Multivariate Phase–Amplitude Cross-Frequency Coupling in Neurophysiological Signals

Authors:

• Ryan T. Canolty

• Charles F. Cadieu

• Kilian Koepsell

• Robert T. Knight

• Jose M. Carmena

Date: 2012

PubMed: 22020662

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Abstract:

Phase-amplitude cross-frequency coupling (CFC)-where the phase of a low-frequency signal modulates the amplitude or power of a high-frequency signal-is a topic of increasing interest in neuroscience. However, existing methods of assessing CFC are inherently bivariate and cannot estimate CFC between more than two signals at a time. Given the increase in multielectrode recordings, this is a strong limitation. Furthermore, the phase coupling between multiple low-frequency signals is likely to produce a high rate of false positives when CFC is evaluated using bivariate methods. Here, we present a novel method for estimating the statistical dependence between one high-frequency signal and N low-frequency signals, termed multivariate phase-coupling estimation (PCE). Compared to bivariate methods, the PCE produces sparser estimates of CFC and can distinguish between direct and indirect coupling between neurophysiological signals-critical for accurately estimating coupling within multiscale brain networks.

Executive functions after orbital or lateral prefrontal lesions: neuropsychological profiles and self-reported executive functions in everyday living

Authors:

• Marianne Lovstad

• Ingrid Funderud

• Tor Endestad

• Paulina Due-Tønnesse

• Torstein Meling

• Magnus Lindgren

• Robert T. Knight

• Anne-Kristin Solbakk

Date: 2012

DOI: 10.3109/02699052.2012.698787

PubMed: 22731818

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Abstract:

OBJECTIVE: This study examined the effects of chronic focal lesions to the lateral prefrontal cortex (LPFC) or orbitofrontal cortex (OFC) on neuropsychological test performance and self-reported executive functioning in everyday living. METHODS: Fourteen adults with OFC lesions were compared to 10 patients with LPFC injuries and 21 healthy controls. Neuropsychological tests with emphasis on measures of cognitive executive function were administered along with the Behavior Rating Inventory of Executive Functions (BRIEF-A) and a psychiatric screening instrument. RESULTS: The LPFC group differed from healthy controls on neuropsychological tests of sustained mental effort, response inhibition, working memory and mental switching, while the BRIEF-A provided more clinically important information on deficits in everyday life in the OFC group compared to the LPFC group. Correlations between neuropsychological test results and BRIEF-A were weak, while the BRIEF-A correlated strongly with emotional distress. CONCLUSIONS: It was demonstrated that LPFC damage is particularly prone to cause cognitive executive deficit, while OFC injury is more strongly associated with self-reported dysexecutive symptoms in everyday living. The study illustrates the challenge of identifying executive deficit in individual patients and the lack of strong anatomical specificity of the currently employed methods. There is a need for an integrative methodological approach where standard testing batteries are supplemented with neuropsychiatric and frontal-specific rating scales.

High gamma oscillations in ECoG allow for pre-movement decoding of dextrous finger movements.

Authors:

• Fanny Quandt

• S. Durschmid

• Hermann Hinrichs

• Robert T. Knight

• Jochem W. Rieger

Date: 2012

Involvement of both grey and white matter in chronic aphasia syndromes.

Authors:

• Nina F. Dronkers

• A. U. Turken

• J. Baldo

• J. Ogar

• C Ludy

• D. Wilkins

• Robert T. Knight

Date: 2012

A dynamical pattern recognition model of gamma activity in auditory cortex

Authors:

• Melissa Zavaglia

• Ryan T. Canolty

• Thomas M. Schofield

• Alexander P. Leff

• Mauro Ursino

• Robert T. Knight

• Will D. Penny

Date: 2012

DOI: 10.1016/j.neunet.2011.12.007

PubMed: 22327049

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Abstract:

This paper describes a dynamical process which serves both as a model of temporal pattern recognition in the brain and as a forward model of neuroimaging data. This process is considered at two separate levels of analysis: the algorithmic and implementation levels. At an algorithmic level, recognition is based on the use of Occurrence Time features. Using a speech digit database we show that for noisy recognition environments, these features rival standard cepstral coefficient features. At an implementation level, the model is defined using a Weakly Coupled Oscillator (WCO) framework and uses a transient synchronization mechanism to signal a recognition event. In a second set of experiments, we use the strength of the synchronization event to predict the high gamma (75-150 Hz) activity produced by the brain in response to word versus non-word stimuli. Quantitative model fits allow us to make inferences about parameters governing pattern recognition dynamics in the brain.

