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Biomedical subjects

Michael D Rugg

Publications and source records attributed to Michael D Rugg.

At least 37 records · Page 2Linked to original sources
PubMed2005

Further dissociating the processes involved in recognition memory: an FMRI study.

Based on an event-related potential study by Rugg et al. [Dissociation of the neural correlates of implicit and explicit memory. Nature, 392, 595-598, 1998], we attempted to isolate the hemodynamic correlates of recollection, familiarity, and implicit memory within a single verbal recognition memory task using event-related fMRI. Words were randomly cued for either deep or shallow processing, and then intermixed with new words for yes/no recognition. The number of studied words was such that, whereas most were recognized ("hits"), an appreciable number of shallow-studied words were not ("misses"). Comparison of deep hits versus shallow hits at test revealed activations in regions including the left inferior parietal gyrus. Comparison of shallow hits versus shallow misses revealed activations in regions including the bilateral intraparietal sulci, the left posterior middle frontal gyrus, and the left frontopolar cortex. Comparison of hits versus correct rejections revealed a relative deactivation in an anterior left medial-temporal region (most likely the perirhinal cortex). Comparison of shallow misses versus correct rejections did not reveal response decreases in any regions expected on the basis of previous imaging studies of priming. Given these and previous data, we associate the left inferior parietal activation with recollection, the left anterior medial-temporal deactivation with familiarity, and the intraparietal and prefrontal responses with target detection. The absence of differences between shallow misses and correct rejections means that the hemodynamic correlates of implicit memory remain unclear.

Adolescent↗
PubMed2005

Electrophysiological dissociation of picture versus word encoding: the distinctiveness heuristic as a retrieval orientation.

Event-related potentials (ERPs) were used to investigate the neural processes underlying the distinctiveness heuristic-a response mode in which participants expect to remember vivid details of an experience and make recognition decisions based on this metacognitive expectation. One group of participants studied pictures and auditory words; another group studied visual and auditory words. Studied and novel items were presented at test as words only, with all novel items repeating after varying lags. ERP differences were seen between the word and picture groups for both studied and novel items. For the novel items, ERP differences were largest in frontal and central midline electrodes. In separate analyses, the picture group showed the greatest ERP differences between item types in a parietally based component from 550 to 1000 msec, whereas the word group showed the greatest differences in a frontally based component from 1000 to 2000 msec. The authors suggest that the distinctiveness heuristic is a retrieval orientation that facilitates reliance upon recollection to differentiate between item types. Although the picture group can use this heuristic and its retrieval orientation on the basis of recollection, the word group must engage additional postretrieval processes to distinguish between item types, reflecting the use of a different retrieval orientation.

Adult↗
PubMed2005

Effects of divided attention on fMRI correlates of memory encoding.

Performing a secondary task concurrently with a study task has a detrimental effect on later memory for studied items. To investigate the mechanisms underlying this effect, the processing resources available for an incidental encoding task were varied by manipulating secondary task difficulty. fMRI data were acquired as volunteers (n = 16) made animacy decisions to visually presented study words while concurrently performing either an easy or a hard auditory monitoring task. "Subsequent memory effects"--greater activity at study for words later remembered versus words later forgotten--were identified in the left ventral inferior frontal gyrus and the left anterior hippocampus. These effects did not vary according to whether the encoding task was performed concurrently with the easy or the hard secondary task. However, as secondary task difficulty increased, study-item activity declined and auditory-item activity increased in dorsolateral prefrontal and superior parietal regions that have been implicated in the support of executive and control functions. The findings suggest that dividing attention during encoding influences the probability of engaging the encoding operations that support later episodic memory, but does not alter the nature of the operations themselves. The findings further suggest that the probability of engaging these encoding operations depends on the level of general processing resources engaged in service of the study task.

Adult↗
PubMed2004

Remembrance of odors past: human olfactory cortex in cross-modal recognition memory.

Episodic memory is often imbued with multisensory richness, such that the recall of an event can be endowed with the sights, sounds, and smells of its prior occurrence. While hippocampus and related medial temporal structures are implicated in episodic memory retrieval, the participation of sensory-specific cortex in representing the qualities of an episode is less well established. We combined functional magnetic resonance imaging (fMRI) with a cross-modal paradigm, where objects were presented with odors during memory encoding. We then examined the effect of odor context on neural responses at retrieval when these same objects were presented alone. Primary olfactory (piriform) cortex, as well as anterior hippocampus, was activated during the successful retrieval of old (compared to new) objects. Our findings indicate that sensory features of the original engram are preserved in unimodal olfactory cortex. We suggest that reactivation of memory traces distributed across modality-specific brain areas underpins the sensory qualities of episodic memories.

