Verb generation in patients with focal frontal lesions: a neuropsychological test of neuroimaging findings

Authors:

• Sharon L. Thompson-Schill

• Diane Swick

• Martha J. Farah

• Mark D'Esposito

• Irene P. Kan

• Robert T. Knight

Date: 1998

PubMed: 9861060

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Abstract:

What are the neural bases of semantic mem- ory? Traditional beliefs that the temporal lobes subserve the retrieval of semantic knowledge, arising from lesion studies, have been recently called into question by functional neuro- imaging studies finding correlations between semantic re- trieval and activity in left prefrontal cortex. Has neuroimag- ing taught us something new about the neural bases of cognition that older methods could not reveal or has it merely identified brain activity that is correlated with but not caus- ally related to the process of semantic retrieval? We examined the ability of patients with focal frontal lesions to perform a task commonly used in neuroimaging experiments, the gen- eration of semantically appropriate action words for concrete nouns, and found evidence of the necessity of the left inferior frontal gyrus for certain components of the verb generation task. Notably, these components did not include semantic retrieval per se.

A distributed cortical network for auditory sensory memory in humans

Authors:

• Claude Alain

• David L. Woods

• Robert T. Knight

Date: 1998

PubMed: 9813226

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Abstract:

Auditory sensory memory is a critical first stage in auditory perception that permits listeners to integrate incoming acoustic information with stored representations of preceding auditory events. Here, we investigated the neural circuits of sensory memory using behavioral and electrophysiological measures of auditory processing in patients with unilateral brain damage to dorsolateral prefrontal cortex, posterior association cortex, or the hippocampus. We used a neurophysiological marker of an automatic component of sensory memory, the mismatch negativity (MMN), which can be recorded without overt attention. In comparison with control subjects, temporal-parietal patients had impaired auditory discrimination and reduced MMN amplitudes with both effects evident only following stimuli presented in the ear contralateral to the lesioned hemisphere. This suggests that auditory sensory memories are predominantly stored in auditory cortex contralateral to the ear of presentation. Dorsolateral prefrontal damage impaired performance and reduced MMNs elicited by deviant stimuli presented in either ear, implying that dorsolateral prefrontal cortices have a bilateral facilitatory effect on sensory memory storage. Hippocampal lesions did not affect either performance or electrophysiological measures. The results provide evidence of a temporal-prefrontal neocortical network critical for the transient storage of auditory stimuli.

Contribution of Human Prefrontal Cortex to Delay Performance

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

• Linda L. Chao

• Robert T. Knight

Date: 1998

DOI: 10.1162/089892998562636 

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Lesion studies of prefrontal cortex and attention

Authors:

• Robert T. Knight

• Diane Swick

Date: 1998

Abstract:

Lesion studies of prefrontal cortex and attention. In The Attentive Brain, R. Parasura- man, ed. Cambridge, Mass.: Bradford Books, MIT Press, pp. 143-162.

Cortical networks underlying mechanisms of time perception

Authors:

• Deborah L. Harrington

• Kathleen Y. Haaland

• Robert T. Knight

Date: 1998

PubMed: 9437028

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Abstract:

Precise timing of sensory information from multiple sensory streams is essential for many aspects of human perception and action. Animal and human research implicates the basal ganglia and cerebellar systems in timekeeping operations, but investigations into the role of the cerebral cortex have been limited. Individuals with focal left (LHD) or right hemisphere (RHD) lesions and control subjects performed two time perception tasks (duration perception, wherein the standard tone pair interval was 300 or 600 msec) and a frequency perception task, which controlled for deficits in time-independent processes shared by both tasks. When frequency perception deficits were controlled, only patients with RHD showed time perception deficits. Time perception competency was correlated with an independent test of switching nonspatial attention in the RHD but not the LHD patients, despite attention deficits in both groups. Lesion overlays of patients with RHD and impaired timing showed that 100% of the patients with anterior damage had lesions in premotor and prefrontal cortex (Brodmann areas 6, 8, 9, and 46), and 100% with posterior damage had lesions in the inferior parietal cortex. All LHD patients with normal timing had damage in these same regions, whereas few, if any, RHD patients with normal timing had similar lesion distributions. These results implicate a right hemisphere prefrontal-inferior parietal network in timing. Time-dependent attention and working memory functions may contribute to temporal perception deficits observed after damage to this network.

