2007

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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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Emotionally arousing stimuli compete with attention to the left hemispace

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Authors:

  • Kaisa M. Hartikainen

  • Keith H. Ogawa

  • Maryam Soltani

  • Robert T. Knight

Date: 2007

PubMed: 18007189

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Abstract:

Rapid interaction of the emotional and attentional networks is critical for adaptive behavior. Here, we examined the effects of emotional stimulation on hemifield attention allocation using event-related potential and behavioral measures. Participants performed a visual-discrimination task on nonemotional targets presented randomly in the left or right hemifield. A brief task-irrelevant emotional (pleasant or unpleasant; 150-ms duration) or neutral picture was presented centrally 350 ms before the next target (150-ms duration). Unpleasant stimuli interfered with the left visual field attention capacity, slowing behavioral responses to attended left field stimuli. In keeping with the behavioral data, event-related potential responses to nonemotional attended left field stimuli were reduced over the right parietal regions when preceded by an unpleasant event. The results provide electrophysiological and behavioral evidence that unpleasant, emotionally arousing stimuli interfere with the right hemisphere-dependent attention capacity.

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Response anticipation and response conflict: an ERP and fMRI study

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Authors:

  • Jin Fan

  • Rachel Kolster

  • Jamshid Ghajar

  • Minah Suh

  • Robert T. Knight

  • Ranjeeta Sarkar

  • Bruce D. McCandliss

Date: 2007

PubMed: 17329424

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Abstract:

Response anticipation and response conflict processes are supported by executive control. However, few neuroimaging studies have attempted to study the relationship between these two processes in the same experimental session. In this study, we isolated brain activity associated with response anticipation (after a cue to prepare vs relax) and with response conflict (responding to a target with incongruent vs congruent flankers) and examined the independence and interaction of brain networks supporting these processes using event-related potentials (ERPs) and functional magnetic resonance imaging. Response anticipation generated a contingent negative variation ERP that correlated with shorter reaction times, and was associated with activation of a thalamo-cortico-striatal network, as well as increased gamma band power in frontal and parietal regions, and decreased spectral power in theta, alpha, and beta bands in most regions. Response conflict was associated with increased activation in the anterior cingulate cortex (ACC) and prefrontal cortex of the executive control network, with an overlap in activation with response anticipation in regions including the middle frontal gyrus, ACC, and superior parietal lobule. Although the executive control network showed increased activation in response to unanticipated versus anticipated targets, the response conflict effect was not altered by response anticipation. These results suggest that common regions of a dorsal frontoparietal network and the ACC are engaged in the flexible control of a wide range of executive processes, and that response anticipation modulates overall activity in the executive control network but does not interact with response conflict processing.

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Positive mood and sleep disturbance in acquired mania following temporal lobe damage

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Authors:

  • June Gruber

  • Julie N. Lemoine

  • Robert T. Knight

  • Allison G. Harvey

Date: 2007

PubMed: 17952718

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Abstract:

PRIMARY OBJECTIVE: To determine the mood profile and sleep functioning of a patient with left anterior temporal region damage characterized by post-operative symptoms of mania. METHODS AND PROCEDURES: In a structured clinical assessment, the patient's mood status, psychiatric diagnosis and sleep functioning - sleep onset latency, total sleep time, wake after sleep onset - were assessed. The sleep-wake cycle and daily mood was measured for 11 consecutive days. RESULTS: The patient met diagnostic criteria for bipolar disorder (excluding the requirement that the disturbance must not be due to a medical disorder) and delayed sleep-phase syndrome. Across 11 days, the patient exhibited elevated positive, but not negative, mood. Correlational analyses indicated a possible association between mood and sleep disturbance. CONCLUSIONS: This pattern of findings implicates the temporal lobe in positive mood regulation and sleep-related impairments.

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Mood and sleep dysregulation in acquired mania following temporal lobe damage

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Authors:

  • June Gruber

  • Julie N. Lemoine

  • Robert T. Knight

  • Allison G. Harvey

Date: 2007

PubMed: 17952718

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Abstract:

PRIMARY OBJECTIVE: To determine the mood profile and sleep functioning of a patient with left anterior temporal region damage characterized by post-operative symptoms of mania. METHODS AND PROCEDURES: In a structured clinical assessment, the patient's mood status, psychiatric diagnosis and sleep functioning - sleep onset latency, total sleep time, wake after sleep onset - were assessed. The sleep-wake cycle and daily mood was measured for 11 consecutive days. RESULTS: The patient met diagnostic criteria for bipolar disorder (excluding the requirement that the disturbance must not be due to a medical disorder) and delayed sleep-phase syndrome. Across 11 days, the patient exhibited elevated positive, but not negative, mood. Correlational analyses indicated a possible association between mood and sleep disturbance. CONCLUSIONS: This pattern of findings implicates the temporal lobe in positive mood regulation and sleep-related impairments.