Single trial discrimination of individual finger movements on one hand: A combined MEG and EEG study

Authors:

• Fanny Quandt

• Christoph Reichert

• Hermann Hinrichs

• Hans-Jochen Heinze

• Robert T. Knight

• Jochem W. Rieger

Date: 2011

DOI: 10.1016/j.neuroimage.2011.11.053

PubMed: 22155040

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Abstract:

It is crucial to understand what brain signals can be decoded from single trials with different recording techniques for the development of Brain-Machine Interfaces. A specific challenge for non-invasive recording methods are activations confined to small spatial areas on the cortex such as the finger representation of one hand. Here we study the information content of single trial brain activity in non-invasive MEG and EEG recordings elicited by finger movements of one hand. We investigate the feasibility of decoding which of four fingers of one hand performed a slight button press. With MEG we demonstrate reliable discrimination of single button presses performed with the thumb, the index, the middle or the little finger (average over all subjects and fingers 57%, best subject 70%, empirical guessing level: 25.1%). EEG decoding performance was less robust (average over all subjects and fingers 43%, best subject 54%, empirical guessing level 25.1%). Spatiotemporal patterns of amplitude variations in the time series provided best information for discriminating finger movements. Non-phase-locked changes of mu and beta oscillations were less predictive. Movement related high gamma oscillations were observed in average induced oscillation amplitudes in the MEG but did not provide sufficient information about the finger's identity in single trials. Importantly, pre-movement neuronal activity provided information about the preparation of the movement of a specific finger. Our study demonstrates the potential of non-invasive MEG to provide informative features for individual finger control in a Brain-Machine Interface neuroprosthesis.

Damage to the prefrontal cortex impairs familiarity but not recollection memory

Authors:

• Mariam Aly

• Andrew P. Yonelinas

• Mark M. Kishiyama

• Robert T. Knight

Date: 2011

PubMed: 21827792

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Abstract:

Frontal lobe lesions impair recognition memory but it is unclear whether the deficits arise from impaired recollection, impaired familiarity, or both. In the current study, recognition memory for verbal materials was examined in patients with damage to the left or right lateral prefrontal cortex. Words were incidentally encoded under semantic or phonological orienting conditions, and recognition memory was tested using a 6-point confidence procedure. Receiver operating characteristics (ROCs) were examined in order to measure the contributions of recollection and familiarity to recognition memory. In both encoding conditions, lateral prefrontal cortex damage led to a deficit in familiarity but not recollection. Similar deficits were observed in left and right hemisphere patients. The results indicate that the lateral prefrontal cortex plays a critical role in the monitoring or decision processes required for accurate familiarity-based recognition responses.

Dynamic communication and connectivity in frontal networks

Authors:

• Bradley Voytek

• Robert T. Knight

Date: 2011

DOI: 10.1093/acprof:oso/9780199791569.003.0028

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Abstract:

How do we maintain a stable percept of the world in the face of the powerful drive of neuroplasticity in both health and disease? This dichotomy forms one of the most fundamental unanswered questions in neuroscience concerning the balance between the dynamic, plastic underpinnings of our neurobiology and the relative stability of our cognition. Th e brain undergoes massive changes in size, morphology, and connectivity during normal development and aging as well as in response to brain injury, yet we can maintain a relatively stable sense of cognition and self during the lifespan. Human brains, each with over 100 billion neurons, develop similarly despite the wide variations in environment and experience. However, within the bounds of this stability there exists a wide range of variability and capacity for change. Here we will discuss the role of neuroplasticity in frontal lobe-dependent cognition by examining the localization of attention and memory functions in the brain and how these seemingly fixed locations may reflect flexible neural networks that change communication properties as required by behavior.

