Effects of frontal lobe damage on interference effects in working memory

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.

Prefrontal cortex regulates inhibition and excitation in distributed neural networks

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.

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

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.

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.

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.

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.

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

Authors:

• Diane Swick

• Robert T. Knight

Date: 1995

PubMed: 8742406

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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.

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

Authors:

• Diane Swick

• Robert T. Knight

Date: 1995

PubMed: 8843069

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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.