Motive related positivity: decision-making during a prisoners' dilemma task.

The neural mechanisms underlying decision-making to cooperate or defect were investigated using event-related potentials during an iterated computer Prisoner's Dilemma task, adapted to induce working memory operation. Event-related potentials from 64 leads of 22 participants were recorded during 90 trials and averaged depending on the condition of cooperation and defect. The P200 component of the event-related potentials provided evidence for activation differences between cooperation and defect. Cooperation elicited significantly increased P200 activation at parieto-occipital leads, while defect activated primarily the prefrontal electrodes. Functional mapping using Low Resolution Electromagnetic Tomography indicated that in the 150-180 ms time window Brodmann areas 19 (precuneus) and 17 (lingual gyrus), exhibited increased activation during cooperation, while Brodmann area 6 (precentral gyrus) exhibited increased activation when participants defected. In conclusion, the current study provides evidence that cooperation and defect elicit different brain activation at specific loci and within specific time windows.

Effect of frequency deviance direction on performance and mismatch negativity.

The mismatch negativity (MMN) component of the auditory event-related potential is associated with automatic perceptual inference concerning changes in auditory stimulation. Recent studies have addressed the question whether performance and MMN is affected by the direction of frequency deviance. In the present study, the frequency MMN and performance is investigated during an auditory identification task. Specifically, we examined the effect of positive and negative differences between the present stimulus and the previous response frequencies on performance as well as on the characteristics of stimulus-locked ERPs and brain activation maps. The results show that frequency deviants creating mismatch conditions increase the likelihood of error commission. The decrease in performance achieves statistical significance in the case of positive frequency deviants. In the latter case, ERP amplitude values of the Fz electrode at 164 ms after stimulus onset are statistically larger for mismatch as opposed to no-mismatch condition. This corresponds to significance differences in the activation maps at Brodmann area 11, superior frontal gyrus, and the frontal lobe. The present findings revealed dissociations in behavioral and ERP responses in the processing of positive and negative frequency deviance, lending support to the notion that MMN is more sensitive to increments than to decrements in frequency.

Mismatch task conditions and error related ERPs.

BACKGROUND: The N200 component of event related potentials (ERPs) is considered an index of monitoring error related responses. The aim of the present work was to study the effect of mismatch conditions on the subjects' responses in an auditory identification task and their relation to the N200 of stimulus-locked ERPs. METHODS: An auditory identification task required to correctly map a horizontal slider onto an active frequency range by selecting a slider position that matched the stimulus tone in each trial. Fourteen healthy volunteers participated in the study and ERPs were recorded by 32 leads. RESULTS: Results showed that the subjects' erroneous responses were equally distributed within trials, but were dependent on mismatch conditions, generated by large differences between the frequencies of the tones of consecutive trials. Erroneous trials showed a significantly greater negativity within the time window of 164-191 ms after stimulus, located mainly at the Cz and Fz electrodes. The LORETA solution showed that maximum activations, as well as maximum differences, were localized mainly at the frontal lobe. CONCLUSIONS: These findings suggest that the fronto-central N200 component, conceived an index of "reorientation of attention", represents a correlate of an error signal, being produced when representation of the actual response and the required response are compared. Furthermore the magnitude of the amplitude of the N200 rests on the relation between the present and the previous stimulus.

Contactless passive diagnosis for brain intracranial applications: A study using dielectric matching materials.

A prototype system for passive intracranial monitoring using microwave radiometry is proposed. It comprises an ellipsoidal conductive wall cavity to achieve beamforming and focusing, in conjunction with sensitive multiband receivers for detection. The system has already shown the capability to provide temperature and/or conductivity variations in phantoms and biological tissue. In this article, a variant of the initially constructed modality is theoretically and experimentally investigated. Specifically, dielectric matching materials are used in an effort to improve the system's focusing attributes. The theoretical study investigates the effect of dielectric matching materials on the system's detection depth, whereas measurements with phantoms focus on the investigation of the system's detection level and spatial resolution. The combined results suggest that the dielectric matching layers lead to the improvement of the system's detection depth and temperature detection level. Also, the system's spatial resolution is explored at various experimental setups. Theoretical and experimental results conclude that with the appropriate combination of operation frequencies and dielectric layers, it is possible to monitor areas of interest inside human head models with a variety of detection depths and spatial resolutions.

