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Biomedical subjects

M D Rugg

Publications and source records attributed to M D Rugg.

At least 73 records · Page 4Linked to original sources
PubMed1995

Cognitive brain potentials and regional cerebral blood flow equivalents during two- and three-sound auditory "oddball tasks".

Ten healthy volunteers were examined with single photon emission tomography and 99mTc-exametazime. They were studied on 2 occasions, during a 2- and a 3-sound auditory discrimination (oddball) task. Twenty healthy volunteers were used as controls, studied once at rest. During the 2-tone task there was a bilateral posterior (occipito-) temporal and medial frontal activation, a left pericentral increase, and posterior cingulate suppression. During the 3-sound task activation was again found in posterior (occipito-) temporal, medial frontal cortex, left pericentral, with a small non-significant reduction in posterior cingulate uptake. Compared with the 2-tone task, there was a trend towards higher activity in left medial frontal, right posterior temporal and posterior cingulate cortex in the 3-sound task. P3b amplitudes were negatively correlated with posterior cingulate tracer uptake during both tasks. Positive correlations with P3b amplitudes were found in various frontal and temporal regions. These results are consistent with more invasive localisation studies of P3b. Posterior cingulate cortex appears to be inhibited during the oddball tasks, the more so, the more restricted the range of stimuli, and the greater the task-related recruitment of neurones (P3b amplitude). As expected from its more frontal distribution, P3a amplitude was positively correlated with anterior cingulate tracer uptake, and negatively correlated with temporal cortical activity.

Aged↗
PubMed1995

Event-related potentials and the recollection of low and high frequency words.

A recognition memory test was conducted in which low and high frequency words were initially presented in one of two different study tasks. A word was defined as recollected if, at test, it was both confidently judged 'old', and confidently assigned to its correct study context. Low frequency words were more accurately recognised than high frequency items, and were also more likely to be assigned to their correct study context. The results are consistent with the view that low frequency words are better recognised because they are more likely to be recollected, rather than because they engender higher levels of relative familiarity. Event-related potentials (ERPs) evoked at test by correctly classified new words were contrasted with those evoked by old, recollected words. The ERPs to low frequency words exhibited large and reliable 'old/new' effects, in that from approx. 300 msec post-stimulus, waveforms were more positive-going for old than for new items. These effects were markedly smaller, and indeed non-significant, in the ERPs evoked by high frequency items. The results show that the interaction between word frequency and old/new differences in ERPs does not arise because of a confound between frequency and the probability of recollection. Together with other findings, they suggest that recollection is better conceived of as a graded, rather than as an all-or-none phenomenon.

Adult↗
PubMed1995

Recognition memory with and without retrieval of context: an event-related potential study.

In two recognition memory tests subjects made initial old/new judgements and subsequently judged whether 'old' words had been presented auditorily or visually at study. Test words were presented visually in Experiment 1 and auditorily in Experiment 2. ERPs evoked at test by words correctly judged 'old' were separated according to whether they were correctly or incorrectly assigned to their study modality. In both experiments, ERPs to correctly assigned words were more positive than those evoked by words correctly judged to be new. This ERP old/new effect was absent for words incorrectly assigned to study modality in Experiment 1, and was observed over a restricted latency range in Experiment 2. The findings are consistent with the hypothesis that the old/new effect is associated with recognition memory based on recollection of the study episode, rather than familiarity.

Acoustic Stimulation↗
PubMed1995

Memory and consciousness: a selective review of issues and data.

Methods for dissociating and independently studying conscious (explicit) and unconscious (implicit) memory are discussed. Recent work in the field of amnesia is then briefly reviewed, focusing on the question of how clearly the disorder fractionates according to the implicit-explicit distinction. Finally, evidence supporting dual-process models of recognition memory is reviewed, and data suggesting that amnesic patients have relatively spared familiarity-based recognition memory are critically assessed.

Amnesia↗
PubMed1995

Modulation of event-related potentials by the repetition of drawings of novel objects.