Cortical Spatio-temporal 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: 2011

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.

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

Authors:

• Ulrike M. Krämer

• Robert T. Knight

• Thomas F. Münte

Date: 2011

DOI: 10.1162/jocn.2010.21573

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.

The medial temporal lobe supports conceptual implicit memory

Authors:

• Wei-Chun Wang

• Michele Lazzara

• Charan Ranganath

• Robert T. Knight

• Andrew P. Yonelinas

Date: 2010

DOI: 10.1016/j.neuron.2010.11.009

PubMed: 21144998

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Abstract:

The medial temporal lobe (MTL) is generally thought to be critical for explicit, but not implicit, memory. Here, we demonstrate that the perirhinal cortex (PRc), within the MTL, plays a role in conceptuallydriven implicit memory. Amnesic patients with MTL lesions that converged on the left PRc exhibited defi- cits on two conceptual implicit tasks (i.e., exemplar generation and semantic decision). A separate functional magnetic resonance imaging (fMRI) study in healthy subjects indicated that PRc activation during encoding of words was predictive of subsequent exemplar generation. Moreover, across subjects, the magnitude of the fMRI and behavioral conceptual priming effects were directly related. Additionally, the PRc region implicated in the fMRI study was the same region of maximal lesion overlap in the patients with impaired conceptual priming. These patient and imaging results converge to suggest that the PRc plays a critical role in conceptual implicit memory, and possibly conceptual processing in general.

Single-trial speech suppression of auditory cortex activity in humans.

Authors:

• Adeen Flinker

• Edward F. Chang

• Heidi E. Kirsch

• Nicholas M. Barbaro

• Nathan E. Crone

• Robert T. Knight

Date: 2010

PubMed: 21148003

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Abstract:

The human auditory cortex is engaged in monitoring the speech of interlocutors as well as self-generated speech. During vocalization, auditory cortex activity is reported to be suppressed, an effect often attributed to the influence of an efference copy from motor cortex. Single-unit studies in non-human primates have demonstrated a rich dynamic range of single-trial auditory responses to self-speech consisting of suppressed, nonsuppressed and excited auditory neurons. However, human research using noninvasive methods has only reported suppression of averaged auditory cortex responses to self-generated speech. We addressed this discrepancy by recording electrocorticographic activity from neurosurgical subjects performing auditory repetition tasks. We observed that the degree of suppression varied across different regions of auditory cortex, revealing a variety of suppressed and nonsuppressed responses during vocalization. Importantly, single-trial high-gamma power (γ(High), 70-150 Hz) robustly tracked individual auditory events and exhibited stable responses across trials for suppressed and nonsuppressed regions.

The functional role of cross-frequency coupling

Authors:

• Ryan T. Canolty

• Robert T. Knight

Date: 2010

DOI: 10.1016/j.tics.2010.09.00

PubMed: 20932795

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Abstract:

Recent studies suggest that cross-frequency coupling (CFC) might play a functional role in neuronal computation, communication and learning. In particular, the strength of phase-amplitude CFC differs across brain areas in a task-relevant manner, changes quickly in response to sensory, motor and cognitive events, and correlates with performance in learning tasks. Importantly, whereas high-frequency brain activity reflects local domains of cortical processing, low-frequency brain rhythms are dynamically entrained across distributed brain regions by both external sensory input and internal cognitive events. CFC might thus serve as a mechanism to transfer information from large-scale brain networks operating at behavioral timescales to the fast, local cortical processing required for effective computation and synaptic modification, thus integrating functional systems across multiple spatiotemporal scales

Shifts in gamma phase-amplitude coupling frequency from theta to alpha over posterior cortex during visual tasks

Authors:

• Bradley Voytek

• Ryan T. Canolty

• Avgusta Shestyuk

• Nathan E. Crone

• Josef Parvizi

• Robert T. Knight

Date: 2010

DOI: 10.3389/fnhum.2010.00191

PubMed: 21060716

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Abstract:

The phase of ongoing theta (4–8 Hz) and alpha (8–12 Hz) electrophysiological oscillations is coupled to high gamma (80–150 Hz) amplitude, which suggests that low-frequency oscillations modulate local cortical activity. While this phase–amplitude coupling (PAC) has been demonstrated in a variety of tasks and cortical regions, it has not been shown whether task demands differentially affect the regional distribution of the preferred low-frequency coupling to high gamma. To address this issue we investigated multiple-rhythm theta/alpha to high gamma PAC in two subjects with implanted subdural electrocorticographic grids. We show that high gamma amplitude couples to the theta and alpha troughs and demonstrate that, during visual tasks, alpha/high gamma coupling preferentially increases in visual cortical regions. These results suggest that low-frequency phase to high-frequency amplitude coupling is modulated by behavioral task and may reflect a mechanism for selection between communicating neuronal networks.

Categorical speech representation in the human superior temporal gyrus

Authors:

• Edward F. Chang

• Jochem W. Rieger

• Keith Johnson

• Mitchel S. Berger

• Nicholas M. Barbaro

• Robert T. Knight

Date: 2010

DOI: 10.1038/nn.264

PubMed: 20890293

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Abstract:

Speech perception requires the rapid and effortless extraction of meaningful phonetic information from a highly variable acoustic signal. A powerful example of this phenomenon is categorical speech perception, in which a continuum of acoustically varying sounds is transformed into perceptually distinct phoneme categories. We found that the neural representation of speech sounds is categorically organized in the human posterior superior temporal gyrus. Using intracranial high-density cortical surface arrays, we found that listening to synthesized speech stimuli varying in small and acoustically equal steps evoked distinct and invariant cortical population response patterns that were organized by their sensitivities to critical acoustic features. Phonetic category boundaries were similar between neurometric and psychometric functions. Although speech-sound responses were distributed, spatially discrete cortical loci were found to underlie specific phonetic discrimination. Our results provide direct evidence for acoustic-to–higher order phonetic level encoding of speech sounds in human language receptive cortex.

Categorical speech representation in human superior temporal gyrus

Authors:

• Edward F. Chang

• Jochem W. Rieger

• Keith Johnson

• Mitchel S. Berger

• Nicholas M. Barbaro

• Robert T. Knight

Date: 2010

PubMed: 20890293

View PDF

Abstract:

Speech perception requires the rapid and effortless extraction of meaningful phonetic information from a highly variable acoustic signal. A powerful example of this phenomenon is categorical speech perception, in which a continuum of acoustically varying sounds is transformed into perceptually distinct phoneme categories. We found that the neural representation of speech sounds is categorically organized in the human posterior superior temporal gyrus. Using intracranial high-density cortical surface arrays, we found that listening to synthesized speech stimuli varying in small and acoustically equal steps evoked distinct and invariant cortical population response patterns that were organized by their sensitivities to critical acoustic features. Phonetic category boundaries were similar between neurometric and psychometric functions. Although speech-sound responses were distributed, spatially discrete cortical loci were found to underlie specific phonetic discrimination. Our results provide direct evidence for acoustic-to–higher order phonetic level encoding of speech sounds in human language receptive cortex.

Categorical speech representation in human superior temporal gyrus

Authors:

• Edward F. Chang

• Jochem W. Rieger

• Keith Johnson

• Mitchel S. Berger

• Nicholas M. Barbaro

• Robert T. Knight

Date: 2010

PubMed: 20890293

View PDF

Abstract:

Speech perception requires the rapid and effortless extraction of meaningful phonetic information from a highly variable acoustic signal. A powerful example of this phenomenon is categorical speech perception, in which a continuum of acoustically varying sounds is transformed into perceptually distinct phoneme categories. We found that the neural representation of speech sounds is categorically organized in the human posterior superior temporal gyrus. Using intracranial high-density cortical surface arrays, we found that listening to synthesized speech stimuli varying in small and acoustically equal steps evoked distinct and invariant cortical population response patterns that were organized by their sensitivities to critical acoustic features. Phonetic category boundaries were similar between neurometric and psychometric functions. Although speech-sound responses were distributed, spatially discrete cortical loci were found to underlie specific phonetic discrimination. Our results provide direct evidence for acoustic-to–higher order phonetic level encoding of speech sounds in human language receptive cortex.

