Nina F. Dronkers

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Neuroplasticity of language in left-hemisphere stroke: evidence linking subsecond electrophysiology and structural connections

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ABSTRACT

The understanding of neuroplasticity following stroke is predominantly based on neuroimaging measures that cannot address the subsecond neurodynamics of impaired language processing. We combined behavioral and electrophysiological measures and structural-connectivity estimates to characterize neuroplasticity underlying successful compensation of language abilities after left-hemispheric stroke. We recorded the electroencephalogram from patients with stroke lesions to the left temporal lobe and from matched controls during context-driven word retrieval. Participants heard lead-in sentences that either constrained the final word (“He locked the door with the”) or not (“She walked in here with the”). The last word was shown as a picture to be named. Individual-participant analyses were conducted, focusing on oscillatory power as a subsecond indicator of a brain region’s functional neurophysiological computations. All participants named pictures faster following constrained than unconstrained sentences, except for two patients, who had extensive damage to the left temporal lobe. Left-lateralized alpha–beta oscillatory power decreased in controls pre-picture presentation for constrained relative to unconstrained contexts. In patients, the alpha–beta power decreases were observed with the same time course as in controls but were lateralized to the intact right hemisphere. The right lateralization depended on the probability of white-matter connections between the bilateral temporal lobes. The two patients who performed poorly behaviorally showed no alpha–beta power decreases. Our findings suggest that incorporating direct measures of neural activity into investigations of neuroplasticity can provide important neural markers to help predict language recovery, assess the progress of neurorehabilitation, and delineate targets for therapeutic neuromodulation.



AUTHORS

  • Vitoria Piai

  • Lars Meyer

  • Nina F. Dronkers

  • Robert T. Knight

Date: 2017

DOI: 10.1002/hbm.23581

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Spatiotemporal dynamics of word retrieval in speech production revealed by cortical high-frequency band activity

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ABSTRACT

Word retrieval is core to language production and relies on complementary processes: the rapid activation of lexical and conceptual representations and word selection, which chooses the correct word among semantically related competitors. Lexical and conceptual activation is measured by semantic priming. In contrast, word selection is indexed by semantic interference and is hampered in semantically homogeneous (HOM) contexts. We examined the spatiotemporal dynamics of these complementary processes in a picture naming task with blocks of semantically heterogeneous (HET) or HOM stimuli. We used electrocorticography data obtained from frontal and temporal cortices, permitting detailed spatiotemporal analysis of word retrieval processes. A semantic interference effect was observed with naming latencies longer in HOM versus HET blocks. Cortical response strength as indexed by high-frequency band (HFB) activity (70–150 Hz) amplitude revealed effects linked to lexical-semantic activation and word selection observed in widespread regions of the cortical mantle. Depending on the subsecond timing and cortical region, HFB indexed semantic interference (i.e., more activity in HOM than HET blocks) or semantic priming effects (i.e., more activity in HET than HOM blocks). These effects overlapped in time and space in the left posterior inferior temporal gyrus and the left prefrontal cortex. The data do not support a modular view of word retrieval in speech production but rather support substantial overlap of lexical-semantic activation and word selection mechanisms in the brain.



AUTHORS

  • Stephanie Ries

  • Rhummit K. Dhillon

  • Alex Clarke

  • David King-Stephens

  • Kenneth Laxer

  • Peter Weber

  • Rachel A. Kuperman

  • Kurtis I. Auguste

  • Peter Brunner

  • Gerwin Schalk

  • Jack J. Lin

  • Josef Parvizi

  • Nathan E. Crone

  • Nina F. Dronkers

  • Robert T. Knight

Date: 2017

DOI: 10.1073/pnas.1620669114

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Direct brain recordings reveal hippocampal rhythm underpinnings of language processing

