Biomedical subjects

R Cabeza

Publications and source records attributed to R Cabeza.

At least 37 records · Page 2Linked to original sources

PubMed2000

Imaging cognition II: An empirical review of 275 PET and fMRI studies.

Positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) have been extensively used to explore the functional neuroanatomy of cognitive functions. Here we review 275 PET and fMRI studies of attention (sustained, selective, Stroop, orientation, divided), perception (object, face, space/motion, smell), imagery (object, space/motion), language (written/spoken word recognition, spoken/no spoken response), working memory (verbal/numeric, object, spatial, problem solving), semantic memory retrieval (categorization, generation), episodic memory encoding (verbal, object, spatial), episodic memory retrieval (verbal, nonverbal, success, effort, mode, context), priming (perceptual, conceptual), and procedural memory (conditioning, motor, and nonmotor skill learning). To identify consistent activation patterns associated with these cognitive operations, data from 412 contrasts were summarized at the level of cortical Brodmann's areas, insula, thalamus, medial-temporal lobe (including hippocampus), basal ganglia, and cerebellum. For perception and imagery, activation patterns included primary and secondary regions in the dorsal and ventral pathways. For attention and working memory, activations were usually found in prefrontal and parietal regions. For language and semantic memory retrieval, typical regions included left prefrontal and temporal regions. For episodic memory encoding, consistently activated regions included left prefrontal and medial temporal regions. For episodic memory retrieval, activation patterns included prefrontal, medial temporal, and posterior midline regions. For priming, deactivations in prefrontal (conceptual) or extrastriate (perceptual) regions were consistently seen. For procedural memory, activations were found in motor as well as in non-motor brain areas. Analysis of regional activations across cognitive domains suggested that several brain regions, including the cerebellum, are engaged by a variety of cognitive challenges. These observations are discussed in relation to functional specialization as well as functional integration.

Adult↗

PubMed2000

Large scale neurocognitive networks underlying episodic memory.

Large-scale networks of brain regions are believed to mediate cognitive processes, including episodic memory. Analyses of regional differences in brain activity, measured by functional neuroimaging, have begun to identify putative components of these networks. To more fully characterize neurocognitive networks, however, it is necessary to use analytical methods that quantify neural network interactions. Here, we used positron emission tomography (PET) to measure brain activity during initial encoding and subsequent recognition of sentences and pictures. For each type of material, three recognition conditions were included which varied with respect to target density (0%, 50%, 100%). Analysis of large-scale activity patterns identified a collection of foci whose activity distinguished the processing of sentences vs. pictures. A second pattern, which showed strong prefrontal cortex involvement, distinguished the type of cognitive process (encoding or retrieval). For both pictures and sentences, the manipulation of target density was associated with minor activation changes. Instead, it was found to relate to systematic changes of functional connections between material-specific regions and several other brain regions, including medial temporal, right prefrontal and parietal regions. These findings provide evidence for large-scale neural interactions between material-specific and process-specific neural substrates of episodic encoding and retrieval.

Adult↗

PubMed2000

Age-related differences in neural activity during item and temporal-order memory retrieval: a positron emission tomography study.

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., Grady, C. L., Nyberg, L., McIntosh, A. R. , Tulving, E., Kapur, S., Jennings, J. M., Houle, S., and Craik, F. I. M., 1997), the old adults showed weaker activations than the young adults in the right prefrontal cortex but stronger activations in the left prefrontal cortex. The age-related increase in left prefrontal activity may be interpreted as compensatory. Taken together, the results suggest that age-related changes in brain activity are rather process- and region-specific, and that they involve increases as well as decreases in neural activity.

Adult↗

PubMed2000

The effect of divided attention on encoding and retrieval in episodic memory revealed by positron emission tomography.

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.

Acoustic Stimulation↗

PubMed2000

The effects of divided attention on encoding- and retrieval-related brain activity: A PET study of younger and older adults.

