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Effects of emotional stimuli on event-related potentials and reaction times in orbitofrontal patients

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Authors:

  • Kaisa M. Hartikainen

  • Keith H. Ogawa

  • Maryam Soltani

  • Robert T. Knight

Date: 2001

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Abstract:

We examined the effects of bilateral orbitofrontal damage on emotional processing and hemispheric attention capacity. Participants (four bilateral orbitofrontal patients and age- matched controls) discriminated between upright and inverted triangles (target). Targets were randomly presented in the left (LVF) or right visual hemifield (RVF, 150 ms). Emotional (pleasant or unpleasant; 150 ms) or neutral stimuli were presented centrally 350 ms prior to the target. Pleasant stimuli decreased whereas unpleasant stimuli increased RTs to LVF targets, with exaggerated effects in patients. Orbitofrontal damage differentially altered processing of emotional stimuli. In addition, orbitofrontal patients showed altered target ERPs, with evidence of increased activity over frontal sites for only LVF targets. The results suggest an interplay between orbitofrontal cortex and the right hemisphere.

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Mechanisms of human attention: event-related potentials and oscillations

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Authors:

  • Christoph S. Herrmann

  • Robert T. Knight

Date: 2001

PubMed: 11595268

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Abstract:

Electrophysiological and hemodynamical responses of the brain allow investigation of the neural origins of human attention. We review attention-related brain responses from auditory and visual tasks employing oddball and novelty paradigms. Dipole localization and intra- cranial recordings as well as functional magnetic resonance imaging reveal multiple areas involved in generating and modulating attentional brain responses. In addition, the in ̄uence of brain lesions of circumscribed areas of the human cortex onto attentional mechanisms are reviewed. While it is obvious that damaged brain tissue no longer functions properly, it has also been shown that functions of non-lesioned brain areas are impaired due to loss of modulatory in ̄uence of the lesioned area. Both early (P1 and N1) and late (P3) event-related potentials are modulated by excitatatory and inhibitory mechanisms.. Oscillatory EEG-correlates of attention in the alpha and gamma frequency range also show attentional modulation.

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Neural representations of skilled movement

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Authors:

  • Kathleen Y. Haaland

  • Deborah L. Harrington

  • Robert T. Knight

Date: 2000

PubMed: 11050030

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Abstract:

The frontal and parietal cortex are intimately involved in the representation of goal-directed movements, but the crucial neuroanatomical sites are not well established in humans. In order to identify these sites more precisely, we studied stroke patients who had the classic syndrome of ideomotor limb apraxia, which disrupts goal-directed movements, such as writing or brushing teeth. Patients with and without limb apraxia were identified by assessing errors imitating gestures and specifying a cut-off for apraxia relative to a normal control group. We then used MRI or CT for lesion localization and compared areas of overlap in those patients with and without limb apraxia. Patients with ideomotor limb apraxia had damage lateralized to a left hemispheric network involving the middle frontal gyrus and intraparietal sulcus region. Thus, the results revealed that discrete areas in the left hemisphere of humans are critical for control of complex goal-directed movements.

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Transient interference of right hemisphere function due to automatic emotional processing

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Authors:

  • Kaisa M. Hartikainen

  • Keith H. Ogawa

  • Robert T. Knight

Date: 2000

PubMed: 11074080

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Abstract:

We examined the effects of emotional stimuli on right and left hemisphere detection performance in a hemifield visual discrimination task. A group of 18 healthy subjects were asked to discriminate between upright and inverted triangles (target). Targets were randomly presented in the left or right visual hemifield (150 ms target duration). A brief emotional picture (pleasant or unpleasant; 150 ms stimulus duration) or neutral picture selected from the International Affective Picture System was randomly presented either in the same (47%) or the opposite (47%) spatial location to the subsequent target. Emotional or neutral stimuli offset 150 ms prior to the subsequent target. Subjects were instructed to ignore the pictures and respond to the targets as quickly and accurately as possible. Independent of field of presentation, emotional stimuli prolonged reaction times (PB 0.01) to LVF targets, with unpleasant stimuli showing a greater effect than pleasant stimuli. The current study shows that brief emotional stimuli selectively impair right hemispheric visual discrimination capacity. The findings suggest automatic processing of emotional stimuli captures right hemispheric processing resources and transiently interferes with other right hemispheric functions.