In experiment 1, event-related potentials (ERPs) were recorded from 13 scalp sites while subjects viewed a series of line drawings of novel objects. Most of the drawings were of objects that were structurally possible, while the remainder were of structurally impossible objects; the task was to respond to each presentation of an impossible object. Approximately one third of the possible objects were repetitions of the immediately preceding drawing. Compared to the ERPs elicited by first presentations, the ERPs elicited by repetitions were more negative-going. This negative repetition effect comprised two temporally and topographically distinct components. In experiment 2, subjects monitored drawings of unstructured patterns, so as to detect occasional 'targets' containing a pair of parallel lines. Repetitions of 'non-target' patterns elicited ERPs which were largely indistinguishable from those elicited by first presentations. Thus, the negative repetition effects found in experiment 1 are not merely a consequence of repeating visual patterns in a demanding discrimination task. Possible reasons why novel objects should elicit ERP repetition effects opposite in polarity to those observed in tasks employing verbal or meaningful pictorial stimuli are discussed.

Analysis of Variance↗
PubMed1994

Word repetition effects on event-related potentials in healthy young and old subjects, and in patients with Alzheimer-type dementia.

Event-related potentials (ERPs) were recorded from 16 healthy young (mean age 21 years) and 16 healthy old subjects (mean age 64 years), and from 11 subjects with a diagnosis of Dementia of Alzheimer Type (DAT). The task requirement was to attend to a series of visually presented words so as to respond to occasional animal names. Non-animal names repeated after either a single or six intervening items. In the young subjects ERPs evoked by repeated words displayed a widespread, sustained positive-going shift relative to ERPs evoked by first presentations (the ERP repetition effect). This effect onset around 220 msec and did not differ as a function of inter-item lag. Other than for a delay in onset of approximately 80 msec, the ERP repetition effect in the healthy old group was in all respects equivalent to that of the young subjects. The ERP repetition effects in the DAT patients were statistically indistinguishable from those of an appropriately matched sub-set of the healthy old subjects. These results indicate that the ERP repetition effect remains robust in subjects in whom explicit memory has declined as a result of normal aging or DAT. Thus they suggest that the effect reflects processes independent of those underlying explicit memory, and that it may index a form of memory relatively unaffected by the pathology underlying DAT.

Adolescent↗
PubMed1994

Modulation of event-related brain potentials by word repetition: effects of local context.

In four experiments, event-related brain potentials (ERPs) were evoked by visually presented word pairs in a task requiring responses to occasional target pairs. In Experiments 1 and 2, some pairs comprised items that had been presented previously. These repeated pairs consisted of words that had been paired together when first presented (same context condition) or words that had first been presented on consecutive trials (different context condition). ERP repetition effects were equivalent in the two conditions. In Experiment 3, same-context repeats were contrasted with a condition in which a repeated word was paired with a new word. Only the same-context pairs evoked a repetition effect. Experiment 4 showed that repetition effects to different- and same-context repeats remained equivalent when first presentations of the members of different-context pairs were separated by six intervening trials. We conclude that the ERP repetition effect shows little sensitivity to local context.

Adult↗
PubMed1993

Cognitive brain potentials in a three-stimulus auditory "oddball" task after closed head injury.

Event-related potentials (ERPs) were recorded in a three stimulus oddball task from 16 patients who had sustained a severe closed head injury at least 6 months before testing, and from 16 control subjects. The stimuli comprised a random sequence of frequent non-target tones (P = 0.70), rare target tones (P = 0.15), and rare novel sounds (P = 0.15). The task requirement was to respond promptly to each target tone. From a latency of 200 msec onwards, the ERPs evoked by frequent non-targets were substantially more negative-going in the head-injured than in the control group. When this difference in the ERPs to the frequent tones was taken into account, there was no evidence to suggest that either the latency or the amplitude of the target-evoked N2 and P3b components differed between the groups. The novel stimuli evoked a prominent P3a component. The amplitude and scalp distribution of this component differed little between the groups, but its peak latency was reliably longer in the head-injured subjects. The findings in respect of the N2 and P3b components suggest that impairments in early processing of task-relevant stimuli are not an invariant feature of closed head injury. The findings regarding P3a suggest that, in the majority of patients, head injury has only a limited effect on the neural systems underlying involuntary shifts of attention.

Acoustic Stimulation↗
PubMed1993

Modulation of event-related potentials by word repetition: the role of visual selective attention.