Divided attention (DA) disrupts episodic encoding, but has little effect on episodic retrieval. Furthermore, normal aging is associated with episodic memory impairments, and when young adults are made to encode information under DA conditions, their memory performance is reduced and resembles that of old adults working under full attention (FA) conditions. Together, these results suggest a common neurocognitive mechanism by which aging and DA during encoding disrupt memory performance. In the current study, we used PET to investigate younger and older adults' brain activity during encoding and retrieval under FA and DA conditions. In FA conditions, the old adults showed reduced activity in prefrontal regions that younger adults activated preferentially during encoding or retrieval, as well as increased activity in prefrontal regions young adults did not activate. These results indicate that prefrontal functional specificity of episodic memory is reduced by aging. During encoding, DA reduced memory performance, and reduced brain activity in left-prefrontal and medial-temporal lobe regions for both age groups, indicating that DA during encoding interferes with encoding processes that lead to better memory performance. During retrieval, memory performance and retrieval-related brain activity were relatively immune to DA for both age groups, suggesting that DA during retrieval does not interfere with the brain systems necessary for successful retrieval. Finally, left inferior prefrontal activity was reduced similarly by aging and by DA during encoding, suggesting that the behavioral correspondence between these effects is the result of a reduced ability to engage in elaborate encoding operations.

Adult↗

PubMed2000

Estimating the frequency of nonevents: the role of recollection failure in false recognition.

Participants studied lists of multiply presented converging associates (e.g., bed, dream, pillow, etc.) and were timed as they estimated how often they saw list items, related foils (e.g., blanket), and nonpresented critical items (SLEEP). Average number of repetitions (few [3] vs. many [6]) and repetition variability (fixed vs. variable) were manipulated between subjects. Participants responded more slowly to critical items (3.18 sec) than to list items (2.45 sec) or foils (2.22 sec). In addition, critical-item judgments of frequency (JOFs) were about as large as list-item JOFs, and false recognition (i.e., nonzero JOFs) of critical items was most likely in the few-fixed condition (96%) and least likely in the many-fixed condition (74%). These findings suggest that people can use recollection failure--the absence of an anticipated recollective experience, coupled with strong familiarity--to distinguish critical items from list items and that recollection failure is weighted most heavily when people expect familiar probes to access episodic information.

Adult↗

PubMed1999

Task-related and item-related brain processes of memory retrieval.

In all cognitive tasks, general task-related processes operate throughout a given task on all items, whereas specific item-related processes operate differentially on individual items. In typical functional neuroimaging experiments, these two sets of processes have usually been confounded. Herein we report a combined positron emission tomography and event-related potential (ERP) experiment that was designed to distinguish between neural correlates of task-related and item-related processes of memory retrieval. Two retrieval tasks, episodic and semantic, were crossed with episodic (old/new) and semantic (living/nonliving) properties of individual items to yield evidence of regional brain activity associated with task-related processes, item-related processes, and their interaction. The results showed that episodic retrieval task was associated with increased blood flow in right prefrontal and posterior cingulate cortex, as well as with a sustained right-frontopolar-positive ERP, but that the semantic retrieval task was associated with left frontal and temporal lobe activity. Retrieval of old items was associated with increased blood flow in the left medial temporal lobe and with a brief late positive ERP component. The results provide converging hemodynamic and electrophysiological evidence for the distinction of task- and item-related processes, show that they map onto spatially and temporally distinct patterns of brain activity, and clarify the hemispheric encoding/retrieval asymmetry (HERA) model of prefrontal encoding and retrieval asymmetry.

Adult↗

PubMed1999

The prototype effect in face recognition: extension and limits.

