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T Shallice

Publications and source records attributed to T Shallice.

At least 19 recordsLinked to original sources
PubMed2006

Left prefrontal cortex control of novel occurrences during recollection: a psychopharmacological study using scopolamine and event-related fMRI.

Recollection and familiarity represent two processes involved in episodic memory retrieval. We investigated how scopolamine (an antagonist of acetylcholine muscarinic receptors) influenced brain activity during memory retrieval, using a paradigm that separated recollection and familiarity. Eighteen healthy volunteers were recruited in a randomized, placebo-controlled, double-blind design using event-related fMRI. Participants were required to perform a verbal recognition memory task within the scanner, either under placebo or scopolamine conditions. Depending on the subcondition, participants were required to make a simple recognition decision (old/new items) or base their decision on more specific information related to prior experience (target/non-target/new items). We show a drug modulation in left prefrontal and perirhinal cortex during recollection. Such an effect was specifically driven by novelty and showed an inverse correlation with accuracy performance. Additionally, we show a direct correlation between drug-related signal change in left prefrontal and perirhinal cortices. We discuss the findings in terms of acetylcholine mediation of the familiarity/novelty signal through perirhinal cortex and the control of the relative signal strength through prefrontal cortex.

Adult↗
PubMed2005

Impaired concentration due to frontal lobe damage from two distinct lesion sites.

BACKGROUND: Investigations of cognitive deficits after frontal lobe damage have commonly relied on multidimensional tests and relatively coarse specification of lesion anatomy. Some form of impairment in attention is often asserted to cause the revealed deficits. OBJECTIVE: To describe a disorder of attention in patients with frontal damage using a theoretical model of the fundamental cognitive processes that underlie attention. METHODS: The ability to perform a task of concentrated responding was studied in 43 patients with well-defined chronic frontal lesions and 38 control subjects using a continuous reaction time (RT) test. Performance measures were mean RT, RT across blocks of the test, and errors. Lesion measures were coarse localization and a hot-spot analysis to detect finer grained lesion effects. RESULTS: Only patients with lesions in the right superomedial (SM) frontal regions had significantly prolonged RT consistently across the entire test. The critical lesion was in Brodmann's areas 24, 32, 9, and 46 days and in the adjacent corpus callosum. Patients with lesions in left lateral frontal (LL) regions made significantly more errors on the 20% of trials in the first block. The critical lesion was in areas 44, 45, and 47/12. CONCLUSION: Concentrating attention to respond is affected by lesions in two different frontal regions for reasons that reflect impairments in different cognitive processes. Right superomedial lesions cause an insufficient energizing of attention to respond. Left lateral lesions cause defective setting of specific stimulus-response contingencies. Constrained tests of attention can demonstrate impairments in specific cognitive operations following lesions to different regions of the frontal lobes.

Adult↗
PubMed2005

Brain tissue damage in dementia with Lewy bodies: an in vivo diffusion tensor MRI study.

The aim of the present study was to apply diffusion tensor MRI (DT-MRI), a quantitative MRI measure which reflects tissue organization, to dementia with Lewy bodies (DLB). DT-MRI scans were obtained from 15 patients with probable DLB and 10 sex- and age-matched healthy controls. Abnormalities were found in the corpus callosum, pericallosal areas and the frontal, parietal, occipital and, less prominently, temporal white matter of patients compared with controls. Abnormalities were also found in the caudate nucleus and the putamen. The average grey matter volume was lower in patients than in controls. These findings of concomitant grey matter atrophy and white matter abnormalities (as detected by DT-MRI) in regions with a high prevalence of long connecting fibre tracts might suggest the presence of neurodegeneration involving associative cortices. The modest involvement of the temporal lobe fits with the relative preservation of global neuropsychological measures and memory tasks in the early stage of DLB. The selective involvement of parietal, frontal and occipital lobes might explain some of the clinical and neuropsychological features of DLB, providing a possible distinctive marker for this disease. The abnormalities found in the subcortical grey matter may indicate that DLB and Parkinson's disease share a similar nigrostriatal involvement caused by common pathophysiological mechanisms.

Aged↗
PubMed2004

The impact of deep dysgraphia on graphemic buffer disorders.

This article describes an investigation into the residual writing skills of a severely dysgraphic patient (DA). We found that they were powerfully influenced by a number of lexical variables (lexicality, frequency, imageability, length and geminates). His error pattern was characterized by semantic, lexical, substitution, deletion errors and fragment responses that preserved the first letter. Thus, DA's written spelling was characterized by both deep dysgraphic and graphemic output buffer effects. It is proposed that this pattern of performance represents a new"putative functional syndrome."

Agraphia↗
PubMed2002

Face repetition effects in implicit and explicit memory tests as measured by fMRI.