Event-related potentials (ERPs) were recorded while subjects viewed visually presented words, some of which occurred twice. Each trial consisted of two colored letter strings, the requirement being to attend to and make a word/nonword discrimination for one of the strings. Attention was manipulated by color in Experiment 1, and color and a precue were used in Experiment 2. As in previous ERP studies of word repetition, a positive offset to repeated words developed when both first and second presentations were the focus of attention. In Experiment 2, ERPs showed evidence of positive-going repetition effects in all conditions in which at least one of the two presentations of the repeated word was attended. In the visual modality, the positive-going ERP repetition effect occurs only when at least one of the two presentations of a repeated item is the object of attention, which suggests that one or more of the processes reflected by the effect is capacity limited.

Adult↗
PubMed1992

The effects of scopolamine on event-related potentials in a continuous recognition memory task.

Event-related potentials (ERPs) were recorded during a task requiring continuous recognition memory for visually-presented words. Twelve subjects each performed the task twice, once following the administration of scopolamine, and once after receiving a saline placebo. In the placebo condition, correctly detected "old" words (i.e., words that had been presented once before during the task) evoked more positive-going ERPs than did "new" words. Scopolamine caused a substantial impairment in task performance, but did not reduce the size of these old-word/new-word ERP differences. It is concluded that old/new ERP effects are unlikely to reflect cholinergically-mediated neural activity underlying normal recognition memory.

Adult↗
PubMed1992

Word frequency and multiple repetition as determinants of the modulation of event-related potentials in a semantic classification task.

We recorded event-related potentials while subjects performed a category membership decision task. The stimuli were words of high and low frequency of occurrence in written English, and each was presented four times. The experiment was intended to explore the interaction of word frequency and multiple repetition on the event-related potential, and thence to investigate the possible loci in time of the effects of these variables. First presentations of low and high frequency words evoked event-related potentials which differed in the presence, in the low word frequency waveforms, of a right-hemisphere dominant negativity peaking at 400 ms. This negativity was very similar to the N400 which may be sensitive to the semantic relations among words in a sequence. Initial repetition diminished this midlatency difference, but gave rise to both earlier and later frequency-related differences. Subsequent multiple repetition abolished the early frequency-related repetition effect, but did not affect amplitudes in the region of N400, nor did it abolish a late positivity, present only for repeated low frequency words.

Adult↗
PubMed1991

Event-related potentials related to recognition memory. Effects of unilateral temporal lobectomy and temporal lobe epilepsy.

Event-related potentials (ERPs) were recorded during a continuous recognition memory task for visually presented words, with a 6 item lag between the first and second presentation of each word. The subjects consisted of: (i) a control group of patients with primary generalized epilepsy; (ii) patients who had undergone either a left or a right anterior temporal lobectomy; (iii) unoperated patients with either left or right unilateral temporal lobe epilepsy. In the controls, ERPs to detected 'old' words were reliably more positive-going in the interval 300 to 600 ms post-stimulus than were ERPs to 'new' items. In both left and right lobectomy patients, 'old/new' ERP differences in the same latency range were significantly smaller than in the controls, and did not differ significantly from zero. At midline electrodes, old/new effects in the temporal lobe epilepsy patients were of similar magnitude to those of the controls. In contrast to the control data, the old/new effects in the temporal lobe epilepsy patients were asymmetric, in that they were smaller over the hemisphere ipsilateral to the seizure focus than over the contralateral hemisphere. No relationship was found across subjects between the magnitude of old/new ERP effects and verbal memory performance. In a second task, occasional non-words had to be discriminated against a background of sequentially presented words, some of which were repetitions of the immediately preceding item. ERPs evoked by repeated words were more positive-going than were those to first presentations; this effect was reliable, and of equivalent size, in all patient groups. It is concluded that in the recognition task, old/new ERP effects are dependent on temporal lobe functioning, but that the anterior temporal lobe is not the principal locus of the generators of these effects. The cognitive processes reflected by these effects do not appear to be strongly lateralized to one hemisphere, and neither do they seem to be necessary for normal verbal memory.

Adolescent↗
PubMed1991

Normal P300 following extensive damage to the left medial temporal lobe.