The prototype effect in face recognition refers to a tendency to recognize the face corresponding to the central value of a series of seen faces, even when this central value or prototype has not been seen. Five experiments investigated the extension and limits of this phenomenon. In all the experiments, participants saw a series of faces, each one in two or more different versions or exemplars, and then performed a recognition test, including seen and unseen exemplars and the unseen prototype face. In Experiment 1, a strong prototype effect for variations in feature location was demonstrated in oldness ratings and in a standard old/new recognition test. Experiments 2A and 2B compared the prototype effect for variations in feature location and variations in head angle and showed that, for the latter, the prototype effect was weaker and more dependent on similarity than for the former. These results suggest that recognition across feature variations is based on an averaging mechanism, whereas recognition across viewpoint variations is based on an approximation mechanism. Experiments 3A and 3B examined the limits of the prototype effect using a face morphing technique that allows a systematic manipulation of face similarity. The results indicated that, as the similarity between face exemplars decreases to the level of similarity between the faces of different individuals, the prototype effect starts to disappear. At the same time, the prototype effect may originate false memories of faces that were never seen.

Adult↗

PubMed1998

Uptake of exogenous gangliosides by rat brain synaptosomes.

Synaptosomes incorporated mixed brain gangliosides at a rapid initial rate followed by a slower phase of net movement from the protein-associated fraction into the membrane core. The pattern of incorporated gangliosides reflected the pattern available for incorporation. Intact synaptosomes incorporated approximately 100 pmol GM1/mg protein. Synaptosomes preincubated with proteolytic enzymes (trypsin, chymotrypsin, and papain) at different pH values (6.2, 7.4, 7.8) incorporated more exogenous gangliosides than synaptosomes preincubated in buffer alone. This effect was maximal at pH 7.8, though analysis of variance revealed that the proteolytic treatment and pH effects were probably independent processes. Overall uptake of exogenous gangliosides correlated significantly with amount of membrane protein loss, indicating that initial access of exogenous gangliosides to synaptosomal membranes is retarded by cell-surface proteins. These results suggest synaptosomes as a useful alternative to cultured cells for investigating the interaction of gangliosides with other cell surface constituents.

Animals↗

PubMed1998

Episodic memory and the self in a case of isolated retrograde amnesia.

Isolated retrograde amnesia is defined as impaired recollection of experiences pre-dating brain injury with relatively preserved anterograde learning and memory. We present findings from a patient (M.L.) with isolated retrograde amnesia following severe traumatic brain injury (TBI) that address hypotheses of the interrelationships of focal neuropathology, episodic memory and the self. M.L. is densely amnesic for experiences predating his injury, but shows normal anterograde memory performance on a variety of standard tests of recall and recognition. The cognitive processes underlying this performance were examined with the remember/know technique, which permits separation of episodic from non-episodic contributions to memory tests by quantifying subjects' reports of re-experiencing aspects of the encoding episode. The results demonstrated that M.L. does not episodically re-experience post-injury events to the same extent as control subjects, although he can use familiarity or other non-episodic processes to distinguish events he has experienced from those he has not experienced. M.L.'s MRI showed damage to the right ventral frontal cortex and underlying white matter, including the uncinate fasciculus, a frontotemporal band of fibres previously hypothesized to mediate retrieval of specific events from one's personal past. Recent functional neuroimaging evidence of an association between right frontal lobe functioning and episodic retrieval demands suggest that M.L.'s memory deficits are related to this focal injury. This hypothesis was supported by right frontal polar hypoactivation in M.L. in response to episodic retrieval demands when he was examined with a cognitive activation H2(15)O PET paradigm that reliably activated this frontal region in both healthy controls and patients with TBI carefully matched to M.L. (but without isolated retrograde amnesia). He also showed increased left inferomedial temporal activation relative to control subjects, suggesting that his spared anterograde memory is mediated through increased reliance on medial temporal lobe structures. Re-experiencing events as part of one's past is based on autonoetic awareness, i.e. awareness of oneself as a continuous entity across time. This form of awareness also supports the formulation of future goals and the implementation of a behavioural guidance system to achieve them. The findings from this study converge to suggest that M.L. has impaired autonoetic awareness attributable to right ventral frontal lobe injury, including right frontal-temporal disconnection. Reorganized brain systems mediate certain preserved cognitive operations in M.L., but without the normal complement of information concerning the self with respect to both past and future events.

Adult↗

PubMed1997

Age-related differences in effective neural connectivity during encoding and recall.