Recent parallels between neurophysiological and neuroimaging findings suggest that repeated stimulus processing produces decreased responses in brain regions associated with that processing--a 'repetition suppression' effect. In the present study, volunteers performed two tasks on repeated presentation of famous and unfamiliar faces during functional magnetic resonance imaging (fMRI). In the implicit task, they made fame-judgements (regardless of repetition); in the explicit task, they made episodic recognition judgements (regardless of familiarity). Only in the implicit task was repetition suppression observed: for famous faces in a right lateral fusiform region, and for both famous and unfamiliar faces in a left inferior occipital region. Repetition suppression is therefore not an automatic consequence of repeated perceptual processing of stimuli.

Adult↗
PubMed2002

Functional magnetic resonance imaging of proactive interference during spoken cued recall.

Though lesions to frontal cortex can increase susceptibility to interference from previously established but irrelevant memories ("proactive interference"), the specific regions underlying this problem are difficult to determine because the lesions are typically large and heterogeneous. We used event-related functional magnetic resonance imaging to investigate proactive interference in healthy volunteers performing an "AB-AC" paired-associate cued-recall paradigm. At Study, participants intentionally encoded semantically related visual word pairs, which were changed three times (high interference), repeated three times (low interference), or presented only once. At Test, participants were presented with the first word of each pair and attempted to recall its most recent associate from the Study phase. To overcome the problem of image artifacts caused by speech-related head motion, we cued speech during a gap between image acquisitions. Regions in left inferior frontal cortex and bilateral frontopolar cortex showed interference effects during both Study and Test. The pattern of responses in these regions differed, however. Left inferior frontal regions showed mainly reduced responses associated with low interference, whereas frontopolar regions showed mainly increased responses associated with high interference. When incorrect as well as correct trials were analyzed at Test, additional activation associated with high interference was observed in right dorsolateral prefrontal cortex. These data suggest that distinct regions within prefrontal cortex subserve different functions in the presence of proactive interference during cued recall.

Artifacts↗
PubMed2001

Introspective physicalism as an approach to the science of consciousness.

Most 'theories of consciousness' are based on vague speculations about the properties of conscious experience. We aim to provide a more solid basis for a science of consciousness. We argue that a theory of consciousness should provide an account of the very processes that allow us to acquire and use information about our own mental states - the processes underlying introspection. This can be achieved through the construction of information-processing models that can account for 'Type-C' processes. Type-C processes can be specified experimentally by identifying paradigms in which awareness of the stimulus is necessary for an intentional action. The Shallice (1988b) framework is put forward as providing an initial account of Type-C processes, which can relate perceptual consciousness to consciously performed actions. Further, we suggest that this framework may be refined through the investigation of the functions of prefrontal cortex. The formulation of our approach requires us to consider fundamental conceptual and methodological issues associated with consciousness. The most significant of these issues concerns the scientific use of introspective evidence. We outline and justify a conservative methodological approach to the use of introspective evidence, with attention to the difficulties historically associated with its use in psychology.

Awareness↗
PubMed2001

Long-term retrograde amnesia...the crucial role of the hippocampus.

For patients with hippocampal pathology, disagreement exists in the literature over whether retrograde amnesia is temporally limited or very extensive depending on whether the anatomical damage is restricted to this structure or also involves additional temporal cortex. We report a comprehensive assessment of retrograde and anterograde memory functions of a severely global amnesic patient (VC). We found that he presented with a remarkably extensive and basically ungraded retrograde amnesia. This impairment profoundly affected four decades preceding the onset of his amnesia and encompassed both non personal and personal facts and events. VC also presented with a severe anterograde amnesia and a deficit in the acquisition of new semantic knowledge in the post-morbid period. Detailed MRI volumetric measurements revealed gross abnormalities in both hippocampi which were markedly shrunken. Of relevance to the debate on retrograde amnesia were the observations that the volumes of both entorhinal cortices and the remainder of both temporal lobes were normal. These data suggest that the hippocampus is critical not only for the efficient encoding and hence normal recall of new information but also for the recall of episodic information acquired before the onset of amnesia. Our results are compatible with the view that retrograde amnesia is both extensive and ungraded when the damage is limited to the hippocampus.

Aged↗
PubMed2001

When living things and other 'sensory quality' categories behave in the same fashion: a novel category specificity effect.