Real-Time Passive Brain Monitoring System Using Near-Field Microwave Radiometry.

OBJECTIVE: Near-field microwave radiometry has emerged as a tool for real-time passive monitoring of local brain activation, possibly attributed to local changes in blood flow that correspond to temperature and/or conductivity changes. The aim of this study is to design and evaluate a prototype system based on microwave radiometry intended to detect local changes of temperature and conductivity in depth in brain tissues. A novel radiometric system that comprises a four port total power Dicke-switch sensitive receiver that operates at 1.5 GHz has been developed. METHODS AND RESULTS: The efficacy of the system was assessed through simulation and experiment on brain tissue mimicking phantoms under different setup conditions, where temperature and conductivity changes were accurately detected. In order to validate the radiometer's capability to sense low power signals occurring spontaneously from regions in the human brain, the somatosensory cortices of one volunteer were measured under pain-inducing psychophysiological conditions. The promising results from the initial in vivo measurements prove the system's potential for more extensive investigative trials. CONCLUSION AND SIGNIFICANCE: The significance of this study lies on the development of a compact and sensitive radiometer for totally passive monitoring of local brain activation as a potential complementary tool for contributing to the research effort for investigating brain functionality.

A condition-independent framework for the classification of error-related brain activity.

The cognitive processing and detection of errors is important in the adaptation of the behavioral and learning processes. This brain activity is often reflected as distinct patterns of event-related potentials (ERPs) that can be employed in the detection and interpretation of the cerebral responses to erroneous stimuli. However, high-accuracy cross-condition classification is challenging due to the significant variations of the error-related ERP components (ErrPs) between complexity conditions, thus hindering the development of error recognition systems. In this study, we employed support vector machines (SVM) classification methods, based on waveform characteristics of ErrPs from different time windows, to detect correct and incorrect responses in an audio identification task with two conditions of different complexity. Since the performance of the classifiers usually depends on the salience of the features employed, a combination of the sequential forward floating feature selection (SFFS) and sequential forward feature selection (SFS) methods was implemented to detect condition-independent and condition-specific feature subsets. Our framework achieved high accuracy using a small subset of the available features both for cross- and within-condition classification, hence supporting the notion that machine learning techniques can detect hidden patterns of ErrP-based features, irrespective of task complexity while additionally elucidating complexity-related error processing variations. Graphical abstract A schematic of the proposed approach. (a) EEG recordings in an auditory experiment in two conditions of different complexity. (b) Characteristic event related activity feature extraction. (c) Selection of feature vector subsets for easy and hard conditions corresponding to correct (Class1) and incorrect (Class2) responses. (d) Performance for individual and cross-condition classification.

Behavioral and brain pattern differences between acting and observing in an auditory task.

BACKGROUND: Recent research has shown that errors seem to influence the patterns of brain activity. Additionally current notions support the idea that similar brain mechanisms are activated during acting and observing. The aim of the present study was to examine the patterns of brain activity of actors and observers elicited upon receiving feedback information of the actor's response. METHODS: The task used in the present research was an auditory identification task that included both acting and observing settings, ensuring concurrent ERP measurements of both participants. The performance of the participants was investigated in conditions of varying complexity. ERP data were analyzed with regards to the conditions of acting and observing in conjunction to correct and erroneous responses. RESULTS: The obtained results showed that the complexity induced by cue dissimilarity between trials was a demodulating factor leading to poorer performance. The electrophysiological results suggest that feedback information results in different intensities of the ERP patterns of observers and actors depending on whether the actor had made an error or not. The LORETA source localization method yielded significantly larger electrical activity in the supplementary motor area (Brodmann area 6), the posterior cingulate gyrus (Brodmann area 31/23) and the parietal lobe (Precuneus/Brodmann area 7/5). CONCLUSION: These findings suggest that feedback information has a different effect on the intensities of the ERP patterns of actors and observers depending on whether the actor committed an error. Certain neural systems, including medial frontal area, posterior cingulate gyrus and precuneus may mediate these modulating effects. Further research is needed to elucidate in more detail the neuroanatomical and neuropsychological substrates of these systems.

Ethical issues of brain functional imaging: reading your mind.

Neuroimaging practice and research are overviewed in this paper through an ethics lens. The main ethical implications in biomedical research concerning functional brain imaging are discussed with the focus on issues related to imaging of personal information and privacy. Specific norms and guidelines will be eventually formed in the future under the umbrella of the new discipline of Neuroethics.

