Short-Term and Long-Term Verbal Memory: A Positron Emission Tomography Study (original) (raw)
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Functional brain imaging of episodic and semantic memory with positron emission tomography
Journal of Molecular Medicine, 1997
Human memory is composed of several independent but interacting systems. These include a system for remembering general knowledge, semantic memory, and a system for recollection of personal events, episodic memory. The results of positron emission tomography (PET) studies of regional cerebral blood flow indicate that networks of distributed brain regions subserve episodic and semantic memory. Some networks seem to be generally engaged in memory processes whereas the involvement of others is specific to factors such as the type of information to be remembered or the level of retrieval success. The PET findings help to understand memory dysfunction (a) by showing that multiple brain regions are involved in different memory processes and (b) by sharpening the interpretation of the functional role of different brain regions.
A positron emission tomography study of the short-term maintenance of verbal information
The Journal of Neuroscience : The Official Journal of the Society for Neuroscience
Positron emission tomography (PET) was used to investigate the functional brain anatomy associated with the short-term maintenance of linguistic information. Subjects were asked to retain five related words, unrelated words, or pseudowords silently for the duration of a 40 sec PET scan. When brain activity during these short-term maintenance tasks was compared with a visual fixation control task, increases were found bilaterally in the dorsolateral prefrontal cortex and cerebellum, and medially in the supplementary motor area. Furthermore, effects of stimulus condition and recall performance were found in the left frontal operculum. To investigate the role of articulatory systems in the maintenance of verbal information, regional activation was compared across the maintenance tasks and a covert articulation task (silent counting). The cerebellum was active in both task conditions, whereas activation in prefrontal regions was specific to the maintenance condition. Conversely, greater...
Journal of Cognitive Neuroscience, 2000
& The effects of divided attention (DA) on episodic memory encoding and retrieval were investigated in 12 normal young subjects by positron emission tomography (PET). Cerebral blood flow was measured while subjects were concurrently performing a memory task (encoding and retrieval of visually presented word pairs) and an auditory tone-discrimination task. The PET data were analyzed using multivariate Partial Least Squares (PLS), and the results revealed three sets of neural correlates related to specific task contrasts. Brain activity, relatively greater under conditions of full attention (FA) than DA, was identified in the occipital-temporal, medial, and ventral-frontal areas, whereas areas showing relatively more activity under DA than FA were found in the cerebellum, temporo-parietal, left anterior-cingulate gyrus, and bilateral dorsolateral-prefrontal areas. Regions more active during encoding than during retrieval were located in the hippocampus, temporal and the prefrontal cortex of the left hemisphere, and regions more active during retrieval than during encoding included areas in the medial and right-prefrontal cortex, basal ganglia, thalamus, and cuneus. DA at encoding was associated with specific decreases in rCBF in the left-prefrontal areas, whereas DA at retrieval was associated with decreased rCBF in a relatively small region in the right-prefrontal cortex. These different patterns of activity are related to the behavioral results, which showed a substantial decrease in memory performance when the DA task was performed at encoding, but no change in memory levels when the DA task was performed at retrieval. &
Functional neuroanatomy of amnesia: Positron emission tomography studies
Microscopy Research and Technique, 2000
In this article, we review the principles of, and provide examples for, the new approach of functional neuropsychology in the field of amnesia. In the permanent amnesic syndrome, positron emission tomography (PET) can provide statistical maps of the brain regions with significantly impaired resting metabolism in comparison with control subjects. These regions include not only Papez's circuit but also the left supramarginal gyrus, which may explain in part the retrograde amnesia present in most cases of amnesic syndrome. This approach is also of great interest in transient global amnesia (TGA) because the defect of episodic memory is highly selective and occurs without permanent damage. The few available PET studies in TGA suggest the dysfunction of a distributed network including the hippocampal region and the prefrontal cortex, with a different pattern individually. Further studies will be necessary to better understand the relationships between the precise cognitive deficits in TGA and the pattern of brain hypometabolism. In Alzheimer's disease (AD), the study of the correlations between memory test scores and metabolic values across a sample of subjects provides a map of those brain structures whose synaptic pathology dysfunction underlies the particular neuropsychological alteration. The distribution of the sites of correlations shows striking differences according to each memory system. This approach should open the way for the unravelling of the neurobiological substrates of both cognitive impairment and compensatory mechanisms in neurodegenerative diseases. Over and above their applications in neurological research, such studies in brain-diseased subjects are particularly useful for establishing cognitive and neurobiological models of human memory, because they allow the highlighting of the neural networks that are essential for memory function. From a cognitive neuroscience perspective, the functional neuropsychology of amnesia is, therefore, complementary to the classic activation paradigm in normal subjects, which identifies the cerebral structures that are involved with, but not necessarily indispensable for, the execution of the task.
