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Sharon L Thompson-Schill

Publications and source records attributed to Sharon L Thompson-Schill.

At least 19 recordsLinked to original sources
PubMed2006

Interfering with theories of sleep and memory: sleep, declarative memory, and associative interference.

Mounting behavioral evidence in humans supports the claim that sleep leads to improvements in recently acquired, nondeclarative memories. Examples include motor-sequence learning; visual-discrimination learning; and perceptual learning of a synthetic language. In contrast, there are limited human data supporting a benefit of sleep for declarative (hippocampus-mediated) memory in humans (for review, see). This is particularly surprising given that animal models (e.g.,) and neuroimaging studies (e.g.,) predict that sleep facilitates hippocampus-based memory consolidation. We hypothesized that we could unmask the benefits of sleep by challenging the declarative memory system with competing information (interference). This is the first study to demonstrate that sleep protects declarative memories from subsequent associative interference, and it has important implications for understanding the neurobiology of memory consolidation.

Adolescent↗
PubMed2006

Role of the left inferior frontal gyrus in covert word retrieval: neural correlates of switching during verbal fluency.

Word retrieval ability is commonly assessed with a semantic verbal fluency task, in which subjects must produce a list of exemplars of a category (e.g., animals). The order in which exemplars are produced is not random; rather, subjects tend to produce "clusters" of semantically related items (e.g., cow, pig, sheep) and occasionally "switch" to other clusters (e.g., lion, tiger, bear). Patients with frontal lobe pathology (associated with focal lesions or Parkinson's disease) exhibit reduced output on semantic fluency tasks that has been characterized as a reduction in switching, in contrast to other impaired patient groups who produce normal switches but smaller clusters (e.g., [Troyer, A. K., Moscovitch, M., Winocur, G., Leach, L., & Freedman, M. (1998). Clustering and switching on verbal fluency tests in Alzheimer's and Parkinson's disease. Journal of the International Neuropsychological Society, 4(2), 137-143]). The ability to initiate a switch between two semantic categories may require the selection of weakly activated representations over active (but already reported) representations. Previous studies have shown that increased demands on selection among competing representations are associated with activity in the left inferior frontal gyrus (LIFG) and with deficits in patients with lesions including LIFG [Thompson-Schill, S. L., Jonides, J., Marshuetz, C., Smith, E. E., D'Esposito, M., Kan, I. P., et al. (2002). Effects of frontal lobe damage on interference effects in working memory. Cognitive Affective & Behavioral Neuroscience, 2(2), 109-120; Thompson-Schill, S. L., Swick, D., Farah, M. J., D'Esposito, M., Kan, I. P., & Knight, R. T. (1998). Verb generation in patients with focal frontal lesions: A neuropsychological test of neuroimaging findings. Proceedings of the National Academy of Sciences of the United States of America, 26, 14792-14797]. In the present study, we investigated the neural correlates of switching in the verbal fluency task, and in particular, the role of the LIFG in switching between semantic sub-categories. We observed greater activation in the LIFG during switching compared to free generation (Experiment 1) and self-reported clustering (Experiment 2), which is consistent with the hypothesis that the switching mechanism is subserved by the LIFG due to high semantic selection demands.

Adult↗
PubMed2006

Neuroanatomically separable effects of imageability and grammatical class during single-word comprehension.

The present study characterizes the neural correlates of noun and verb imageability and addresses the question of whether components of the neural network supporting word recognition can be separately modified by variations in grammatical class and imageability. We examined the effect of imageability on BOLD signal during single-word comprehension of nouns and verbs. Subjects made semantic similarity judgments while undergoing functional magnetic resonance imaging (fMRI). Nouns and verbs were matched on imageability, and imageability varied continuously within a grammatical category. We observed three anatomically separable effects: a main effect of grammatical class, a main effect of imageability, and an imageability by grammatical class cross-over interaction. The left superior parietal lobule and a region in the left fusiform responded similarly to increases in noun and verb imageability; the left superior temporal gyrus showed greater activity for verbs than nouns after imageability was matched across grammatical class; and, in both the left middle temporal gyrus and the left inferior frontal lobe, a decrease in noun but not verb imageability resulted in higher BOLD signal. The presence of reliable and anatomically separable main effects of both imageability and grammatical class renders unlikely the hypothesis that previously reported dissociations between nouns and verbs can be dismissed as imageability effects. However, some regions previously thought to respond to grammatical class or imageability instead respond to the interaction of these variables.

