Biomedical subjects

Tobias Egner

Publications and source records attributed to Tobias Egner.

At least 19 recordsLinked to original sources

PubMed2006

Predictive codes for forthcoming perception in the frontal cortex.

Incoming sensory information is often ambiguous, and the brain has to make decisions during perception. "Predictive coding" proposes that the brain resolves perceptual ambiguity by anticipating the forthcoming sensory environment, generating a template against which to match observed sensory evidence. We observed a neural representation of predicted perception in the medial frontal cortex, while human subjects decided whether visual objects were faces or not. Moreover, perceptual decisions about faces were associated with an increase in top-down connectivity from the frontal cortex to face-sensitive visual areas, consistent with the matching of predicted and observed evidence for the presence of faces.

Amygdala↗

PubMed2006

Resolving emotional conflict: a role for the rostral anterior cingulate cortex in modulating activity in the amygdala.

Effective mental functioning requires that cognition be protected from emotional conflict due to interference by task-irrelevant emotionally salient stimuli. The neural mechanisms by which the brain detects and resolves emotional conflict are still largely unknown, however. Drawing on the classic Stroop conflict task, we developed a protocol that allowed us to dissociate the generation and monitoring of emotional conflict from its resolution. Using functional magnetic resonance imaging (fMRI), we find that activity in the amygdala and dorsomedial and dorsolateral prefrontal cortices reflects the amount of emotional conflict. By contrast, the resolution of emotional conflict is associated with activation of the rostral anterior cingulate cortex. Activation of the rostral cingulate is predicted by the amount of previous-trial conflict-related neural activity and is accompanied by a simultaneous and correlated reduction of amygdalar activity. These data suggest that emotional conflict is resolved through top-down inhibition of amygdalar activity by the rostral cingulate cortex.

Adult↗

PubMed2006

Organ-preserving endoscopic kidney cancer resection.

OBJECTIVE: Recently, minimally invasive therapies for renal cell carcinoma have been devised to minimise operative morbidity yet achieve comparable oncologic and functional outcomes. This video summary of laparoscopic transperitoneal organ-preserving kidney cancer resection shows the procedure from the surgeon's view. METHODS: The video and photos show the main steps of the procedure. The results of 40 transperitoneal and retroperitoneal procedures performed during 2001-2005 are discussed. Preoperative preparation includes abdominal computed tomography and ureteral catheterisation. Tumour margins were determined by laparoscopic renal ultrasonography. Vessel control was done by en bloc clamping or solitary clamping of the artery. For optimal macroscopic evaluation of the resection margins, tumour excision was solely done with cold Endoshears followed by pelvicaliceal suture repair and parenchymal closure over surgical bolsters with a biologic haemostatic agent. RESULTS: In 40 cases, we converted to the open procedure only once. The average patients age was 53 yr and mean tumour size was 26 mm. No patient showed positive surgical margins. The mean warm ischemia time was 21 min. Final histopathology revealed renal clear cell carcinoma as the major cell type followed by papillary renal carcinoma. Two patients required blood transfusion. Estimated mean blood loss was 270 ml. Median time of hospitalisation was 6 d. CONCLUSION: Endoscopic partial nephrectomy can be performed by experienced surgeons in selected patients. Tumour location and size and the surgeons' experience and preference are the main parameters to make the decision of the type of access.

Endoscopy↗

PubMed2006

Neocortical connectivity during episodic memory formation.

During the formation of new episodic memories, a rich array of perceptual information is bound together for long-term storage. However, the brain mechanisms by which sensory representations (such as colors, objects, or individuals) are selected for episodic encoding are currently unknown. We describe a functional magnetic resonance imaging experiment in which participants encoded the association between two classes of visual stimuli that elicit selective responses in the extrastriate visual cortex (faces and houses). Using connectivity analyses, we show that correlation in the hemodynamic signal between face- and place-sensitive voxels and the left dorsolateral prefrontal cortex is a reliable predictor of successful face-house binding. These data support the view that during episodic encoding, "top-down" control signals originating in the prefrontal cortex help determine which perceptual information is fated to be bound into the new episodic memory trace.