Event-related potentials (ERPs) were recorded during auditory and visual "oddball" tasks from a patient with a severe verbal memory deficit due to a low grade infiltrating glioma which involved the full extent of the left medial temporal lobe. In both sensory modalities, the patient's oddball-evoked P300s were symmetrical and of normal amplitude. These findings are difficult to reconcile with the hypothesis that the hippocampus, or any other medial temporal structure, makes a substantial contribution to the scalp P300.

Adult↗
PubMed1990

Endogenous event-related potentials from sphenoidal electrodes.

Event-related potentials (ERPs) were recorded from left and right sphenoidal electrodes during 2 cognitive tasks (visual oddball and a word repetition procedure) known to evoke endogenous ERP activity in the medial temporal lobe. Both tasks gave rise to large, reliable modulations of scalp-recorded ERPs. In the oddball task, no consistent task-related ERP activity could be recorded from the sphenoidal electrodes concurrently with the scalp-recorded P3 component, although in the latency region following the peak of P3 these electrodes exhibited an enhanced late negative wave to target stimuli. In the word repetition task, no consistent repetition-related ERP effects of any kind were observed from the sphenoidal electrodes. Sphenoidal electrodes do not appear to detect the endogenous ERP components that are generated in the medial temporal lobe concurrently with scalp-recorded components.

Acoustic Stimulation↗
PubMed1990

Event-related potentials and the phonological matching of picture names.

Event-related potentials (ERPs) were recorded from one midline and three pairs of lateral electrodes while subjects determined whether a pair of sequentially presented pictures had rhyming or nonrhyming names. During the 1.56-sec interval between the two pictures, the slow ERP wave recorded over the left hemisphere was more negative-going than that over the right, especially at frontal electrodes. The ERPs evoked by the second picture differed as a function of whether its name rhymed with its predecessor. This difference, taking the form of increased negativity in ERPs to nonrhyming items, had an earlier onset and a greater magnitude at right than at left hemisphere electrodes. This pattern of ERP asymmetries is qualitatively similar to that found when words are rhyme-matched. It is therefore concluded that such asymmetries do not depend on the employment of orthographic material and may reflect some aspect(s) of the phonological processing of visually presented material.

Adolescent↗
PubMed1990

Event-related potentials and the semantic matching of pictures.

Event-related potentials (ERPs) were recorded from one midline and three pairs of lateral electrodes while subjects determined whether pairs of sequentially presented pictures were semantically associated. The ERPs evoked by the second picture of each pair differed as a consequence of whether it was associated with its predecessor, such that ERPs to nonassociated pictures were more negative-going than those to associated items. These differences resulted from the modulation of two ERP components, one frontally distributed and centered on an N300 deflection, the other distributed more widely over the scalp and encompassing an N450 deflection. The modulation of N450 is interpreted as further evidence that the "N400" ERP component is sensitive to semantic relationships between nonverbal stimuli. The earlier N300 effects, which do not appear to occur when ERPs are evoked by semantically primed and unprimed words, could suggest that the semantic processing of pictorial stimuli involves neural systems different from those associated with the semantic processing of words.

Adolescent↗
PubMed1990

Event-related brain potentials dissociate repetition effects of high- and low-frequency words.

Event-related brain potentials (ERPs) were recorded while subjects detected nonwords interspersed among sequences of words of high or low frequency of occurrence. In Phase 1, a proportion of the words were repeated after six intervening items. In Phase 2, which followed after a break of approximately 15 min, the words were either repeats of items presented in the previous phase or new. Unrepeated low-frequency words evoked larger N400 components than did high-frequency items. In Phase 1, this effect interacted with repetition, such that no frequency effects were observed on N400s evoked by repeated words. In addition, the post-500-msec latency region of the ERPs exhibited a substantial repetition effect for low-frequency words, but did not differentiate unrepeated and repeated high-frequency words. In Phase 2, ERPs evoked by "old" and "new" high-frequency words did not differ in any latency region, while those evoked by old and new low-frequency words differed only after 500 msec. The interactive effects of frequency and repetition suggest that these variables act jointly at multiple loci during the processing of a word. The specificity of the post-500-msec repetition effect for low-frequency words may reflect a process responsive to a discrepancy between words' intra and extraexperimental familiarity.

Adult↗