over a five month period included women presenting to A&E with vaginal bleeding at <20/40. Exclusion criteria were haemodynamic instability or known cervical carcinoma. The clinician recorded a diagnosis and management plan on a standard questionnaire after bimanual examination and after subsequent speculum examination. RESULTS: 236 women were included in the study. Of these, a total of three (1.3%) had a change of management plan and 10 (4.2%) patients had a change of diagnosis after speculum examination. CONCLUSION: The results suggest that speculum examination contributes to a minority of management decisions. The need for speculum examination should be assessed on a case by case basis depending on whether the findings on bimanual are conclusive.

Abortion, Spontaneous↗
PubMed2001

The effect of retrieval cues on post-retrieval monitoring in episodic memory: an electrophysiological study.

The aim of the present experiment was to examine whether episodic retrieval and 'post-retrieval' monitoring are affected by the nature of the cue that guides a search of memory. We recorded event-related brain potentials (ERPs) from young healthy adult participants while they tried to recall studied words (e.g. 'MOTHER') with the aid of word-stem (e.g. 'MOT') and word-fragment (e.g. 'M-TH--') retrieval cues. Analyses of the behavioural data showed that while it was far more difficult to generate completions per se for the fragments, the levels of conscious, or 'explicit', recall obtained with each type of cue were statistically identical. ERP analyses focussed upon differences in neural activity evoked by each type of cue (termed 'old/new' ERP effects) during successful versus unsuccessful retrieval. The stem and fragment old/new ERP effects were remarkably similar in their time course and magnitude, and also in their scalp distribution, which changed over time as multiple neuronal populations, and hence multiple cognitive operations, became activated. These behavioural and ERP findings suggest that the cognitive operations reflected by old/new effects in cued recall tasks may be insensitive to changes in the retrieval strategy, or effort, that participants apply to monitor the episodic status of retrieved information. The findings are discussed in relation to previous ERP and functional imaging studies that have investigated task-specific features of retrieval and post-retrieval processing in episodic memory.

Adolescent↗
PubMed2000

The role of the right anterior prefrontal cortex in episodic retrieval.

Regional brain activity was measured with H(2) (15)O PET while participants attempted to complete word-stem and word-fragment retrieval cues with previously studied words. The retrieval cue manipulation was employed to gain control over the monitoring operations associated with evaluating the episodic status of alternative cue completions. These operations were more constrained for fragments, which had fewer possible completions than each corresponding stem. In one condition (zero target), during the scanning interval none of the cues could be completed with studied items, whereas in another condition (high target), 80% of cues belonged to studied items. Relative to baseline tasks, right anterior prefrontal activity was greater for stems than for fragments in the zero target condition. The target density manipulation did not modulate right anterior prefrontal activity, but was associated with increased activity in right dorsolateral prefrontal cortex. These findings are consistent with the proposal that the right anterior prefrontal cortex supports monitoring operations during episodic retrieval tasks. In addition, the findings add to evidence suggesting that the dorsolateral and anterior right prefrontal cortex make functionally distinct contributions to episodic retrieval.

Adult↗
PubMed2000

The effect of encoding manipulations on neural correlates of episodic retrieval.

The present experiments investigated whether the neural correlates of explicit (conscious) retrieval from episodic memory vary qualitatively according to conditions at encoding, as is predicted by current views of the neural basis of memory retrieval. Event-related potential (ERP) correlates of word stem (e.g. MOT_) cued recall were compared for items studied under different encoding conditions. In Experiment 1, encoding was either 'shallow' or 'deep' whereas in Experiment 2 the presentation modality of the study items was either visual or auditory. In both experiments robust ERP memory effects were observed for stems completed with explicitly retrieved items from each encoding condition. The effects varied in their magnitude, such that they were largest when elicited by the more memorable class of item in each experiment. The scalp distributions of the effects did not differ according to encoding condition, a finding which offers no support for the view that retrieval involves the literal reinstatement of neural activity engaged at the time of encoding. The findings instead point to the existence of a set of retrieval operations that are engaged regardless of the conditions under which retrieved information is encoded.

Adolescent↗
PubMed2000

Recognition memory for emotionally negative and neutral words: an ERP study.

