Pasi Kauppinen

Differential electrocortical responses to increasing intensities of fearful and happy emotional expressions.

Previous studies have shown differential event-related potentials (ERPs) to fearful and happy/neutral facial expressions. To investigate whether the brain systems underlying these ERP differences are sensitive to the intensity of fear and happiness, behavioral recognition accuracy and reaction times as well as ERPs were measured while observers categorized low-intensity (50%), prototypical (100%), and caricatured (150%) fearful and happy facial expressions. The speed and accuracy of emotion categorization improved with increasing levels of expression intensity, and 100% and 150% expressions were consistently classified as expressions of the intended emotions. Comparison of ERPs to 100% and 150% expressions revealed a differential pattern of ERPs to 100% and 150% fear expressions over occipital-temporal electrodes 190-290 ms post-stimulus (a negative shift in ERP activity for high-intensity fearful expressions). Similar ERP differences were not observed for 100% and 150% happy expressions, ruling out the possibility that the ERPs to high-intensity fear reflected a response to increased expression intensity per se. Together, these results suggest that differential electrocortical responses to fearful facial expressions over posterior electrodes are generated by a neural system that responds to the intensity of negative but not positive emotional expressions.

Measurement of noise and impedance of dry and wet textile electrodes, and textile electrodes with hydrogel

Textile sensors, when embedded into clothing, can provide new ways of monitoring physiological signals, and improve the usability and comfort of such monitoring systems in the areas of medical, occupational health and sports. However, good electrical and mechanical contact between the electrode and the skin is very important, as it often determines the quality of the signal. This paper introduces a study where the properties of dry textile electrodes, textile electrodes moistened with water, and textile electrodes covered with hydrogel were studied with five different electrode sizes. The aim was to study how the electrode size and preparation of the electrode (dry electrode/wet electrode/electrode covered with hydrogel membrane) affect the measurement noise, and the skin-electrode impedance. The measurement noise and skin-electrode impedance were determined from surface biopotential measurements. These preliminary results indicate that noise level increases as the electrode size decreases. The noise level is high in dry textile electrodes, as expected. Yet, the noise level of wet textile electrodes is quite low and similar to that of textile electrodes covered with hydrogel. Hydrogel does not seem to improve noise properties, however it may have effects on movement artifacts. Thus, it is feasible to use textile embedded sensors in physiological monitoring applications when moistening or hydrogel is applied

Sensitivity Distributions of Impedance Cardiography Using Band and Spot Electrodes Analyzed by a Three-Dimensional Computer Model

AbstractImpedance cardiography (ICG) offers a safe, noninvasive, and inexpensive method to track stroke volume estimates over long periods of time. Several modified ICG measurement configurations have been suggested where for convenience or improved performance the standard band electrodes are replaced with electrocardiogram electrodes. This report assesses the sensitivity of the conventional and three modified ICG methods in detecting regional conductivity changes in the simulated human thorax. The theoretical analyses of the measurement sensitivity employ the reciprocity theorem and the lead field theory with a highly detailed, anatomically accurate, three-dimensional computer thorax model. This model is based on the finite-difference element method and the U.S. National Library of Medicines Visible Human Man anatomy data. The results obtained indicate that the conventional four-band ICG is not specifically sensitive to detect conductivity changes in the region of the heart, aortas, and lungs. Analyzed modified electrode configurations do not reproduce exactly the measurement sensitivity distribution of the conventional four-band ICG. Thus, although the signals measured with modified spot arrangements may appear similar to the four-band configuration, the distribution of the signal origin may not be the same. Changing from band to spot electrodes does not overcome the methodological problems associated with ICG.

The Influence of CSF on EEG Sensitivity Distributions of Multilayered Head Models

We examined how the cerebrospinal fluid (CSF) affects the distribution of electroencephalogram (EEG) measurement sensitivity. We used concentric spheres and realistic head models to investigate the difference between computed-tomography (CT) and magnetic resonance image (MRI) models that exclude the CSF layer. The cortical EEG sensitivity distributions support these phenomena and show that the CSF layer significantly influences them, thus identifying the importance of including the CSF layer inside the head volume conductor models. The results show that the highly conductive CSF channels the current, thus decreasing the maximum cortical current density relative to models that do not include the CSF. We found that the MRI and CT models yielded HSV results 20% and 45%, respectively, too small when compared with CSF-inclusive models.

