, , , , , , , , , ,

Spatial localization of cortical time-frequency dynamics

, , , , , , , , , ,

Authors:

  • Sarang S. Dalal

  • Adrian G. Guggisberg

  • Erik Edwards

  • Kensuke Sekihara

  • Anne M. Findlay

  • Ryan T. Canolty

  • Robert T. Knight

  • Nicholas M. Barbaro

  • Heidi E. Kirsch

  • Srikantan S. Nagarajan

Date: 2007

PubMed: 18003115

View PDF

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. 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 real MEG data from a self-paced finger movement task. The algorithm reliably reveals modulations both in the beta band (12-30 Hz) and a 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. We also revealed observed high gamma activity in the cerebellum. The proposed algorithm is highly parallelizable and runs efficiently on modern high performance computing clusters. This method enables non-invasive five-dimensional imaging of space, time, and frequency activity in the brain and renders it applicable for widespread studies of human cortical dynamics.

, ,

Theoretical sequelae of a chronic neglect and unawareness of prefrontotectal pathways in the human brain

, ,

Authors:

  • Francisco Barceló

  • Robert T. Knight

Date: 2007

DOI: 10.1017/S0140525X07000921

View PDF

Abstract:

Attention research with prefrontal patients supports Merker's argument regarding the crucial role for the midbrain in higher cognition, through largely overlooked and misunderstood prefrontotectal connectivity. However, information theoretic analyses reveal that both exogenous (i.e., collicular) and endogenous (prefrontal) sources of information are responsible for large-scale context-sensitive brain dynamics, with prefrontal cortex being at the top of the hierarchy for cognitive control.

, ,

An information theoretical approach to contextual processing in the human brain: evidence from prefrontal lesions

, ,

Authors:

  • Francisco Barceló

  • Robert T. Knight

Date: 2007

DOI: 10.1093/cercor/bhm111

PubMed: 17726004

View PDF

Abstract:

Context shapes perception, thought, and action, but little is known about the neural mechanisms supporting these modulations. Here, we addressed the role of lateral prefrontal cortex (PFC) in context updating and maintenance from an information-theoretic perspective. Ten patients with PFC lesions and 10 age-matched controls responded to bilaterally displayed visual targets intermixed with repetitive and novel distracters in 2 different task contexts. In a predictable context, targets were always preceded by a novel event, whereas this temporal contingency was removed in an unpredictable context condition. We applied information theory to the analysis and interpretation of behavioral and electrophysiological data. The results revealed deficits in both the selection and the suppression of familiar versus novel information mainly observed at the visual hemifield contralateral to PFC damage due to disrupted frontocortical and frontosubcortical connectivity. The findings support a deficit in the representation of the temporal contingency between contextually related novel and familiar stimulation subsequent to lateral PFC damage.

, , , , , , , , ,

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

View PDF

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.

, , , ,

Amygdala response to facial expressions reflects emotional learning

, , , ,

Authors:

  • Christine I. Hooker

  • Laura T. Germine

  • Robert T. Knight

  • Mark D'Esposito

Date: 2006

PubMed: 16943547

View PDF

Abstract:

The functional role of the human amygdala in the evaluation of emotional facial expressions is unclear. Previous animal and human research shows that the amygdala participates in processing positive and negative reinforcement as well as in learning predictive associations between stimuli and subsequent reinforcement. Thus, amygdala response to facial expressions could reflect the processing of primary reinforcement or emotional learning. Here, using functional magnetic resonance imaging, we tested the hypothesis that amygdala response to facial expressions is driven by emotional association learning. We show that the amygdala is more responsive to learning object-emotion associations from happy and fearful facial expressions than it is to the presentation of happy and fearful facial expressions alone. The results provide evidence that the amygdala uses social signals to rapidly and flexibly learn threatening and rewarding associations that ultimately serve to enhance survival.

