Robert T. Knight

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Prefrontal cortex and episodic memory: integrating findings from neuropsychology and event-related neuroimaging.

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ABSTRACT

Although it has been speculated for many years that the prefrontal cortex plays a role in long-term memory for events, or episodic memory, only recently have researchers made a concerted attempt to define this role. Most theories of prefrontal function suggest that this region implements “topdown” or “executive” processes that influence a variety of domains, including memory. For example, Luria (1966) postulated a role for the frontal lobes in the regulation of voluntary attention and the organisation of goal-directed behavior. Building on the work of Luria, Shallice (1982) argued that the frontal lobes are required for the attentional selection of schemes of action in novel situations. A complementary role suggested for the prefrontal cortex is the suppression of irrelevant or interfering stimuli (Brutkowski, 1965; Fuster, 1997; Knight, Staines, Swick, & Chao, 1999; Pribram, Ahumada, Hartog, & Roos, 1964; Shimamura, 1995). Teuber (1964) additionally proposed that the frontal lobes prepare sensory areas for environmental changes that will be induced by motor actions. This concept was later extended to include the generation of anticipatory behavioural sets (Fuster, 1997; Nauta, 1971). Several researchers have also postulated a central role for the prefrontal cortex in active, or working memory (Fuster, 1997; Goldman-Rakic, 1987).





AUTHORS

  • Charan Ranganath

  • Robert T. Knight

Date: 2003

ISBN-13: 978-1841692463

ISBN-10: 9781841692463


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A new ERP paradigm for studying individual differences in the executive control of attention

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Authors:

  • Francisco Barceló

  • Jose A. Perianìez

  • Robert T. Knight

Date: 2003

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Abstract:

Event-related potentials (ERPs) provide valuable information about the fast brain dynamics subserving cognitive functions such as atten- tion and working memory. Most ERP studies employ cognitive para- digms with a fixed task-set (i.e., press a button to named targets), but few have measured ERPs time-locked to shifts in set using a task- switching paradigm. The Madrid Card Sorting Test (MCST) is a dual task protocol in which feedback cues signal unpredictable shifts in set (i.e., from “sort cards by colour” to “sort cards by shape”). This pro- tocol offers an integrated analysis of ERPs to both feedback cues and target card events, providing separate ERP indexes for the shifting, updating and rehearsal of attention sets in working memory. Two of these ERP indices are the frontal and posterior aspects of the P300 response. Feedback cues that direct a shift in set also elicit both a frontally distributed P3a potential (300 to 400 ms) and a posteriorly distributed P3b potential (350 to 600 ms). In turn, target card events evoke posterior P3b responses whose amplitude increases as the new task set is gradually rehearsed. In line with current models about the role of prefrontal cortex in the executive control of attention, this P3a/P3b response system appears to reflect the coordinated action of prefrontal and posterior association cortices during the switching and updating of task sets in working memory.

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Spatial asymmetries of auditory event-synthesis in humans

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Authors:

  • Leon Y. Deouell

  • Christina M. Karns

  • Tamara B. Harrison

  • Robert T. Knight

Date: 2003

PubMed: 12531460

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Abstract:

We used the mismatch negativity event-related potential to examine how spatial location and feature variation affect the capacity of the auditory system to automatically respond to pairs of rapid (180 ms apart) acoustic changes within a single tone. When a tone first deviated from a standard tone in source location and then in its duration, we found independent responses to both deviations for right but not left field stimuli. In contrast, when the first deviation was in pitch and the second in duration, only the first deviation elicited a response, regardless of presentation side. These results suggest that information from either side of space is asymmetrically processed even in a free-field, and that the extent of the temporal window of integration is not a fixed property of the auditory system.