Scalp recorded event-related potentials were used to investigate the neural activity elicited by emotionally negative and emotionally neutral words during the performance of a recognition memory task. Behaviourally, the principal difference between the two word classes was that the false alarm rate for negative items was approximately double that for the neutral words. Correct recognition of neutral words was associated with three topographically distinct ERP memory 'old/new' effects: an early, bilateral, frontal effect which is hypothesised to reflect familiarity-driven recognition memory; a subsequent left parietally distributed effect thought to reflect recollection of the prior study episode; and a late onsetting, right-frontally distributed effect held to be a reflection of post-retrieval monitoring. The old/new effects elicited by negative words were qualitatively indistinguishable from those elicited by neutral items and, in the case of the early frontal effect, of equivalent magnitude also. However, the left parietal effect for negative words was smaller in magnitude and shorter in duration than that elicited by neutral words, whereas the right frontal effect was not evident in the ERPs to negative items. These differences between neutral and negative words in the magnitude of the left parietal and right frontal effects were largely attributable to the increased positivity of the ERPs elicited by new negative items relative to the new neutral items. Together, the behavioural and ERP findings add weight to the view that emotionally valenced words influence recognition memory primarily by virtue of their high levels of 'semantic cohesion', which leads to a tendency for 'false recollection' of unstudied items.

Adult↗
PubMed2000

Electrophysiological evidence for the modulation of retrieval orientation by depth of study processing.

Event-related potentials (ERPs) were employed to investigate whether brain activity elicited by retrieval cues in a memory test varies according to the encoding task undertaken at study. Two recognition memory test blocks were administered, preceded, in one case, by a "shallow" study task (alphabetic judgement) and, in the other case, by a "deep" task (sentence generation). ERPs elicited by the new words in each test block differed, the ERPs elicited in the block following the shallow study task exhibiting the more positive-going waveforms. This finding was taken as evidence that subjects adopt different "retrieval sets" when attempting to retrieve items that had been encoded in terms of alphabetic versus semantic attributes. Differences between the ERPs elicited by correctly classified old and new words (old/new effects) also varied with encoding task. The effects for deeply studied words resembled those found in previous ERP studies of recognition memory, whereas old/new effects for shallowly studied words were confined to a late-onsetting, right frontal positivity. Together, the findings indicate that the depth of study processing influences two kinds of memory-related neural activity, associated with memory search operations, and the processing of retrieved information, respectively.

Adult↗
PubMed2000

Overexpression of cyclin A and cyclin B1 proteins in astrocytomas.

BACKGROUND: Cyclins are proteins that are expressed during the progression of a normal cell through the cell cycle. In a number of cancers, overexpression of cyclin A and cyclin B1 proteins has been reported, and in some instances the levels of expression correlated well with the grades of malignancy. The expression of cyclin A and cyclin B1 proteins in astrocytoma may be linked to the histologic grade or proliferative activities. OBJECTIVE: To study the expression of cyclin A and cyclin B1 proteins in astrocytomas and correlate the labeling indices (LIs) of cyclin A and cyclin B1 with histologic grade and Ki-67 LI. DESIGN: The surgical biopsy specimens from 65 adults with astrocytomas were reviewed and divided into grades based on the World Health Organization system. The paraffin sections were immunostained using primary antibodies against Ki-67, cyclin A, and cyclin B1. The LIs of these astrocytomas for the 3 different antibodies were determined by computerized image analysis. RESULTS: The cyclin A LI showed good correlation with astrocytoma grade and Ki-67 LI. Both the nuclear and cytoplasmic cyclin B LIs correlated well with the tumor grade but showed poor correlation with Ki-67 LI. CONCLUSIONS: This study suggests that although both cyclin A and B protein expression are related to the grade of malignancy in astrocytomas, cyclin A levels more generally reflect the proliferative state of these tumors. We also provide indirect evidence that cyclin B1 is associated with the aberrant progression through the G2-M phase checkpoint in astrocytomas.

Astrocytoma↗
PubMed1999

Versican enhances locomotion of astrocytoma cells and reduces cell adhesion through its G1 domain.

Versican is a large extracellular proteoglycan and is expressed in a variety of tissues including the central nervous system. A malignant astrocytoma cell line U87 with high motility expressed a higher level of versican than another malignant astrocytoma cell line U343 with lower motility. We observed that the U87 cells were less adherent to tissue culture plates than the U343 cells. To investigate the role of versican in astrocytoma cell migration, we generated recombinant products of a mini-versican construct expressed in COS-7 cells. We found that the mini-versican products enhanced astrocytoma cell migration. Furthermore, enhanced migration was promoted by the G1 domain but not the G3 domain of versican. We introduced culture medium containing products of the mini-versican, the G1, and the G3 constructs separately into the astrocytoma cell lines U87 and U343. The mini-versican and the G1 construct, but not the G3 construct, were shown to reduce astrocytoma cell adhesion. The present data suggest that versican exerts its effect on astrocytoma cell migration and adhesion through the G1 domain.