In this study, the performance on semantic tests of five patients with a diagnosis of probable herpes simplex encephalitis was examined. Only one of the patients, MU, showed a marked category-specific deficit for living things, unlike the other patients. Results which closely mirrored those obtained with the category living things were found in each of the five patients for the other categories, edible substances, materials, and liquids, selected for a priori theoretical reasons. The processing of these additional categories was investigated with tasks involving naming abilities in different modalities, matching to sample, and questionnaires exploring the status of the patients' knowledge about the semantic features of both living things and exemplars of novel 'sensory quality' categories. MU showed in all tasks a comparable impairment for both living things and the other three new categories, in spite of a performance closely equivalent to that of the other four patients with man-made artefacts. This finding supports an explanation of MU's performance in terms of an impairment relating to categories highly dependent on the sensory quality of stimuli. In addition, his difficulty involved all aspects of the processing of the impaired categories.

Adult↗
PubMed2000

Neuroimaging evidence for dissociable forms of repetition priming.

Repetition priming has been characterized neurophysiologically as a decreased response following stimulus repetition. The present study used event-related functional magnetic resonance imaging to investigate whether this repetition-related response is sensitive to stimulus familiarity. A right fusiform region exhibited an attenuated response to the repetition of familiar stimuli, both faces and symbols, but exhibited an enhanced response to the repetition of unfamiliar stimuli. Moreover, both repetition effects were modulated by lag between successive presentations. Further experiments replicated the interactions between repetition, familiarity, and lag and demonstrated the persistence of these effects over multiple repetitions. Priming-related responses are therefore not unitary but depend on the presence or absence of preexisting stimulus representations.

Adult↗
PubMed2000

Attractor dynamics in word recognition: converging evidence from errors by normal subjects, dyslexic patients and a connectionist model.

People make both semantic and visual errors when trying to recognise the meaning of degraded words. This result mirrors the finding that deep dyslexic patients make both semantic and visual errors when reading aloud. We link the results with the demonstration that a recurrent connectionist network which produces the meaning of words in response to their spelling pattern produces this distinctive combination of errors both when its input is degraded and when it is lesioned. The reason why the network can simulate the errors of both normal subjects and patients lies in the nature of the attractors which it develops as it learns to map orthography to semantics. The key role of attractor structure in the successful simulation suggests that the normal adult semantic reading route may involve attractor dynamics.

Adult↗
PubMed2000

Selective preservation of naming from description and the "restricted preverbal message".

We report the case of a patient, LEW, who presents with modality-specific naming deficits. He is seriously impaired in naming pictures of both objects and actions. His naming to auditory verbal definitions and of actions carried out by the experimenter is, however, relatively well preserved. He has no visual perceptual deficits and his access to the semantics of pictures is as good as that to the semantics of spoken words. While LEW is not an optic aphasic patient, his pattern of performance is relevant to the debate that has taken place of the organization of the semantic system. We discuss his case from this perspective and argue that LEW's selective deficits support the multiple semantics position. We also argue that the "preverbal message" level in the speech production model of Levelt (1989) is the equivalent of "verbal semantics." We provide additional constraints and principles to the concept of the preverbal message and we term the system so constrained the "restricted preverbal message."

Aphasia↗
PubMed2000

Time-dependent changes in learning audiovisual associations: a single-trial fMRI study.

Functional imaging studies of learning and memory have primarily focused on stimulus material presented within a single modality (see review by Gabrieli, 1998, Annu. Rev. Psychol. 49: 87-115). In the present study we investigated mechanisms for learning material presented in visual and auditory modalities, using single-trial functional magnetic resonance imaging. We evaluated time-dependent learning effects under two conditions involving presentation of consistent (repeatedly paired in the same combination) or inconsistent (items presented randomly paired) pairs. We also evaluated time-dependent changes for bimodal (auditory and visual) presentations relative to a condition in which auditory stimuli were repeatedly presented alone. Using a time by condition analysis to compare neural responses to consistent versus inconsistent audiovisual pairs, we found significant time-dependent learning effects in medial parietal and right dorsolateral prefrontal cortices. In contrast, time-dependent effects were seen in left angular gyrus, bilateral anterior cingulate gyrus, and occipital areas bilaterally. A comparison of paired (bimodal) versus unpaired (unimodal) conditions was associated with time-dependent changes in posterior hippocampal and superior frontal regions for both consistent and inconsistent pairs. The results provide evidence that associative learning for stimuli presented in different sensory modalities is supported by neural mechanisms similar to those described for other kinds of memory processes. The involvement of posterior hippocampus and superior frontal gyrus in bimodal learning for both consistent and inconsistent pairs supports a putative function for these regions in associative learning independent of sensory modality.

Acoustic Stimulation↗
PubMed2000

"Sculpting the response space"--an account of left prefrontal activation at encoding.