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Prefrontal-cingulate interactions in action monitoring

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Authors:

  • William J. Gehring

  • Robert T. Knight

Date: 2000

PubMed: 10769394

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Abstract:

We found that medial frontal cortex activity associated with action monitoring (detecting errors and behavioral conflict) depended on activity in the lateral prefrontal cortex. We recorded the error- related negativity (ERN), an event-related brain potential proposed to reflect anterior cingulate action monitoring, from individuals with lateral prefrontal damage or age-matched or young control participants. In controls, error trials generated greater ERN activity than correct trials. In individuals with lateral prefrontal damage, however, correct-trial ERN activity was equal to error-trial ERN activ- ity. Lateral prefrontal damage also affected corrective behavior. Thus the lateral prefrontal cortex seemed to interact with the anterior cingulate cortex in monitoring behavior and in guiding compensatory systems.

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Prefrontal modulation of visual processing in humans

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Authors:

  • Francisco Barceló

  • Shugo Suwazono

  • Robert T. Knight

Date: 2000

PubMed: 10725931

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Abstract:

Single neuron, evoked potential and metabolic techniques show that attention influences visual pro- cessing in extrastriate cortex. We provide anatomical, electrophysiological and behavioral evidence that prefrontal cortex regulates neuronal activity in extrastriate cortex during visual discrimination. Event-related potentials (ERPs) were recorded during a visual detection task in patients with damage in dorsolateral prefrontal cortex. Prefrontal damage reduced neuronal activity in extrastriate cortex of the lesioned hemisphere. These electrophysiological abnormalities, beginning 125 ms after stimulation and lasting for another 500 ms, were accompanied by behavioral deficits in detection ability in the contralesional hemifield. The results provide evidence for intrahemispheric prefrontal modulation of visual processing.

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The contribution of recollection and familiarity to yes-no and forced-choice recognition tests in healthy subjects and amnesics

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Authors:

  • Wayne Khoe

  • Neal E. A. Kroll

  • Andrew P. Yonelinas

  • Ian G. Dobbins

  • Robert T. Knight

Date: 2000

PubMed: 10869576

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Abstract:

Recent reports suggest that some amnesic patients perform relatively normally on forced-choice recognition memory tests. Their preserved performance may re ̄ect the fact that the test relies more heavily on assessments of familiarity, a process that is relatively preserved in these patients, than do other recognition tests such as yes±no tests, which may rely more on recollection. The current study examined recognition memory using yes±no and forced-choice procedures in control and amnesic patients in order to determine whether the two tasks di€erentially relied on recollection and familiarity, and whether the extent of the recognition memory de®cit observed in amnesia was dependent upon the type of recognition test used to measure performance. Results using the remember±know procedure with healthy subjects showed that there were no substantial di€erences in recognition accuracy or in the contribution of recollection to these two tasks. Moreover, amnesic patients were not found to perform better on a forced-choice test than on a yes±no test, suggesting that familiarity contributed equally to these two types of recognition test.

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An analysis of atrophy in the medial mammillary nucleus following hippocampal and fornix lesions in humans and nonhuman primates

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Authors:

  • Mirela Loftus

  • Robert T. Knight

  • David G. Amaral

Date: 2000

PubMed: 10785457

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Abstract:

Lesions of the hippocampal formation or transec- tions of the fornix are followed by shrinkage of the medial mammillary nucleus (MMN). We determined whether the shrinkage of this nucleus was due to loss and/or shrinkage of neurons in addition to the loss of neuropil. We examined the MMN in a patient (KB) with an infarct that led to marked atrophy of the left hippocampus and subiculum, leaving the right MMN intact. Unbiased, stereological measure- ment techniques were used to compare the total cell number and individual neuronal cross-sectional ar- eas in both left and right MMN in this patient and in two control human brains. We also analyzed the MMN in four macaque monkeys that underwent ex- perimental unilateral transections of the fornix. The volume of the MMN on the lesioned side in KB was 55% of the unlesioned side (2.8 mm 3 vs 5.1 mm 3 ); the MMN in the monkey cases were reduced to 47–58% of the volume of the nonlesioned side. Neurons in the deafferented MMN of KB and of the monkey subjects were decreased in cross-sectional area (16 –20%, P < 0.0001). There was a trend toward decreased cell numbers (11–15%) on the lesioned side in all cases. We have estimated that the loss in cell number and shrinkage of remaining cells contribute negligibly to the 45% reduction in MMN volume. Therefore, the loss of neuropil (dendrites and afferent and efferent axons) appears to be the major contributor to the change in MMN volume.