, , , ,

Spatial location is accurately tracked by human auditory sensory memory: evidence from the mismatch negativity

, , , ,

Authors:

  • Leon Y. Deouell

  • Ariel Parnes

  • Natasha Pickard

  • Robert T. Knight

Date: 2006

PubMed: 16987229

View PDF


Abstract:

The nature of spatial representation in human auditory cortex remains elusive. In particular, although humans can discriminate the locations of sounds as close as 1-10 degrees apart, such resolution has not been shown in auditory cortex of humans or animals. We used the mismatch negativity (MMN) event related brain potential to measure the neural response to spatial change in humans in narrow 10 degree spatial steps. Twelve participants were tested using a dense array EEG setup while watching a silent movie and ignoring the sounds. The MMN was reliably elicited by infrequent changes of spatial location of sounds in free field. The MMN amplitude was linearly related to the degree of spatial change with a resolution of at least 10 degrees. These electrophysiological responses occurred within a window of 100-200 milliseconds from stimulus onset, and were localized to the posterior superior temporal gyrus. We conclude that azimuthal spatial displacement is rapidly, accurately and automatically represented in auditory sensory memory in humans, at the level of the auditory cortex.

, , ,

Controlling the integration of emotion and cognition: the role of frontal cortex in distinguishing helpful from hurtful emotional information

, , ,

Authors:

  • Jennifer S. Beer

  • Robert T. Knight

  • Mark D'Esposito

Date: 2006

PubMed: 16683934

View PDF

Abstract:

Emotion has been both lauded and vilified for its role in decision making. How are people able to ensure that helpful emotions guide decision making and irrelevant emotions are kept out of decision making? The orbitofrontal cortex has been identified as a neural area involved in incorporating emotion into decision making. Is this area's function specific to the integration of emotion and cognition, or does it more broadly govern whether emotional information should be integrated into cognition? The present research examined the role of orbitofrontal cortex when it was appropriate to control (i.e., prevent) the influence of emotion in decision making (Experiment 1) and to incorporate the influence of emotion in decision making (Experiment 2). Together, the two studies suggest that activity in lateral orbitofrontal cortex is associated with evaluating the contextual relevance of emotional information for decision making.

, , ,

Orbitofrontal Cortex and Social Behavior: Integrating Self-monitoring and Emotion-Cognition Interactions

, , ,

Authors:

  • Jennifer S. Beer

  • Oliver P. John

  • Robert T. Knight

Date: 2006

PubMed: 16839295

View PDF

Abstract:

The role of the orbitofrontal cortex in social behavior remains a puzzle. Various theories of the social functions of the orbitofrontal cortex focus on the role of this area in either emotional processing or its involvement in online monitoring of behavior (i.e., self-monitoring). The present research attempts to integrate these two theories by examining whether improving the self-monitoring of patients with orbitofrontal damage is associated with the generation of emotions needed to guide interpersonal behavior. Patients with orbitofrontal damage, patients with lateral prefrontal damage, and healthy controls took part in an interpersonal task. After completing the task, participants' self-monitoring was increased by showing them a videotape of their task performance. In comparison to healthy controls and patients with lateral prefrontal damage, orbitofrontal damage was associated with objectively inappropriate social behavior. Although patients with orbitofrontal damage were aware of social norms of intimacy, they were unaware that their task performance violated these norms. The embarrassment typically associated with inappropriate social behavior was elicited in these patients only after their self-monitoring increased from viewing their videotaped performance. These findings suggest that damage to the orbitofrontal cortex impairs self-insight that may preclude the generation of helpful emotional information. The results highlight the role of the orbitofrontal cortex in the interplay of self-monitoring and emotional processing and suggest avenues for neurorehabilitation of patients with social deficits subsequent to orbitofrontal damage.

, , , ,

Intact recollection memory in high-performing older adults: ERP and behavioral evidence

, , , ,

Authors:

  • Audrey Duarte

  • Charan Ranganath

  • Celina Trujillo

  • Robert T. Knight

Date: 2006

PubMed: 16417681

View PDF

Abstract:

Numerous behavioral studies have suggested that normal aging has deleterious effects on episodic memory and that recollection is disproportionately impaired relative to familiarity-based recognition. However, there is a wide degree of variability in memory performance within the aging population and this generalization may not apply to all elderly adults. Here we investigated these issues by using event-related potentials (ERPs) to measure the effects of aging on the neural correlates of recollection and familiarity in older adults with recognition memory performance that was equivalent to (old-high) or lower than (old-low) that of young adults. Results showed that, behaviorally, old-high subjects exhibited intact recollection but reduced familiarity, whereas old-low subjects had impairments in both recollection and familiarity, relative to the young. Consistent with behavioral results, old-high subjects exhibited ERP correlates of recollection that were topographically similar to those observed in young subjects. However, unlike the young adults, old-high subjects did not demonstrate any neural correlates of familiarity-based recognition. In contrast to the old-high group, the old-low group exhibited neural correlates of recollection that were topographically distinct from those of the young. Our results suggest that the effects of aging on the underlying brain processes related to recollection and familiarity are dependent on individual memory performance and highlight the importance of examining performance variability in normal aging.

