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P C Fletcher

Publications and source records attributed to P C Fletcher.

45 records · Page 3Linked to original sources
PubMed1995

The functional anatomy of memory.

A review of recent work using Positron Emission Tomography (PET) to examine brain systems involved in auditory-verbal memory is presented. Initial work delineated widespread brain regions which were, to a large extent, in agreement with existing neuropsychological literature. Expanding on this, a number of studies have examined memory encoding and retrieval separately. Additionally, experiments have been carried out to specifically address sub-components of memory such as the use of visual imagery as a mnemonic strategy, the functional anatomical evidence for the episodic/semantic memory distinction and the different brain regions involved in explicit and implicit memory tasks.

Animals↗
PubMed1995

The mind's eye--precuneus activation in memory-related imagery.

We examined brain activity associated with visual imagery at episodic memory retrieval using positron emission tomography (PET). Twelve measurements of regional cerebral blood flow (rCBF) were taken in six right-handed, healthy, male volunteers. During six measurements, they were engaged in the cued recall of imageable verbal paired associates. During the other six measurements, they recalled nonimageable paired associates. Memory performance was equalized across all word lists. The subjects' use of an increased degree of visual imagery during the recall of imageable paired associates was confirmed using subjective rating scales after each scan. Memory-related imagery was associated with significant activation of a medial parietal area, the precuneus. This finding confirms a previously stated hypothesis about the precuneus and provides strong evidence that it is a key part of the neural substate of visual imagery occurring in conscious memory recall.

Adult↗
PubMed1995

Other minds in the brain: a functional imaging study of "theory of mind" in story comprehension.

The ability of normal children and adults to attribute independent mental states to self and others in order to explain and predict behaviour ("theory of mind") has been a focus of much recent research. Autism is a biologically based disorder which appears to be characterised by a specific impairment in this "mentalising" process. The present paper reports a functional neuroimaging study with positron emission tomography in which we studied brain activity in normal volunteers while they performed story comprehension tasks necessitating the attribution of mental states. The resultant brain activity was compared with that measured in two control tasks: "physical" stories which did not require this mental attribution, and passages of unlinked sentences. Both story conditions, when compared to the unlinked sentences, showed significantly increased regional cerebral blood flow in the following regions: the temporal poles bilaterally, the left superior temporal gyrus and the posterior cingulate cortex. Comparison of the "theory of mind" stories with "physical" stores revealed a specific pattern of activation associated with mental state attribution: it was only this task which produced activation in the medial frontal gyrus on the left (Brodmann's area 8). This comparison also showed significant activation in the posterior cingulate cortex. These surprisingly clear-cut findings are discussed in relation to previous studies of brain activation during story comprehension. The localisation of brain regions involved in normal attribution of mental states and contextual problem solving is feasible and may have implication for the neural basis of autism.

Adolescent↗
PubMed1995

Brain systems for encoding and retrieval of auditory-verbal memory. An in vivo study in humans.

Long-term auditory-verbal memory comprises, at a neuropsychological level, a number of distinct cognitive processes. In the present study we determined the brain systems engaged during encoding (experiment 1) and retrieval (experiment 2) of episodic auditory-verbal material. In the separate experiments, PET measurements of regional cerebral blood flow (rCBF), an index of neural activity, were performed in normal volunteers during either the encoding or the retrieval of paired word associates. In experiment 1, a dual task interference paradigm was used to isolate areas involved in episodic encoding from those which would be concurrently activated by other cognitive processes associated with the presentation of paired associates, notably priming. In experiment 2, we used the cued retrieval of paired associates from episodic or from semantic memory in order to isolate the neural correlates of episodic memories. Encoding of episodic memory was associated with activation of the left prefrontal cortex and the retrosplenial area of the cingulate cortex, while retrieval from episodic memory was associated with activation of the precuneus bilaterally and of the right prefrontal cortex. These results are compatible with the patterns of activation reported in a previous PET memory experiment in which encoding and retrieval were studied concurrently. They also indicate that separate brain systems are engaged during the encoding and retrieval phases of episodic auditory-verbal memory. Retrieval from episodic memory engages a different, but overlapping, system to that engaged by retrieval from semantic memory, a finding that lends functional anatomical support to this neuropsychological distinction.