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ABSTRACT

Language is classically thought to be supported by perisylvian cortical regions. Here we provide intracranial evidence linking the hippocampal complex to linguistic processing. We used direct recordings from the hippocampal structures to investigate whether theta oscillations, pivotal in memory function, track the amount of contextual linguistic information provided in sentences. Twelve participants heard sentences that were either constrained (“She locked the door with the”) or unconstrained (“She walked in here with the”) before presentation of the final word (“key”), shown as a picture that participants had to name. Hippocampal theta power increased for constrained relative to unconstrained contexts during sentence processing, preceding picture presentation. Our study implicates hippocampal theta oscillations in a language task using natural language associations that do not require memorization. These findings reveal that the hippocampal complex contributes to language in an active fashion, relating incoming words to stored semantic knowledge, a necessary process in the generation of sentence meaning.


AUTHORS

  • Vitoria Piai

  • Kristopher L. Anderson

  • Jack J. Lin

  • Callum Dewar

  • Josef Parvizi

  • Nina F. Dronkers

  • Robert T. Knight

Date: 2016

DOI: www.pnas.org/cgi/doi/10.1073/pnas.1603312113

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Choosing words: left hemisphere, right hemisphere, or both? Perspective on the lateralization of word retrieval

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ABSTRACT

Language is considered to be one of the most lateralized human brain functions. Left hemisphere dominance for language has been consistently confirmed in clinical and experimental settings and constitutes one of the main axioms of neurology and neuroscience. However, functional neuroimaging studies are finding that the right hemisphere also plays a role in diverse language functions. Critically, the right hemisphere may also compensate for the loss or degradation of language functions following extensive stroke-induced damage to the left hemisphere. Here, we review studies that focus on our ability to choose words as we speak. Although fluidly performed in individuals with intact language, this process is routinely compromised in aphasic patients. We suggest that parceling word retrieval into its subprocesses—lexical activation and lexical selection—and examining which of these can be compensated for after left hemisphere stroke can advance the understanding of the lateralization of word retrieval in speech production. In particular, the domain-general nature of the brain regions associated with each process may be a helpful indicator of the right hemisphere’s propensity for compensation.






AUTHORS

  • Stephanie Ries

  • Nina F. Dronkers

  • Robert T. Knight

Date: 2016

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Specifying the role of the left prefrontal cortex in word selection

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Abstract:

Word selection allows us to choose words during language production. This is often viewed as a competitive process wherein a lexical representation is retrieved among semantically-related alternatives. The left prefrontal cortex (LPFC) is thought to help overcome competition for word selection through top-down control. However, whether the LPFC is always necessary for word selection remains unclear. We tested 6 LPFC-injured patients and controls in two picture naming paradigms varying in terms of item repetition. Both paradigms elicited the expected semantic interference effects (SIE), reflecting interference caused by semantically-related representations in word selection. However, LPFC patients as a group showed a larger SIE than controls only in the paradigm involving item repetition. We argue that item repetition increases interference caused by semantically-related alternatives, resulting in increased LPFC-dependent cognitive control demands. The remaining network of brain regions associated with word selection appears to be sufficient when items are not repeated.

Authors:

  • Stephanie Ries

  • C.R. Karzmark

  • E. Navarrete

  • Robert T. Knight

  • Nina F. Dronkers

Date: 2015

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Redefining the role of Broca’s area in speech

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Authors:

  • Adeen Flinker

  • Anna Korzeniewska

  • Avgusta Shestyuk

  • Piotr Franaszczuk

  • Nina F. Dronkers

  • Robert T. Knight

  • Nathan E. Crone

Date: 2015

DOI: 10.1073/pnas.1414491112

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Abstract:

