Contributions of right inferior temporal-occipital cortex to visual word and non-word priming

Authors:

• Diane Swick

• Robert T. Knight

Date: 1995

PubMed: 8742406

View PDF

Abstract:

Little is known about the neural substrates of indirect forms of memory such as priming. Electrophysiological (ERP) and behavioral data were recorded from controls and three patients with damage in the right parahippocampal and lingual gyri, with variable extension into posterior hippocampus and striate/extrastriate cortex. Visually presented words and non-words were repeated after one of three delays in a lexical decision task. The late positive ERP deflection related to stimulus repetition was diminished at all scalp sites, suggesting dysfunction in a neural system associated with priming. The patients also failed to show significant reaction time priming at intermediate and long delays. These results demonstrate the importance of right inferior temporal-occipital cortex for ERP and behavioral manifestations of verbal priming.

Prefrontal alterations during memory processing in aging

Authors:

• Lynn Nielsen-Bohlman

• Robert T. Knight

Date: 1995

PubMed: 8590826

View PDF

Abstract:

Studies of human amnesia provide evidence for a short-term memory store with information transfer to long-term memory occurring within 60 sec of encoding. Frontal cortical activation is critical for maintenance of the short-term store, and limbic structure are necessary for access to the long-term store. The P3 and N4 components of the event-related potential (ERP) are generated during memory processes mediated by these brain regions. The current study examines the effects of age on ERPs generated to correctly identified stimuli presented at delays of 1-150 sec in a visual recognition memory task. Consistently different evoked potentials and performance were obtained to stimuli repeated at 1.2 sec delay as opposed to stimuli repeated at delays of over 4 sec in all subjects. At the 1.2 sec delay, the performance and posterior P3 amplitudes generated by old and young subjects were comparable. At longer delays, the older subjects had impaired performance and decreased P3 amplitude at posterior scalp sites. In addition, fronto-central N4 activity was reduced at long delays in the elderly. Older subjects generated a sustained frontal positivity (50-800 msec) to both short and long delay stimuli that was not observed in the younger group. The late phase of the frontal positivity was enhanced at long delays in the elderly. The data provide evidence of intact rapid and impaired delayed recognition memory in aging. Alternations in frontal cortical control of posterior and limbic regions may contribute to the memory changes observed in aging.

Is prefrontal cortex involved in cued recall? A neuropsychological test of PET findings

Authors:

• Diane Swick

• Robert T. Knight

Date: 1995

PubMed: 8843069

View PDF

Abstract:

Positron emission tomography (PET) experiments have detected blood flow activations in right anterior prefrontal cortex during performance of a word stem cued recall task [3, 38]. Based on findings from a variety of PET studies, the "hemispheric encoding/retrieval asymmetry model" [44] was proposed to explain the role of the frontal lobes in episodic memory. This model asserts that left prefrontal cortex is preferentially involved in the encoding of new information into episodic memory, whereas right prefrontal cortex is more involved in episodic memory retrieval. As a neuropsychological test of this hypothesis, a group of frontal patients with lesions in areas 6, 8, 9, 10, 44, 45 and/or 46 (11 left, five right) were run on word stem cued recall under two semantic study conditions. As a group, these patients were not significantly impaired in cued recall. In the first but not the second experiment, left frontal patients recalled fewer words than controls. Right frontal patients were not impaired on either list. Right prefrontal cortex could be activated by several strategic aspects of the cued recall paradigm that were minimized in the present experiment. Brain reorganization in the lesioned patients could also account for their intact performance. The regions of prefrontal cortex activated in PET studies of young controls are not necessary for patients to perform the task.

Prefrontal and posterior cortical activation during auditory working memory

Authors:

• Linda L. Chao

• Robert T. Knight

Date: 1995

PubMed: 8813410

View PDF

Abstract:

The present study investigated brain mechanisms underlying auditory memory. In a modified Sternberg memory scanning task, 11 subjects indicated whether a probe sound was part of a previously presented 4-item memory set by a button press. Behaviorally, subjects responded fastest and most accurately to probes that matched the last memory set items and slowest and least accurately to negative probes and to positive probes to the first two memory set items. Electrophysiologically, probes to the last memory set items elicited the largest amplitude and earliest latency P3 components while other probes elicited smaller amplitude, prolonged P3s as well as a negativity around 400 ms. These results suggest that subjects utilized a trace strength/self-terminating search model to perform the memory scanning task. Subjects only generated the P3 component during the matching phase of the auditory memory task while a sustained frontal negativity was elicited during both the encoding and matching phase. Taken together these findings provide evidence of differential activation of distributed neural activity during non-linguistic auditory memory.