Anatomic Bases of Event-Related Potentials and Their Relationship to Novelty Detection in Humans

ABSTRACT

Voluntary of involuntary detection of an infrequent stimulus generates a large scalp P300 response. This P300 ERP (P for positive; 300 for the approximate peak latency poststimulation) has been widely used to study phasic attention and memory mechanisms. The P300 phenomenon, first reported in 1965 (Desmedt et al., 1965; Sutton et al., 1965) has been the subject of extensive research in normal, neurologic, and psychiatric populations. P300-like potentials have been described in rats(Ehlers et al., 1991; Yamaguchi et al., 1993), cats(Katayama et al., 1985; O'Connor and Starr, 1985; Wilder et al., 1981), and monkeys(Arthur and Starr, 1984; Neville and Foote, 1984; Paller et al., 1988; Pineda et al., 1989) supporting a broad ethologic significance of this electrophysiological marker of cognition(Fig. 1) (Swick et al., 1994).Theorists have focused on attention and memory formulations to account for the cognitive basis of the P300, although no clear consensus has emerged(Donchin and Coles, 1988; Verleger, 1988). Some of this disagreement results from the fact that the P300 does not represent a unitary brain potential arising from a discrete brain region or cognitive process as initially proposed. Instead, scalp positivities generated in the 300- to 700-ms poststimulus delivery measure activation of multiple neocortical and limbic regions dependent on the degree of voluntary and involuntary attention allocated to a stimulus. Support for this contention is provided by scalp topographic studies in normal subjects(Courchesne et al., 1975; Squires and Hillyard, 1975; Ruchkin et al., 1990a, 1992; Yamaguchi and Knight, 1991a; Bruyant et al., 1993), intracranial recording in epileptic patients (McCarthy et al., 1989; Puce et al., 1991; Paller et al., 1992; Baudena et al., 1995; Halgren et al., 1995a,b) and lesion studies in neurologic patients(Knight, 1984, 1997a; Knight et al., 1989; Yamaguchi and Knight, 1991b, 1992; Scabini, 1992).

AUTHORS

• Robert T. Knight

• Donatella Scabini

Date: 1998

DOI: 10.1097/00004691-199801000-00003

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Recollection and familiarity deficits in amnesia: convergence of remember-know, process dissociation, and receiver operating characteristic data

Authors:

• Andrew P. Yonelinas

• Neal E. A. Kroll

• Ian G. Dobbins

• Michele Lazzara

• Robert T. Knight

Date: 1998

PubMed: 9673991

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Abstract:

Previous studies using the process dissociation and the remember-know procedures led to conflicting conclusions regarding the effects of anterograde amnesia on recollection and familiarity. We argue that these apparent contradictions arose because different models were used to interpret the results and because differences in false-alarm rates between groups biased the estimates provided by those models. A reanalysis of those studies with a dual-process signal-detection model that incorporates response bias revealed that amnesia led to a pronounced reduction in recollection and smaller but consistent reduction in familiarity. To test the assumptions of the model and to further assess recognition deficits in amnesics, we examined receiver operating characteristics (ROCs) in amnesics and controls. The ROCs of the controls were curved and asymmetrical, whereas those of the amnesics were curved and symmetrical. The results supported the predictions of the model and indicated that amnesia was associated with deficits in both recollection and familiarity.

Cortico-limbic circuits and novelty: a review of EEG and blood flow data

Authors:

• Robert T. Knight

• Tsutomu Nakada

Date: 1998

PubMed: 9683327

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Abstract:

Novelty detection is a fundamental capacity of all mammalian nervous systems /64/. The ability to orient to unexpected events is critical for both survival and normal memory function /82/. The mechanisms whereby the brain detects and responds to novelty have become of increasing interest to neuroscientists. A review is provided of human electrophysiological and blood flow data focused on delineating the neural systems engaged by novelty. Electrophysiological recording of event-related potentials (ERPs) has shown that novel stimuli activate a distributed network involving prefrontal and posterior association cortex as well as the hippocampus /4,23,24,32,33,36,86,88/. Activation of this network facilitates subsequent memory for novel events /27/. Neural modeling provides additional support for a prominent role of novelty in normal memory function /43/. Blood flow studies employing PET and fMRI have also begun to define the neural regions activated by novelty. The blood flow data provide converging evidence on the role of the hippocampus and cortical association regions in the processing of novelty /30,66,75,76/. The results of the behavioral, ERP and blood flow research confirm that a distributed neocortical-limbic circuit is activated by stimulus novelty. These distributed circuits maintain a template of the recent past /74/. Deviations from the template activate a neocortical-limbic network facilitating behavioral response to and memory storage of novel events.

