Effective Connectivity of the Fronto-parietal Network during Attentional Control

Authors:

• Liang Wang

• Xun Liu

• Kevin Guise

• Robert T. Knight

• Jamshid Ghajar

• Jin Fan

Date: 2010

DOI: 10.1162/jocn.2009.21210

PubMed: 19301995

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Abstract:

The ACC, the dorsolateral prefrontal cortex (DLPFC), and the parietal cortex near/along the intraparietal sulcus (IPS) are members of a network subserving attentional control. Our recent study revealed that these regions participate in both response anticipation and conflict processing. However, little is known about the relative contribution of these regions in attentional control and how the dynamic interactions among these regions are modulated by detection of predicted versus unpredicted targets and conflict processing. Here, we examined effective connectivity using dynamic causal modeling among these three regions during a flanker task with or without a target onset cue. We compared various models in which different connections among ACC, DLPFC, and IPS were modulated by bottom-up stimulus-driven surprise and top-down conflict processing using Bayesian model selection procedures. The most optimal of these models incorporated contextual modulation that allowed processing of unexpected (surprising) targets to mediate the influence of the IPS over ACC and DLPFC and conflict processing to mediate the influence of ACC and DLPFC over the IPS. This result suggests that the IPS plays an initiative role in this network in the processing of surprise targets, whereas ACC and DLPFC interact with each other to resolve conflict through attentional modulation implemented via the IPS.

Cortical spatiotemporal dynamics underlying phonological target detection in humans

Authors:

• Edward F. Chang

• Erik Edwards

• Srikantan S. Nagarajan

• Noa Fogelson

• Sarang S. Dalal

• Ryan T. Canolty

• Heidi E. Kirsch

• Nicholas M. Barbaro

• Robert T. Knight

Date: 2010

DOI: 10.1162/jocn.2010.21466

PubMed: 20465359

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Abstract:

Selective processing of task-relevant stimuli is critical for goal-directed behavior. We used electrocorticography to assess the spatio-temporal dynamics of cortical activation during a simple phonological target detection task, in which subjects press a button when a prespecified target syllable sound is heard. Simultaneous surface potential recordings during this task revealed a highly ordered temporal progression of high gamma (HG, 70–200 Hz) activity across the lateral hemisphere in less than 1 sec. The sequence demonstrated concurrent regional sensory processing of speech syllables in the posterior superior temporal gyrus (STG) and speech motor cortex, and then transitioned to sequential task-dependent processing from prefrontal cortex (PFC), to the final motor response in the hand sensorimotor cortex. STG activation was modestly enhanced for target over nontarget sounds, supporting a selective gain mechanism in early sensory processing, whereas PFC was entirely selective to targets, supporting its role in guiding response behavior. These results reveal that target detection is not a single cognitive event, but rather a process of progressive target selectivity that involves large-scale rapid parallel and serial processing in sensory, cognitive, and motor structures to support goal-directed human behavior.

Hemicraniectomy: A New Model for Human Electrophysiology with High Spatio-temporal Resolution

Authors:

• Bradley Voytek

• Lavi Secundo

• Aurélie Bidet-Caulet

• Shirley I. Stiver

• Alisa D. Gean

• Geoffrey T. Manley

• Robert T. Knight

Date: 2010

DOI: 10.1162/jocn.2009.21384

PubMed: 19925193

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Abstract:

Human electrophysiological research is generally restricted to scalp EEG, magneto-encephalography, and intracranial electrophysiology. Here we examine a unique patient cohort that has undergone decompressive hemicraniectomy, a surgical procedure wherein a portion of the calvaria is removed for several months during which time the scalp overlies the brain without intervening bone. We quantify the differences in signals between electrodes over areas with no underlying skull and scalp EEG electrodes over the intact skull in the same subjects. Signals over the hemicraniectomy have enhanced amplitude and greater task-related power at higher frequencies (60–115 Hz) compared with signals over skull. We also provide evidence of a metric for trial-by-trial EMG/EEG coupling that is effective over the hemicraniectomy but not intact skull at frequencies >60 Hz. Taken together, these results provide evidence that the hemicraniectomy model provides a means for studying neural dynamics in humans with enhanced spatial and temporal resolution.

