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.

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.

Altered prefrontal function with aging: insights into age-associated cognitive decline

Authors:

• Anne-Kristin Solbakk

• Galit Fuhrmann Alpert

• Ansgar J. Furst

• Laura A. Hale

• Tatsuhide Oga

• Sundari Chetty

• Natasha Pickard

• Robert T. Knight

Date: 2008

DOI: 10.1016/j.brainres.2008.07.060

PubMed: 18691562

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Abstract:

We examined the effects of aging on visuo-spatial attention. Participants performed a bi-field visual selective attention task consisting of infrequent target and task-irrelevant novel stimuli randomly embedded among repeated standards in either attended or unattended visual fields. Blood oxygenation level dependent (BOLD) responses to the different classes of stimuli were measured using functional magnetic resonance imaging. The older group had slower reaction times to targets, and committed more false alarms but had comparable detection accuracy to young controls. Attended target and novel stimuli activated comparable widely distributed attention networks, including anterior and posterior association cortex, in both groups. The older group had reduced spatial extent of activation in several regions, including prefrontal, basal ganglia, and visual processing areas. In particular, the anterior cingulate and superior frontal gyrus showed more restricted activation in older compared with young adults across all attentional conditions and stimulus categories. The spatial extent of activations correlated with task performance in both age groups, but the regional pattern of association between hemodynamic responses and behavior differed between the groups. Whereas the young subjects relied on posterior regions, the older subjects engaged frontal areas. The results indicate that aging alters the functioning of neural networks subserving visual attention, and that these changes are related to cognitive performance.

Mentalizing about emotion and its relationship to empathy

Authors:

• Christine I. Hooker

• Sara C. Verosky

• Laura T. Germine

• Robert T. Knight

• Mark D'Esposito

Date: 2008

DOI: 10.1093/scan/nsn019

PubMed: 19015112

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Abstract:

Mentalizing involves the ability to predict someone else’s behavior based on their belief state. More advanced mentalizing skills involve integrating knowledge about beliefs with knowledge about the emotional impact of those beliefs. Recent research indicates that advanced mentalizing skills may be related to the capacity to empathize with others. However, it is not clear what aspect of mentalizing is most related to empathy. In this study, we used a novel, advanced mentalizing task to identify neural mechanisms involved in predicting a future emotional response based on a belief state. Subjects viewed social scenes in which one character had a False Belief and one character had a True Belief. In the primary condition, subjects were asked to predict what emotion the False Belief Character would feel if they had a full understanding about the situation. We found that neural regions related to both mentalizing and emotion were involved when predicting a future emotional response, including the superior temporal sulcus, medial prefrontal cortex, temporal poles, somatosensory related cortices (SRC), inferior frontal gyrus and thalamus. In addition, greater neural activity in primarily emotion-related regions, including right SRC and bilateral thalamus, when predicting emotional response was significantly correlated with more self-reported empathy. The findings suggest that predicting emotional response involves generating and using internal affective representations and that greater use of these affective representations when trying to understand the emotional experience of others is related to more empathy.

Age-related top down suppression deficit in the early stages of cortical visual memory processing

Authors:

• Adam Gazzaley

• Wesley Clapp

• Jon Kelley

• Kevin McEvoy

• Robert T. Knight

• Mark D'Esposito

Date: 2008

DOI: 10.1073/pnas.0806074105

PubMed: 18765818

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Abstract:

In this study, electroencephalography (EEG) was used to examine the relationship between two leading hypotheses of cognitive aging, the inhibitory deficit and the processing speed hypothesis. We show that older adults exhibit a selective deficit in suppressing task-irrelevant information during visual working memory encoding, but only in the early stages of visual processing. Thus, the employment of suppressive mechanisms are not abolished with aging but rather delayed in time, revealing a decline in processing speed that is selective for the inhibition of irrelevant information. EEG spectral analysis of signals from frontal regions suggests that this results from excessive attention to distracting information early in the time course of viewing irrelevant stimuli. Subdividing the older population based on working memory performance revealed that impaired suppression of distracting information early in the visual processing stream is associated with poorer memory of task-relevant information. Thus, these data reconcile two cognitive aging hypotheses by revealing that an interaction of deficits in inhibition and processing speed contributes to agerelated cognitive impairment.