Auditory event-related potentials dissociate early and late memory processes

Authors:

• Linda L. Chao

• Lynn Nielsen-Bohlman

• Robert T. Knight

Date: 1994

PubMed: 7535221

View PDF

Abstract:

Event-related potentials (ERPs) to environmental sounds were recorded from 15 young control subjects in an auditory recognition memory task. Subjects listened to a continuous string of binaurally presented sounds, 20% of which were presented once and 80% were repeated. Of the repeated sounds, some repeated immediately after the initial presentation (2 sec; short delay repetition) while others repeated after 2-6 intervening sounds (4-12 sec; long delay repetition). Subjects were instructed to indicate whether they had heard the sounds before by pressing a "yes" or "no" button. The initial stimulus presentation and long delay repetition stimuli generated both an N4 component and a prolonged latency P3 component while the short delay repetition stimuli elicited no N4 component and an earlier latency P3 component. Subjects' responses were faster and more accurate for short delay repetition. All stimuli generated a sustained frontal negative component (SFN). These data indicate that auditory recognition memory for environmental sounds may involve two processes. The P3 generated by both short and long delay repetition stimuli may index activation of a neocortical template matching system. The N4 generated by initial stimulus presentations and long delay repetition is proposed to measure additional activation of limbic memory systems at long retention intervals.

Human prefrontal lesions increase distractibility to irrelevant sensory inputs

Authors:

• Linda L. Chao

• Robert T. Knight

Date: 1995

PubMed: 8527724

View PDF

Abstract:

Neurological patients with focal lesions in either the dorsolateral prefrontal cortex, temporal-parietal junction or the posterior hippocampus, and control subjects, were tested on a task requiring short-term retention of environmental sounds. Subjects had to indicate whether initial and subsequent test sounds were identical in two conditions. The initial and test sounds were separated by either a silent period varying from 4 to 12.6 s (no-distractor condition) or a series of irrelevant tones (distractor condition). Prefrontal patients were significantly impaired by distractors at all delays, hippocampal patients were impaired only at longer delays, while temporal-parietal patients performed similar to controls. The findings suggest that dorsolateral prefrontal cortex is crucial for gating of distracting information during delay tasks.

Susceptibility to memory interference effects following frontal lobe damage: findings from tests of paired-associate learning.

Authors:

• Arthur P. Shimamura

• Paul J. Jurica

• Jennifer A. Mangels

• Felicia B. Gershberg

• Robert T. Knight

Date: 1995

View PDF

Abstract:

Patients with frontal lobe lesions were administered tests of paired-associate learning in which cue and response words are manipulated to increase interference across two study lists. In one test of paired-associate learning (AB-AC test), cue words used in one list are repeated in a second list but are associated with different response words (e.g., LION-HUNTER, LION-CIRCUS). In another test (AB-ABr test), words used in one list are repeated in a second list but are rearranged to form new pairs. Compared to control subjects, patients with frontal lobe lesions exhibited disproportionate impairment of second-list learning as a result of interference effects. In particular, patients exhibited the poorest performance during the initial trial of the second list, a trial in which interference effects from the first list would be most apparent. These findings suggest that the on-line control of irrelevant or competing memory associations is disrupted following frontal lobe lesions. This disruption may be indicative of an impaired gating or filtering mechanism that affects not only memory function but other cognitive function as well.

Escape from linear time: prefrontal cortex and conscious experience

Authors:

• Robert T. Knight

• Marcia Grabowecky

Date: 1995

Abstract:

Insights into the brain mechanisms of conscious experience are provided by the study of neurological patients / patients with prefrontal damage exhibit deficits in behaviors that are crucial for normal conscious experience / problems with inhibitory control of external sensory inputs and internal cognitive processes, coupled with abnormalities in the detection of novel events, lead to a cascade of behavioral deficits / reviews neuropsychological and neurophysiological evidence linking prefrontal cortex to these deficits and to conscious experience.