Frontal lobe contributions to theory of mind

Authors:

• Valerie E. Stone

• Simon Baron-Cohen

• Robert T. Knight

Date: 1998

PubMed: 9802997

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Abstract:

"Theory of mind," the ability to make inferences about others" mental states, seems to be a modular cognitive capacity that underlies humans" ability to engage in complex social interaction. It develops in several distinct stages, which can be measured with social reasoning tests of increasing difficulty. Individuals with Asperger"s syndrome, a mild form of autism, perform well on simpler theory of mind tests but show deficits on more developmentally advanced theory of mind tests. We tested patients with bilateral damage to orbito-frontal cortex (n = 5) and unilateral damage in left dorsolateral prefrontal cortex (n = 5) on a series of theory of mind tasks varying in difficulty. Bilateral orbito-frontal lesion patients performed similarly to individuals with Asperger"s syndrome, performing well on simpler tests and showing deficits on tasks requiring more subtle social reasoning, such as the ability to recognize a faux pas. In contrast, no specific theory of mind deficits were evident in the unilateral dorsolateral frontal lesion patients. The dorsolateral lesion patients had difficulty only on versions of the tasks that placed demands on working memory.

Unilateral medial temporal lobe memory impairment: type deficit, function deficit or both?

Authors:

• Ian G. Dobbins

• Neal E. A. Kroll

• Endel Tulving

• Robert T. Knight

• Michael S. Gazzaniga

Date: 1997

PubMed: 9539232

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Abstract:

Previous research has characterized memory deficits resulting from unilateral hippocampal system damage as 'material specific', suggesting that left damage results in verbal memory impairment with preservation of visuospatial function and the converse with right damage. Implicit within this hypothesis are the assumptions that the systems are independent and memory is lateralized for each type of material. To test the verbal component of this hypothesis, unilateral hippocampal lesion and commissurotomy patients were compared with controls on a multiple-list free-recall task. The material specific hypothesis predicts severe impairment only with left lesions; right lesions and commissurotomy patients should be only minimally impaired. However, secondary memory was compromised at immediate recall for all patient groups, with both unilateral groups showing comparable and severe verbal episodic memory deficits. Final testing across all lists also revealed severe impairment in commissurotomy patients. Finding both unilateral groups to be similarly impaired for verbal material is taken as evidence against a material specific deficit during this verbal episodic memory task. Although previous data suggest that left patients are considerably more impaired during some verbal tasks, this may not be specific to the material, but rather the combination of material and task demands. Implications for the material specific hypothesis are discussed.

Retrieval of old memories: the temporofrontal hypothesis

Authors:

• Neal E. A. Kroll

• Hans J Markowitsch

• Robert T. Knight

• D. Yves Von Cramon

Date: 1997

PubMed: 9278629

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Abstract:

Extensive neuropsychological testing is reported on two chronic patients with combined temporopolar and prefrontal damage, dominantly left-hemispheric, and, as control, one chronic patient with bi-hemispheric prefrontal damage. The principal finding is that combined temporofrontal damage, but not substantial prefrontal damage alone, results in marked retrograde memory deficits while leaving intelligence and new learning relatively unimpaired. Although their general world knowledge was good, the temporopolar patients demonstrated retrograde memory impairments on several tests of past events and faces of previously famous people. With respect to retrograde autobiographical memory, one of the temporopolar patients was severely impaired and the other was judged to be moderately impaired. The control patient appeared to be normal. These results, together with corresponding data from related single case and dynamic imaging studies, strongly support a crucial role of the temporofrontal junction area in the ecphory of old memories.