Acoustic Stimulation↗
PubMed2006

Fractionating the left frontal response to tools: dissociable effects of motor experience and lexical competition.

A number of theories about the evolution of language posit a close (and perhaps causal) relationship between tool use and speech. Consistent with this idea, neuroimaging studies have found that tool knowledge retrieval activates not only a region of the left premotor cortex involved in hand action, but also an adjacent region that is typically described as a language center. We examined whether this pattern of activation is best described as the result of a single process, related to both action and language, or the result of two independent processes. We identified two distinct neural components that jointly contribute to this response: a posterior region centered in the premotor cortex, which responds to motor knowledge retrieval, and an anterior region centered in the left frontal operculum, which responds to lexical competition. Crucial to the interpretation of the premotor response, individual variation in motor experience was highly correlated with the magnitude of the response in the premotor cortex, but not in the prefrontal cortex.

Adolescent↗
PubMed2006

Resolving conflict: a response to Martin and Cheng (2006).

Martin and Cheng (2006) report the results of an experiment aimed at disentangling the effects of association strength from those of competition on performance on a verb generation task. Their experiment is situated at the center of a putative debate regarding the function of the left inferior frontal gyrus in language processing (see, e.g., Wagner, Pard-Blagoev, Clark, and Poldrack, 2001). Following in this tradition, Martin and Cheng purport to contrast two processes--selection between competing representations and controlled retrieval of weak associates--that we argue can be reduced to the same mechanism. We contend that the distinction between competition and association strength is a false dichotomy, and we attempt to recast this discussion within a Bayesian framework in an attempt to guide research in this area in a more fruitful direction.

Choice Behavior↗
PubMed2005

The frontal lobes and the regulation of mental activity.

Results of neuroimaging and neuropsychological studies of frontal lobe function have been interpreted by some as evidence for specialized modules that are localized to distinct regions of frontal cortex, and that differ in both content and process from those in neighboring regions. These descriptions stand in stark contrast to the many domain-general theoretical accounts of the regulatory role of the frontal lobes in cognition. Recent attempts to understand how general regulatory mechanisms might operate across multiple domains (e.g. working memory, sentence comprehension) have been increasingly important in our understanding of the frontal lobes.

Cognition↗
PubMed2005

Learning places from views: variation in scene processing as a function of experience and navigational ability.

Humans and animals use information obtained from different viewpoints to form representations of the spatial structure of the world. We used functional magnetic resonance imaging (fMRI) adaptation to investigate the neural basis of this learning process and to show how the concomitant representations vary across individuals as a function of navigational ability. In particular, we examined the effect of repeating viewpoint and/ or place information over both short (within-trial) and long (across-scan) intervals on the neural response in scene processing regions. Short-term fMRI adaptation effects in the parahippocampal cortex were initially highly viewpoint-specific but became less so over time. Long-term fMRI repetition effects included a significant viewpoint-invariant component. When individual differences in navigational ability were considered, a significant correlation between the strength of these effects and self-reported navigational competence was observed. In particular, good navigators encoded representations that differed between new and old views and new and old places, whereas bad navigators did not. These results suggest that cortical scene representations evolve over time to become more viewpoint-invariant and that the quality of these representations directly impacts navigational ability.

Adult↗
PubMed2005

Conceptual representations of action in the lateral temporal cortex.

Retrieval of conceptual information from action pictures causes greater activation than from object pictures bilaterally in human motion areas (MT/MST) and nearby temporal regions. By contrast, retrieval of conceptual information from action words causes greater activation in left middle and superior temporal gyri, anterior and dorsal to the MT/MST. We performed two fMRI experiments to replicate and extend these findings regarding action words. In the first experiment, subjects performed conceptual judgments of action and object words under conditions that stressed visual semantic information. Under these conditions, action words again activated posterior temporal regions close to, but not identical with, the MT/MST. In the second experiment, we included conceptual judgments of manipulable object words in addition to judgments of action and animal words. Both action and manipulable object judgments caused greater activity than animal judgments in the posterior middle temporal gyrus. Both of these experiments support the hypothesis that middle temporal gyrus activation is related to accessing conceptual information about motion attributes, rather than alternative accounts on the basis of lexical or grammatical factors. Furthermore, these experiments provide additional support for the notion of a concrete to abstract gradient of motion representations with the lateral occipito-temporal cortex, extending anterior and dorsal from the MT/MST towards the peri-sylvian cortex.