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Cerebral responses to change in spatial location of unattended sounds

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Authors:

  • Leon Y. Deouell

  • Aaron S. Heller

  • Rafael Malach

  • Mark D'Esposito

  • Robert T. Knight

Date: 2007

DOI: 10.1016/j.neuron.2007.08.019

PubMed: 17880900

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Abstract:

The neural basis of spatial processing in the auditory cortex has been controversial. Human fMRI studies suggest that a part of the planum temporale (PT) is involved in auditory spatial processing, but it was recently argued that this region is active only when the task requires voluntary spatial localization. If this is the case, then this region cannot harbor an ongoing spa- tial representation of the acoustic environment. In contrast, we show in three fMRI experiments that a region in the human medial PT is sensitive to background auditory spatial changes, even when subjects are not engaged in a spatial lo- calization task, and in fact attend the visual mo- dality. During such times, this area responded to rare location shifts, and even more so when spatial variation increased, consistent with spatially selective adaptation. Thus, acoustic space is represented in the human PT even when sound processing is not required by the ongoing task.

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Analysis of oxygen metabolism implies a neural origin for the negative BOLD response in human visual cortex

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Authors:

  • Brian Pasley

  • B. A. Inglis

  • Ralph D. Freeman

Date: 2007

PubMed: 17113313

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Abstract:

The sustained negative blood oxygenation level-dependent (BOLD) response in functional MRI is observed universally, but its interpretation is controversial. The origin of the negative response is of fundamental importance because it could provide a measurement of neural deactivation. However, a substantial component of the negative response may be due to a non-neural hemodynamic artifact. To distinguish these possibilities, we have measured evoked BOLD, cerebral blood flow (CBF), and oxygen metabolism responses to a fixed visual stimulus from two different baseline conditions. One is a normal resting baseline, and the other is a lower baseline induced by a sustained negative response. For both baseline conditions, CBF and oxygen metabolism responses reach the same peak amplitude. Consequently, evoked responses from the negative baseline are larger than those from the resting baseline. The larger metabolic response from negative baseline presumably reflects a greater neural response that is required to reach the same peak amplitude as that from resting baseline. Furthermore, the ratio of CBF to oxygen metabolism remains approximately the same from both baseline states (approximately 2:1). This tight coupling between hemodynamic and metabolic components implies that the magnitude of any hemodynamic artifact is inconsequential. We conclude that the negative response is a functionally significant index of neural deactivation in early visual cortex.

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Spatial localization of cortical time-frequency dynamics

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Authors:

  • Sarang S. Dalal

  • Adrian G. Guggisberg

  • Erik Edwards

  • Kensuke Sekihara

  • Anne M. Findlay

  • Ryan T. Canolty

  • Robert T. Knight

  • Nicholas M. Barbaro

  • Heidi E. Kirsch

  • Srikantan S. Nagarajan

Date: 2007

PubMed: 18003115

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Abstract:

The spatiotemporal dynamics of cortical oscillations across human brain regions remain poorly understood because of a lack of adequately validated methods for reconstructing such activity from noninvasive electrophysiological data. We present a novel adaptive spatial filtering algorithm optimized for robust source time-frequency reconstruction from magnetoencephalography (MEG) and electroencephalography (EEG) data. The efficacy of the method is demonstrated with real MEG data from a self-paced finger movement task. The algorithm reliably reveals modulations both in the beta band (12-30 Hz) and a high gamma band (65-90 Hz) in sensorimotor cortex. The performance is validated by both across-subjects statistical comparisons and by intracranial electrocorticography (ECoG) data from two epilepsy patients. We also revealed observed high gamma activity in the cerebellum. The proposed algorithm is highly parallelizable and runs efficiently on modern high performance computing clusters. This method enables non-invasive five-dimensional imaging of space, time, and frequency activity in the brain and renders it applicable for widespread studies of human cortical dynamics.

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Theoretical sequelae of a chronic neglect and unawareness of prefrontotectal pathways in the human brain

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Authors:

  • Francisco Barceló

  • Robert T. Knight

Date: 2007

DOI: 10.1017/S0140525X07000921

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Abstract:

Attention research with prefrontal patients supports Merker's argument regarding the crucial role for the midbrain in higher cognition, through largely overlooked and misunderstood prefrontotectal connectivity. However, information theoretic analyses reveal that both exogenous (i.e., collicular) and endogenous (prefrontal) sources of information are responsible for large-scale context-sensitive brain dynamics, with prefrontal cortex being at the top of the hierarchy for cognitive control.

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An information theoretical approach to contextual processing in the human brain: evidence from prefrontal lesions

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Authors:

  • Francisco Barceló

  • Robert T. Knight

Date: 2007

DOI: 10.1093/cercor/bhm111

PubMed: 17726004

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Abstract:

Context shapes perception, thought, and action, but little is known about the neural mechanisms supporting these modulations. Here, we addressed the role of lateral prefrontal cortex (PFC) in context updating and maintenance from an information-theoretic perspective. Ten patients with PFC lesions and 10 age-matched controls responded to bilaterally displayed visual targets intermixed with repetitive and novel distracters in 2 different task contexts. In a predictable context, targets were always preceded by a novel event, whereas this temporal contingency was removed in an unpredictable context condition. We applied information theory to the analysis and interpretation of behavioral and electrophysiological data. The results revealed deficits in both the selection and the suppression of familiar versus novel information mainly observed at the visual hemifield contralateral to PFC damage due to disrupted frontocortical and frontosubcortical connectivity. The findings support a deficit in the representation of the temporal contingency between contextually related novel and familiar stimulation subsequent to lateral PFC damage.