Cortical representation of ipsilateral arm movements in monkey and man

Authors:

• Karunesh Ganguly

• Lavi Secundo

• Gireeja Ranade

• Amy Orsborn

• Edward F. Chang

• Dragan F. Dimitrov

• Johnathan D. Wallis

• Nicholas M. Barbaro

• Robert T. Knight

• Jose M. Carmena

Date: 2009

DOI: 10.1523/JNEUROSCI.2471-09.2009

PubMed: 19828809

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Abstract:

A fundamental organizational principle of the primate motor system is cortical control of contralateral limb movements. Motor areas also appear to play a role in the control of ipsilateral limb movements. Several studies in monkeys have shown that individual neurons in primary motor cortex (M1) may represent, on average, the direction of movements of the ipsilateral arm. Given the increasing body of evidence demonstrating that neural ensembles can reliably represent information with a high temporal resolution, here we characterize the distributed neural representation of ipsilateral upper limb kinematics in both monkey and man. In two macaque monkeys trained to perform center-outreaching movements, we found thatthe ensemble spiking activity in M1 could continuously representipsilateral limb position. Interestingly, this representation was more correlated with joint angles than hand position. Using bilateral electromyography recordings, we excluded the possibility that postural or mirror movements could exclusively account for these findings. In addition, linear methods could decode limb position from cortical field potentials in both monkeys. We also found that M1 spiking activity could control a biomimetic brain–machine interface reflecting ipsilateral kinematics. Finally, we recorded cortical field potentials from three human subjects and also consistently found evidence of a neural representation for ipsilateral movement parameters. Together, our results demonstrate the presence of a high-fidelity neural representation for ipsilateral movement and illustrates that it can be successfully incorporated into a brain–machine interface.

Multimodal effects of local context on target detection: evidence from P3b

Authors:

• Noa Fogelson

• Xue Wang

• Jeffrey B. Lewis

• Mark M. Kishiyama

• Mingzhou Ding

• Robert T. Knight

Date: 2009

DOI: 10.1162/jocn.2009.21071

PubMed: 18702574

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Abstract:

We used the P300 component to investigate how changes in local context influenced the ability to detect target stimuli. Local context was defined as the occurrence of a short predictive series of stimuli before delivery of a target event. EEG was recorded in 12 subjects during auditory and visual sessions. Stimuli were presented in the center of the auditory and visual field and consisted of 15% targets (1000 Hz tone or downward facing triangle) and 85% of equal amounts of three types of standards (1500, 2000, and 2500 Hz tones or triangles facing left, upward, and right). Recording blocks consisted of targets preceded by either randomized sequences of standards or by sequences including a three-standard predictive sequence signaling the occurrence of a subsequent target event. Subjects pressed a button in response to targets. Peak target P300 (P3b) amplitude and latency were evaluated for targets after predictive and nonpredictive sequences using conventional averaging and a novel single-trial analysis procedure. Reaction times were shorter for predictable targets than for nonpredicted targets. P3b latency was shorter for predicted targets than for nonpredictive targets, and there were no significant P3b amplitude differences between predicted and random targets, as determined by both conventional averaging and single-trial analysis. Comparable effects on amplitude and latency were observed in both the auditory and visual modalities. The results indicate that local context has differential effects on P3b amplitude and latency, and exerts modality-independent effects on cognitive processing.