Dynamic neuroplacticity after human prefrontal cortex damage

Authors:

• Bradley Voytek

• Matar Davis

• Elena Yago

• Francisco Barceló

• Edward K. Vogel

• Robert T. Knight

Date: 2010

DOI: 10.1016/j.neuron.2010.09.018

PubMed: 21040843

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Abstract:

Memory and attention deficits are common after prefrontal cortex (PFC) damage, yet people generally recover some function over time. Recovery is thought to be dependent upon undamaged brain regions, but the temporal dynamics underlying cognitive recovery are poorly understood. Here, we provide evidence that the intact PFC compensates for damage in the lesioned PFC on a trial-by-trial basis dependent on cognitive load. The extent of this rapid functional compensation is indexed by transient increases in electrophysiological measures of attention and memory in the intact PFC, detectable within a second after stimulus presentation and only when the lesioned hemisphere is challenged. These observations provide evidence supporting a dynamic and flexible model of compensatory neural plasticity.

Poverty, stress and cognitive functioning

Authors:

• Mark M. Kishiyama

• Robert T. Knight

Date: 2010

Abstract:

Social inequalities in income and wealth have a profound effect on the physical and mental health of children. For example, children from low-socioeconomic-status (SES) backgrounds are at greater risk for most forms of childhood morbidities compared to children from higher-SES backgrounds. [Note that the determination of SES is based on varying indices of family income (in relation to federally determined poverty thresholds), parental education (for example, those with college degrees versus those without), and parental occupation (for example, professional versus unskilled labor)]. Impoverished conditions during childhood are associated with poorer adult health, and low childhood SES may be the single most powerful contributor to premature mortality and morbidity worldwide. Significant relationships have been observed between SES and cognitive ability and between SES and academic achievement in childhood. In fact, SES has a stronger relationship with cognitive performance than does physical health. Children from low-SES backgrounds perform below children from higher-SES backgrounds on tests of intelligence and academic achievement. In addition, SES has been found to have a major effect on language development. For example, one study found that the average vocabulary size of 3-year-old children from families receiving welfare was less than half the size of the average vocabulary of children from higher-SES (professional) families. Low-SES children are also more likely to fail courses, be placed in special education, and drop out of high school compared to high-SES children.

Faces are special but not too special: spared face recognition in amnesia is based on familiarity

Authors:

• Mariam Aly

• Robert T. Knight

• Andrew P. Yonelinas

Date: 2010

DOI: 10.1016/j.neuropsychologia.2010.09.005

PubMed: 20833190

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Abstract:

Most current theories of human memory are material-general in the sense that they assume that the medial temporal lobe (MTL) is important for retrieving the details of prior events, regardless of the specific type of materials. Recent studies of amnesia have challenged the material-general assumption by suggesting that the MTL may be necessary for remembering words, but is not involved in remembering faces. We examined recognition memory for faces and words in a group of amnesic patients, which included hypoxic patients and patients with extensive left or right MTL lesions. Recognition confidence judgments were used to plot receiver operating characteristics (ROCs) in order to more fully quantify recognition performance and to estimate the contributions of recollection and familiarity. Consistent with the extant literature, an analysis of overall recognition accuracy showed that the patients were impaired at word memory but had spared face memory. However, the ROC analysis indicated that the patients were generally impaired at high confidence recognition responses for faces and words, and they exhibited significant recollection impairments for both types of materials. Familiarity for faces was preserved in all patients, but extensive left MTL damage impaired familiarity for words. These results show that face recognition may appear to be spared because performance tends to rely heavily on familiarity, a process that is relatively well preserved in amnesia. In addition, the findings challenge material-general theories of memory, and suggest that both material and process are important determinants of memory performance in amnesia.