Adult↗

PubMed2006

Foundation and practice of neurofeedback for the treatment of epilepsy.

This review provides an updated overview of the neurophysiological rationale, basic and clinical research literature, and current methods of practice pertaining to clinical neurofeedback. It is based on documented findings, rational theory, and the research and clinical experience of the authors. While considering general issues of physiology, learning principles, and methodology, it focuses on the treatment of epilepsy with sensorimotor rhythm (SMR) training, arguably the best established clinical application of EEG operant conditioning. The basic research literature provides ample data to support a very detailed model of the neural generation of SMR, as well as the most likely candidate mechanism underlying its efficacy in clinical treatment. Further, while more controlled clinical trials would be desirable, a respectable literature supports the clinical utility of this alternative treatment for epilepsy. However, the skilled practice of clinical neurofeedback requires a solid understanding of the neurophysiology underlying EEG oscillation, operant learning principles and mechanisms, as well as an in-depth appreciation of the ins and outs of the various hardware/software equipment options open to the practitioner. It is suggested that the best clinical practice includes the systematic mapping of quantitative multi-electrode EEG measures against a normative database before and after treatment to guide the choice of treatment strategy and document progress towards EEG normalization. We conclude that the research literature reviewed in this article justifies the assertion that neurofeedback treatment of epilepsy/seizure disorders constitutes a well-founded and viable alternative to anticonvulsant pharmacotherapy.

Animals↗

PubMed2006

Validating the efficacy of neurofeedback for optimising performance.

The field of neurofeedback training has largely proceeded without validation. Here we review our studies directed at validating SMR, beta and alpha-theta protocols for improving attention, memory, mood and music and dance performance in healthy participants. Important benefits were demonstrable with cognitive and neurophysiological measures which were predicted on the basis of regression models of learning. These are initial steps in providing a much needed scientific basis to neurofeedback, but much remains to be done.

Alpha Rhythm↗

PubMed2006

Neurofeedback treatment of epilepsy: from basic rationale to practical application.

The treatment of epilepsy through operant conditioning of the sensorimotor rhythm electroencephalogram has a 35-year history. Neurophysiological studies have shown that this phasic oscillation reflects an inhibitory state of the sensorimotor system. Operant learning of sensory motor rhythm production results in an upregulation of excitation thresholds within the thalamocortical sensory and motor circuitry, which in turn is associated with reduced susceptibility to seizures. The clinical benefits derived from this neurofeedback training protocol, particularly in patients that are nonresponsive to pharmacotherapy, have been documented in many independent laboratories. Recent advances in computer technology have resulted in the availability of relatively inexpensive high-quality equipment for the application of neurofeedback therapy, thus presenting a viable and promising treatment alternative to the interested clinician.

Animals↗

PubMed2005

Cognitive control mechanisms resolve conflict through cortical amplification of task-relevant information.

A prominent model of how the brain regulates attention proposes that the anterior cingulate cortex monitors the occurrence of conflict between incompatible response tendencies and signals this information to a cognitive control system in dorsolateral prefrontal cortex. Cognitive control is thought to resolve conflict through the attentional biasing of perceptual processing, emphasizing task-relevant stimulus information. It is not known, however, whether conflict resolution is mediated by amplifying neural representations of task-relevant information, inhibiting representations of task-irrelevant information, or both. Here we manipulated trial-by-trial levels of conflict and control during a Stroop task using face stimuli, while recording hemodynamic responses from human visual cortex specialized for face processing. We show that, in response to high conflict, cognitive control mechanisms enhance performance by transiently amplifying cortical responses to task-relevant information rather than by inhibiting responses to task-irrelevant information. These results implicate attentional target-feature amplification as the primary mechanism for conflict resolution through cognitive control.

Adult↗

PubMed2005

Hypnosis decouples cognitive control from conflict monitoring processes of the frontal lobe.