Astrocytoma↗
PubMed1998

Neural correlates of cued recall with and without retrieval of source memory.

A source memory procedure was used to investigate whether event-related potentials (ERPs) reflect the retrieval of episodic information (recollection) on tests of word-stem cued recall. 'Cued recall ERP effects' for recalled items were found to differ only in their magnitudes, and not their scalp distributions, according to the accuracy of source memory. This finding strongly supports the hypothesis that cued recall ERP effects reflect quantitative variation in the amount or quality of information which can be retrieved about recently experienced events. Topographic analyses also revealed that the distribution of the cued recall ERP effects changed over time, reflecting the activity of at least two temporally and neuroanatomically dissociable neural populations contributing to recollection on this task.

Adolescent↗
PubMed1998

Dissociation of the neural correlates of implicit and explicit memory.

One presentation of a word to a subject is enough to change the way in which the word is processed subsequently, even when there is no conscious (explicit) memory of the original presentation. This phenomenon is known as implicit memory. The neural correlates of implicit memory have been studied previously, but they have never been compared with the correlates of explicit memory while holding task conditions constant or while using a procedure that ensured that the neural correlates were not 'contaminated' by explicit memory. Here we use scalp-recorded event-related brain potentials to identify neural activity associated with implicit and explicit memory during the performance of a recognition memory task. Relative to new words, recently studied words produced activity in three neuroanatomically and functionally dissociable neural populations. One of these populations was activated whether or not the word was consciously recognized, and its activity therefore represents a neural correlate of implicit memory. Thus, when task and memory contamination effects are eliminated, the neural correlates of explicit and implicit memory differ qualitatively.

Adult↗
PubMed1998

Neural correlates of memory retrieval during recognition memory and cued recall.

Regional brain activity, measured by H215O PET, was investigated during recognition memory and word-stem cued recall of words in order to compare the neural correlates of two components of memory retrieval-effort and success-as a function of task. For each task there was a baseline and two retrieval conditions. In one retrieval condition (zero density), none of the test items corresponded to words encoded in a preceding study phase. Differences in activity between this condition and the baseline were employed to characterize the neural correlates of retrieval effort in each task. In the other retrieval condition (high density), 80% of the test items had been studied previously. Differences in brain activity between this condition and the zero-density condition were taken to represent the neural correlates of successful retrieval. The principal findings concern the right anterior prefrontal cortex, a region demonstrated previously to be active during episodic retrieval. Relative to baseline, this region showed no evidence of activation in the zero-density condition of the recognition task, but did show enhanced activity in the equivalent condition of the cued-recall task. In contrast, relative to the zero-density condition, the high-density condition was associated with increased right prefrontal activity during recognition, but reduced activity during cued recall. It is proposed that the right prefrontal cortex supports cognitive processes that operate on information retrieved in response to a test item and that these processes contribute to the evaluation of whether the information represents an appropriate prior episode.

Adult↗
PubMed1998

Electrophysiological evidence for dissociable processes contributing to recollection.

This paper reviews a number of studies in which we have employed event-related potentials (ERPs) to investigate the cognitive processes which contribute to conscious recollection. Across a range of tasks (including recognition memory, source memory, associative recall and word-stem cued recall) there is evidence for the proposal that recollection involves processes which are both functionally and neurologically dissociable. This evidence takes the form of temporally and topographically dissociable ERP effects, which attain their maximum amplitude when elicited by items that satisfy operational definitions for having been recollected. The ERP effects are interpreted as reflecting retrieval and post-retrieval processes which, we argue, constitute two separate components of recollection as defined within the process dissociation framework of Jacoby and colleagues. The ERP findings suggest that post-retrieval processing is particularly sensitive to task variables, implying that recollection may be neither functionally nor neurologically homogeneous.

Association Learning↗
PubMed1998

A study of vestibular schwannomas using positron emission tomography and monoclonal antibody Ki-67.