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Effects of extensive temporal lobe damage or mild hypoxia on recollection and familiarity

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Authors:

  • Andrew P. Yonelinas

  • Neal E. A. Kroll

  • Joel R. Quamme

  • Michele Lazzara

  • Mary Jane Sauve

  • Keith F. Widaman

  • Robert T. Knight

Date: 2002

PubMed: 12379865

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Abstract:

Memory for past events can be based on recollection or on assessments of familiarity. These two forms of human memory have been studied extensively by philosophers and psychologists, but their neuroanatomical substrates are largely unknown. Here we examined the brain regions that are involved in these two forms of memory by studying patients with damage to different temporal lobe regions. Our results come from (i) structural covariance modeling of recall and recognition, (ii) introspective reports during recognition and (iii) analysis of receiver operating characteristics. In sum, we found that the regions disrupted in mild hypoxia, such as the hippocampus, are centrally involved in conscious recollection, whereas the surrounding temporal lobe supports familiarity-based memory discrimination.

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Grouping Influences in Unilateral Visual Neglect

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Authors:

  • Lynn C. Robertson

  • Mirjam Eglin

  • Robert T. Knight

Date: 2003

PubMed: 12916644

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Abstract:

Effects of grouping on unilateral neglect were investigated in 8 neurological patients with right hemisphere damage. It is well documented that arranging items to form a group spanning the midline decreases the magnitude of neglect. In the present study we examined how clusters of groups within the left or right visual field affect neglect and whether isolated groups within the neglected field deflect attention from right-sided displays. We orthogonally varied the strength of grouping on the right and left sides of a display and measured the time to find a predesignated target in one of those groups. Groups on the neglected left side did not affect right-sided target detection any more than an empty left page. However, strength of grouping did affect left sided target detection. These findings are discussed as they relate to attention and preattention in unilateral visual neglect.

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Separable effects of priming and imageability on word processing: an ERP study

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Authors:

  • Tamara Y. Swaab

  • Kathleen Baynes

  • Robert T. Knight

Date: 2002

PubMed: 12433385

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Abstract:

Concrete, highly imageable words (e.g. banana) are easier to understand than abstract words for which it is difficult to generate an image (e.g. justice). This effect of concreteness or imageability has been taken by some as evidence for the existence of separable verbal- and image-based semantic systems. Instead, however, effects of concreteness may result from better associations to relevant contextual representations for concrete than for abstract words within a single semantic system. In this study, target words of high and low imageability were preceded by supportive (related) or non-supportive (unrelated) context words. The influence of contextual support on the imageability effect was measured by recording event-related brain potentials (ERPs) to the high and low imageable target words in both context conditions. The topographic distributions of the ERPs elicited by the high versus low imageable target words were found to be different, and this effect was independent of contextual support. These data are consistent with the idea that distinct verbal- and image-based semantic codes exist for word representations, and that as a result, concrete words that are highly imageable can be understood more easily.


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Think differently: a brain orienting response to task novelty

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Authors:

  • Francisco Barceló

  • Jose A. Perianìez

  • Robert T. Knight

Date: 2002

PubMed: 12395085

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Abstract:

Cognitive flexibility hinges on a readiness to direct attention to novel events, and on an ability to change one's mental set to find new solutions for old problems. Human event-related potential (ERP) studies have described a brain 'orienting' response to discrete novel events, marked by a frontally distributed positive potential peaking 300-400 ms post-stimulus (P3a). This brain potential has been typically related to bottom-up processing of novel non-targets under a fixed task-set (i.e., press a button to coloured targets), but had never been related to top-down attention control in dual-task paradigms. In this study, 27 subjects had their ERPs measured while they performed a version of the Wisconsin card sorting test (WCST), a dual-task paradigm where the same feedback cue signalled unpredictable shifts to a new task set (i.e., from 'sort by colour' to 'sort by shape'). Feedback cues that directed a shift in the subject's mental set to a new task-set elicited frontally distributed P3a activity, thus suggesting a role of the P3a response system in task-set shifting. Feedback cues also evoked a longer latency positive potential (350-600 ms; P3b), that was larger the more task rules were held in memory. In line with current models of prefrontal function in the executive control of attention, this P3a/P3b response system appears to reflect the co-ordinated action of prefrontal and posterior association cortices during the switching and updating of task sets in working memory.