Hypnosis can profoundly alter sensory awareness and cognitive processing. While the cognitive and behavioral phenomena associated with hypnosis have long been thought to relate to attentional processes, the neural mechanisms underlying susceptibility to hypnotic induction and the hypnotic condition are poorly understood. Here, we tested the proposal that highly hypnotizable individuals are particularly adept at focusing attention at baseline, but that their attentional control is compromised following hypnosis due to a decoupling between conflict monitoring and cognitive control processes of the frontal lobe. Employing event-related fMRI and EEG coherence measures, we compared conflict-related neural activity in the anterior cingulate cortex (ACC) and control-related activity in the lateral frontal cortex (LFC) during Stroop task performance between participants of low and high hypnotic susceptibility, at baseline and after hypnotic induction. The fMRI data revealed that conflict-related ACC activity interacted with hypnosis and hypnotic susceptibility, in that highly susceptible participants displayed increased conflict-related neural activity in the hypnosis condition compared to baseline, as well as with respect to subjects with low susceptibility. Cognitive-control-related LFC activity, on the other hand, did not differ between groups and conditions. These data were complemented by a decrease in functional connectivity (EEG gamma band coherence) between frontal midline and left lateral scalp sites in highly susceptible subjects after hypnosis. These results suggest that individual differences in hypnotic susceptibility are linked with the efficiency of the frontal attention system, and that the hypnotized condition is characterized by a functional dissociation of conflict monitoring and cognitive control processes.

Adult↗

PubMed2005

Mistaking a house for a face: neural correlates of misperception in healthy humans.

Individuals with normal vision can sometimes momentarily mistake one object for another. In this functional magnetic resonance imaging study, we investigated how extrastriate visual regions respond during these erroneous perceptual judgements. Subjects were asked to discriminate images of houses and faces that were degraded such that they were close to an individually defined threshold for perception. On correct trials, voxels localized on the inferior occipital (OFA), fusiform (FFA) and parahippocampal (PPA) gyri exhibited selectivity for face and house images as expected. On incorrect trials, no face- or place-selectivity was observed for OFA or PPA. However, consistent with 'predictive coding' accounts of perception, we observed that the FFA also responded robustly on trials where a house was misperceived as a face, and concurrent activation was observed in medio-frontal and right parietal regions previously implicated in decision making under uncertainty. We suggest that FFA responses during misperception may be driven by a predictive top-down signal from these regions.

Adult↗

PubMed2005

The neural correlates and functional integration of cognitive control in a Stroop task.

It is well known that performance on a given trial of a cognitive task is affected by the nature of previous trials. For example, conflict effects on interference tasks, such as the Stroop task, are reduced subsequent to high-conflict trials relative to low-conflict trials. This interaction effect between previous and current trial types is called "conflict adaptation" and thought to be due to processing adjustments in cognitive control. The current study aimed to identify the neural substrates of cognitive control during conflict adaptation by isolating neural correlates of reduced conflict from those of increased cognitive control. We expected cognitive control to be implemented by prefrontal cortex through context-specific modulation of posterior regions involved in sensory and motor aspects of task performance. We collected event-related fMRI data on a color-word naming Stroop task and found distinct fronto-parietal networks of current trial conflict detection and conflict adaptation through cognitive control. Conflict adaptation was associated with increased activity in left middle frontal gyrus (GFm) and superior frontal gyrus (GFs), consistent with increased cognitive control, and with decreased activity in bilateral prefrontal and parietal cortices, consistent with reduced response conflict. Psychophysiological interaction analysis (PPI) revealed that cognitive control activation in GFs and GFm was accompanied by increased functional integration with bilateral inferior frontal, right temporal and parietal areas, and the anterior cerebellum. These data suggest that cognitive control is implemented by medial and lateral prefrontal cortices that bias processes in regions that have been implicated in high-level perceptual and motor processes.

Adult↗

PubMed2005

Intentional false responding shares neural substrates with response conflict and cognitive control.