Consciousness Unchained: Ethical Issues and the Vegetative and Minimally Conscious State

Authors:

• Robert T. Knight

Date: 2008

DOI: 10.1080/15265160802414524

PubMed: 18853369

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Prefrontal cortex is critical for contextual processing: evidence from brain lesions

Authors:

• Noa Fogelson

• Mona Shah

• Robert T. Knight

Date: 2009

DOI: 10.1093/brain/awp230

PubMed: 19713281

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Abstract:

We investigated the role of prefrontal cortex (PFC) in local contextual processing using a combined event-related potentials and lesion approach. Local context was defined as the occurrence of a short predictive series of visual stimuli occurring before delivery of a target event. Targets were preceded by either randomized sequences of standards or by sequences including a three-stimulus predictive sequence signalling the occurrence of a subsequent target event. PFC lesioned patients were impaired in their ability to use local contextual information. The response time for controls revealed a larger benefit for predictable targets than for random targets relative to PFC patients. PFC patients had reduced amplitude of a context-dependent positivity and failed to generate the expected P3b latency shift between predictive and non-predictive targets. These findings show that PFC patients are unable to utilize predictive local context to guide behaviour, providing evidence for a critical role of PFC in local contextual processing.

Prefrontal cortex is critical for contextual processing: evidence from brain lesions

Authors:

• Noa Fogelson

• Mona Shah

• Robert T. Knight

Date: 2009

DOI: 10.1093/brain/awp230

PubMed: 19713281

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Abstract:

We investigated the role of prefrontal cortex (PFC) in local contextual processing using a combined event-related potentials and lesion approach. Local context was defined as the occurrence of a short predictive series of visual stimuli occurring before delivery of a target event. Targets were preceded by either randomized sequences of standards or by sequences including a three-stimulus predictive sequence signalling the occurrence of a subsequent target event. PFC lesioned patients were impaired in their ability to use local contextual information. The response time for controls revealed a larger benefit for predictable targets than for random targets relative to PFC patients. PFC patients had reduced amplitude of a context-dependent positivity and failed to generate the expected P3b latency shift between predictive and non-predictive targets. These findings show that PFC patients are unable to utilize predictive local context to guide behaviour, providing evidence for a critical role of PFC in local contextual processing.

Ipsilateral trajectory control is related to contralesional paralysis after left hemisphere damage

Authors:

• Kathleen Y. Haaland

• Sydney Y. Schaefer

• Robert T. Knight

• John Adair

• Alvaro Magalhaes

• Joseph Sadek

• Robert L. Sainburg

Date: 2009

DOI: 10.1007/s00221-009-1836-z

PubMed: 19479246

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Abstract:

We have recently shown ipsilateral dynamic deficits in trajectory control are present in left hemisphere damaged (LHD) patients with paresis, as evidenced by impaired modulation of torque amplitude as response amplitude increases. The purpose of the current study is to determine if these ipsilateral deficits are more common with contralateral hemiparesis and greater damage to the motor system, as evidenced by structural imaging. Three groups of right-handed subjects (healthy controls, LHD stroke patients with and without upper extremity paresis) performed single-joint elbow movements of varying amplitudes with their left arm in the left hemispace. Only the paretic group demonstrated dynamic deficits characterized by decreased modulation of peak torque (reflected by peak acceleration changes) as response amplitude increased. These results could not be attributed to lesion volume or peak velocity as neither variable differed across the groups. However, the paretic group had damage to a larger number of areas within the motor system than the non-paretic group suggesting that such damage increases the probability of ipsilesional deficits in dynamic control for modulating torque amplitude after left hemisphere damage.

Temporal characteristics of audiovisual information processing

Authors:

• Galit Fuhrmann Alpert

• Grit Hein

• Nancy Tsai

• Marcus J. Naumer

• Robert T. Knight

Date: 2008

DOI: 10.1523/JNEUROSCI.5039-07.2008

PubMed: 18480290

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Abstract:

In complex natural environments, auditory and visual information often have to be processed simultaneously. Previous functional magnetic resonance imaging (fMRI) studies focused on the spatial localization of brain areas involved in audiovisual (AV) information processing, but the temporal characteristics of AV information flow in these regions remained unclear. In this study, we used fMRI and a novel information–theoretic approach to study the flow of AV sensory information. Subjects passively perceived sounds and images of objects presented either alone or simultaneously. Applying the measure of mutual information, we computed for each voxel the latency in which the blood oxygenation level-dependent signal had the highest information content about the preceding stimulus. The results indicate that, after AV stimulation, the earliest informative activity occurs in right Heschl’s gyrus, left primary visual cortex, and the posterior portion of the superior temporal gyrus, which is known as a region involved in object-related AV integration. Informative activity in the anterior portion of superior temporal gyrus, middle temporal gyrus, right occipital cortex, and inferior frontal cortex was found at a later latency. Moreover, AV presentation resulted in shorter latencies in multiple cortical areas compared with isolated auditory or visual presentation. The results provide evidence for bottom-up processing from primary sensory areas into higher associ- ation areas during AV integration in humans and suggest that AV presentation shortens processing time in early sensory cortices.

Novelty Enhancements in Memory Are Dependent on Lateral Prefrontal Cortex

Authors:

• Mark M. Kishiyama

• Andrew P. Yonelinas

• Robert T. Knight

Date: 2009

DOI: 10.1523/JNEUROSCI.5507-08.2009

PubMed: 19553451

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Abstract:

Physiological evidence indicates thatseveral brain regions, including the medial temporal lobes and prefrontal cortex (PFC), are involved in processing events that are novel or distinctive in their immediate context. However, behavioral studies that investigate whether these regions are critical for producing stimulus novelty advantages in memory are limited. For example, evidence from an animal lesion study indicated that the PFC is involved in stimulus novelty effects, but this has not been examined in humans. In the current study, we used a von Restorff novelty paradigm to testa large cohortof lateral PFC patients (n
16). We found thatpatients with lateral PFC damage were impaired in recollection- and familiarity-based recognition, and they did not exhibit a normal memory advantage for novel compared with non-novel items. These results provide neuropsychological evidence supporting a key role for the lateral PFC in producing stimulus novelty advantages in memory.

Comparison of time-frequency responses and the event related potential to auditory speech stimuli in the human cortex

Authors:

• Erik Edwards

• Maryam Soltani

• Won Kim

• Sarang S. Dalal

• Srikantan S. Nagarajan

• Mitchel S. Berger

• Robert T. Knight

Date: 2009

DOI: 10.1152/jn.90954.2008

PubMed: 19439673

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Abstract:

Comparison of time–frequency responses and the event-related potential to auditory speech stimuli in human cortex. J Neurophysiol 102: 377–386, 2009. First published May 13, 2009; doi:10.1152/jn.90954.2008. We recorded the electrocorticogram directly from the exposed cortical surface of awake neurosurgical patients during the presentation of auditory syllable stimuli. All patients were unanesthetized as part of a language-mapping procedure for subsequent left-hemisphere tumor resection. Time–frequency analyses showed significant high-gamma (
high : 70 –160 Hz) responses from the left superior temporal gyrus, but no reliable response from the left inferior frontal gyrus. Alpha suppression (: 7–14 Hz) and event-related potential responses exhibited a more widespread topography. Across electrodes, the  suppression from 200 to 450 ms correlated with the preceding (50 –200 ms)
high increase. The results are discussed in terms of the different physiological origins of these electrocortical signals.

Intermodal auditory, visual, and tactile attention modulates early stages of neural processing

Authors:

• Christina M. Karns

• Robert T. Knight

Date: 2009

DOI: 10.1162/jocn.2009.21037

PubMed: 18564047

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Abstract:

We used event-related potentials (ERPs) and gamma band oscillatory responses (GBRs) to examine whether intermodal attention operates early in the auditory, visual, and tactile modalities. To control for the effects of spatial attention, we spatially coregistered all stimuli and varied the attended modality across counterbalanced blocks in an intermodal selection task. In each block, participants selectively responded to either auditory, visual, or vibrotactile stimuli from the stream of intermodal events. Auditory and visual ERPs were modulated at the latencies of early cortical processing, but attention manifested later for tactile ERPs. For ERPs, auditory processing was modulated at the latency of the Na (29 msec), which indexes early cortical or thalamocortical processing and the subsequent P1 (90 msec) ERP components. Visual processing was modulated at the latency of the early phase of the C1 (62-72 msec) thought to be generated in the primary visual cortex and the subsequent P1 and N1 (176 msec). Tactile processing was modulated at the latency of the N160 (165 msec) likely generated in the secondary association cortex. Intermodal attention enhanced early sensory GBRs for all three modalities: auditory (onset 57 msec), visual (onset 47 msec), and tactile (onset 27 msec). Together, these results suggest that intermodal attention enhances neural processing relatively early in the sensory stream independent from differential effects of spatial and intramodal selective attention.

Brain activity during landmark and line bisection tasks

Authors:

• Metehan Cicek

• Leon Y. Deouell

• Robert T. Knight

Date: 2009

DOI: 10.3389/neuro.09.007.2009

PubMed: 19521543

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Abstract:

Neglect patients bisect lines far rightward of center whereas normal subjects typically bisect lines with a slight leftward bias supporting a right hemisphere bias for attention allocation. We used fMRI to assess the brain regions related to this function in normals, using two complementary tasks. In the Landmark task subjects were required to judge whether or not a presented line was bisected correctly. During the line bisection task, subjects moved a cursor and indicated when it reached the center of the line. The conjunction of BOLD activity for both tasks showed right lateralized intra-parietal sulcus and lateral peristriate cortex activity. The results provide evidence that predominantly right hemisphere lateralized processes are engaged in normal subjects during tasks that are failed in patients with unilateral neglect and highlight the importance of a right fronto-parietal network in attention allocation.

State-dependent variability of neuronal responses to transcranial magnetic stimulation of the visual cortex

Authors:

• Brian Pasley

• Elena A. Allen

• Ralph D. Freeman

Date: 2009

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Abstract:

Electrical brain stimulation is a promising tool for both experimental and clinical applications. However, the effects of stimulation on neuronal activity are highly variable and poorly understood. To investigate the basis of this variability, we performed extracellular recordings in the visualcortex following application of transcranialmagneticstimulation (TMS). Our measurements of spiking and local field potential activity exhibit two types of response patterns which are characterized by the presence or absence of spontaneous discharge following stimulation. This variability can be partially explained by state-dependent effects, in which higher pre-TMS activity predicts larger post-TMS responses. These results reveal the possibility that variability in the neural response to TMS can be exploited to optimize the effects of stimulation. It is conceivable that this feature could be utilized in real time during the treatment of clinical disorders.

A generalized mechanism for perception of pitch patterns

Authors:

• Psyche Loui

• Elaine Wu

• David Wessel

• Robert T. Knight

Date: 2009

DOI: 10.1523/JNEUROSCI.4503-08.200

PubMed: 2779050

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Abstract:

Surviving in a complex and changeable environment relies on the ability to extract probable recurring patterns. Here we report a neurophysiological mechanism for rapid probabilistic learning of a new system of music. Participants listened to different combinations of tones from a previously unheard system of pitches based on the Bohlen-Pierce scale, with chord progressions that form 3:1 ratios in frequency, notably different from 2:1 frequency ratios in existing musical systems. Event-related brain potentials elicited by improbable sounds in the new music system showed emergence over a 1 h period of physiological signatures known to index sound expectation in standard Western music. These indices of expectation learning were eliminated when sound patterns were played equiprobably, and covaried with individual behavioral differences in learning. These results demonstrate that humans use a generalized probability-based perceptual learning mechanism to process novel sound patterns in music.

