Prefrontal lesions impair object-spatial integration.

Authors:

• Bradley Voytek

• Maryam Soltani

• Natasha Pickard

• Mark M. Kishiyama

• Robert T. Knight

Date: 2012

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Abstract:

How and where object and spatial information are perceptually integrated in the brain is a central question in visual cognition. Single-unit physiology, scalp EEG, and fMRI research suggests that the prefrontal cortex (PFC) is a critical locus for object-spatial integration. To test the causal participation of the PFC in an object-spatial integration network, we studied ten patients with unilateral PFC damage performing a lateralized object-spatial integration task. Consistent with single-unit and neuroimaging studies, we found that PFC lesions result in a significant behavioral impairment in object-spatial integration. Furthermore, by manipulating inter-hemispheric transfer of object-spatial information, we found that masking of visual transfer impairs performance in the contralesional visual field in the PFC patients. Our results provide the first evidence that the PFC plays a key, causal role in an object-spatial integration network. Patient performance is also discussed within the context of compensation by the non-lesioned PFC.

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.

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.

High Gamma Power is Phase-Locked to Theta Oscillations in Human Neocortex

Authors:

• Ryan T. Canolty

• Erik Edwards

• Sarang S. Dalal

• Maryam Soltani

• Srikantan S. Nagarajan

• Heidi E. Kirsch

• Mitchel S. Berger

• Nicholas M. Barbaro

• Robert T. Knight

Date: 2006

PubMed: 16973878

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Abstract:

We observed robust coupling between the high- and low-frequency bands of ongoing electrical activity in the human brain. In particular, the phase of the low-frequency theta (4 to 8 hertz) rhythm modulates power in the high gamma (80 to 150 hertz) band of the electrocorticogram, with stronger modulation occurring at higher theta amplitudes. Furthermore, different behavioral tasks evoke distinct patterns of theta/high gamma coupling across the cortex. The results indicate that transient coupling between low- and high-frequency brain rhythms coordinates activity in distributed cortical areas, providing a mechanism for effective communication during cognitive processing in humans.

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.

ERPS and intracranial recording

Authors:

• Maryam Soltani

• Robert T. Knight

Date: 2005

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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.

Effects of emotional stimuli on event-related potentials and reaction times in orbitofrontal patients

Authors:

• Kaisa M. Hartikainen

• Keith H. Ogawa

• Maryam Soltani

• Robert T. Knight

Date: 2001

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Abstract:

We examined the effects of bilateral orbitofrontal damage on emotional processing and hemispheric attention capacity. Participants (four bilateral orbitofrontal patients and age- matched controls) discriminated between upright and inverted triangles (target). Targets were randomly presented in the left (LVF) or right visual hemifield (RVF, 150 ms). Emotional (pleasant or unpleasant; 150 ms) or neutral stimuli were presented centrally 350 ms prior to the target. Pleasant stimuli decreased whereas unpleasant stimuli increased RTs to LVF targets, with exaggerated effects in patients. Orbitofrontal damage differentially altered processing of emotional stimuli. In addition, orbitofrontal patients showed altered target ERPs, with evidence of increased activity over frontal sites for only LVF targets. The results suggest an interplay between orbitofrontal cortex and the right hemisphere.

Neural Origins of the P300

Authors:

• Maryam Soltani

• Robert T. Knight

Date: 2000

PubMed: 12645958

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Abstract:

A review of the literature investigating the neural origins of detection behavior in humans reveals two event-related potential components, P3a and P3b, each with a distinct neural organization and cognitive func- tion. The P3a is involved in automatic novelty detection and characterized by a more anterior cortical distribution, whereas the P3b is concerned with volitional target detection and has a more posterior cortical distribution. Intra- cranial investigation, studies with patients with focal brain lesions, and functional neuroimaging (fMRI) studies converge with the scalp-recorded ERP data in suggesting that a widespread cortical network gives rise to both automatic and controlled detection behavior. The main regions consistently attributed to generating detection related brain activation include the temporal-parietal junction, medial temporal complex, and the lateral prefrontal cortex. The extant human and animal literature addressing the neural networks, neuropharmacological underpinnings, and behavioral signicance of “the P300” potential will be reviewed.