Localization of neurosurgically implanted electrodes via photograph–MRI–radiograph coregistration

Authors:

• Sarang S. Dalal

• Erik Edwards

• Heidi E. Kirsch

• Nicholas M. Barbaro

• Robert T. Knight

• Srikantan S. Nagarajan

Date: 2008

DOI: 10.1016/j.jneumeth.2008.06.028

PubMed: 18657573

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Abstract:

Intracranial electroencephalography (iEEG) is clinically indicated for medically refractory epilepsy and is a promising approach for developing neural prosthetics. These recordings also provide valuable data for cognitive neuroscience research. Accurate localization of iEEG electrodes is essential for evaluating specific brain regions underlying the electrodes that indicate normal or pathological activity, as well as for relating research findings to neuroimaging and lesion studies. However, electrodes are frequently tucked underneath the edge of a craniotomy, inserted via a burr hole, or placed deep within the brain, where their locations cannot be verified visually or with neuronavigational systems. We show that one existing method, registration of postimplant computed tomography (CT) with preoperative magnetic resonance imaging (MRI), can result in errors exceeding 1 cm. We present a novel method for localizing iEEG electrodes using routinely acquired surgical photographs, X-ray radiographs, and magnetic resonance imaging scans. Known control points are used to compute projective transforms that link the different image sets, ultimately allowing hidden electrodes to be localized, in addition to refining the location of manually registered visible electrodes. As the technique does not require any calibration between the different image modalities, it can be applied to existing image databases. The final result is a set of electrode positions on the patient’s rendered MRI yielding locations relative to sulcal and gyral landmarks on individual anatomy, as well as MNI coordinates. We demonstrate the results of our method in eight epilepsy patients implanted with electrode grids spanning the left hemisphere.

The influence of personality on neural mechanisms of observational fear and reward learning

Authors:

• Christine I. Hooker

• Sara C. Verosky

• Asako Miyakawa

• Robert T. Knight

• Mark D'Esposito

Date: 2008

DOI: 10.1016/j.neuropsychologia.2008.05.005

PubMed: 18573512

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Abstract:

Fear and reward learning can occur through direct experience or observation. Both channels can enhance survival or create maladaptive behavior. We used fMRI to isolate neural mechanisms of observational fear and reward learning and investigate whether neural response varied according to individual differences in neuroticism and extraversion. Participants learned object-emotion associations by observing a woman respond with fearful (or neutral) and happy (or neutral) facial expressions to novel objects. The amygdala–hippocampal complex was active when learning the object-fear association, and the hippocampus was active when learning the object-happy association. After learning, objects were presented alone; amygdala activity was greater for the fear (vs. neutral) and happy (vs. neutral) associated object. Importantly, greater amygdala–hippocampal activity during fear (vs. neutral) learning predicted better recognition of learned objects on a subsequent memory test. Furthermore, personality modulated neural mechanisms of learning. Neuroticism positively correlated with neural activity in the amygdala and hippocampus during fear (vs. neutral) learning. Low extraversion/high introversion was related to faster behavioral predictions of the fearful and neutral expressions during fear learning. In addition, low extraversion/high introversion was related to greater amygdala activity during happy (vs. neutral) learning, happy (vs. neutral) object recognition, and faster reaction times for predicting happy and neutral expressions during reward learning. These findings suggest that neuroticism is associated with an increased sensitivity in the neural mechanism for fear learning which leads to enhanced encoding of fear associations, and that low extraversion/high introversion is related to enhanced conditionability for both fear and reward learning.

Detecting violations of sensory expectancies following cerebellar degeneration: a mismatch negativity study

Authors:

• Torgeir Moberget

• Christina M. Karns

• Leon Y. Deouell

• Magnus Lindgren

• Robert T. Knight

• Richard B. Ivry

Date: 2008

DOI: 10.1016/j.neuropsychologia.2008.03.016

PubMed: 18486157

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Abstract:

Two hypotheses concerning cerebellar function and predictive behavior are the sensory prediction hypothesis and the timing hypothesis. The former postulates that the cerebellum is critical in generating expectancies regarding forthcoming sensory information. The latter postulates that this structure is critical in generating expectancies that are precisely timed; for example, the expected duration of an event or the time between events. As such, the timing hypothesis constitutes a more specific form of prediction. The present experiment contrasted these two hypotheses by examining the mismatch negativity (MMN) response in patients with cerebellar cortical atrophy and matched controls. While watching a silent movie, a stream of task-irrelevant sounds was presented. A standard sound was presented 60% of the time, whereas the remaining sounds deviated from the standard on one of four dimensions: duration, intensity, pitch, or location. The timing between stimuli was either periodic or aperiodic. Based on the sensory prediction hypothesis, the MMN for the patients should be abnormal across all four dimensions. In contrast, the timing hypothesis would predict a selective impairment of the duration MMN. Moreover, the timing hypothesis would also predict that the enhancement of the MMN observed in controls when the stimuli are presented periodically should be attenuated in the patients. Compared to controls, the patients exhibited a delayed latency in the MMN to duration deviants and a similar trend for the intensity deviants, while pitch and location MMNs did not differ between groups. Periodicity had limited and somewhat inconsistent effects. The present results are at odds with a general role for the cerebellum in sensory prediction and provide partial support for the timing hypothesis.