Adult↗
PubMed2005

Cognitive control and parsing: reexamining the role of Broca's area in sentence comprehension.

A century of investigation into the role of the human frontal lobes in complex cognition, including language processing, has revealed several interesting but apparently contradictory findings. In particular, the results of numerous studies suggest that left inferior frontal gyrus (LIFG), which includes Broca's area, plays a direct role in sentence-level syntactic processing. In contrast, other brain-imaging and neuropsychological data indicate that LIFG is crucial for cognitive control--specifically, for overriding highly regularized, automatic processes, even when a task involves syntactically undemanding material (e.g., single words, a list of letters). We provide a unifying account of these findings, which emphasizes the importance of general cognitive control mechanisms for the syntactic processing of sentences. On the basis of a review of the neurocognitive and sentence-processing literatures, we defend the following three hypotheses: (1) LIFG is part of a network of frontal lobe subsystems that are generally responsible for the detection and resolution of incompatible stimulus representations; (2) the role of LIFG in sentence comprehension is to implement reanalysis in the face of misinterpretation; and (3) individual differences in cognitive control abilities in nonsyntactic tasks predict correlated variation in sentence-processing abilities pertaining to the recovery from misinterpretation.

Aphasia, Broca↗
PubMed2004

Selection ability in Alzheimer's disease: investigation of a component of semantic processing.

Selection ability (selecting a response from several competing semantic and/or lexical representations) was tested in 21 participants with Alzheimer's disease (AD) and 28 control participants to help clarify the nature of semantic impairments in AD. Selection demands were manipulated in 3 tasks (lexical fluency, comparison, and verb generation). In each, high-selection conditions required response selection from competing alternatives, whereas low-selection conditions had a reduced need for selection. Patients with AD were disproportionately impaired on the high-selection conditions of all tasks, even when this condition was easier. Selection deficits on verb generation were evident only relative to nonspeeded controls. Overall results indicate impaired semantic selection abilities in AD, which may contribute to poor performance on some semantic tasks.

Aged↗
PubMed2004

Dissociating semantic and phonological maintenance using fMRI.

Functional magnetic resonance imaging (fMRI) distinguished regions of neural activity associated with active maintenance of semantic and phonological information. Subjects saw a single word for 2 sec, and following a 10-sec delay, made a judgment about that word. In the semantic task, subjects focused on the meaning of the word and decided whether a second word was synonymous with it. In the phonological task, subjects repeated the word silently and decided whether it shared a vowel sound with a nonsense word. Analyses allowed for isolation of neural activity during the maintenance delay. Semantic maintenance elicited greater activity in bilateral inferior frontal gyrus and left middle temporal gyrus regions of interest (ROI). In contrast, there was greater activity for phonological maintenance in the left superior parietal ROI. These results show a frontal-temporal network involved in actively maintaining the meanings of words, and they indicate that semantic and phonological maintenance processes are dissociable within working memory.

Adult↗
PubMed2004

Effect of name agreement on prefrontal activity during overt and covert picture naming.

In recent neuroimaging studies, various tasks have been used to examine prefrontal cortex involvement in semantic retrieval and selection. One such task, picture naming, has yielded inconsistent results across studies. One potential explanation for this inconsistency is that the magnitude of prefrontal activity during picture naming depends on the extent to which a given picture evokes a single reliable meaning. To test this hypothesis, fMRI activity in the prefrontal cortex was measured while subjects named pictures with either high or low name agreement. In Experiment 1, subjects named black-and-white line drawings, either covertly or overtly. Across both modalities, we found more left inferior frontal gyrus (LIFG) activity when the subjects named low-agreement pictures than when they named high-agreement pictures. No significant difference in head movement was detected between the two modalities. In Experiment 2, we replicated the effect of name agreement on LIFG activity during picture naming, using black-and-white photographs. These results provide further support for the idea that the LIFG mediates selection among competing alternatives and suggest a means for understanding the naming deficits observed in nonfluent aphasia.

Adolescent↗
PubMed2004

Selection from perceptual and conceptual representations.

The lateral prefrontal cortex has been implicated in a wide variety of functions that guide our behavior, and one such candidate function is selection. Selection mechanisms have been described in several domains spanning different stages of processing, from visual attention to response execution. Here, we consider two such mechanisms: selecting relevant information from the perceptual world (e.g., visual selective attention) and selecting relevant information from conceptual representations (e.g., selecting a specific attribute about an object from long-term memory). Although the mechanisms involved in visual selective attention have been well characterized, much less is known about the latter case of selection. In this article, we review the relevant literature from the attention domain as a springboard to understanding the mechanisms involved in conceptual selection.