, ,

The functional neuroanatomy of working memory: contributions from human brain lesion studies

, ,

Authors:

  • Notger G. Muller

  • Robert T. Knight

Date: 2006

PubMed: 16352402

View PDF

Abstract:

Studies of patients with focal brain lesions remain critical components of research programs attempting to understand human brain function. Whereas functional imaging typically reveals activity in distributed brain regions that are involved in a task, lesion studies can define which of these brain regions are necessary for a cognitive process. Further, lesion studies are less critical regarding the selection of baseline conditions needed in functional brain imaging research. Lesion studies suggest a functional subdivision of the visuospatial sketchpad of working memory with a ventral stream reaching from occipital to temporal cortex supporting object recognition and a dorsal stream connecting the occipital with parietal cortex enabling spatial operations. The phonological loop can be divided into a phonological short-term store in inferior parietal cortex and an articulatory subvocal rehearsal process relying on brain areas necessary for speech production, i.e. Broca's area, the supplementary motor association area and possibly the cerebellum. More uncertainty exists regarding the role of the prefrontal cortex in working memory. Whereas single cell studies in non-human primates and functional imaging studies in humans have suggested an extension of the ventral and dorsal path into different subregions of the prefrontal cortex, lesion studies together with recent single-cell and imaging studies point to a non-mnemonic role of the prefrontal cortex, including attentional control of sensory processing, integration of information from different domains, stimulus selection and monitoring of information held in memory. Our own data argue against a modulatory view of the prefrontal cortex and suggest that processes supporting working memory are distributed along ventral and dorsal lateral prefrontal cortex.

, , , ,

Lapses in a Prefrontal-Extrastriate Preparatory Attention Network Predict Mistakes

, , , ,

Authors:

  • Mayra Padilla

  • Richard A. Wood

  • Laura A. Hale

  • Robert T. Knight

Date: 2006

PubMed: 16989549

View PDF


Abstract:

Mistakes are common to all forms of behavior but there is disagreement about what causes errors. We recorded electrophysiological and behavioral measures in a letter discrimination task to examine whether deficits in preparatory attention predicted subsequent response errors. Error trials were characterized by decreased frontal-central preparatory attention event-related potentials (ERPs) prior to stimulus presentation and decreased extrastriate sensory ERPs during visual processing. These findings indicate that transient lapses in a prefrontal-extrastriate preparatory attention network can lead to response errors.

, , ,

Effects of unilateral prefrontal lesions on familiarity, recollection, and source memory

, , ,

Authors:

  • Audrey Duarte

  • Charan Ranganath

  • Robert T. Knight

Date: 2005

PubMed: 16148241

View PDF

Abstract:

Recognition memory can be supported by both the assessment of the familiarity of an item and by recollection of the context in which an item was encountered. Some have hypothesized that the prefrontal cortex (PFC) disproportionately contributes to recollection, whereas an alternative view is that the PFC contributes to both recollection and familiarity. Here, we examined the effects of prefrontal lesions on recollection and familiarity. Patients with unilateral PFC lesions and age-, gender-, and education-matched controls encoded pictures of meaningful objects that were presented briefly to the left or right visual field and subsequently performed recognition tests for centrally presented objects. Laterality effects within the PFC were also assessed in relation to recollection and familiarity processes. Patients with prefrontal lesions showed impaired familiarity-based recognition, and this deficit was specific for objects encoded by the lesioned hemisphere. In addition, recollection of the context in which each item was encountered was impaired independent of the visual field of presentation in patients with left prefrontal lesions. Recollection measured by subjective reports ("remember") was not impaired in either left or right frontal patients. These findings suggest that the PFC plays a critical role in recognition memory based on familiarity as well as recollection. Furthermore, these results suggest that left PFC regions are critical for source recollection.

, , , , ,

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

View PDF

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

View PDF

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

View PDF

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.

, , , , ,

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

View PDF

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.