Impaired word-stem priming in patients with temporal-occipital lesions

Authors:

• Lynn Nielsen-Bohlman

• Michael Ciranni

• Arthur P. Shimamura

• Robert T. Knight

Date: 1997

PubMed: 9256373

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Abstract:

In the word-stem priming test, words are presented (e.g., MOTEL, PARADE), and later subjects are shown three-letter word stems (e.g., MOT, PAR) and asked to complete each stem with the first word that comes to mind. Word-stem priming, as well as other aspects of implicit memory, are intact in amnesic patients with medial temporal lesions. However, this form of priming has been shown to be impaired in patients with Alzheimer's disease, suggesting that damage to neocortical areas outside the medial temporal lobe contributes to impaired priming in these patients. To examine the role of posterior cortical areas on word-stem priming, we administered the test to patients with unilateral temporal-occipital lesions. Patients with temporal-occipital lesions exhibited significantly impaired priming on this test. The findings suggest a critical role of the inferior posterior neocortex in the expression of this form of implicit memory.

Prefrontal deficits in attention and inhibitory control with aging

Authors:

• Linda L. Chao

• Robert T. Knight

Date: 1997

PubMed: 9023433

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Abstract:

Event-related potentials and behavioral measures were obtained from young and elderly subjects while they performed two different auditory delayed match-to-sample tasks. In each experiment, subjects had to indicate whether an initial and a subsequent test sound were identical in two different conditions: one filled with distracting tone pips and one with no distractors. Electrophysiologically, elderly subjects had reduced attention-related activity over frontal regions. In addition, the distracting stimuli elicited an enhanced primary auditory evoked response in the elderly. The percentage of perseverative errors on the Wisconsin card sorting test, a putative measure of frontal lobe function, was positively correlated with the amplitude of the primary auditory evoked response in elderly subjects. Behaviorally, elderly subjects were impaired by distractors at long but not short delays. Taken together, these results suggest that increased distractibility and impaired sustained attention with aging may be due to altered prefrontal cortex function. These data support the loss of prefrontal suppression over the primary auditory regions with aging.

Distributed Cortical Network for Visual Attention

Authors:

• Robert T. Knight

Date: 1997

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Abstract:

The contribution of prefrontal and posterior association cortex to voluntary and involuntary visual attention was as sessed using electrophysiological techniques in patients with focal lesions in prefrontal (n = 11), temporal-parietal (n = 10), or lateral parietal cortex (n = 7). Subjects participated in a task requiring detection of designated target stimuli embedded in trains of repetitive stimuli. Infrequent and irrelevant novel visual stimuli were randomly interspersed with the target and background stimuli. Controls generated attention dependent N1 (170 msec) and N2 (243 msec) potentials maximal over extrastriate cortex. Anterior and posterior association cortex lesions reduced the amplitude of both the N1 and N2 potentials recorded over extrastriate cortex of the lesioned hemisphere. The pattern of results obtained reveals that an intrahemispheric network involving prefrontal and posterior association cortex modulates early visual processing in extrastriate regions. Voluntary target detection generated a parietal maximal P300 response (P3b) and irrelevant novel stimuli generated a more frontocentrally distributed P300 (P3a). Cortical lesions had differential effects on P3a and P3b potentials. The P3b was not significantly reduced in any cortical lesioned group. Conversely, the P3a was reduced by both prefrontal and posterior lesions with decrements most severe throughout the lesioned hemisphere. These data provide evidence that an association cortex network involving prefrontal and posterior regions is activated during orientation to novel events. The lack of a significant effect on the visual target P3b in patients with novelty P3a reductions supports the notion that different neural systems are engaged during voluntary vs involuntary atten-tion to visual stimuli.

Event-Related Potentials Differentiate the Effects of Aging on Word and Nonword Repetition in Explicit and Implicit Memory Tasks

Authors:

• Diane Swick

• Robert T. Knight

Date: 1997

PubMed: 9028023

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Abstract:

Explicit memory declines with age while implicit memory remains largely intact. These experiments extended behavioral findings by recording event-related potentials (ERPs) in young and elderly adults during repetition priming and recognition memory paradigms. Words and pronounceable nonwords repeated after 1 of 3 delays. Stimuli were categorized as either word-nonword or old-new. Repeated items elicited more positive-going potentials in both tasks. Hemispheric asymmetries for word and nonword processing were observed during lexical decision: Repetition effects were larger over the left hemisphere for words and over the right hemisphere for nonwords. For the young, ERP repetition effects were larger during recognition memory. For old adults, conversely, repetition produced more positive-going waveforms during lexical decision. The elderly had ERP and behavioral deficits at long recognition delays. ERP repetition effects in the elderly, like behavioral performance, were preserved in an implicit task but impaired in an explicit memory task.