Attention↗
PubMed2003

Neuroimaging studies of semantic memory: inferring "how" from "where".

For nearly two decades, functional neuroimaging studies have attempted to shed light on questions about the representation, organization, and retrieval of semantic knowledge. This review examines some of the major findings in this area. For example, functional neuroimaging studies have examined the extent to which there is a unitary semantic system or a series of multiple semantic subsystems organized by input modality, knowledge attribute, and/or taxonomic category. Additionally, functional neuroimaging studies have investigated the contributions of frontal cortex to semantic retrieval and selection. Collectively, these studies demonstrate that functional neuroimaging can offer more than neuroanatomical localization information; in addition, these studies offer new insights into longstanding questions about semantic memory.

Brain↗
PubMed2003

Dorsal stream activation during retrieval of object size and shape.

We investigated dorsal visual stream involvement in the retrieval of a variety of visual attributes of common objects, using functional magnetic resonance imaging. Seven subjects made binary decisions about the shape, color, and size of named objects during scanning. Bilateral parietal activity was significantly greater during retrieval of shape and size information than during retrieval of color information. Consistent with a domain-specific distributed model of semantic organization, the finding that dorsal stream activity is associated with size and shape retrieval, as compared with color retrieval, may indicate that both size and shape information are learned partly through dorsally mediated processes, such as visually guided grasping. These results demonstrate that both visual-processing streams (i.e., the ventral "what" pathway and the dorsal "where" pathway) are involved in the storage and/or retrieval of knowledge of object appearance but that, just as in vision, these two pathways may play different roles in conceptual processing.

Adolescent↗
PubMed2002

Models of functional organization of the lateral prefrontal cortex in verbal working memory: evidence in favor of the process model.

Research on the functional organization of the lateral prefrontal cortex (PFC) in working memory continues to be fairly equivocal between two major frameworks: organization-by-process or organization-by-material. Although there is fairly strong evidence for organization-by-process models from event-related fMRI studies, some investigators argue that the nature of the stimulus material better defines the functional organization of the lateral PFC, particularly in more ventral regions (BA 47/45/44). Specifically, the anterior region of the ventrolateral PFC (BA 47/45) is hypothesized to subserve semantic processing while the posterior region (BA 44) may subserve phonological processing. In the current event-related fMRI study, we directly compared process-related versus material-related organizational principles in a verbal working memory task. Subjects performed a modified delayed response task in which they (1) retained a list of five words or five nonwords during the delay period ("maintenance"), or (2) performed a semantic (size reordering) or phonological (alphabetical reordering) task on the word or nonword lists, respectively ("manipulation"). We did not find evidence during the delay period of our task to support claims of anterior-posterior specializations in the ventrolateral PFC for semantic versus phonological processing. Subjects did, however, display greater neuronal activity during the delay period of manipulation trials than maintenance trials in both the dorsolateral PFC and posterior ventrolateral regions. These data are more consistent with the process model of the organization of lateral PFC in verbal working memory.

Adolescent↗
PubMed2002

Modulation of amygdalar activity by the conscious regulation of negative emotion.

Lesion and neuroimaging studies suggest the amygdala is important in the perception and production of negative emotion; however, the effects of emotion regulation on the amygdalar response to negative stimuli remain unknown. Using event-related fMRI, we tested the hypothesis that voluntary modulation of negative emotion is associated with changes in neural activity within the amygdala. Negative and neutral pictures were presented with instructions to either "maintain" the emotional response or "passively view" the picture without regulating the emotion. Each picture presentation was followed by a delay, after which subjects indicated how they currently felt via a response keypad. Consistent with previous reports, greater signal change was observed in the amygdala during the presentation of negative compared to neutral pictures. No significant effect of instruction was found during the picture presentation component of the trial. However, a prolonged increase in signal change was observed in the amygdala when subjects maintained the negative emotional response during the delay following negative picture offset. This increase in amygdalar signal due to the active maintenance of negative emotion was significantly correlated with subjects' self-reported dispositional levels of negative affect. These results suggest that consciously evoked cognitive mechanisms that alter the emotional response of the subject operate, at least in part, by altering the degree of neural activity within the amygdala.

Adult↗