Susceptibility to memory interference effects following frontal lobe damage: findings from tests of paired-associate learning

Authors:

• Arthur P. Shimamura

• Paul J. Jurica

• Jennifer A. Mangels

• Felicia B. Gershberg

• Robert T. Knight

Date: 1995

View PDF

Abstract:

Patients with frontal lobe lesions were administered tests of paired-associate learning in which cue and response words are manipulated to increase interference across two study lists. In one test of paired-associate learning (AB-AC test), cue words used in one list are repeated in a second list but are associated with different response words (e.g., LION-HUNTER, LION-CIRCUS). In another test (AB-ABr test), words used in one list are repeated in a second list but are rearranged to form new pairs. Compared to control subjects, patients with frontal lobe lesions exhibited disproportionate impairment of second-list learning as a result of interference effects. In particular, patients exhibited the poorest performance during the initial trial of the second list, a trial in which interference effects from the first list would be most apparent. These findings suggest that the on-line control of irrelevant or competing memory associations is disrupted following frontal lobe lesions. This disruption may be indicative of an impaired gating or filtering mechanism that affects not only memory function but other cognitive function as well.

Role of prefrontal cortex in generation of the contingent negative variation

Authors:

• Steffen K. Rosahl

• Robert T. Knight

Date: 1995

PubMed: 7620289

View PDF

Abstract:

The contingent negative variation (CNV) is a brain potential generated during delay periods that has been proposed to measure prefrontal cortex (PFCx) activity. The CNV was recorded in neurological patients with PFCx damage centered in Brodmann areas 9, 44, 45, and 46 in a classical auditory S1-S2 paradigm employing a 3 sec interstimulus interval. Subjects pressed a button upon detection of an acoustically cued imperative tone (S2, 1000 Hz, GO). Responses were withheld if the warning tone (S1, 1500 Hz in GO trials) was lower in frequency (500 Hz, NOGO). The early phase of the CNV (500-700 msec after S1) was not reduced in patients with PFCx damage. PFCx lesions reduced the later phase of the CNV beginning about 1000 msec prior to S2. Reductions were maximal over PFCx sites but extended to posterior scalp electrodes over the lesioned hemisphere. The results are consistent with a late CNV generator in dorsolateral PFCx that also modulates generation of the potential in posterior regions of the ipsilateral hemisphere. The CNV findings coupled with behavioral evidence of impaired preparatory processes in these patients support the role of PFCx in sustaining distributed neural activity during delay periods.

Role of human prefrontal cortex in attention control

Authors:

• Robert T. Knight

• Marcia Grabowecky

Date: 1995

PubMed: 7771302

View PDF

Abstract:

Without a functioning dorsolateral prefrontal cortex, humans are stimulus bound and have little confidence in their ability to interact with the environment. Deficits in inhibitory control of external and internal processes coupled with impaired temporal coding of stimuli and detection capacity for novel events leave the patient functioning in a noisy internal environment without critical spatiotemporal cues. Some of these proposals are similar to those of Nauta (104). Based on connectivity of the prefrontal cortex, Nauta suggested that this region was ideally suited to generate and evaluate internal models of action. It is proposed that, in addition to this generation function, the prefrontal cortex is crucial for detecting changes in the external environment and for discriminating internally and externally derived models of the world. This chapter has described a cascade of deficits that result from damage to the dorsolateral prefrontal cortex. Awareness of the sensory world, and of the apparent stream of internal and external events, is impaired by deficits in novelty detection. Changes in the world, internal or external, may not be noticed in a noisy internal milieu. These deficits contribute to impaired reality monitoring and to a subsequent lack of confidence in behavior. An inability to bridge temporal gaps and temporally sequence internal events, together with deficits in inhibitory control systems, contribute to an impairment in the ability to generate coherent representations of alternate or counterfactual realities.

