High gamma activity in response to deviant auditory stimuli recorded directly from human cortex

Authors:

• Erik Edwards

• Maryam Soltani

• Leon Y. Deouell

• Mitchel S. Berger

• Robert T. Knight

Date: 2005

PubMed: 16093343

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Abstract:

We recorded electrophysiological responses from the left frontal and temporal cortex of awake neurosurgical patients to both repetitive background and rare deviant auditory stimuli. Prominent sensory event-related potentials (ERPs) were recorded from auditory association cortex of the temporal lobe and adjacent regions surrounding the posterior Sylvian fissure. Deviant stimuli generated an additional longer latency mismatch response, maximal at more anterior temporal lobe sites. We found low gamma (30-60 Hz) in auditory association cortex, and we also show the existence of high-frequency oscillations above the traditional gamma range (high gamma, 60-250 Hz). Sensory and mismatch potentials were not reliably observed at frontal recording sites. We suggest that the high gamma oscillations are sensory-induced neocortical ripples, similar in physiological origin to the well-studied ripples of the hippocampus.

Behavioral and electrophysiological evidence of a right hemisphere bias for the influence of negative emotion on higher cognition

Authors:

• Emiliana R. Simon-Thomas

• Kemi O. Role

• Robert T. Knight

Date: 2005

PubMed: 15814010

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Abstract:

We examined how responses to aversive pictures affected performance and stimulus-locked event-related potentials (ERPs) recorded during a demanding cognitive task. Numeric Stroop stimuli were brief ly presented to either left or right visual hemifield (LVF and RVF, respectively) after a centrally presented aversive or neutral picture from the International Affective Picture System. Subjects indicated whether a quantity value from each Stroop stimulus matched the preceding Stroop stimulus while passively viewing the pictures. After aversive pictures, responses were more accurate for LVF Stroops and less accurate for RVF Stroops. Early-latency extrastriate attention-dependent visual ERPs were enhanced for LVF Stroops. The N2 ERP was enhanced for LVF Stroops over the right frontal and parietal scalp sites. Slow potentials (300-800 msec) recorded over the frontal and parietal regions showed enhanced picture related modulation and amplitude for LVF Stroops. These results suggest that emotional responses to aversive pictures selectively facilitated right hemisphere processing during higher cognitive task performance.

ERP measures of multiple attention deficits following prefrontal damage

Authors:

• Leon Y. Deouell

• Robert T. Knight

Date: 2005

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Abstract:

Maintaining a goal-directed behavior requires selectively attending to a subset of the sensory input at the expense of the rest of the input. At the same time, a surveillance mechanism must be in operation, so that deviant or novel events may bring about reorientation of attention and avoidance of potential hazards. Event- related potential (ERP) studies in patients with lateral prefrontal damage, due mainly to stroke, reveal deficits in all of these components of the attentional system. These deficits may explain some pervasive neuropsychological impairment in these patients.

ERPS and intracranial recording

Authors:

• Maryam Soltani

• Robert T. Knight

Date: 2005

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Top-down enhancement and suppression of the magnitude and speed of neural activity

Authors:

• Adam Gazzaley

• Jeffrey W. Cooney

• Kevin McEvoy

• Robert T. Knight

• Mark D'Esposito

Date: 2005

PubMed: 15814009

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Abstract:

Top-down modulation underlies our ability to selectively attend to relevant stimuli and to ignore irrelevant stimuli. Theories addressing neural mechanisms of top-down modulation are driven by studies that reveal increased magnitude of neural activity in response to directed attention, but are limited by a lack of data reporting modulation of neural processing speed, as well as comparisons with a perceptual (passive view) baseline necessary to evaluate the presence of enhancement and suppression. Utilizing functional MRI (fMRI) and event-related potential recordings (ERPs), we provide converging evidence that both the magnitude of neural activity and the speed of neural processing are modulated by top-down influences. Furthermore, both enhancement and suppression occur relative to a perceptual baseline depending on task instruction. These findings reveal the fine degree of influence that goal-directed attention exerts upon activity within the visual association cortex. We further document capacity limitations in top-down enhancement corresponding with working memory performance deficits.