No disillusions in auditory extinction: perceiving a melody comprised of unperceived notes

Authors:

• Leon Y. Deouell

• D. Deutsch

• Nachum Soroker

• Robert T. Knight

Date: 2008

DOI: 10.3389/neuro.09.015.2007

PubMed: 18958228

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Abstract:

The formation of coherent percepts requires grouping together spatio-temporally disparate sensory inputs. Two major questions arise: (1) is awareness necessary for this process; and (2) can non-conscious elements of the sensory input be grouped into a conscious percept? To address this question, we tested two patients suffering from severe left auditory extinction following right hemisphere damage. In extinction, patients are unaware of the presence of left side stimuli when they are presented simultaneously with right side stimuli. We used the ‘scale illusion’ to test whether extinguished tones on the left can be incorporated into the content of conscious awareness. In the scale illusion, healthy listeners obtain the illusion of distinct melodies, which are the result of grouping of information from both ears into illusory auditory streams. We show that the two patients were susceptible to the scale illusion while being consciously unaware of the stimuli presented on their left. This suggests that awareness is not necessary for auditory grouping and non-conscious elements can be incorporated into a conscious percept.

Five-dimensional neuroimaging: localization of the time-frequency dynamics of cortical activity

Authors:

• Sarang S. Dalal

• Adrian G. Guggisberg

• Erik Edwards

• Kensuke Sekihara

• Anne M. Findlay

• Ryan T. Canolty

• Mitchel S. Berger

• Robert T. Knight

• Nicholas M. Barbaro

• Heidi E. Kirsch

• Srikantan S. Nagarajan

Date: 2008

DOI: 10.1016/j.neuroimage.2008.01.023

PubMed: 18356081

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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. In this paper, 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 simulated sources and is also applied to real MEG data from a self-paced finger movement task. The algorithm reliably reveals modulations both in the beta band (12–30 Hz) and 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. Inter- estingly, we also reliably observed high frequency activity (30–300 Hz) in the cerebellum, although with variable locations and frequencies across subjects. The proposed algorithm is highly parallelizable and runs efficiently on modern high-performance computing clusters. This method enables the ultimate promise of MEG and EEG for five- dimensional imaging of space, time, and frequency activity in the brain and renders it applicable for widespread studies of human cortical dynamics during cognition.

Spatio-temporal dynamics of neural mechanisms underlying component operations in working memory

Authors:

• Brian T. Miller

• Leon Y. Deouell

• Cathrine Dam

• Robert T. Knight

• Mark D'Esposito

Date: 2008

DOI: 10.1016/j.brainres.2008.01.059

PubMed: 18358455

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Abstract:

Neuroimaging and neurophysiology evidence suggests that component operations in working memory (WM) emerge from the coordinated interaction of posterior perceptual cortices with heteromodal regions in the prefrontal and parietal cortices. Still, little is known about bottom– up and top–down signaling during the formation and retrieval of WM representations. In the current set of experiments, we combine complementary fMRI and EEG measures to obtain high-resolution spatial and temporal measures of neural activity during WM encoding and retrieval processes. Across both experiments, participants performed a face delayed recognition WM task in which the nature of sensory input across stages was held constant. In experiment 1, we utilized a latency-resolved fMRI approach to assess temporal parameters of the BOLD response during stage-specific encoding and retrieval waveforms. Relative to the latency at encoding, the PFC exhibited an earlier peak of fMRI activity at retrieval showing stage-specific differences in the temporal dynamics of PFC engagement across WM operations. In experiment 2, we analyzed the first 200 ms of the ERP response during this WM task providing a more sensitive temporal measure of these differences. Divergence of the ERP pattern during encoding and retrieval began as early as 60 ms post-stimulus. The parallel fMRI and ERP results during memory-guided decisions support a key role of the PFC in top–down biasing of perceptual processing and reveal rapid differences across WM component operations in the presence of identical bottom–up sensory input.

Superior Temporal Sulcus—It’s My Area: Or Is It?

Authors:

• Grit Hein

• Robert T. Knight

Date: 2008

DOI: 10.1162/jocn.2008.20148

PubMed: 18457502

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Abstract:

The superior temporal sulcus (STS) is the chameleon of the human brain. Several research areas claim the STS as the host brain region for their particular behavior of interest. Some see it as one of the core structures for theory of mind. For others, it is the main region for audiovisual integration. It plays an important role in biological motion perception, but is also claimed to be essential for speech processing and processing of faces. We review the foci of activations in the STS from multiple functional magnetic resonance imaging studies, focusing on theory of mind, audiovisual integration, motion processing, speech processing, and face processing. The results indicate a differentiation of the STS region in an anterior portion, mainly involved in speech processing, and a posterior portion recruited by cognitive demands of all these different research areas. The latter finding argues against a strict functional subdivision of the STS. In line with anatomical evidence from tracer studies, we propose that the function of the STS varies depending on the nature of network coactivations with different regions in the frontal cortex and medialtemporal lobe. This view is more in keeping with the notion that the same brain region can support different cognitive operations depending on task-dependent network connections, emphasizing the role of network connectivity analysis in neuroimaging.

Spatiotemporal dynamics of word processing in the human brain

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.

Emotionally arousing stimuli compete with attention to the left hemispace

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.