Is prefrontal cortex involved in cued recall? A neuropsychological test of PET findings
Neuropsychologia, 1996
Positronemissiontomography (PET) experimentshave detected blood flowactivations in right anterior prefrontal cortex during performance of a word stem cued recall task [3, 38]. Based on findingsfrom a variety of PET studies, the "hemispheric encoding/retrieval asymmetry model" [44]was proposed to explain the role of the frontal lobes in episodic memory. This model asserts that left prefrontal cortex is preferentiallyinvolvedin the encodingof new information into episodicmemory,whereasright prefrontal cortex is more involvedin episodicmemory retrieval. As a neuropsychologicaltest of this hypothesis,a group of frontal patients with lesionsin areas 6, 8, 9, 10,44, 45 and/or 46 (11left, fiveright) were run on word stem cued recall under two semantic study conditions. As a group, these patients werenot significantlyimpaired in cued recall. In the first but not the secondexperiment, left frontal patients recalled fewer words than controls. Right frontal patients were not impaired on either list. Right prefrontal cortex could be activated by several strategic aspects of the cued recall paradigm that were minimizedin the present experiment. Brain reorganization in the lesioned patients could also account for their intact performance. The regions of prefrontal cortex activatedin PET studiesof youngcontrolsare not necessaryfor patientsto performthe task. Copyright01996 ElsevierScienceLtd
The functional anatomy of memory
Experientia, 1995
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.
Remembering the past: two facets of episodic memory explored with positron emission tomography
American Journal of Psychiatry, 1995
This study used positron emission tomography to examine two kinds of personal memory that are used in psychiatric evaluation: focused episodic memory (recall ofpast experience, employed in "taking a history ") and random episodic memory (uncensored thinking about experience, examined during analytic therapy using free association). For comparison, a third memory task was used to tap impersonal memory that represents general information about the world ("semantic memory "). Method: Thirteen subjects were studied using the ('50JH20 method to obtain quantitative measurements of cerebral blood flow. The three conditions were subtracted and their relative relationships examined. Results: The random episodic condition produced activations in widely distributed association cortex (right and left frontal, parietal, angular/supramarginal, and posterior inferior temporal regions). Focused episodic memory engaged a network that included the medial inferior frontal regions, precuneus/retrosplenial cingulate, anterior cingulate, thalamus, and cerebellum. The use of medial frontal regions and the precuneus/retrosplenial cingulate was common to both focused and random episodic memory. The major difference between semantic and episodic memory was activation ofBroca's area and the left frontal operculum by semantic memory. Conclusions: These results indicate that freeranging mental activity (random episodic memory) produces large activations in association cortex and may reflect both active retrieval of past experiences and planning of future experiences. Focused episodic memory shares some components of this circuit (inferior frontal and precuneus), which may reflect the time-linked components ofboth aspects ofepisodic memory, and which permit human beings to experience personal identity, consciousness, and self-awareness.
1997
& Positron emission tomography (PET) was used to investigate the hypothesis that older adults' difficulties with temporal-order memory are related to deficits in frontal function. Young (mean 24.7 years) and old (mean 68.6 years) participants studied a list of words, and were then scanned while retrieving information about what words were in the list (item retrieval) or when they occurred within the list (temporal-order retrieval). There were three main results. First, whereas the younger adults engaged right prefrontal regions more during temporal-order retrieval than during item retrieval, the older adults did not. This result is consistent with the hypothesis that context memory deficits in older adults are due to frontal dysfunction. Second, ventromedial temporal activity during item memory was relatively unaffected by aging. This finding concurs with evidence that item memory is relatively preserved in old adults and with the notion that medial temporal regions are involved in automatic retrieval operations. Finally, replicating the result of a previous study (Cabeza, R.
Neuroanatomical correlates of encoding in episodic memory: Levels of processing effect
1994
Cognitive studies of memory processes demonstrate that memory for stimuli is a function of how they are encoded; stimuli processed semantically are better remembered than those processed in a perceptual or shallow fashion. This study investigates the neural correlates of this cognitive phenomenon. Twelve subjects performed two different cognitive tasks on a series of visually presented nouns. In one task, subjects detected the presence or absence of the letter a; in the other, subjects categorized each noun as living or nonliving. Positron emission tomography (PET) scans using 15O-labeled water were obtained during both tasks. Subjects showed substantially better recognition memory for nouns seen in the living/nonliving task, compared to nouns seen in the a-checking task. Comparison of the PET images between the two cognitive tasks revealed a significant activation in the left inferior prefrontal cortex (Brodmann's areas 45, 46, 47, and 10) in the semantic task as compared to the perceptual task. We propose that memory processes are subserved by a wide neurocognitive network and that encoding processes involve preferential activation of the structures in the left inferior prefrontal cortex.