Affective and cognitive modulation of performance monitoring: behavioral and ERP evidence

Authors:

• Emiliana R. Simon-Thomas

• Robert T. Knight

Date: 2005

PubMed: 16396095

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Abstract:

This study investigates the effects of negative affect on performance monitoring. EEG was acquired during a lateralized, numeric Stroop working memory task that featured task-irrelevant aversive and neutral pictures between stimuli. Performance accuracy showed a right-hemisphere advantage for stimuli that followed aversive pictures. Response-locked event-related potentials (ERPs) from accurate trials showed an early negative component (CRN; correct response/conflict-related negativity) followed by a positive wave comparable to the Pe (error positivity). The CRN was bi-peaked with an earlier peak that was sensitive to aversive pictures during early portions of the experiment and a later peak that increased with error likelihood later in the experiment. Pe amplitude was increased with aversive pictures early in the experiment and was sensitive to picture type, Stroop interference, and hemisphere of stimulus delivery during later trials. This suggests that ERP indices of performance monitoring, the CRN and Pe, are dynamically modulated by both affective and cognitive demands.

Temporal kinetics of prefrontal modulation of the extrastriate cortex during visual attention

Authors:

• Elena Yago

• Audrey Duarte

• Ting Wong

• Francisco Barceló

• Robert T. Knight

Date: 2004

PubMed: 15849901

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Abstract:

Single-unit, event-related potential (ERP), and neuroimaging studies have implicated the prefrontal cortex (PFC) in top-down control of attention and working memory. We conducted an experiment in patients with unilateral PFC damage (n = 8) to assess the temporal kinetics of PFC-extrastriate interactions during visual attention. Subjects alternated attention between the left and the right hemifields in successive runs while they detected target stimuli embedded in streams of repetitive task-irrelevant stimuli (standards). The design enabled us to examine tonic (spatial selection) and phasic (feature selection) PFC-extrastriate interactions. PFC damage impaired performance in the visual field contralateral to lesions, as manifested by both larger reaction times and error rates. Assessment of the extrastriate P1 ERP revealed that the PFC exerts a tonic (spatial selection) excitatory input to the ipsilateral extrastriate cortex as early as 100 msec post stimulus delivery. The PFC exerts a second phasic (feature selection) excitatory extrastriate modulation from 180 to 300 msec, as evidenced by reductions in selection negativity after damage. Finally, reductions of the N2 ERP to target stimuli supports the notion that the PFC exerts a third phasic (target selection) signal necessary for successful template matching during postselection analysis of target features. The results provide electrophysiological evidence of three distinct tonic and phasic PFC inputs to the extrastriate cortex in the initial few hundred milliseconds of stimulus processing. Damage to this network appears to underlie the pervasive deficits in attention observed in patients with prefrontal lesions.

High-field, T2 reversed MRI imaging of the hippocampus in transient global amnesia

Authors:

• Tsutomu Nakada

• Ingrid L. Kwee

• Yukihiko Fujii

• Robert T. Knight

Date: 2005

PubMed: 15824342

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Abstract:

OBJECTIVE: To investigate the fine structural integrity of the hippocampus in patients with transient global amnesia (TGA) using high-resolution T2 reversed (T2R) MRI. METHODS: The authors performed detailed structural analysis of the hippocampus in 15 patients who had recovered from an episode of TGA and 150 randomly recruited normal volunteers across the adult age spectrum using high-resolution T2R MRI obtained on a 3.0-T system. An additional 100 subjects, with stroke or tumor, were similarly studied and served as disease controls. RESULTS: The overall incidence of hippocampal cavities detected in normal volunteers increased with age but never exceeded 40%, whereas the incidence in disease control group was 31%. They were always unilateral. In contrast, cavities were found in all 15 patients with TGA (100%), an incidence higher than in normal or disease controls (p < 0.05; Ryan's multiple comparison test), and were bilateral in eight patients (53%). The cavities in all but one of the normal volunteers (99%) and all disease controls (100%) were crescent shaped and < or =2 mm in width. The cavities in 14 of 15 patients with TGA (93%) were considerably larger (>3 mm in width), and five of the patients had giant cavities (>5 mm in width). Most of the cavities in patients with TGA had a rounded shape and resembled pathologic cavities described in specimens of hypoxia-related CA1 necrosis. CONCLUSION: The data indicate that transient global amnesia may not be a benign entity. Delayed neuronal loss within CA1 area of Lorente de No may represent its important sequel.

Mild hypoxia disrupts recollection, not familiarity

Authors:

• Andrew P. Yonelinas

• Joel R. Quamme

• Keith F. Widaman

• Neal E. A. Kroll

• Mary Jane Sauve

• Robert T. Knight

Date: 2004

PubMed: 15535174

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Abstract:

Yonelinas et al. (2002) found that hypoxic patients exhibited deficits in recollection that left familiarity relatively unaffected. In contrast, Manns, Hopkins, Reed, Kitchener, and Squire (2003) studied a group of hypoxic patients who suffered severe and equivalent deficits in recollection and familiarity. We reexamine those studies and argue that the discrepancy in results is likely due to differences in the hypoxic groups that were tested (i.e., differences in amnestic severity, subject sampling methods, and patient etiology). Yonelinas et al. examined memory in 56 cardiac arrest patients who suffered a brief hypoxic event, whereas Manns et al. examined a group of severely amnesic patients that consisted of 2 cardiac arrest patients, 2 heroin overdose patients, 1 carbon monoxide poisoning patient, and 2 patients with unknown etiologies. We also consider an alternative explanation proposed by Wixted and Squire (2004), who argued that the two patient groups suffered similar deficits, but that statistical or methodological artifacts distorted the results of each of Yonelinas et al.'s experiments. A consideration of those results, however, indicates that such an explanation does not account for the existing data. All of the existing evidence indicates that recollection, but not familiarity, is disrupted in mild hypoxic patients. In more severe cases of hypoxia, or those with more complex etiologies such as heroin overdose, more profound deficits may be observed.

Neurobiology: sleep on it

Authors:

• Ilana S. Hairston

• Robert T. Knight

Date: 2004

PubMed: 15229587

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Abstract:

Is the function of sleep to replenish energy resources or to modify neural connections in the brain? Recordings of the brain’s ‘reverberating circuits’ evident during sleep shed light on the question.

Rapid Prefrontal-Hippocampal Habituation to Novel Events

Authors:

• Shuhei Yamaguchi

• Laura A. Hale

• Mark D'Esposito

• Robert T. Knight

Date: 2004

PubMed: 15190108

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Abstract:

Unexpected novel events generate an orienting response that plays an important role in some forms of learning and memory. The orienting response involuntarily captures attention and rapidly habituates as events become familiarized. Although evidence from patients with focal lesions and scalp and intracranial event-related brain potential recordings supports the involvement of a distributed neural network involving association cortex and the limbic system in novelty detection, the key neural substrates and temporal dynamics have not been defined. While subjects performed a bi-field visual-selective attention task with random novel stimuli embedded in either attended or unattended visual fields, we measured rapid changes of regional blood oxygenation level-dependent (BOLD) signal to target and novel stimuli using single-trial analysis of event-related functional magnetic resonance imaging with a 4T scanner. Habituation was quantified by serial BOLD signal changes during the first 10 novel stimuli for each subject. Novel stimuli activated the bilateral superior/middle frontal gyrus, temporal-parietal junction, superior parietal lobe, cingulate gyrus, hippocampus, and fusiform gyrus. The superior/middle frontal gyrus and hippocampus showed significant reduction of BOLD signal during the first few novel stimuli, whereas the signals in the fusiform and cingulate gyrus were constant. Prefrontal and hippocampal responses to attended and unattended novel stimuli were comparably habituated. These results, and previous data from lesion studies, support the view that prefrontal and hippocampal regions are involved in rapid automatic detection and habituation to unexpected environmental events and are key elements of the orienting response in humans.