Left lateral prefrontal cortex (PFC) is consistently activated in neuroimaging studies of memory encoding. Its role, however, remains unclear. We describe two functional magnetic resonance imaging (fMRI) studies addressing this question. In the first we used a blocked experimental design to explore the effect of repeated encoding of word paired associates. Initial presentation of word pairs was associated with left ventrolateral PFC activation that attenuated with subsequent presentations of the same lists. When well-learned lists were presented with word pairs rearranged, a left PFC activation, greater than that associated with the initial presentation, was observed. In a second experiment, the formation of these associative relationships was explored using an event-related design. Two types of word pairs were presented: closely related (e.g., King...Queen) and distantly related (e.g., Net...Ship). The same region of left PFC was differentially sensitive to these two event-types, showing a greater response for distantly related pairs. We suggest that left PFC activity, at memory encoding, reflects operations necessary to the formation of meaningful associations in the service of optimal learning. A crucial feature of such associative processing lies in selecting appropriate, and inhibiting inappropriate, semantic attributes of the study material.

Adult↗
PubMed2000

The cognitive and neuroanatomical correlates of multitasking.

Patients who show the "strategy application disorder" can show deficits restricted to situations requiring multitasking, but the precise neuroanatomical and cognitive correlates of this problem have been rarely investigated. In this study, 60 people with circumscribed cerebral lesions and 60 age- and IQ-matched controls were given a multitasking procedure which allowed consideration of the relative contributions of task learning and remembering, planning, plan-following and remembering one's actions to multitasking performance. Lesions to the left posterior cingulate and forceps major regions gave deficits on all measures except planning. Remembering task contingencies after a delay was also affected by lesions in the region of the left anterior cingulate, and rule-breaking and failures of task switching were additionally found in people with lesions affecting the medial and more polar aspects of Brodmann's areas 8, 9 and especially 10. Planning deficits were associated with lesions to the right dorsolateral prefrontal cortex (RDLPFC). A theory of the relationships between the cognitive constructs underpinning multitasking was tested using structural equation modelling. The results suggest that there are three primary constructs that support multitasking: retrospective memory, prospective memory, and planning, with the second two drawing upon the products of the first. It is tentatively suggested that the left anterior and posterior cingulates together play some part in the retrospective memory demands, while the prospective memory and planning components make demands on processes supported by the left areas 8, 9 and 10 and the RDLPFC respectively.

Adolescent↗
PubMed2000

Confidence in recognition memory for words: dissociating right prefrontal roles in episodic retrieval.

We used event-related functional magnetic resonance imaging (efMRI) to investigate brain regions showing differential responses as a function of confidence in an episodic word recognition task. Twelve healthy volunteers indicated whether their old-new judgments were made with high or low confidence. Hemodynamic responses associated with each judgment were modeled with an "early" and a "late" response function. As predicted by the monitoring hypothesis generated from a previous recognition study [Henson, R. N. A., Rugg, M. D., Shallice, T., Josephs, O., & Dolan, R. J. (1999a). Recollection and familiarity in recognition memory: An event-related fMRI study. Journal of Neuroscience, 19, 3962-3972], a right dorsolateral prefrontal region showed a greater response to correct low- versus correct high-confidence judgements. Several regions, including the precuneus, posterior cingulate, and left lateral parietal cortex, showed greater responses to correct old than correct new judgements. The anterior left and right prefrontal regions also showed an old-new difference, but for these regions the difference emerged relatively later in time. These results further support the proposal that different subregions of the prefrontal cortex subserve different functions during episodic retrieval. These functions are discussed in relation to a monitoring process, which operates when familiarity levels are close to response criterion and is associated with nonconfident judgements, and a recollective process, which is associated with the confident recognition of old words.

Adult↗
PubMed1999

Recollection and familiarity in recognition memory: an event-related functional magnetic resonance imaging study.

The question of whether recognition memory judgments with and without recollection reflect dissociable patterns of brain activity is unresolved. We used event-related, functional magnetic resonance imaging (fMRI) of 12 healthy volunteers to measure hemodynamic responses associated with both studying and recognizing words. Volunteers made one of three judgments to each word during recognition: whether they recollected seeing it during study (R judgments), whether they experienced a feeling of familiarity in the absence of recollection (K judgments), or whether they did not remember seeing it during study (N judgments). Both R and K judgments for studied words were associated with enhanced responses in left prefrontal and left parietal cortices relative to N judgments for unstudied words. The opposite pattern was observed in bilateral temporoccipital regions and amygdalae. R judgments for studied words were associated with enhanced responses in anterior left prefrontal, left parietal, and posterior cingulate regions relative to K judgments. At study, a posterior left prefrontal region exhibited an enhanced response to words subsequently given R versus K judgments, but the response of this region during recognition did not differentiate R and K judgments. K judgments for studied words were associated with enhanced responses in right lateral and medial prefrontal cortex relative to both R judgments for studied words and N judgments for unstudied words, a difference we attribute to greater monitoring demands when memory judgments are less certain. These results suggest that the responses of different brain regions do dissociate according to the phenomenology associated with memory retrieval.

Adult↗