A software implementation for detailed volume conductor modelling in electrophysiology using finite difference method

There is an evolving need for new information available by employing patient tailored anatomically accurate computer models of the electrical properties of the human body. Because construction of a computer model can be difficult and laborious to perform sufficiently well, devised models have varied greatly in the level of anatomical accuracy incorporated in them. This has restricted the validity of conducted simulations. In the present study, a versatile software package was developed to transform anatomic voxel data into accurate finite difference method volume conductor models conveniently and in a short time. The package includes components for model construction, simulation, visualisation and detailed analysis of simulation output based on volume conductor theory. Due to the methods developed, models can comprise more anatomical details than the prior computer models. Several models have been constructed, for example, a highly detailed 3-D anatomically accurate computer model of the human thorax as a volume conductor utilising the US National Library of Medicines (NLM) Visible Human Man (VHM) digital anatomy data. Based on the validation runs the developed software package is readily applicable in analysis of a wide range of bioelectric field problems.

Facing a real person: an event-related potential study

Although faces are typically perceived in the context of human interaction, face processing is commonly studied by displaying faces on a computer screen. This study on event-related potential examined whether the processing of faces differs depending on whether participants are viewing faces live or on a computer screen. In both the conditions, the participants were shown a real face, a dummy face, and a control object. N170 and early posterior negativity discriminated between faces and control object in both the conditions. Interestingly, early posterior negativity differentiated between the real face and the dummy face only in the live condition. The results indicate that a live face, as a potentially interacting stimulus, is processed differently than an inanimate face already at the early processing stages.

Detailed model of the thorax as a volume conductor based on the visible human man data

A large number of computerized conductivity models of the human thorax have been created to study bioelectric phenomena in human beings. Devised models have varied greatly in the level of anatomical detail incorporated thus restricting the accuracy and validity of conducted simulations. This paper introduces a highly detailed anatomically accurate three-dimensional computer model of the conductive anatomy of the human thorax for calculating electric fields generated by equivalent bioelectric sources and different externally applied sources. The anatomy of the devised model is based on high resolution colour cryosection images of the US National Library of Medicines Visible Human Man data set and is comprised of more anatomical detail than prior computer models. The model is based on the finite difference method and is readily applicable for the analysis of a wide range of biomedical field problems, such as electrocardiography, impedance cardiography, tissue stimulations, and especially, in development of measurement systems.

Effects of tissue resistivities on electroencephalogram sensitivity distribution

The effects of tissue resistivities on EEG amplitudes were studied using an anatomically accurate computer model based on the finite difference method (FDM) and lead field analysis covering the whole brain area with 180 000 nodes. Five tissue types and three lead fields were considered for analysis. The changes in sensitivity distribution are directly comparable to changes in the potential distribution on the scalp. The results indicate that a 10% decrease in any tissue resistivity caused 3.0–4.1% differences in the sensitivity distributions of the selected EEG leads. The applied 10% decrease in the resistivity values covers only a fraction of the range of variation of 50% to 100% reported in the literature. The use of a 55% decreased skull resistivity value or a commonly applied three-compartment model increased the differences to 28% and 33%, respectively. In conclusion, both a realistic anatomy and accurate resistivity data are important in EEG head models.

Effects of hypertonic 75 mg/ml (7.5%) saline on extracellular water volume when used for preloading before spinal anaesthesia

Background: Prevention of hypotension during spinal anaesthesia is commonly achieved using fluid preloading. This may result in a substantial amount of excess free water retained in the body after spinal anaesthesia. We aimed to evaluate the effects of 7.5% hypertonic saline on extracellular water volume and haemodynamics when used for fluid preloading before spinal anaesthesia.

Novel wireless electroencephalography system with a minimal preparation time for use in emergencies and prehospital care

BackgroundAlthough clinical applications such as emergency medicine and prehospital care could benefit from a fast-mounting electroencephalography (EEG) recording system, the lack of specifically designed equipment restricts the use of EEG in these environments.MethodsThis paper describes the design and testing of a six-channel emergency EEG (emEEG) system with a rapid preparation time intended for use in emergency medicine and prehospital care. The novel system comprises a quick-application cap, a device for recording and transmitting the EEG wirelessly to a computer, and custom software for displaying and streaming the data in real-time to a hospital. Bench testing was conducted, as well as healthy volunteer and patient measurements in three different environments: a hospital EEG laboratory, an intensive care unit, and an ambulance. The EEG data was evaluated by two experienced clinical neurophysiologists and compared with recordings from a commercial system.ResultsThe bench tests demonstrated that the emEEG systems performance is comparable to that of a commercial system while the healthy volunteer and patient measurements confirmed that the system can be applied quickly and that it records quality EEG data in a variety of environments. Furthermore, the recorded data was judged to be of diagnostic quality by two experienced clinical neurophysiologists.ConclusionsIn the future, the emEEG system may be used to record high-quality EEG data in emergency medicine and during ambulance transportation. Its use could lead to a faster diagnostic, a more accurate treatment, and a shorter recovery time for patients with neurological brain disorders.