Social prospecting.

The goal of social prospecting is to steer the user community into defining the guidelines for self care and lifestyle management. Using an evidence based approach, social prospecting combines the interest in keeping personal or family health care records with the momentum of user-generated healthcare (or health 2.0). The personal healthcare record containing self-documented and self-collected information, or observations, can be used when a symptom or concern arises to identify a retrospective pathology. Coalesce of individual pathologies, related to a particular symptom or concern, can correlate a generic pathology or pathway in the self care domain. Using health 2.0 technologies, the user community can augment these self care pathways with advice, suggestions and recommendations and collectively define self care guidelines.

The effect of using a dielectric matching medium in focused microwave radiometry: an anatomically detailed head model study.

Microwave radiometry is a passive technique used to measure in-depth temperature distributions inside the human body, potentially useful in clinical applications. Experimental data imply that it may provide the capability of detecting in-depth local variations of temperature and/or conductivity of excitable tissues at microwave frequencies. Specifically, microwave radiometry may allow the real-time monitoring of brain temperature and/or conductivity changes, associated with local brain activation. In this paper, recent results of our ongoing research regarding the capabilities of focused microwave radiometry for brain intracranial applications are presented. Electromagnetic and thermal simulation analysis was performed using an anatomically detailed head model and a dielectric cap as matching medium placed around it, in order to improve the sensitivity and the focusing attributes of the system. The theoretical results were compared to experimental data elicited while exploring that the sensing depth and spatial resolution of the proposed imaging method at 2.1 GHz areas located 3 cm deep inside the brain can be measured, while at 2.5 GHz, the sensing area is confined specifically to the area of interest. The results exhibit the system's potential as a complementary brain imaging tool for multifrequency in-depth passive monitoring which could be clinically useful for therapeutic, diagnostic, and research applications.

Temporal processing dysfunction in schizophrenia as measured by time interval discrimination and tempo reproduction tasks.

OBJECTIVE: Time perception deficiency has been implicated in schizophrenia; however the exact nature of this remains unclear. The present study was designed with the aim to delineate timing deficits in schizophrenia by examining performance of patients with schizophrenia and healthy volunteers in an interval discrimination test and their accuracy and precision in a pacing reproduction­replication test. METHODS: The first task involved temporal discrimination of intervals, in which participants (60 patients with schizophrenia and 35 healthy controls) had to judge whether intervals were longer, shorter or equal than a standard interval. The second task required repetitive self-paced tapping to test accuracy and precision in the reproduction and replication of tempos. RESULTS: Patients were found to differ significantly from the controls in the psychoticism scale of EPQ, the proportion of correct responses in the interval discrimination test and the overall accuracy and precision in the reproduction and replication of sound sequences (p < 0.01). Within the patient group bad responders concerning the ability to discriminate time intervals were associated with increased scores in the Positive and Negative Syndrome Scale (PANSS) and in the Brief Psychiatric Rating Scale (BPRS) in comparison to good responders (p < 0.01). There were no gender effects and there were no differences between subgroups of patients taking different kinds or combinations of drugs. CONCLUSIONS: Analysis has shown that performance on timing tasks decreased with increasing psychopathology and therefore that timing dysfunctions are directly linked to the severity of the illness. Different temporal dysfunctions can be traced to different psychophysiological origins that can be explained using the Scalar Expectancy Theory (SET).

Experimental study of a hybrid microwave radiometry-hyperthermia apparatus with the use of an anatomical head phantom.

This paper presents the latest progress made concerning a hybrid diagnostic and therapeutic system able to provide focused microwave radiometric temperature and/or conductivity variation measurements and hyperthermia treatment. Previous experimental studies of our group have demonstrated the system performance and focusing properties in phantom as well as human experiments. The system is able to detect temperature and conductivity variations with frequency-dependent detection depth and spatial sensitivity. Numerous studies have also demonstrated the improvement of the system focusing properties attributed to the use of dielectric and left handed matching layers. In this study, similar experimental procedures are performed but this time using an anatomical head model as phantom aiming to achieve a more accurate modeling of the system's future real function. This way, another step is made toward the deeper understanding of the system's capabilities, with the view to further use it in experimental procedures with laboratory animals and human volunteers.

Passive monitoring using a combination of focused and phased array radiometry: a simulation study.