Lesions of frontal cortex diminish the auditory mismatch negativity

Authors:

• Kimmo Ahlo

• David L. Woods

• Alain Algazi

• Robert T. Knight

• Risto Näätänen

Date: 1994

PubMed: 7525232

View PDF

Abstract:

Event-related brain potentials to non-attended auditory stimuli were recorded from patients with dorsolateral prefrontal cortex (DPFCx) lesions and from age-matched control subjects as they performed a visual reaction time task. Auditory stimuli consisted of monaural sequences of repetitive standard tones (1000 Hz) and occasional deviant tones of a higher frequency (1300 Hz). In comparison with control subjects, DPFCx patients showed enhanced P1 amplitudes (mean peak latency 50 msec), consistent with reduced frontally mediated gating of sensory input to the auditory cortex. The mismatch negativity (MMN) elicited by deviant tones was reduced in DPFCx patients over a broad latency range (130-210 msec), especially over the lesioned hemisphere and for tones delivered to the ear ipsilateral to the lesion. The results suggest that DPFCx and DPFCx-temporal projections play a critical role in involuntary orienting to physical changes in sequences of non-attended auditory stimuli.

Auditory event-related potentials dissociate early and late memory processes

Authors:

• Linda L. Chao

• Lynn Nielsen-Bohlman

• Robert T. Knight

Date: 1994

PubMed: 7535221

View PDF

Abstract:

Event-related potentials (ERPs) to environmental sounds were recorded from 15 young control subjects in an auditory recognition memory task. Subjects listened to a continuous string of binaurally presented sounds, 20% of which were presented once and 80% were repeated. Of the repeated sounds, some repeated immediately after the initial presentation (2 sec; short delay repetition) while others repeated after 2-6 intervening sounds (4-12 sec; long delay repetition). Subjects were instructed to indicate whether they had heard the sounds before by pressing a "yes" or "no" button. The initial stimulus presentation and long delay repetition stimuli generated both an N4 component and a prolonged latency P3 component while the short delay repetition stimuli elicited no N4 component and an earlier latency P3 component. Subjects' responses were faster and more accurate for short delay repetition. All stimuli generated a sustained frontal negative component (SFN). These data indicate that auditory recognition memory for environmental sounds may involve two processes. The P3 generated by both short and long delay repetition stimuli may index activation of a neocortical template matching system. The N4 generated by initial stimulus presentations and long delay repetition is proposed to measure additional activation of limbic memory systems at long retention intervals.

Electrophysiological dissociation of rapid memory mechanisms in humans

Authors:

• Lynn Nielsen-Bohlman

• Robert T. Knight

Date: 1994

PubMed: 7948852

View PDF

Abstract:

Human memory involves an interaction between transient working memory and a long-term store. We found electrophysiological evidence supporting the existence of two distinct mechanisms subserving these processes. Stimuli held in memory for less than 4 s generate large, early latency P300 potentials which may index activation of a frontally-mediated rapid working memory system. Stimuli held in memory for over 4 s selectively generate N400 potentials which may reflect activation of mesial temporal cortices involved in access to the long-term store. These results suggest that memory processing in the initial 10 s after stimulus detection involves at least two distinct distributed cortical-limbic systems.

Electrophysiological dissociation of rapid memory mechanisms in humans

Authors:

• Lynn Nielsen-Bohlman

• Robert T. Knight

Date: 1994

PubMed: 7948852

View PDF

Abstract:

Human memory involves an interaction between transient working memory and a long-term store. We found electrophysiological evidence supporting the existence of two distinct mechanisms subserving these processes. Stimuli held in memory for less than 4 s generate large, early latency P300 potentials which may index activation of a frontally-mediated rapid working memory system. Stimuli held in memory for over 4 s selectively generate N400 potentials which may reflect activation of mesial temporal cortices involved in access to the long-term store. These results suggest that memory processing in the initial 10 s after stimulus detection involves at least two distinct distributed cortical-limbic systems.

Lesions of frontal cortex diminish the auditory mismatch negativity

Authors:

• Kimmo Ahlo

• David L. Woods

• Alain Algazi

• Robert T. Knight

• Risto Näätänen

Date: 1994

PubMed: 7525232

View PDF

Abstract:

Event-related brain potentials to non-attended auditory stimuli were recorded from patients with dorsolateral prefrontal cortex (DPFCx) lesions and from age-matched control subjects as they performed a visual reaction time task. Auditory stimuli consisted of monaural sequences of repetitive standard tones (1000 Hz) and occasional deviant tones of a higher frequency (1300 Hz). In comparison with control subjects, DPFCx patients showed enhanced P1 amplitudes (mean peak latency 50 msec), consistent with reduced frontally mediated gating of sensory input to the auditory cortex. The mismatch negativity (MMN) elicited by deviant tones was reduced in DPFCx patients over a broad latency range (130-210 msec), especially over the lesioned hemisphere and for tones delivered to the ear ipsilateral to the lesion. The results suggest that DPFCx and DPFCx-temporal projections play a critical role in involuntary orienting to physical changes in sequences of non-attended auditory stimuli.