For over a century neuroscientists have debated the dynamics by which human cortical language networks allow words to be spoken. Although it is widely accepted that Broca’s area in the left inferior frontal gyrus plays an important role in this process, it was not possible, until recently, to detail the timing of its recruitment relative to other language areas, nor how it interacts with these areas during word production. Using direct cortical surface recordings in neurosurgical patients, we studied the evolution of activity in cortical neuronal populations, as well as the Granger causal interactions between them. We found that, during the cued production of words, a temporal cascade of neural activity proceeds from sensory representations of words in temporal cortex to their corresponding articulatory gestures in motor cortex. Broca’s area mediates this cascade through reciprocal interactions with temporal and frontal motor regions. Contrary to classic notions of the role of Broca’s area in speech, while motor cortex is activated during spoken responses, Broca’s area is surprisingly silent. Moreover, when novel strings of articulatory gestures must be produced in response to non- word stimuli, neural activity is enhanced in Broca’s area, but not in motor cortex. These unique data provide evidence that Broca’s area coordinates the transformation of information across large-scale cortical networks involved in spoken word production. In this role, Broca’s area formulates an appropriate articulatory code to be implemented by motor cortex.

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Double Dissociation of the roles of the left and right prefrontal cortices in anticipatory regulation of action

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Authors:

  • Stephanie Ries

  • Ian Greenhouse

  • Nina F. Dronkers

  • Kathleen Y. Haaland

  • Robert T. Knight

Date: 2014

DOI: 10.1016/j.neuropsychologia.2014.08.026

PubMed: 25201047

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Abstract:

Recent actions can benefit or disrupt our current actions and the prefrontal cortex (PFC) is thought to play a major role in the regulation of these actions before they occur. The left PFC has been associated with overcoming interference from past events in the context of language production and working memory. The right PFC, and especially the right IFG, has been associated with preparatory inhibition processes. But damage to the right PFC has also been associated with impairment in sustaining actions in motor intentional disorders. Moreover, bilateral dorsolateral PFC has been associated with the ability to maintain task-sets, and improve the performance of current actions based on previous experience. However, potential hemispheric asymmetries in anticipatory regulation of action have not yet been delineated. In the present study, patients with left (n=7) vs. right (n=6) PFC damage due to stroke and 14 aged- and education-matched controls performed a picture naming and a verbal Simon task (participants had to say "right" or "left" depending on the color of the picture while ignoring its position). In both tasks, performance depended on the nature of the preceding trial, but in different ways. In the naming task, performance decreased if previous pictures were from the same rather than from different semantic categories (i.e., semantic interference effect). In the Simon task, performance was better for both compatible (i.e., response matching the position of the stimulus) and incompatible trials when preceded by a trial of the same compatibility (i.e. Gratton effect) relative to sequential trials of different compatibility. Left PFC patients were selectively impaired in picture naming; they had an increased semantic interference effect compared to both right PFC patients and aged-matched controls. Conversely, right PFC patients were selectively impaired in the Simon task compared to controls or left PFC patients; they showed no benefit when sequential trials were compatible (cC vs. iC trials) or a decreased Gratton effect. These results provide evidence for a double dissociation between left and right PFC in the anticipatory regulation of action. Our results are in agreement with a preponderant role of the left PFC in overcoming proactive interference from competing memory representations and provide evidence that the right PFC, plays a role in sustaining goal-directed actions consistent with clinical data in right PFC patients with motor intentional disorders.

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Role of the lateral prefrontal cortex in speech monitoring

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Authors:

  • Stephanie Ries

  • Kira Xie

  • Kathleen Y. Haaland

  • Nina F. Dronkers

  • Robert T. Knight

Date: 2013

DOI: 10.3389/fnhum.2013.00703

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Abstract:

The role of lateral prefrontal cortex (LPFC) in speech monitoring has not been delineated. Recent work suggests that medial frontal cortex (MFC) is involved in overt speech monitoring initiated before auditory feedback. This mechanism is reflected in an event- related potential (ERP), the error negativity (Ne), peaking within 100 ms after vocal-onset. Critically, in healthy individuals the Ne is sensitive to the accuracy of the response; it is larger for error than correct trials. By contrast, patients with LPFC damage are impaired in non-verbal monitoring tasks showing no amplitude difference between the Ne measured in correct vs. error trials. Interactions between the LPFC and the MFC are assumed to play a necessary role for normal action monitoring. We investigated whether the LPFC was involved in speech monitoring to the same extent as in non-linguistic actions by comparing performance and EEG activity in patients with LPFC damage and in aged-matched controls performing linguistic (Picture Naming) and non-linguistic (Simon) tasks. Controls did not produce enough errors to allow the comparison of the Ne or other ERP in error vs. correct trials. PFC patients had worse performance than controls in both tasks, but their Ne was larger for error than correct trials only in Naming. This task-dependent pattern can be explained by LPFC-dependent working-memory requirements present in non-linguistic tasks used to study action monitoring but absent in picture naming. This suggests that LPFC may not be necessary for speech monitoring as assessed by simple picture naming. In addition, bilateral temporal cortex activity starting before and peaking around vocal-onset was observed in LPFC and control groups in both tasks but was larger for error than correct trials only in Naming, suggesting the temporal cortex is associated with on-line monitoring of speech specifically when access to lexical representations is necessary.

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Spatiotemporal dynamics of word processing in the human brain

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Authors:

  • Ryan T. Canolty

  • Maryam Soltani

  • Sarang S. Dalal

  • Erik Edwards

  • Nina F. Dronkers

  • Srikantan S. Nagarajan

  • Heidi E. Kirsch

  • Nicholas M. Barbaro

  • Robert T. Knight

Date: 2007

PubMed: 18982128

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Abstract:

We examined the spatiotemporal dynamics of word processing by recording the electrocorticogram (ECoG) from the lateral frontotemporal cortex of neurosurgical patients chronically implanted with subdural electrode grids. Subjects engaged in a target detection task where proper names served as infrequent targets embedded in a stream of task-irrelevant verbs and nonwords. Verbs described actions related to the hand (e.g, throw) or mouth (e.g., blow), while unintelligible nonwords were sounds which matched the verbs in duration, intensity, temporal modulation, and power spectrum. Complex oscillatory dynamics were observed in the delta, theta, alpha, beta, low, and high gamma (HG) bands in response to presentation of all stimulus types. HG activity (80-200 Hz) in the ECoG tracked the spatiotemporal dynamics of word processing and identified a network of cortical structures involved in early word processing. HG was used to determine the relative onset, peak, and offset times of local cortical activation during word processing. Listening to verbs compared to nonwords sequentially activates first the posterior superior temporal gyrus (post-STG), then the middle superior temporal gyrus (mid-STG), followed by the superior temporal sulcus (STS). We also observed strong phase-locking between pairs of electrodes in the theta band, with weaker phase-locking occurring in the delta, alpha, and beta frequency ranges. These results provide details on the first few hundred milliseconds of the spatiotemporal evolution of cortical activity during word processing and provide evidence consistent with the hypothesis that an oscillatory hierarchy coordinates the flow of information between distinct cortical regions during goal-directed behavior.

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Differential effects of semantic and identity priming in patients with left and right hemisphere lesions

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Authors:

  • Avishai Henik

  • Nina F. Dronkers

  • Robert T. Knight

  • Alicia Osimani

Date: 1993

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Abstract:

Patients with single brain lesions in the anterior or posterior left and right hemispheres and a group of controls were studied in two priming experiments. The first experiment employed associative pairs (DOCTOR-NURSE) and the second employed identical pairs (NURSE-nurse). Short and long prime-target stimulus onset asynchronies (SOAs) (i.e., 250 and 1850 msec) were manipulated within block in both experiments. In the first experiment, patients with left hemisphere injury showed a deficient priming effect while patients with right hemisphere injury and controls showed a normal pattern. In contrast, all groups showed an identity priming effect in the second experiment. These results indicate that while entries in the mental lexicon are available for the groups of patients studied, the spread of activation to related concepts in this lexicon is disrupted in the left hemisphere-damaged group.