Adolescent↗
PubMed2004

An event-related potential study of two kinds of source judgment errors.

The neural correlates of source judgment errors for confusable and nonconfusable source-item pairings were investigated. At study, subjects were presented with a series of lists of word pairs. Word pairs belonging to the same list were formed by pairing one of two associated words with different associates of an unstudied theme word (e.g., ship-frost, captain-chilly, ship-freeze, captain-frigid, etc., in one list; wife-pane, husband-glass, wife-curtain, husband-sill, etc., in another list). At test, subjects discriminated 'Old pairs' (e.g., ship-frost) from 'Intra' rearranged pairs (e.g., ship-chilly), 'Inter' rearranged pairs (e.g., ship-pane), and 'Old-New' pairs (e.g., ship-bulb). Event-related potentials (ERPs) were recorded for each class of test item. Similar proportions of 'yes' responses to Old and Intra rearranged pairs were observed, but the false alarm rate for Inter rearranged pairs was markedly lower. ERPs elicited by correctly classified Old pairs and false alarms to Intra rearranged pairs were indistinguishable and exhibited 'left parietal' and 'right frontal' effects, characteristic of recollection-based recognition. ERPs for false alarms to Inter rearranged pairs did not show these effects. It is concluded that source judgment errors for confusable source-item pairings are mediated by the same processes that support correct source judgments. Such errors reflect recollection of gist information which is nondiagnostic with respect to source.

Analysis of Variance↗
PubMed2004

Probability effects on the neural correlates of retrieval success: an fMRI study.

Event-related fMRI was employed to investigate the influence of the relative probability of old and new test items on the neural correlates of recognition memory. Twelve subjects undertook three study-test cycles, each consisting of an identical study phase in which a series of words was encoded in an incidental task, followed by a test phase in which yes/no recognition judgments were made to a mixture of studied (old) and unstudied (new) words. The ratio of old to new words differed in each test phase, and was either 25:75, 50:50, or 75:25. In lateral inferior and medial parietal cortex, and the posterior cingulate, greater activity was elicited by correctly classified old than new items independently of old:new ratio. By contrast, in other regions, including anterior, dorsolateral, and ventrolateral prefrontal cortex, differences in the activity elicited by old and new items varied according to old:new ratio, demonstrating in some cases a complete crossover interaction. The results suggest that differential activity elicited by old and new test items is likely to support successful recognition in only a subset of the regions identified in previous studies as exhibiting such differences. In other regions, most notably prefrontal cortex, differences in the activity elicited by old and new items appear to reflect processes that are contingent upon, rather than in support of, successful recognition.

Adolescent↗
PubMed2004

The impact of change in stimulus format on the electrophysiological indices of recognition.

The present study investigated the impact of changes in stimulus format between study and test on the event-related potential (ERP) correlates of recognition. To this end subjects studied the names and pictures of common objects. At retrieval, subjects were presented with old items for which the presentational format had changed (from picture to name or vice versa), old items that were shown in the same format as at study, and new items. ERPs revealed three temporally, spatially and functionally dissociable memory-related effects: an early bilateral frontal effect, which was sensitive to the perceptual similarity between study and test stimulus; a left temporo-parietal effect, which was sensitive to the type of stimulus that was encoded; and a late frontal effect, which was largest over right electrode sites and appeared to be sensitive to the type of test stimulus. The results provide further evidence for a functional dissociation between the early bilateral frontal and the later temporo-parietal old/new effect, suggesting an interpretation in terms of processes contributing to a perceptually-driven familiarity or novelty assessment and recollection, respectively.

Adolescent↗
PubMed2004

Effects of age on retrieval cue processing as revealed by ERPs.

The electrophysiological correlates of retrieval cue processing were investigated in healthy young (18-30 years) and older (63-75 years) subjects (n = 16 per group). Retrieval orientation--the differential processing of cues according to the form of the sought-for information--and retrieval difficulty were manipulated in a factorial design. In separate study-test cycles, subjects studied either words or pictures, and performed a yes/no recognition memory task with words as the test items. ERPs elicited by correctly classified new words differed markedly according to study material in the young subjects, replicating previous findings. In the older subjects, this effect was smaller than in the young, and had a later onset and earlier offset. The scalp topography of the effect was however statistically indistinguishable in the two groups. These age-related ERP differences were unmodulated by task difficulty, and remained reliable when recognition performance was matched across the groups. By contrast, the magnitude and timing of ERP difficulty effects were unaffected by age. The findings suggest that older subjects are less able than young individuals to vary their processing of retrieval cues in response to different retrieval demands.