OBJECTIVE: This study aimed to evaluate the role of positron emission tomography (PET) as an in vivo determinant of tumor aggressiveness and growth. STUDY DESIGN: The study design was a prospective pilot study. SETTING: Positron emission tomography was performed at the Clarke Institute of Psychiatry. All patients were treated at the Sunnybrook Health Science Centre. Both institutions are affiliated with the University of Toronto, Toronto, Canada. PATIENTS: The study consisted of five consecutive patients with vestibular schwannomas with tumor size of 1 cm or larger within the cerebellopontine angle. One was a recurrent tumor and four were primary tumors. INTERVENTIONS: Preoperative PET studies were conducted using 18-fluorodeoxyglucose (FDG) as a radionuclide tracer to measure glucose metabolism within tumors. Tumors were processed and immunostained against Ki-67 nuclear antigen; their proliferative potentials were quantified based on immunoreactivity of tumor cells. MAIN OUTCOME MEASURES: Tumor metabolic activity on PET was compared with that of contralateral cerebellum to arrive at an FDG index. This number was compared with clinical parameters and Ki-67 reactivity. RESULTS: On PET, all tumors showed less metabolic activity than the cerebellum. The FDG uptake varied greatly between tumors independent of clinical parameters. All the tumors had a low proliferative index (<5%) with immunohistochemistry; there were quite a bit of intralesional variations in proliferative activities. CONCLUSION: Large tumor size and recurrent disease did not correlate well with increased FDG uptake on PET. Similarly, they did not show increased cellular activities as expressed by Ki-67 immunostaining.

Adult↗
PubMed1997

An event-related potential study of explicit memory on tests of cued recall and recognition.

The event-related potential (ERP) correlates of performance on test of word-stem cued recall and recognition memory were contrasted. ERPs elicited by stems attracting successful recall exhibited a sustained positive-going shift relative to ERPs elicited by stems completed with unstudied items. This positive shift was maximal at electrode sites on and adjacent to the midline. An equally sustained positive-going ERP modulation was observed for the recognition memory task in ERPs elicited by recognised 'old' items relative to ERPs elicited by correctly rejected 'new' items. The scalp topography of this effect shifted from a parietally distributed asymmetry favouring left hemisphere sites, to a frontally distributed effect maximal over midline and right hemisphere sites. The findings indicate that ERP correlates of explicit memory are task-dependent. The disparate ERP effects are interpreted as reflecting a common explicit retrieval mechanism which is sensitive to the nature of retrieval cues provided at test.

Adult↗
PubMed1996

A motor signal and "visual" size perception.

Recent models of the visual system in primates suggest that the mechanisms underlying visual perception and visuomotor control are implemented in separate functional streams in the cerebral cortex. However, a little-studied perceptual illusion demonstrates that a motor-related signal representing arm position can contribute to the visual perception of size. The illusion consists of an illusory size change in an afterimage of the hand when the hand is moved towards or away from the subject. The motor signal necessary for the illusion could be specified by feedforward and/or feedback sources (i.e. efference copy and/or proprioception/kinesthesis). We investigated the nature of this signal by measuring the illusion's magnitude when subjects moved their own arm (active condition, feedforward and feedback information available), and when arm movement was under the control of the experimenter (passive condition, feedback information available). Active and passive movements produced equivalent illusory size changes in the afterimages. However, the illusion was not obtained when an after-image of subject's hand was obtained prior to movement of the other hand from a very similar location in space. This evidence shows that proprioceptive/kinesthetic feedback was sufficient to drive the illusion and suggests that a specific three-dimensional registration of proprioceptive input and the initial afterimage is necessary for the illusion to occur.

Afterimage↗
PubMed1996

An event-related potential study of word-stem cued recall.

Event-related potentials (ERPs) were recorded from 13 scalp sites while subjects attempted to recall studied words using word-stems. If recall failed, stems were to be completed with the first suitable word to come to mind. To distinguish between correct completions accompanied and unaccompanied by explicit memory, subjects were required to make an overt recognition ("old/new") judgement for each completion. Semantically studied words were associated with higher levels of recall and recognition than were words subjected to non-semantic study. The sole ERP effect was a sustained positive shift in ERPs evoked by stems attracting correct completions that were correctly judged to be old. The shift was anteriorly distributed, and onset was around 300 ms post stimulus. It is interpreted as a reflection of processes either contributing to, or contingent upon, explicit memory retrieval.

Adolescent↗