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Potential of telephonic and television technology for appraising and diagnosing neurogenic communication disorders in remote settings

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Authors:

  • Robert T. Wertz

  • Nina F. Dronkers

  • Ellen Bernstein-Ellis

  • Lisa K. Sterling

  • Yvonne Shubitowski

  • Roberta Elman

  • Gregory K Shenaut

  • Robert T. Knight

  • Jon L. Deal

Date: 1992

External link to publication

Abstract:

Telephonic and television technology was employed in a simulation study to determine its potential for providing appraisal and diagnosis of patients who suffer neurogenic communication disorders and reside in remote settings. Traditional, face-to-face appraisal and diagnosis was compared with appraisal and diagnosis by closed circuit television and computer-controlled video laserdisc over the telephone. Significant agreement in diagnosis among the three appraisal conditions and essentially the same performance on appraisal measures in all conditions suggests either closed circuit television or computer-controlled video laserdisc over the telephone could be substituted for traditional, face-to-face appraisal and diagnosis to reach patients who reside where traditional services do not exist.

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Right-Sided Neglect in a Left-Hander: Evidence for Reversed Hemispheric Specialization of Attention Capacity

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Authors:

  • Nina F. Dronkers

  • Robert T. Knight

Date: 1988

PubMed: 2739895

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Abstract:

Severe hemi-spatial neglect, anosognosia, contralateral hypokinesia, aprosodia, and visual-spatial constructive difficulties--typically seen in right-handers with right hemisphere lesions--were observed in a left-handed patient with an acute left frontal cortical and subcortical infarct. There was no evidence of accompanying aphasia and the neglect syndrome gradually resolved over a 2-week period. The assumption by the left hemisphere of a classic right hemisphere attention, visuo-spatial and prosodic superiority may represent a case of reversed hemispheric specialization.

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Appraisal and diagnosis of neurogenic communicative disorders in remote settings

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Authors:

  • Robert T. Wertz

  • Nina F. Dronkers

  • Ellen Bernstein-Ellis

  • Yvonne Shubitowski

  • Roberta Elman

  • Gregory K Shenaut

  • Robert T. Knight

  • Jon L. Deal

Date: 1987

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Abstract:

Patients who suffer neurogenic communication disorders and reside in remote settings either do not receive services or they must travel long distances or become inpatients for extended periods. No services is unacceptable, because all patients merit appraisal and a diagnosis, and many respond to treatment with improvement in their communication. Traveling long distances for services is unacceptable, because it is expensive, inconvenient, may be contraindicated by the patient's medical condition, requires a means of transportation which often does not exist, and must be frequent and protracted. Hospitalization is also unacceptable, because the communication disorder does not necessitate hospitalization, it usurps a bed, carries a patient beyond DRG length-of-stay criteria, removes him or her from the home environment, and is expensive. There is a need to develop means for managing patients who live in remote settings.

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Appraisal and diagnosis of neurogenic communicative disorders in remote settings

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Authors:

  • Robert T. Wertz

  • Nina F. Dronkers

  • Ellen Bernstein-Ellis

  • Yvonne Shubitowski

  • Roberta Elman

  • Gregory K Shenaut

  • Robert T. Knight

  • Jon L. Deal

Date: 1987

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Right-sided neglect in a left-hander: Evidence for reversed hemispheric specialization of attention capacity

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Abstract

Severe hemi-spatial neglect, anosognosia, contralateral hypokinesia, aprosodia, and visual-spatial constructive difficulties—typically seen in right-handers with right hemisphere lesions—were observed in a left-handed patient with an acute left frontal cortical and subcortical infarct. There was no evidence of accompanying aphasia and the neglect syndrome gradually resolved over a 2-week period. The assumption by the left hemisphere of a classic right hemisphere attention, visuo-spatial and prosodic superiority may represent a case of reversed hemispheric specialization.

Authors

  • Nina F. Dronkers

  • Robert T. Knight

Date: 1985

DOI: 10.1016/0028-3932(89)90118-8

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