The ability to deceive others is a high-level social and cognitive function. It has been suggested that response conflict and cognitive control increase during deceptive acts but this hypothesis has not been evaluated directly. Using fMRI, we tested this prediction for the execution of an intentional false response. Subjects were instructed to respond truthfully or falsely to a series of yes/no questions that were also varied in autobiographical and nonautobiographical content to further examine the influence of personal relevance when lying. We observed an interference effect (longer reaction times for false versus true responses) that was accompanied by increased activation within the anterior cingulate, caudate and thalamic nuclei, and dorsolateral prefrontal cortex (DLPFC), a circuit that has been implicated in response conflict and cognitive control. Behavioral and neural effects were more robust when falsifying autobiographical responses relative to nonautobiographical responses. Furthermore, a correlation between reaction time and left caudate activity supported the presence of increased response inhibition when falsifying responses. When presented with self-relevant (autobiographical) stimuli regardless of response condition, the mesial prefrontal and posterior cingulate cortices were recruited. Neural activity within these two regions and the anterior cingulate cortex (ACC) also showed correlations with self-report personality measures from the Psychopathic Personality Inventory (PPI). Overall, we conclude that the process of interference is inherent to the act of falsifying information and that the amount of conflict induced and cognitive control needed to successfully execute false responses is greater when dealing with personal information.

Adult↗

PubMed2005

Critical validation studies of neurofeedback.

The field of neurofeedback training has proceeded largely without validation. In this article the authors review studies directed at validating sensory motor rhythm, beta and alpha-theta protocols for improving attention, memory, and music performance in healthy participants. Importantly, benefits were demonstrable with cognitive and neurophysiologic measures that were predicted on the basis of regression models of learning to enhance sensory motor rhythm and beta activity. The first evidence of operant control over the alpha-theta ratio is provided, together with remarkable improvements in artistic aspects of music performance equivalent to two class grades in conservatory students. These are initial steps in providing a much needed scientific basis to neurofeedback.

Adolescent↗

PubMed2005

Where memory meets attention: neural substrates of negative priming.

The negative priming (NP) effect refers to the observed increase in identification time for a current target stimulus or stimulus feature (the "probe") that has been employed as a distractor stimulus or stimulus feature on the previous trial (the "prime"), representing strong evidence that ignored information is actively processed to a high level by selective attention systems. However, theoretical accounts of NP differ in whether they attribute the effect to processes of selective inhibition or episodic memory retrieval. Here we derived neurophysiological predictions from the rival "selective inhibition" and "episodic retrieval" models of NP, and employed event-related fMRI in a color-naming Stroop task to assess neural responses to probe trials that were subject to either no priming or negative priming. Compared to no-priming probe trials, NP resulted in increased activation of the right dorsolateral prefrontal cortex, in a region which has been closely linked with episodic memory retrieval functions. NP was also accompanied by activation of the right thalamus, particularly the mediodorsal nucleus, which has been implicated in the pathophysiology of schizophrenia, a condition associated with diminished NP effects. Our results support the proposal that ignored stimulus information is fully encoded in memory, and that episodic retrieval, not selective inhibition, of such information affects selective attention performance on subsequent trials.

Adolescent↗

PubMed2004

The effects of neurofeedback training on the spectral topography of the electroencephalogram.

OBJECTIVE: To investigate the impact of EEG frequency band biofeedback (neurofeedback) training on spectral EEG topography, which is presumed to mediate cognitive-behavioural training effects. In order to assess the effect of commonly applied neurofeedback protocols on spectral EEG composition, two studies involving healthy participants were carried out. METHODS: In Experiment 1, subjects were trained on low beta (12-15 Hz), beta1 (15-18 Hz), and alpha/theta (8-11 Hz/5-8 Hz) protocols, with spectral resting EEG assessed before and after training. The specific associations between learning indices of each individual training protocol and changes in absolute and relative spectral EEG topography was assessed by means of partial correlation analyses. Results of Experiment 1 served to generate hypotheses for Experiment 2, where subjects were randomly allocated to independent groups of low beta, beta1, and alpha/theta training. Spectral resting EEG measures were contrasted prior and subsequent to training within each group. RESULTS: Only few associations between particular protocols and spectral EEG changes were found to be consistent across the two studies, and these did not correspond to expectations based on the operant contingencies trained. Low-beta training was found to be somewhat associated with reduced post-training low-beta activity, while more reliably, alpha/theta training was associated with reduced relative frontal beta band activity. CONCLUSIONS: The results document that neurofeedback training of frequency components does affect spectral EEG topography in healthy subjects, but that these effects do not necessarily correspond to either the frequencies or the scalp locations addressed by the training contingencies. The association between alpha/theta training and replicable reductions in frontal beta activity constitutes novel empirical neurophysiological evidence supporting inter alia the training's purported role in reducing agitation and anxiety. SIGNIFICANCE: These results underline the complexity of the neural dynamics involved EEG self-regulation and emphasize the need for empirical validation of predictable neurophysiological outcomes of training EEG biofeedback protocols.