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Orbitofrontal cortex and dynamic filtering of emotions

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Authors:

  • Randall R. Rule

  • Arthur P. Shimamura

  • Robert T. Knight

Date: 2002

PubMed: 12775190

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Abstract:

Event-related potentials (ER) were recorded in response to mildly aversive somatosensory and auditory stimuli. Patients with orbitofrontal lesions exhited enhanced ERPs (i.e., P3 amplitudes), as compared with control subjects. Moreover, these patients did not habituate to somatoensory stimuli across blocks of trials. The results were specific to orbitofrontal damage, since patients with damage to the dorsolateral prefontal cortex did not exhibit enhanced P3 amplitudes. These findings suggest damage to the orbitofrontal cortex impairs the ability to modulate or inhibit neural responses to aversive stimuli. The findings are couched in terms of dynamic filtering theory, which suggests that the orbitofrontal cortex is involved in the selection and active inhibition of neural circuits associated with emotional responses.

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Principles of Frontal Lobe Function

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This volume provides a comprehensive review of historical and current research on the function of the frontal lobes and frontal systems of the brain. The content spans frontal lobe functions from birth to old age, from biochemistry and anatomy to rehabilitation, and from normal to disrupted function. The book is intended to be a standard reference work on the frontal lobes for researchers, clinicians, and students in the field of neurology, neuroscience, psychiatry, psychology, and health care.




AUTHORS

  • Donald T. Stuss

  • Robert T. Knight

Date: 2002

ISBN: 9780198030836


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Selective impairment of reasoning about social exchange in a patient with bilateral limbic system damage

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Authors:

  • Valerie E. Stone

  • Leda Cosmides

  • John Tooby

  • Neal E. A. Kroll

  • Robert T. Knight

Date: 2002

PubMed: 12177408

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Abstract:

Social exchange is a pervasive feature of human social life. Models in evolutionary biology predict that for social exchange to evolve in a species, individuals must be able to detect cheaters (nonreciprocators). Previous research suggests that humans have a cognitive mechanism specialized for detecting cheaters. Here we provide neurological evidence indicating that social exchange reasoning can be selectively impaired while reasoning about other domains is left intact. The patient, R.M., had extensive bilateral limbic system damage, affecting orbitofrontal cortex, temporal pole, and amygdala. We compared his performance on two types of reasoning problem that were closely matched in form and equally difficult for control subjects: social contract rules (of the form, "If you take the benefit, then you must satisfy the requirement") and precaution rules (of the form, "If you engage in hazardous activity X, then you must take precaution Y"). R.M. performed significantly worse in social contract reasoning than in precaution reasoning, when compared both with normal controls and with other brain-damaged subjects. This dissociation in reasoning performance provides evidence that reasoning about social exchange is a specialized and separable component of human social intelligence, and is consistent with other research indicating that the brain processes information about the social world differently from other types of information.

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Effects of frontal lobe damage on interference effects in working memory

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Authors:

  • Sharon L. Thompson-Schill

  • John Jonides

  • Christy Marshuetz

  • Edward E. Smith

  • Mark D'Esposito

  • Irene P. Kan

  • Robert T. Knight

  • Diane Swick

Date: 2002

PubMed: 12455679

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Abstract:

Working memory is hypothesized to comprise a collection of distinct components or processes, each of which may have a unique neural substrate. Recent neuroimaging studies have isolated a region of the left inferior frontal gyrus that appears to be related specifically to one such component: resolving interference from previous items in working memory. In the present study, we examined working memory in patients with unilateral frontal lobe lesions by using a modified version of an item recognition task in which interference from previous trials was manipulated. In particular, we focused on patient R.C., whose lesion uniquely impinged on the region identified in the neuroimaging studies of interference effects. We measured baseline working memory performance and interference effects in R.C. and other frontal patients and in age-matched control subjects and young control subjects. Comparisons of each of these groups supported the following conclusions. Normal aging is associated with changes to both working memory and interference effects. Patients with frontal damage exhibited further declines in working memory but normal interference effects, with the exception of R.C., who exhibited a pronounced interference effect on both response time and accuracy. We propose that the left inferior frontal gyrus subserves a general, nonmnemonic function of selecting relevant information in the face of competing alternatives and that this function may be required by some working memory tasks.