Adolescent↗
PubMed2004

Neural correlates of retrieval orientation: effects of study-test similarity.

ERPs elicited by correctly classified unstudied items in tests of yes/no recognition memory were used to investigate the neural correlates of retrieval cue processing. Items in Experiment 1 consisted of pictures and their corresponding names, allowing study and test material to be factorially crossed in four separate study-test cycles. The ERPs elicited by unstudied pictures and words were, in each case, more negative-going when the study material belonged to the alternative rather than the same class of items. These findings demonstrate that previously reported ERP "retrieval orientation effects" depend on differences in similarity between study and test items, and not on the form of the sought for material. In Experiments 2a and 2b, study materials were auditory words and pictures, and the test items were visual words. In both experiments, ERPs elicited by unstudied test words were more negative-going when pictures rather than auditory words were the study material. Thus, ERP retrieval orientation effects do not depend on the employment of a copy cue condition. It is proposed that the effects reflect differences in the processing necessary to maximize overlap between cue and memory representations.

Acoustic Stimulation↗
PubMed2004

Event-related potential correlates of the retrieval of emotional and nonemotional context.

In two experiments, we examined event-related potentials (ERPs) elicited in an old/new recognition memory test by emotionally neutral visual objects that, at encoding, had been associated with neutrally, negatively, or positively valenced background contexts. In Experiment 2, subjects also judged the context in which the item had been studied. In Experiment 1, "left parietal" old/new ERP effects were elicited by correctly recognized items. Items encoded in emotional contexts, but not those studied in neutral contexts, elicited additional effects early in the recording epoch over lateral temporal scalp and, later, over left temporo-frontal scalp. In Experiment 2, "left parietal" and "right frontal" ERP effects were elicited by recognized items that attracted correct source judgments. Additional effects, an early lateral temporal positivity and a late-onset, left-sided positivity, were elicited by items studied in emotionally valenced contexts and attracting correct source judgments. Together, the findings indicate that retrieval processing is influenced by the emotional valence of the context in which an item is encoded, regardless of whether contextual information is task relevant.

Adolescent↗
PubMed2004

The effects of age on the neural correlates of successful episodic retrieval: an ERP study.

The neural correlates of successful episodic retrieval (recollection), as reflected in event-related potentials (ERPs), were investigated in young (ca 20 years; n = 18) and older (ca 70 years; n = 16) healthy individuals. Subjects classified a series of pictures according to whether each item was new or had been encountered at study in the context of an animacy or a size judgment task. By manipulating the number of times items were presented for study, subsets of test items were formed for which source accuracy did not differ according to age. Relative to ERPs elicited by unstudied pictures, ERPs elicited by items attracting equivalent levels of source accuracy showed marked age-related differences. Those from younger subjects demonstrated the positive-going left parietal and right frontal old/new effects described in several previous studies of source memory. By contrast, analogous ERPs from older subjects contained a large left-lateralized negative effect that overshadowed the positive-going effects evident in the young. No age-related differences in either parietal or frontal ERP old/new effects were detected at electrode sites overlying the right hemisphere. It is possible that the age-related ERP differences observed in this task primarily reflect the use of different kinds of information as a basis for source judgments.

Adolescent↗
PubMed2003

Late frontal brain potentials distinguish true and false recognition.

Brain potentials associated with true and false recognition were recorded using a paradigm consisting of categorized color photographs. Two ERP components were identified. A parietal component was most positive for both true and false recognition, less positive for rejection of lures, and least positive for rejection of novel items. A later frontal component was more positive for false recognition, rejection of lures, and misses than for true recognition and rejection of novel items. The authors suggest that the parietal component may reflect the extent to which test items engender recollection of the gist representation of the study list, while the late frontal component may reflect the engagement of effortful post-retrieval processes.

Adult↗
PubMed2003

Retrieval orientation and the control of recollection.

Event-related potentials (ERPs) were employed to investigate whether recognition test items are processed differently according to whether they are used to probe memory for previously studied words or pictures. In each of two study-test blocks, subjects encoded a mixed list of words and pictures, and then performed a recognition memory task with words as the test items. In one block, the requirement was to respond positively to test items corresponding to studied words, and to reject both new items and items corresponding to the studied pictures. In the other block, positive responses were made to test items corresponding to pictures, and items corresponding to words were classified along with the new items. ERPs elicited during the test phase by correctly classified new items differed according to whether words or pictures were the sought-for modality. This finding was interpreted as a neural correlate of the different retrieval orientations adopted when searching memory for words versus pictures. Relative to new items, correctly classified items studied in both target modalities elicited robust, positive-going "old/new" effects. When pictures were targets, test items corresponding to studied words also elicited large effects. By contrast, when words were targets, old/new effects were absent for the items corresponding to studied pictures. These findings were interpreted as evidence that, in some circumstances, adoption of an appropriate retrieval orientation permits retrieval cues to be employed with a high degree of specificity.