Adult↗

PubMed2004

Memory structures for encoding and retrieving a piece of music: an ERP investigation.

This study examined behavioral and neural correlates of expert musical memory, specifically the hypothesis that particular bars within a complex piece of music would serve as structural markers for encoding to and retrieval from memory. Six pianists were asked to learn and memorize a set prelude by J.S. Bach for performance, and to identify bars that they employed for structuring the prelude into component sections. Following performance from memory, the participants took part in a visual recognition memory task, in which single bars from the prelude had to be distinguished from matched new bars. During the recognition task, the electroencephalogram (EEG) was recorded, and event-related potentials (ERPs) from correctly identified prelude stimulus trials were averaged according to their hypothesized status into "structural" and "nonstructural" bars. The results showed that correct identification of structural bars was significantly faster (and tended to display higher accuracy) than recognition of non-structural ones. In addition, recognition of structural bars was associated with a significantly greater negative ERP peak of 300-400 ms latency and a right centro-parietal scalp distribution. This mid-latency negativity appears to index processing of stimuli that served as cues for encoding and retrieval of a complex semantic structure, and is qualitatively and conceptually different from other previously identified recognition memory ERPs (such as the "old/new" effect), as well as from the classic N400 ERP. The data support existing theories of expert memory and music cognition.

Adult↗

PubMed2003

Ecological validity of neurofeedback: modulation of slow wave EEG enhances musical performance.

Biofeedback-assisted modulation of electrocortical activity has been established to have intrinsic clinical benefits and has been shown to improve cognitive performance in healthy humans. In order to further investigate the pedagogic relevance of electroencephalograph (EEG) biofeedback (neurofeedback) for enhancing normal function, a series of investigations assessed the training's impact on an ecologically valid real-life behavioural performance measure: music performance under stressful conditions in conservatoire students. In a pilot study, single-blind expert ratings documented improvements in musical performance in a student group that received training on attention and relaxation related neurofeedback protocols, and improvements were highly correlated with learning to progressively raise theta (5-8 Hz) over alpha (8-11 Hz) band amplitudes. These findings were replicated in a second experiment where an alpha/theta training group displayed significant performance enhancement not found with other neurofeedback training protocols or in alternative interventions, including the widely applied Alexander technique.

Adult↗

PubMed2003

The effect of training distinct neurofeedback protocols on aspects of cognitive performance.

The use of neurofeedback as an operant conditioning paradigm has disclosed that participants are able to gain some control over particular aspects of their electroencephalogram (EEG). Based on the association between theta activity (4-7 Hz) and working memory performance, and sensorimotor rhythm (SMR) activity (12-15 Hz) and attentional processing, we investigated the possibility that training healthy individuals to enhance either of these frequencies would specifically influence a particular aspect of cognitive performance, relative to a non-neurofeedback control-group. The results revealed that after eight sessions of neurofeedback the SMR-group were able to selectively enhance their SMR activity, as indexed by increased SMR/theta and SMR/beta ratios. In contrast, those trained to selectively enhance theta activity failed to exhibit any changes in their EEG. Furthermore, the SMR-group exhibited a significant and clear improvement in cued recall performance, using a semantic working memory task, and to a lesser extent showed improved accuracy of focused attentional processing using a 2-sequence continuous performance task. This suggests that normal healthy individuals can learn to increase a specific component of their EEG activity, and that such enhanced activity may facilitate semantic processing in a working memory task and to a lesser extent focused attention. We discuss possible mechanisms that could mediate such effects and indicate a number of directions for future research.

Adult↗