Aim of this simulation study is to use the focusing properties of a conductive ellipsoidal reflector in conjunction with directive phased microwave antenna configurations in order to achieve brain passive monitoring with microwave radiometry. One of the main modules of the proposed setup which ensures the necessary beamforming and focusing on the body and brain areas of interest is a symmetrical axis ellipsoidal conductive wall cavity. The proposed system operates in an entirely non-invasive contactless manner providing temperature and/or conductivity variations monitoring and is designed to also provide hyperthermia treatment. In the present paper, the effect of the use of patch antennas as receiving antennas on the system's focusing properties and specifically the use of phased array setups to achieve scanning of the areas under measurement is investigated. Extensive simulations to compute the electric field distributions inside the whole ellipsoidal reflector and inside two types of human head models were carried out using single and two element microstrip patch antennas. The results show that clear focusing (creation of "hot spots") inside the head models is achieved at 1.53GHz. In the case of the two element antennas, the "hot spot" performs a linear scan around the brain area of interest while the phase difference of the two microstrip patch antennas significantly affects the way the scanning inside the head model is achieved. In the near future, phased array antennas with multiband and more elements will be used in order to enhance the system scanning properties toward the acquisition of tomography images without the need of subject movement.

Noninvasive focused monitoring and irradiation of head tissue phantoms at microwave frequencies.

In this study, new aspects of our research regarding a novel hybrid system able to provide focused microwave radiometric temperature and/or conductivity measurements and hyperthermia treatment via microwave irradiation are presented. On one hand, it is examined whether the system is capable of sensing real-time progressive local variations of temperature and/or conductivity in customized phantom setups; on the other hand, the focusing attributes of the system are explored for different positions and types of phantoms used for hyperthermia in conjunction with dielectric matching layers surrounding the areas of interest. The main module of the system is an ellipsoidal cavity, which provides the appropriate focusing of the electromagnetic energy on the area of interest. The system has been used for the past few years in experiments with different configuration setups including phantom, animal, and human volunteer measurements yielding promising outcome. The present results show that the system is able to detect local concentrated gradual temperature and conductivity variations expressed as an increase of the output radiometric voltage. Moreover, when contactless focused hyperthermia is performed, the results show significant temperature increase at specific phantom areas. In this case, the effect of the dielectric matching layers placed around the phantoms is critical, thus resulting in the enhancement of the energy penetration depth.

New nonlinear multivariable model shows the relationship between central corneal thickness and HRTII topographic parameters in glaucoma patients.

PURPOSE: In this paper a new nonlinear multivariable regression method is presented in order to investigate the relationship between the central corneal thickness (CCT) and the Heidelberg Retina Tomograph (HRTII) optic nerve head (ONH) topographic measurements, in patients with established glaucoma. METHODS: Forty nine eyes of 49 patients with glaucoma were included in this study. Inclusion criteria were patients with (a) HRT II ONH imaging of good quality (SD < 30 mum), (b) reliable Humphrey visual field tests (30-2 program), and (c) bilateral CCT measurements with ultrasonic contact pachymetry. Patients were classified as glaucomatous based on visual field and/or ONH damage. The relationship between CCT and topographic parameters was analyzed by using the new nonlinear multivariable regression model. RESULTS: In the entire group, CCT was 549.78 +/- 33.08 mum (range: 484-636 mum); intraocular pressure (IOP) was 16.4 +/- 2.67 mmHg (range: 11-23 mmHg); MD was -3.80 +/- 4.97 dB (range: 4.04 - [-20.4] dB); refraction was -0.78 +/- 2.46 D (range: -6.0 D to +3.0 D). The new nonlinear multivariable regression model we used indicated that CCT was significantly related (R(2) = 0.227, p < 0.01) with rim volume nasally and type of diagnosis. CONCLUSIONS: By using the new nonlinear multivariable regression model, in patients with established glaucoma, our data showed that there is a statistically significant correlation between CCT and HRTII ONH structural measurements, in glaucoma patients.

Enhancing the focusing properties of a prototype non-invasive brain hyperthermia system: a simulation study.