Electrophysiological evidence for different inhibitory mechanisms when stopping or changing a planned response

Authors:

• Mark A. Kramer

• Robert T. Knight

• Thomas F. Münte

Date: 2009

PubMed: 20849230

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Abstract:

People are able to adapt their behavior to changing environmental contingencies by rapidly inhibiting or modifying their actions. Response inhibition is often studied in the stop-signal paradigm that requires the suppression of an already prepared motor response. Less is known about situations calling for a change of motor plans such that the prepared response has to be withheld but another has to be executed instead. In the present study, we investigated whether electrophysiological data can provide evidence for distinct inhibitory mechanisms when stopping or changing a response. Participants were instructed to perform in a choice RT task with two classes of embedded critical trials: Stop signals called for the inhibition of any response, whereas change signals required participants to inhibit the prepared response and execute another one instead. Under both conditions, we observed differences in go-stimulus processing, suggesting a faster response preparation in failed compared with successful inhibitions. In contrast to stop-signal trials, changing a response did not elicit the inhibition-related frontal N2 and did not modulate the parietal mu power decrease. The results suggest that compared with changing a response, additional frontal and parietal regions are engaged when having to inhibit a response.

Facilitation and inhibition mechanisms in auditory selective attention: scalp EEG and ECoG data

Authors:

• Aurélie Bidet-Caulet

• Constanze Mikyska

• J Besle

• C. A. Schevon

• G. M. McKahn

• R. R. Goodman

• A. D. Mehta

• R. G. Emerson

• Robert T. Knight

Date: 2009

Executive function and higher-order cognition: EEG studies

Authors:

• Leon Y. Deouell

• Robert T. Knight

Date: 2009

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Abstract:

Multiple goals, from survival to pleasure, coexist at every given moment, and internal needs as well as external events act in a push–pull manner to bias behavior. To maintain optimal goal-directed behavior, a control (‘executive’) system is needed that will dynamically prioritize the processing of information as well as the planning of actions and their execution. In addition to direct motor planning, major components of this executive system are working memory, attention, and conflict/error monitoring. Working memory would allow maintaining a goal across time, as well as information required to achieve the goal. Selective attention (‘voluntary’ or ‘endogenous’ attention) would facilitate the processing of one stream of input and suppress another while involuntary attention mechanisms allow for changes in the environment, as well as changes in internal drives, to interfere with ongoing behavior in a rapid and flexible manner. A monitoring module is needed to assess the efficiency of the executed behavior so that behavior can be adjusted in an optimal way. Consequently, the executive system needs to interact with multiple sensory regions of the brain, as well as with motor output regions involved in orientation, locomotion, and speech. Event-related brain potentials (ERPs), recorded on the scalp (and recently also intracranially) have established scalp-recorded signatures of executive functions. The effect of brain lesions on these measures of electrical brain activity provides a window into the networks supporting the executive system. This article describes ERP studies conducted specifically with patients suffering from well-circumscribed brain lesions involving mainly the lateral prefrontal cortex (LPFC), a major hub of the executive system.

Socioeconomic disparities affect prefrontal function in children

Authors:

• Mark M. Kishiyama

• W. Thomas Boyce

• Amy M. Jimenez

• Lee M. Perry

• Robert T. Knight

Date: 2009

DOI: 10.1162/jocn.2009.21101

PubMed: 18752394

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Abstract:

Social inequalities have profound effects on the physical and mental health of children. Children from low socioeconomic status (SES) backgrounds perform below children from higher SES backgrounds on tests of intelligence and academic achievement, and recent findings indicate that low SES (LSES) children are impaired on behavioral measures of prefrontal function. However, the influence of socioeconomic disparity on direct measures of neural activity is unknown. Here, we provide electrophysiological evidence indicating that prefrontal function is altered in LSES children. We found that prefrontal-dependent electrophysiological measures of attention were reduced in LSES compared to high SES (HSES) children in a pattern similar to that observed in patients with lateral prefrontal cortex (PFC) damage. These findings provide neurophysiological evidence that social inequalities are associated with alterations in PFC function in LSES children. There are a number of factors associated with LSES rearing conditions that may have contributed to these results such as greater levels of stress and lack of access to cognitively stimulating materials and experiences. Targeting specific prefrontal processes affected by socioeconomic disparity could be helpful in developing intervention programs for LSES children.