Adult↗
PubMed1994

A graded task approach to the functional mapping of brain areas implicated in auditory-verbal memory.

Positron emission tomography measurements of regional cerebral blood flow (rCBF) were performed in normal volunteers during a graded auditory-verbal memory task. Subjects were required to remember and then immediately, and freely, recall a series of auditorily presented word lists varying from two to 13 words in length. Significant regional correlations between rCBF and memory load (word list length) were identified using statistical parametric mapping. Increasing memory load correlated with increasing rCBF in the cerebellar vermis and hemispheres, thalamus bilaterally, the superior and middle frontal gyri bilaterally, anterior insular regions bilaterally, anterior cingulate, precuneus and left and right lateral premotor areas. Increasing memory load also correlated with decreasing rCBF in the left and right superior temporal/insular regions, medial frontal gyrus, Brodmann's area 37 bilaterally, cuneus, inferior parietal lobule bilaterally and the mid-portion of the cingulate cortex. The pattern of rCBF change closely resembled that identified in a previously reported study using a cognitive subtraction paradigm and provides further evidence for a widespread neural system subserving auditory-verbal memory. The patterns of rCBF response suggest that the areas identified are associated with limited capacity processes for encoding and retrieval.

Adult↗
PubMed1989

Central station data displays: an experimental evaluation of observer performance. Part 2: Factors affecting performance, and a comparison of analogue and digital data.

16 experienced ICU nurses monitored simulated central station VDU displays for the occurrence of ectopic beats and for signs of deterioration in general cardiovascular status. Each period of monitoring lasted for 1 h, and on separate occasions each nurse monitored 1, 2, 4 or 6 displays simultaneously. For primary clinical tasks, the data showed that the nurses' performance improved with each test. The identification of ventricular ectopic beats (VEBs) improved within the 1 h of each test except when 6 screens were being viewed simultaneously, with a similar result for the identification of deterioration of cardiovascular status. The nurses showed a marked preference for analogue signals over digits for the identification of VEBs. The highest priority clinical task was the identification of deteriorating cardiovascular status. When this task was performed efficiently less attention was given to minor tasks, and the nurse rated herself as very tired.

Attitude of Health Personnel↗
PubMed1989

Central station data displays: an experimental evaluation of observer performance. Part 1: Number of displays and observation time.

16 experienced ICU nurses monitored simulated central station VDU displays for the occurrence of ectopic beats and for signs of deterioration in general cardiovascular status. Each period of monitoring lasted for 1 h, and on separate occasions each nurse monitored 1, 2, 4 or 6 displays simultaneously. As the number of observed screens increased, performance declined significantly, with reduced identifications of discrete events (e.g., ectopic beat detections), and with increased delays in determining a deterioration in cardiovascular status; in addition, a secondary task was less accurately and efficiently performed, and the nurses tended to become increasingly fatigued. Efficient observing was maintained over the 1 h monitoring period, but only at considerable cost in terms of fatigue and a loss of alertness. The results suggest that there may be restrictions in the use of complex central station facilities at first-line observation posts for patient care.

Cardiac Complexes, Premature↗
PubMedDate not supplied

Right prefrontal cortex responds to item familiarity during a memory encoding task.

In a previous word-pair encoding study (Dolan & Fletcher, 1997), we examined the effect of introducing novelty, either in studied words or in their mutual associations. A left medial temporal lobe (MTL) sensitivity to novel words and left prefrontal cortex (PFC) to novel associations was observed. In this further report on the data, we explored the extent to which the right PFC, more generally implicated in retrieval operations (Fletcher, Frith, & Rugg, 1997), was sensitive to these manipulations. Specifically, we characterised changes associated with increasing familiarity of study material. We demonstrate that the response in right ventrolateral PFC is preferentially sensitive to a condition in which all material was familiar (that is, in which all material had been presented prior to scanning). A more dorsal region in right PFC was found to be relatively more active in association with a condition in which one item in the pair was familiar but was paired with a novel associate. Our results suggest that sensitivity to stimulus familiarity is expressed in right PFC, even within the context of an encoding task. The data also provide further evidence for functional heterogeneity within right PFC, with a more ventral region responding to familiarity of complete word pairs and a more dorsal region responding to familiar single words occurring in the context of new associative relationships.

Humans↗