Age-related differences in brain activity may reflect local neural changes in the regions involved or they may reflect a more global transformation of brain function. To investigate this issue, we applied structural equation modeling to the results of a positron emission tomography (PET) study in which young and old adults encoded and recalled word pairs. In the young group there was a shift from positive interactions involving the left prefrontal cortex during encoding to positive interactions involving the right prefrontal cortex during recall, whereas in the old group frontal interactions were mixed during encoding and bilaterally positive during recall. The present results suggest that age-related changes in neural activation are partly due to age-related changes in effective connectivity in the neural network underlying the task.

Adult↗

PubMed1997

Age-related differences in neural activity during memory encoding and retrieval: a positron emission tomography study.

Positron emission tomography (PET) was used to compare regional cerebral blood flow (rCBF) in young (mean 26 years) and old (mean 70 years) subjects while they were encoding, recognizing, and recalling word pairs. A multivariate partial-least-squares (PLS) analysis of the data was used to identify age-related neural changes associated with (1) encoding versus retrieval and (2) recognition versus recall. Young subjects showed higher activation than old subjects (1) in left prefrontal and occipito-temporal regions during encoding and (2) in right prefrontal and parietal regions during retrieval. Old subjects showed relatively higher activation than young subjects in several regions, including insular regions during encoding, cuneus/precuneus regions during recognition, and left prefrontal regions during recall. Frontal activity in young subjects was left-lateralized during encoding and right-lateralized during recall [hemispheric encoding/retrieval asymmetry (HERA)], whereas old adults showed little frontal activity during encoding and a more bilateral pattern of frontal activation during retrieval. In young subjects, activation in recall was higher than that in recognition in cerebellar and cingulate regions, whereas recognition showed higher activity in right temporal and parietal regions. In old subjects, the differences in blood flow between recall and recognition were smaller in these regions, yet more pronounced in other regions. Taken together, the results indicate that advanced age is associated with neural changes in the brain systems underlying encoding, recognition, and recall. These changes take two forms: (1) age-related decreases in local regional activity, which may signal less efficient processing by the old, and (2) age-related increases in activity, which may signal functional compensation.

Adult↗

PubMed1997

Brain regions differentially involved in remembering what and when: a PET study.

Recollecting a past episode involves remembering not only what happened but also when it happened. We used positron emission tomography (PET) to directly contrast the neural correlates of item and temporalorder memory. Subjects studied a list of words and were then scanned while retrieving information about what words were in the list or when they occurred within the list. Item retrieval was related to increased neural activity in medial temporal and basal forebrain regions, whereas temporal-order retrieval was associated with activations in dorsal prefrontal, cuneus/precuneus, and right posterior parietal regions. The dissociation between temporal and frontal lobe regions confirms and extends previous lesion data. The results show that temporal-order retrieval involves a network of frontal and posterior brain regions.

Adult↗

PubMed1997

Investigating the relation between imagery and perception: evidence from face priming.

The relation between imagery and perception was investigated in face priming. Two experiments are reported in which subjects either saw or imagined the faces of celebrities. They were later given a speeded perceptual test (familiarity judgement to pictures of celebrities) or a speeded imagery test (in which they were told the names of celebrities and asked to make a decision about their appearance). Seeing faces primed the perceptual test, and imaging faces primed the imagery test; however, there was no priming between seeing and imaging faces. These results show that perception and imagery can be dissociated in normal subjects. In two further experiments, we examined the effects of imaging faces on a subsequent face-naming task and on a task requiring familiarity judgements to partial faces. Both these tasks were facilitated by prior imaging of faces. These results are discussed in relation to those of McDermott & Roediger (1994), who found that imagery promoted object priming in a perceptual test involving naming partial line drawings. The implications for models of face recognition are also discussed.

Eidetic Imagery↗

PubMed1996

General and specific brain regions involved in encoding and retrieval of events: what, where, and when.