CT findings of hypoxic basal ganglia damage

Authors:

• Thomas Yee

• Arthur Gronner

• Robert T. Knight

Date: 1994

PubMed: 8202772

View PDF

Abstract:

The outcome of hypoxic ischemic injury ranges from complete recovery to a persistent vegetative state or death, depending on the length of time the patient remains unconscious and the degree of associated cardiac failure. We describe three patients who were comatose from a hypoxic and/or ischemic injury and whose principal computed tomographic (CT) finding was bilateral basal ganglia hypodensities. Two of these patients were discharged from the hospital with minimal residual neurologic deficits. These cases and review of the literature suggest that ischemic basal ganglia signs on CT scan are not necessarily a predictor of severe neurologic sequelae.

Attention Regulation and Human Prefrontal Cortex

ABSTRACT

The prefrontal cortex is critical for integrative cognitive function, although it is unlikely that this capacity resides in specialized modules in prefrontal regions. Rather, prefrontal cortex appears to modulate activity in multiple cortical and subcortical regions through an extensive network of bidirectional pathways. The net result of neuronal activity in these distributed prefrontal systems sums to produce the higher level capacity attributed to this area.

AUTHORS

• Robert T. Knight

Date: 1994

DOI: 10.1007/978-3-642-85007-3_11

View PDF

Event-Related Potentials Dissociate Immediate and Delayed Memory

ABSTRACT

According to the competition account of lexical selection in word production, conceptually driven word retrieval involves the activation of a set of candidate words in left temporal cortex and competitive selection of the intended word from this set, regulated by frontal cortical mechanisms. However, the relative contribution of these brain regions to competitive lexical selection is uncertain. In the present study, five patients with left prefrontal cortex lesions (overlapping in ventral and dorsal lateral cortex), eight patients with left lateral temporal cortex lesions (overlapping in middle temporal gyrus), and 13 matched controls performed a picture-word interference task. Distractor words were semantically related or unrelated to the picture, or the name of the picture (congruent condition). Semantic interference (related vs. unrelated), tapping into competitive lexical selection, was examined. An overall semantic interference effect was observed for the control and left-temporal groups separately. The left-frontal patients did not show a reliable semantic interference effect as a group. The left-temporal patients had increased semantic interference in the error rates relative to controls. Error distribution analyses indicated that these patients had more hesitant responses for the related than for the unrelated condition. We propose that left middle temporal lesions affect the lexical activation component, making lexical selection more susceptible to errors.

AUTHORS

• Lynn Nielsen-Bohlman

• Robert T. Knight

Date: 1994

DOI: 10.1007/978-1-4612-0283-7_7

View PDF

Search deficits in neglect patients are dependent on size of the visual scene.

Authors:

• Mirjam Eglin

• Lynn C. Robertson

• Robert T. Knight

• Peter Brugger

Date: 1994

DOI: 10.1037/0894-4105.8.3.451

View PDF

Abstract:

Patients with hemispatial neglect are impaired at moving their attention to a target on the contralesional display side. In the present study, visual display area was varied independently of the number of items displayed within the area. Patients searched for the absence of a simple visual feature in displays that produce serial search performance in normals (R. Klein, 1988; A. Treisman & J. Souther, 1985; J. M. Wolfe & C. W. Pokorny, 1990). The contralesional delay was enhanced for stimulus arrays that were distributed over a larger display area, which suggests that neglect is more severe when attention has to be moved over a larger distance. The directional disengage deficit in neglect (M. I. Posner, J. A. Walker, F. A. Friedrich, & R. D. Rafal, 1984, 1987) therefore depends on the target's relative position within a display, the number of ipsilesional items competing for attention (M. Eglin, L. C. Robertson, & R. T. Knight, 1989), and the distance of the contralesional attention movements.