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Prefrontal cortex, time and consciousness

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Authors:

  • Robert T. Knight

  • Marcia Grabowecky

Date: 2000

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Abstract:

A central feature of consciousness is the ability to control the fourth dimension, time. Humans can effortlessly move their internal mental set from the present moment to a past remembrance and just as easily project themselves into a future event. It is proposed that this capacity to extract oneself from the present and fluidly move forward or backward in time is dependent on the evolution of the human prefrontal cortex. Prefrontal cortex modulates activity in multi-modal association and limbic cortices through widely distributed inhibitory and excitatory pathways. Prefrontal cortex also has a selective bias to novelty, crucial for detecting change and hence for the correct temporal coding of events. These extensive modulatory pathways coupled with an intrinsic link to temporal coding provide a mechanism for rapid engagement of distributed neural networks critical for seamless transitions through the time continuum. Support for this hypothesis is found in the fact that prefrontal damage results in a failure in the ability to extract oneself from the present. Indeed, the hallmark of the severe prefrontal syndrome is persevatory and stimulus-bound behavior--a classic example of a failure in temporal control.

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Neural Origins of the P300

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Authors:

  • Maryam Soltani

  • Robert T. Knight

Date: 2000

PubMed: 12645958

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Abstract:

A review of the literature investigating the neural origins of detection behavior in humans reveals two event-related potential components, P3a and P3b, each with a distinct neural organization and cognitive func- tion. The P3a is involved in automatic novelty detection and characterized by a more anterior cortical distribution, whereas the P3b is concerned with volitional target detection and has a more posterior cortical distribution. Intra- cranial investigation, studies with patients with focal brain lesions, and functional neuroimaging (fMRI) studies converge with the scalp-recorded ERP data in suggesting that a widespread cortical network gives rise to both automatic and controlled detection behavior. The main regions consistently attributed to generating detection related brain activation include the temporal-parietal junction, medial temporal complex, and the lateral prefrontal cortex. The extant human and animal literature addressing the neural networks, neuropharmacological underpinnings, and behavioral signicance of “the P300” potential will be reviewed.

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Predictive value of novel stimuli modifies visual event-related potentials and behavior

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Authors:

  • Shugo Suwazono

  • Liana Machado

  • Robert T. Knight

Date: 1999

PubMed: 10656508

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Abstract:

Objective: We examined how behavioral context in ̄uences novelty processing by varying the degree that a novel event predicted the occurrence of a subsequent target stimulus. Methods: Visual event-related potentials (ERPs) and reaction times (RTs) were recorded in 3 detection experiments (23 subjects). The predictive value of a novel stimulus on the occurrence of a subsequent target was varied as was novel-target pairing intervals (200±900 ms). In Experiment 1, novel stimuli always preceded a target, in Experiment 2, 40% of novel stimuli were followed by a target, and in Experiment 3, novel stimuli occurred randomly. Results: In Experiment 1, RTs following 100% predictive novels were shortened for targets at all spatial locations and novel-target pairing intervals. Novel stimuli predicting a target generated a central negativity peaking at 300 ms and reduced P3a and P3b ERPs. In Experiments 2 and 3, target RTs were prolonged only when novel and target stimuli were presented in the same spatial location at short ISIs (200 ms). The central novel N2 was smaller in amplitude in comparison to Experiment 1, and novelty P3a and target extrastriate N2 and posterior scalp P3b ERPs were enhanced. Conclusions: The enhanced N2 for100% predictive novel stimuli appears to index an alerting system facilitating behavioral detection. The same novel stimuli with no predictive value distract attention and generate a different ERP pattern characterized by increased novelty P3a and target P3b responses. The results indicate that behavioral context determines how novel stimuli are processed and in ̄uence behavior.

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Prefrontal cortical involvement in visual working memory

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Authors:

  • Lynn Nielsen-Bohlman

  • Robert T. Knight

Date: 1999

PubMed: 10556607

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Abstract:

Studies of human amnesia provide evidence for a short-term memory store with information transfer to long term memory occurring within 60 s of sensory encoding. Human and nonhuman primate research has shown that maintenance of this short-term or working memory store is dependent upon frontal cortical activation, although the critical temporal parameters of frontal involvement throughout this 60-s window are undetermined. We examined prefrontal contributions to rapid Žunder 2 s. and sustained Žover 4 s. visual working memory by recording behavioral performance and event-related potentials ŽERPs. in patients with lesions in dorsolateral frontal cortex and age-matched control subjects. Prefrontal lesioned patients generated a reduced sustained frontal positivity at all delays. At short delays, patients generated reduced performance to stimuli presented in the contralesional field. Patients generated a negative potential ŽN400., greatest to contralesionally presented stimuli, that was observed in the control subjects only at long delays. The results indicate that prefrontal lesions impair the frontal component of an anterior–posterior working memory network activated during rapid and sustained visual memory processing. Frontal patients may require activation of limbic cortex, indexed by N400, for maintenance of both rapid and sustained working memory.