Adolescent↗
PubMed2003

Repetition effects elicited by objects and their contexts: an fMRI study.

Event-related fMRI responses were recorded during a recognition memory test for previously studied visual objects. Some studied objects were superimposed on the same context (landscape scenes) as at study, some were superimposed on a different studied context, and some were paired with new contexts. Unstudied objects were paired with either a studied or a new context. Relative to all other stimulus classes, test stimuli where both components were unstudied elicited enhanced responses in lateral and ventral extrastriate visual cortex. This effect, which is analogous to a previously described electrophysiological result obtained with the same experimental procedure, had the same magnitude regardless of whether a test item was composed of one or two studied components, or whether a single studied component was task relevant or task irrelevant. The findings point to the existence of repetition-sensitive neural mechanisms that operate in a non-linear manner.

Adult↗
PubMed2003

Neural correlates of retrieval processing in the prefrontal cortex during recognition and exclusion tasks.

Event-related fMRI was employed to contrast the neural activity elicited in prefrontal cortex during recognition memory and exclusion tests. The study phases preceding each memory test were identical, involving the presentation of study items (visually presented words) in one of two study contexts. For the recognition test subjects were required to respond positively to all old items regardless of study context, and to respond negatively to new items. For the exclusion task, positive responses were required to old items presented in one of the study contexts only; negative responses were required both to unstudied items and studied items from the alternative context (non-targets). No prefrontal region demonstrated greater activity for new items in the exclusion task. Thus, there was no evidence that retrieval cues were processed differently according to the specificity of the sought-for information. In several regions, most notably bilateral anterior prefrontal cortex, activity was greater for old than for new items regardless of task. Activity in right dorsolateral prefrontal cortex was also greater for old than for new items; these effects however were larger in the exclusion task. The findings are consistent with previous reports that activity in anterior prefrontal cortex elicited by recognition retrieval cues is sensitive to retrieval success, and extend these findings to the exclusion task. The findings for the right dorsolateral cortex add further weight to the proposal that this region supports post-retrieval monitoring of retrieved information.

Adult↗
PubMed2003

Probability effects on event-related potential correlates of recognition memory.

A common finding in event-related potential (ERP) studies of recognition memory is that recognised items elicit greater positivity at parietal electrode sites than new items (the 'left parietal old/new effect'). Parietal positivity (the P300 or P3b) is also elicited in detection tasks with no memory demands by items of low probability of occurrence and high 'target value'. It has been argued that correctly recognised items are typically associated with lower probability and higher target value than new items, raising the question of the extent to which the old/new effect receives a contribution from, or interacts with, P300 activity. The present study explored this issue by comparing ERPs associated with correctly classified old and new items across three different ratios of old to new items: 25:75, 50:50 and 75:25. The left parietal old/new effect was not influenced by this manipulation in the latency range in which it is conventionally measured. Probability did influence the parietal ERPs to correctly recognised items post-800 ms; the scalp distribution of this probability effect was however qualitatively distinct from that of the preceding old/new effect. The left parietal old/new effect appears to be a relatively pure reflection of episodic retrieval, uncontaminated by the non-mnemonic factors of probability and target value.

Adolescent↗
PubMed2003

Age effects on the neural correlates of successful memory encoding.

Event-related functional MRI (fMRI) was used to investigate the neural correlates of memory encoding as a function of age. While fMRI data were obtained, 14 younger (mean age 21 years) and 14 older subjects (mean age 68 years) made animacy decisions about words. Recognition memory for these words was tested at two delays such that older subjects' performance at the short delay was comparable to that of the young subjects at the long delay. This allowed age-associated changes in the neural correlates of encoding to be dissociated from the correlates of differential recognition performance. Activity in left inferior prefrontal cortex and the left hippocampal formation was greater for subsequently recognized words in both age groups, consistent with the findings of previous studies in young adults. In the prefrontal cortex, these 'subsequent memory effects' were, however, left-lateralized in the younger group but bilateral in the older subjects. In addition, for the younger group only, greater activity for remembered words was observed in anterior inferior temporal cortex, as were reversed effects ('subsequent forgetting' effects) in anterior prefrontal regions. The data indicate that older subjects engage much of the same neural circuitry as younger subjects when encoding new memories. However, the findings also point to age-related differences in both prefrontal and temporal activity during successful episodic encoding.

Adolescent↗