Remembering an event involves not only what happened, but also where and when it occurred. We measured regional cerebral blood flow by positron emission tomography during initial encoding and subsequent retrieval of item, location, and time information. Multivariate image analysis showed that left frontal brain regions were always activated during encoding, and right superior frontal regions were always activated at retrieval. Pairwise image subtraction analyses revealed information-specific activations at (i) encoding, item information in left hippocampal, location information in right parietal, and time information in left fusiform regions; and (ii) retrieval, item in right inferior frontal and temporal, location in left frontal, and time in anterior cingulate cortices. These results point to the existence of general encoding and retrieval networks of episodic memory whose operations are augmented by unique brain areas recruited for processing specific aspects of remembered events.

Adult↗

PubMed1996

Network analysis of positron emission tomography regional cerebral blood flow data: ensemble inhibition during episodic memory retrieval.

Two important objectives in the neuroscience of memory are (1) identification of neural pathways involved in memory processes; and (2) characterization of the pattern of interactions between these pathways. Functional neuroimaging can contribute to both of these goals. Using image subtraction analysis of regional cerebral blood flow data measured with positron emission tomography, we identified brain regions that changed activity during episodic memory retrieval (visual work recognition). Relative to a baseline reading task, decreased activity was observed in bilateral prefrontal, bilateral anterior and posterior temporal, and posterior cingulate cortices. Brain regions showing increased activity were the right prefrontal (different from deactivated regions), left anterior cingulate, and left occipital cortices, and vermis of cerebellum. We then performed a network analysis with structural equation modeling to test the hypothesis that regional decreases came about through active inhibition by regions showing increased activity during retrieval. This analysis demonstrated that the influence of activated regions on deactivated regions was more negative during retrieval than during reading, confirming the inhibition hypothesis. Such confirmation could not have been made from the subtraction analysis alone because decreases can come about, at the very least, through reduction of functional influences as well as by active inhibition. The concepts of ensemble excitation and inhibition, as defined through network analysis, are introduced. We argue that is is critical to examine the combined pattern of excitatory and inhibitory influences to fully appreciate the neural basis of episodic memory.

Analysis of Variance↗

PubMed1996

The neural correlates of intentional learning of verbal materials: a PET study in humans.

The purpose of this study was to identify the brain regions invoked when subjects attempt to learn verbal materials for a subsequent memory test. Twelve healthy subjects undertook two different tasks: reading and encoding of word pairs, while they were being scanned using [15O]H2O positron emission tomography (PET). As expected, the encoding pairs were remembered much better (recall 39% vs. 8%; P < 0.001) than reading pairs in a subsequent memory test. The encoding scans, as compared to reading scans, showed activation of the left prefrontal cortex, the anterior cingulate cortex and the left medial temporal cortex. The left prefrontal activations were in two discrete regions: (i) a left anterior and inferior left prefrontal (Brodmann's areas 45, 46) which we attribute to semantic processing; and (ii) a left posterior mid-frontal region (BA 6, 44) which may reflect rote rehearsal. We interpret the data to suggest that when subjects use cognitive strategies of semantic processing and rote-rehearsal to learn words, they invoke discrete regions of the left prefrontal cortex. And this activation of the left prefrontal cortex along with the medial temporal region leads to a neurophysiological memory trace which can be used to guide subsequent memory retrieval.

Adult↗

PubMed1995

Functional brain maps of retrieval mode and recovery of episodic information.

Positron emission tomography (PET) was used to identify brain regions associated with two component processes of episodic retrieval; those related to thinking back in subjective time (retrieval mode) and those related to actual recovery of stored information (ecphory). Healthy young subjects recognized words that had been encoded with respect to meaning or the speaker's voice. Regardless of how the information had been encoded, recognition was associated with increased activation in regions in right prefrontal cortex, left anterior cingulate, and cerebellum. These activations reflect retrieval mode. Recognition following meaning encoding was specifically associated with increased activation in left temporal cortex, and recognition following voice encoding involved regions in right orbital frontal and parahippocampal cortex. These activations reflect ecphory of differentially encoded information.

Adult↗