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Spatial deficits in ideomotor limb apraxia: a kinematic analysis of aiming movements

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Authors:

  • Kathleen Y. Haaland

  • Deborah L. Harrington

  • Robert T. Knight

Date: 1999

PubMed: 10356068

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Abstract:

Ideomotor limb apraxia is a classic neurological disorder manifesting as a breakdown in co-ordinated limb control with spatiotemporal deficits. We employed kinematic analyses of simple aiming movements in left hemisphere- damaged patients with and without limb apraxia and a normal control group to examine preprogramming and response implementation deficits in apraxia. Damage to the frontal and parietal lobes was more common in apraxics, but neither frontal nor parietal damage was associated with different arm movement deficits. Limb apraxia was associated with intact preprogramming but impaired response implementation. The response implementation deficits were characterized by spatial but not temporal deficits, consistent with decoupling of spatial and temporal features of movement in limb apraxia. While the apraxics’ accuracy was normal when visual feedback was available, it was impaired when visual feedback of either target location or hand position was unavailable. This finding suggests that ideomotor limb apraxia is associated with disruption of the neural representations for the extrapersonal (spatial location) and intrapersonal (hand position) features of movement. The non-apraxic group’s normal kinematic performance demonstrates that the deficits demonstrated in the apraxic group are not simply a reflection of left hemisphere damage per se.

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Prefrontal cortex regulates inhibition and excitation in distributed neural networks

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Authors:

  • Robert T. Knight

  • W Richard Staines

  • Diane Swick

  • Linda L. Chao

Date: 1999

PubMed: 10344184

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Abstract:

Prefrontal cortex provides both inhibitory and excitatory input to distributed neural cir- cuits required to support performance in diverse tasks. Neurological patients with prefrontal damage are impaired in their ability to inhibit task-irrelevant information during behavioral tasks requiring performance over a delay. The observed enhancements of primary auditory and somatosensory cortical responses to task-irrelevant distractors suggest that prefrontal damage disrupts inhibitory modulation of inputs to primary sensory cortex, perhaps through abnormalities in a prefrontal-thalamic sensory gating system. Failure to suppress irrelevant sensory information results in increased neural noise, contributing to the de®cits in decision making routinely observed in these patients. In addition to a critical role in inhibitory control of sensory ̄ow to primary cortical regions, and tertiary prefrontal cortex also exerts excitatory input to activity in multiple sub-regions of secondary association cortex. Unilateral prefrontal damage results in multi-modal decreases in neural activity in posterior association cortex in the hemisphere ipsilateral to damage. This excitatory modulation is necessary to sustain neural activity during working memory. Thus, prefrontal cortex is able to sculpt behavior through parallel inhibitory and excitatory regulation of neural activity in distributed neural net- works.

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Contributions of prefrontal cortex to recognition memory: electrophysiological and behavioral evidence

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Authors:

  • Diane Swick

  • Robert T. Knight

Date: 1999

PubMed: 10353368

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Abstract:

To clarify the involvement of prefrontal cortex in episodic memory, behavioral and event-related potential (ERP) measures of recognition were examined in patients with dorsolateral prefrontal lesions. In controls, recognition accuracy and the ERP old-new effect declined with increasing retention intervals. Although frontal patients showed a higher false-alarm rate to new words, their hit rate to old words and ERP old-new effect were intact, suggesting that recognition processes were not fundamentally altered by prefrontal damage. The opposite behavioral pattern was observed in patients with hippocampal lesions: a normal false-alarm rate and a precipitous decline in hit rate at long lags. The intact ERP effect and the change in response bias during recognition suggest that frontal patients exhibited a deficit in strategic processing or postretrieval monitoring, in contrast to the more purely mnemonic deficit shown by hippocampal patients.

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The neural substrates of recollection and familiarity (pp. 468-469)

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Authors:

  • Andrew P. Yonelinas

  • Neal E. A. Kroll

  • Ian G. Dobbins

  • Michele Lazzara

  • Robert T. Knight

Date: 1999

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Abstract:

Aggleton & Brown argue that a hippocampal-anterior thalamic system supports the “recollection” of contextual information about previ- ous events, and that a separate perirhinal-medial dorsal thalamic system supports detection of stimulus “familiarity.” Although there is a growing body of human literature that is in agreement with these claims, when rec- ollection and familiarity have been examined in amnesics using the process dissociation or the remember/know procedures, the results do not seem to provide consistent support. We reexamine these studies and describe the results of an additional experiment using a receiver operating charac- teristic (ROC) technique. The results of the reanalysis and the ROC ex- periment are consistent with Aggleton & Brown’s proposal. Patients with damage to both regions exhibit severe deficits in recollection and smaller, but consistent, deficits in familiarity.