Contribution of human hippocampal region to novelty detection

Authors:

• Robert T. Knight

Date: 1996

PubMed: 8805701

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Abstract:

The ability to respond to unexpected stimuli (the 'orienting response') is a fundamental characteristic of mammalian behaviour, but the brain mechanisms by which novelty is detected remain poorly defined. Electrophysiological recordings of scalp and intracranial event-related potentials (ERPs) have shown that novel stimuli activate a distributed network involving prefrontal and posterior association cortex. In addition, ERP and single-neuron recordings, as well as neuroimaging and modelling studies, have suggested that temporal cortical regions, including the hippocampus, are also involved. To examine further the role of the medial temporal lobe in novelty processing, I measured physiological responses to novel auditory and tactile stimuli in patients with damage to the posterior hippocampal region. In normal control subjects, unexpected novel stimuli produce a characteristic ERP signal, accompanied by an autonomic skin response. Both responses are reduced in hippocampal lesion patients, whereas the response to expected control stimuli is unaffected. Thus the hippocampal region, in addition to its known role in memory formation, is an essential component of the distributed limbic-cortical network that detects and responds to novel stimuli.

Age-related prefrontal alterations during auditory memory

Authors:

• Linda L. Chao

• Robert T. Knight

Date: 1996

PubMed: 8983036

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Abstract:

Event-related potentials were recorded from young and elderly subjects while they performed a modified auditory Sternberg memory task. Aging was associated with a decrease in frontal activation, suggesting that prefrontal alterations may be central to age-related impairments in auditory working memory. Young subjects showed significant serial position effects electrophysiologically, while elderly subjects showed no recency effects for P3 latency and no serial position effects for N4 and SFN amplitude. This finding, in combination with increased false alarm rates in the elderly, suggest that the two group of subjects employed different cortico-limbic circuits to perform the task.

An active, microfabricated, scalp electrode array for EEG recording

Authors:

• Babak Alizadeh-Taheri

• Rosemary L. Smith

• Robert T. Knight

Date: 1996

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Abstract:

We describe the microfabrication,packaging, and testing of an active,dry, scalp electroencephalogram (EEG) electrode. The electrode consists of a silicon sensor subs(tale and a custom circuit substrate (2 #m CMOS technology). A via-holelechnologyhas been developed using reactiveion etchingwilh SFJO2 gas mixture 10 make electricalcontacts between the sensor and circuit subs(rates. These substrates and batteries (power source) are then assembled in a custom package for testingon bench and human subjects.

Cohesion failure as a source of memory illusions

Authors:

• Neal E. A. Kroll

• Robert T. Knight

• Janet Metcalfe

• Elizabeth S. Wolf

• Endel Tulving

Date: 1996

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Abstract:

One source of ‘‘false’’ memories may be that often only memory fragments are retained. This would then result in a person being unable to distinquish a false conjunction, constructed of memory components, from what had been actually experienced. Experiment 1, employing two- syllable words in a continuous recognition paradigm, found that patients with left hippocampal damage classified more new verbal conjunctions as ‘‘old’’ than did normal subjects or patients with only right hippocampal damage. Experiment 2, employing simple face drawings in a study- test paradigm, found that patients with damage to either side of their hippocampal formation made more conjunction errors with pictorial stimuli than did normal subjects. The results are seen as supporting the hypothesis that binding is an important early step in the consolidation process and that the hippocampal system is a critical component of the neural system involved in the appropriate binding of memory components.

Impaired retrieval from remote memory in patients with frontal lobe damage

Authors:

• Jennifer A. Mangels

• Felicia B. Gershberg

• Arthur P. Shimamura

• Robert T. Knight

Date: 1996

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Abstract:

Patients with unilateral dorsolateral frontal lobe lesions and matched controls were given 2 tests of remote memory for public information, the Public Events Test and the Famous Faces Test. On both tests, the patients with frontal lobe lesions exhibited impaired recall for remote information. Recognition memory was relatively preserved. Provision of semantic and phonemic cues in the Famous Faces Test did not completely compensate for their recall deficit. These findings suggest that the remote memory impairment exhibited by frontal patients may be related to deficits in strategic search of memory. These deficits in retrieval from remote memory extend the array of memory deficits associated with damage to the frontal lobes.