The impact of orbital prefrontal cortex damage on emotional activation to unanticipated and anticipated acoustic startle stimuli

Authors:

• Nicole A. Roberts

• Jennifer S. Beer

• Kelly H. Werner

• Sara M. Levens

• Robert T. Knight

• Robert W. Levenson

Date: 2004

PubMed: 15535166

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Abstract:

Damage to the orbital prefrontal cortex has been implicated in selectively diminishing electrodermal autonomic nervous system responses to anticipated punishing stimuli (e.g., losing money; Bechara, Damasio, & Damasio, 2000), but not to unanticipated punishing stimuli (e.g., loud noises; Damasio, Tranel, & Damasio, 1990). We extended this research by examining the effects of orbitofrontal damage on emotional responses to unanticipated and anticipated acoustic startles and collecting a more extensive set of physiological measures, emotional facial behavior, and self-reported emotional experience. Consistent with previous research, patients showed intact physiology to an unanticipated startle but failed to show appropriate anticipatory cardiovascular responses (patients' heart rates decreased, controls' increased). In addition, patients displayed more surprise facial behavior and reported marginally more fear than did controls in response to the unanticipated startle. Thus, orbitofrontal damage may compromise the ability to anticipate physiologically the onset of aversive stimuli, despite intact or enhanced emotional responses when such stimuli occur unexpectedly.

Hemispheric asymmetries for kinematic and positional aspects of reaching

Authors:

• Kathleen Y. Haaland

• Jillian L. Prestopnik

• Robert T. Knight

• Roland R. Lee

Date: 2004

PubMed: 15033898

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Abstract:

Kinematic analyses of reaching have suggested that the left hemisphere is dominant for controlling the open loop component of the movement, which is more dependent on motor programmes; and the right hemisphere is dominant for controlling the closed loop component, which is more dependent on sensory feedback. This open and closed loop hypothesis of hemispheric asymmetry would also predict that advance planning should be dependent on the left hemisphere, and on-line response modification, which defines closed loop processes, should be dependent on the right hemisphere. Using kinematic analyses of reaching in patients with left or right hemisphere damage (LHD or RHD), we examined the ability: (i) to plan reaching movements in advance by examining changes in reaction time (RT) when response amplitude and visual feedback were cued prior to the response; and (ii) to modify the response during implementation when target location changed at the RT. Performance was compared between the stroke groups, using the ipsilesional arm, and age-matched control groups using their right (RNC) or left (LNC) arm. Aiming movements to a target that moved once or twice, with the second step occurring at the RT, were performed with or without visual feedback of hand position. There were no deficits in advance planning in either stroke group, as evidenced by comparable group changes in RT with changes in amplitude and visual feedback. Response modification deficits were seen for the LHD group in secondary velocity only. In addition, LHD produced slower initial peak velocity with prolongation of the deceleration phase and faster secondary peak velocities, and the RHD group produced deficits in final error only. These differences are more consistent with the dynamic dominance hypothesis, which links left hemisphere specialization to movement trajectory control and right hemisphere specialization to position control, rather than to global deficits in open and closed loop processing.