Aim of this study is the improvement of the focusing properties of a prototype system for deep brain hyperthermia able to provide also passive measurements of temperature distributions inside the human body and especially the brain. One of the main modules of the system which ensures the necessary beamforming and focusing on the body and brain cortex areas of interest is the symmetrical axis ellipsoidal conductive wall cavity. The proposed system operates in a total non-invasive contactless passive manner and is designed to provide hyperthermia treatment and temperature monitoring. Extensive simulations to compute electric field distributions and SAR values at several frequencies inside the human head model and inside the whole ellipsoidal reflector were carried out. One of the main problems that have to be tackled in order to achieve the desired depth and focusing resolution is to reduce back scattering while improving penetration. With this view, the FEM simulations using a commercial tool aimed at improving the system's focusing properties following various approaches. In order to enhance the matching conditions on the air-head interface, layers made of metamaterials (left handed materials) and dielectric materials were placed around the human head model. The results show that the use of a metamaterial layer in conjunction with a layer of lossless dielectric material generates the largest improvement. Measurements using phantoms with the proposed focusing improvement techniques in future studies will complement the present research and reveal the potential practical value of the system.

FDTD study of the focusing properties of a hybrid hyperthermia and radiometry imaging system using a realistic human head model.

Aim of this study is twofold; on one hand, the investigation of the focusing attributes of a microwave radiometry tomography system with the use of a realistic human head model and on the other hand, the system's ability to perform a hyperthermia treatment. The operation principle of the device is based on an ellipsoidal conductive wall cavity, which provides the required beamforming and focusing. The biological tissue under treatment and/or measurement is placed on one of the two focal points whereas on the other one, a radiating or receiving antenna, which measures the black body type radiation emitted from the head's tissue, is placed. In previous studies simple spherical head models were used, comprising one or two layers for simulating the head tissues, along with a commercial FEM tool. In this work, a realistic adult head model developed from MRI scans of a human head is used. The realistic model with detailed structural and electromagnetic tissue characteristics enables more in depth theoretical investigation of the system capabilities. Extensive simulations using a commercial FDTD tool are performed in a wide range of operating frequencies. In order to explore the feasibility of heating and monitoring specific brain areas, the capability of focusing the electric field in specific areas inside the human head is investigated and further discussed. The results show that simple spherical head models, used in previous studies, provide similar results with the realistic one used herein for the given geometry; that is, the electric field focuses on the head's center, assuming the head as a homogeneous sphere. However, the deposition of the electromagnetic energy on the head tissues depends on the operating frequency and position of the head in the given geometry, so in therefore calculated, revealing the ability of the system to operate as a hyperthermia clinical tool, not as a stand alone device but in conjunction with other already validated devices/methods.

Study of a brain hyperthermia system providing also passive brain temperature monitoring.

A newly developed system for deep brain hyperthermia able to provide also passive measurements of temperature distributions inside the human body and especially the brain, is presented in this paper. The proposed system able to comprise both therapeutic and diagnostic modules operates in a totally non-invasive contactless way based on the use of an ellipsoidal conductive wall cavity to achieve beamforming and focusing on the areas under treatment and temperature monitoring. The performance of the system's diagnostic module designed and developed for brain imaging, has been previously studied in phantom, animal and human tests illustrating promising results. In the present paper theoretical analysis of the therapeutic module designed for hyperthermia treatment, elicited during simulation performance, exhibit the system's focusing attributes. Moreover, initial phantom experimental results verify the proof of concept. Taking into consideration the present initial theoretical and experimental study and the great advantage of the proposed brain hyperthermia system of being non invasive and with a very acceptable cost, it is concluded that further research is required in order to explore its potentials at becoming a part of the standard treatment protocol of brain malignancy in the future.

Enhancing the focusing properties of an ellipsoidal beamformer based imaging system: a simulation study.

Aim of this study is the improvement of the focusing properties of a microwave radiometry tomography system, used for the imaging of the product of temperature and conductivity in biological tissues via contactless measurements. The operation principle of the device in question is based on an ellipsoidal conductive wall cavity, which provides the required beamforming and focusing. The biological tissue under measurement is placed on one of the two focal points whereas on the other one, a dipole antenna measures the black body type radiation emitted from the head's tissue. In the framework of the present research several approaches are followed in order to improve and optimize the system's focusing properties on the tissue area of interest. Extensive simulations using a commercial FEM tool are performed in a wide range of operation frequencies. Dielectric spheres of various electromagnetic characteristics are placed either around the source (human head model) or the receiver (dipole antenna) in order to improve the matching on the head-air interface. The ability of focusing the electromagnetic energy in specific areas inside the human head is herein investigated in detail and further discussed.