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Both random and perseverative errors underlie WCST deficits in prefrontal patients

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Authors:

  • Francisco Barceló

  • Robert T. Knight

Date: 2002

PubMed: 11684168

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Abstract:

The specificity of the Wisconsin Card Sorting Test (WCST) as a marker of frontal lobe pathology remains controversial. One problem is the lack of a well established correspondence between WCST errors and specific cognitive or neural processes. The conventional scoring of non-perseverative WCST errors does not discriminate between errors related to the efficient test of hypotheses during set shifting ('efficient errors'), and random failures to maintain set ('random errors'). This inherent confusion in the non-perseverative error score probably minimizes the relative importance of random errors in frontal lobe pathology. In this study, we used a WCST version sensitive to differences between 'efficient' and random errors to examine set shifting deficits in patients with focal lesions to their lateral prefrontal cortex. As expected, patients showed abnormally high rates of perseverative errors. Interestingly, patients also showed enhanced rates of random errors suggesting constant shifts or fluctuations in their choice of sorting principle. These results suggest that more sensitive tests are needed to elucidate the association between a specific type of set shifting error and a particular type of frontal lobe pathology.

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Lateral prefrontal damage affects processing selection but not attention switching

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Authors:

  • William J. Gehring

  • Robert T. Knight

Date: 2002

PubMed: 11958971

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Abstract:

A challenge for cognitive neuroscience is to determine how the prefrontal cortex (PFC) contributes to the cognitive control operations that oversee thought and action. We studied the effects of damage to the lateral PFC in two types of attentional control. Subjects performed a choice reaction time task that required attention switching and processing selection. The performance of individuals with PFC or parietal cortex damage was compared with that of age-matched and young control subjects. Damage to the lateral PFC did not significantly impair the switch from attending to one color to attending to another. PFC damage did, however, significantly increase the effects of distractor stimuli, implicating the lateral PFC in processing selection. Individual subjects' performance suggested that the left inferior posterior PFC was the most critical for processing selection. Our data are consistent with the view that the lateral PFC contributes to the top-down control of the information flow along pathways from sensory input to motor output.

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Age-related changes in fronto-parietal networks during spatial memory: an ERP study

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Authors:

  • Notger G. Muller

  • Robert T. Knight

Date: 2002

PubMed: 11958965

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Abstract:

Spatial attention and memory were compared in young and old subjects using non-delayed and delayed matching-to-sample tests. Both young and older subjects revealed a right hemisphere superiority for spatial processing. Older subjects were as accurate as young controls in the non-delay task supporting preserved attention ability in this spatial task. However, older subjects were impaired at 3 s retention intervals supporting an encoding and/or retrieval deficit in spatial memory. Stimulus evaluation demands were highest in the non-delay task and younger subjects generated the largest posterior P3 in this condition plus an additional frontal P3. The frontal P3 was reduced in amplitude in the delay tasks in the young subjects. Retention of spatial information during the delay period was characterized by a negative slow wave maximal over Pz that predicted later memory performance and was enhanced in those subjects with high memory performance. Conversely, older subjects generated a frontal P3 in both delay and non-delay conditions and a reduced sustained posterior scalp negativity in some delay conditions. The results support age-related alterations in frontal-parietal networks during spatial memory.

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Contribution of subregions of the prefrontal cortex to working memory: Evidence from brain lesions in humans

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Authors:

  • Notger G. Muller

  • Liana Machado

  • Robert T. Knight

Date: 2002

PubMed: 12167253

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Abstract:

We investigated working memory in patients with focal brain damage involving subregions of the prefrontal cortex (PFC). Lesions in the dorsal portion of lateral PFC or the ventromedial portion of orbital PFC did not impair performance in tasks that required maintenance and monitoring of object or spatial information. Larger lesions involving both ventral and dorsal parts of the lateral PFC impaired maintenance and monitoring of spatial and object information, with more severe deficits observed in the spatial tasks. The results support a distributed localization of function in lateral PFC during working memory.