Synchronization measures of bursting data: Application to the electrocoricogram of an auditory event-related experiment

Authors:

• Mark A. Kramer

• Erik Edwards

• Maryam Soltani

• Mitchel S. Berger

• Robert T. Knight

• Andrew J. Szeri

Date: 2004

PubMed: 15324095

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Abstract:

Synchronization measures have become an important tool for exploring the relationships between time series. We review three recently proposed nonlinear synchronization measures and expand their definitions in a straightforward way to apply to an ensemble of measurements. We also develop a synchronization measure in which nearest neighbors are determined across the ensemble. We compare these four nonlinear synchronization measures and show that our measure succeeds in physically motivated examples where the other methods fail. We apply the synchronization measure to human electrocorticogram data collected during an auditory event-related potential experiment. The results suggest a crude model of cortical connectivity.

Distributed neural activity during object, spatial and integrated processing in humans

Authors:

• Emiliana R. Simon-Thomas

• Kim Brodsky

• Cammy Willing

• Rashmi Sinha

• Robert T. Knight

Date: 2003

PubMed: 12706225

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Abstract:

Information about the form and the spatial location of objects is seamlessly integrated during visual perception. We used event-related potentials (ERPs) to explore neural activity related to processing form, location or the combination of both kinds of features. Healthy subjects performed three versions of a 'match-to-sample' task: a two-object task, a two-location task and an integrated object-location task. Responses were quickest and most accurate during the integrated task, slower and less accurate in the two-location task and slowest and least accurate in the two-object task. ERPs locked to the 'sample' stimulus at encoding, and to the 'target' stimulus during feature comparison differentiated between tasks. 'Sample' stimulus ERPs exhibited task-specific posterior cortical involvement in processing distinct visual features. 'Target' stimulus ERPs revealed task-related differences in features associated with frontal lobe mediated attentional processes: an early latency P300 showed increased amplitude during the integrated task. Results from this experiment support the view that distinct neural circuits mediate form vs. location processing and that form-location integration engages both pathways and upregulates frontal-parietal association networks.

Does the representation of time depend on the cerebellum? Effect of cerebellar stroke

Authors:

• Deborah L. Harrington

• Roland R. Lee

• Lara A. Boyd

• Steven Z. Rapcsak

• Robert T. Knight

Date: 2004

PubMed: 14711883

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Abstract:

Behaviours that appear to depend on processing temporal information are frequently disrupted after cerebellar damage. The present study examined the role of the cerebellum in explicit timing and its relationship to other psychological processes. We hypothesized that if the cerebellum regulates timekeeping operations then cerebellar damage should disrupt the perception and the reproduction of intervals, since both are thought to be supported by a common timekeeper mechanism. Twenty-one patients with cerebellar damage from stroke and 30 normal controls performed time perception and time reproduction tasks. In the time reproduction task, timing variability was decomposed into a central timing component (clock variability) and a motor component (motor implementation variability). We found impairments only in time reproduction (increased clock variability) in patients with medial and lateral damage involving the middle- to superior-cerebellar lobules. To explore potential reasons for the temporal processing deficits, time reproduction and perception performance were correlated with independent measures of attention, working memory, sensory discrimination and processing speed. Poorer working memory correlated with increased variability in the 'clock' component of time reproduction. In contrast, processing speed correlated best with time perception. The results did not support a role for the cerebellum in timekeeping operations. Rather, deficits in timing movements may be related to a disruption in acquiring sensory and cognitive information relevant to the task, coupled with an additional impairment in the motor-output system.

Dissociable neural correlates for familiarity and recollection during the encoding and retrieval of pictures

Authors:

• Audrey Duarte

• Charan Ranganath

• Laurel Winward

• Dustin Hayward

• Robert T. Knight

Date: 2004

PubMed: 14741312

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Abstract:

Results from behavioral studies have supported the idea that recognition memory can be supported by at least two different processes, recollection and familiarity. However, it remains unclear whether these two forms of memory reflect neurally distinct processes. Furthermore, it is unclear whether recollection and familiarity can be best conceived as differing primarily in terms of retrieval processing, or whether they additionally differ at encoding. To address these issues, we used event-related brain potentials (ERPs) to monitor neural correlates of familiarity and recollection at both encoding and retrieval. Participants studied pictures of objects in two types of study blocks and subsequently made remember-know and source memory judgments during retrieval. Results showed that, during encoding, neural correlates of subsequent familiarity and recollection onsetted in parallel, but exhibited differences in scalp topography and time course. Subsequent familiarity-based recognition was associated with a left-lateralized enhanced positivity and observed at anterior scalp sites from 300 to 450 ms, whereas subsequent recollection was associated with a topographically distinct right-lateralized positivity at anterior scalp sites from 300 to 450 ms and bilateral activity from 450 to 600 ms. During retrieval, neural correlates of familiarity emerged earlier than correlates of recollection. Familiarity was associated with an enhanced positivity at frontopolar scalp sites from 150 to 450 ms, whereas recollection was associated with positive ERP modulations over bilateral frontal (300-600 ms) and parietal (450-800 ms) sites. These results demonstrate that familiarity and recollection reflect the outcome of neurally distinct memory processes at both encoding and retrieval.

The regulatory function of self-conscious emotion: insights from patients with orbitofrontal damage

Authors:

• Jennifer S. Beer

• Erin A. Heerey

• Dacher Keltner

• Robert T. Knight

Date: 2003

PubMed: 14561114

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Abstract:

Although once considered disruptive, self-conscious emotions are now theorized to be fundamentally involved in the regulation of social behavior. The present study examined the social regulation function of self-conscious emotions by comparing healthy participants with a neuropsychological population--patients with orbitofrontal lesions--characterized by selective regulatory deficits. Orbitofrontal patients and healthy controls participated in a series of tasks designed to assess their social regulation and self-conscious emotions. Another task assessed the ability to infer others' emotional states, an appraisal process involved in self-conscious emotion. Consistent with the theory that self-conscious emotions are important for regulating social behavior, the findings show that deficient behavioral regulation is associated with inappropriate self-conscious emotions that reinforce maladaptive behavior. Additionally, deficient behavioral regulation is associated with impairments in interpreting the self-conscious emotions of others.

Voxel-based lesion-symptom mapping

Authors:

• Elizabeth Bates

• Stephen M. Wilson

• Ayse Pinar Saygin

• Frederic Dick

• Martin I. Sereno

• Robert T. Knight

• Nina F. Dronkers

Date: 2003

PubMed: 12704393

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The neural substrates of visual implicit memory: do the two hemispheres play different roles?

Authors:

• Neal E. A. Kroll

• Andrew P. Yonelinas

• Mark M. Kishiyama

• Kathleen Baynes

• Robert T. Knight

• Michael S. Gazzaniga

Date: 2003

PubMed: 14511536

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Abstract:

Identification of visually presented words is facilitated by implicit memory, or visual priming, for past visual experiences with those words. There is disagreement over the neuro-anatomical substrates of this form of implicit memory. Several studies have suggested that this form of priming relies on a visual word-form system localized in the right occipital lobe, whereas other studies have indicated that both hemispheres are equally involved. The discrepancies may be related to the types of priming tasks that have been used because the former studies have relied primarily on word-stem completion tasks and the latter on tasks like word-fragment completion. The present experiments compared word-fragment and word-stem measurements of visual implicit memory in patients with right occipital lobe lesions and patients with complete callosotomies. The patients showed normal visual implicit memory on fragment completion tests, but essentially no visual priming on standard stem completion tests. However, when we used a set of word stems that had only one correct solution for each test item, as was true of the items in the fragment completion tests, the patients showed normal priming effects. The results indicate that visual implicit memory for words is not solely dependent upon the right hemisphere, rather it reflects changes in processing efficiency in bilateral visual regions involved in the initial processing of the items. However, under conditions of high lexical competition (i.e., multiple completion word stems), the lexical processes, which are dominant in the left hemisphere, overshadow the visual priming supported by the left hemisphere.