Biomedical subjects

Ralph Mager

Publications and source records attributed to Ralph Mager.

6 recordsLinked to original sources

PubMed2006

Age-related changes in cognitive conflict processing: an event-related potential study.

Cognitive tasks involving conflicting stimuli and responses are associated with an early age-related decline in performance. Conflict and conflict-induced interference can be stimulus- or response-related. In classical stimulus-response compatibility tasks, such as the Stroop task, the event-related potential (ERP) usually reveals a greater negativity on incongruent versus congruent trials which has often been linked with conflict processing. However, it is unclear whether this negativity is related to stimulus- or response-related conflict, thus rendering the meaning of age-related changes inconclusive. In the present study, a modified Stroop task was used to focus on stimulus-related interference processes while excluding response-related interference. Since we intended to study work-relevant effects ERPs and performance were determined in young (about 30 years old) and middle-aged (about 50 years old) healthy subjects (total n=80). In the ERP, a broad negativity developed after incongruent versus congruent stimuli between 350 and 650 ms. An age-related increase of the latency and amplitude of this negativity was observed. These results indicate age-related alterations in the processing of conflicting stimuli already in middle age.

Adult↗

PubMed2005

Stimulation of cortisol during mental task performance in a provocative virtual environment.

Fully immersive and stereoscopic Virtual Environments (VE) represent a powerful multimedia tool for laboratory-based simulations of distinct scenarios including scenarios for evaluating stressful situations resembling reality. Thus far, cortisol secretion as a neuroendocrine parameter of stress has not been evaluated within a Virtual Reality (VR)-based paradigm. In this study 94 healthy volunteers were subjected to a provocative VR-paradigm and a cognitive stress task. Provocative in this context means the VE was designed to provoke physiological reactions (cortisol secretion) within the respective users by purpose. It was tested (a) if a fully dynamic VE as opposed to a static VE can be regarded as a stressor and (b) if such a fully dynamic VE can modify an additional response to a cognitive stressor presented within the VE additionally. Furthermore, possible gender-related impacts on cortisol responses were assessed. A significant cortisol increase was observed only after the combined application of the fully dynamic VE and the cognitive stressor, but not after application of the dynamic VE or the cognitive stressor alone. Cortisol reactivity was greater for men than for women. We conclude that a fully dynamic VE does not affect cortisol secretion per se, but increases cortisol responses to a dual task paradigm that includes performance of a stressful mental task. This provides the basis for the application of VR-based technologies in neuroscientific research, including the assessment of the human Hypothalamus-Pituitary-Adrenal (HPA) axis regulation.

Adult↗

PubMed2005

Neurophysiological age differences during task-performance in a stereoscopic virtual environment.

In today's society, there is an increasing number of workplaces in virtual environments (VE). But, there are only a few reports dealing with occupational health issues or age effects. The question arises how VR generally interferes with cognitive processes. This interference might have relevant implications for workability and work-efficiency in virtual environments. Event-related potentials are known to reflect different stages of stimulus reception, evaluation, and response. We have established an electroencephalographic (EEG) monitoring, focussing on event-related potentials (N100; mismatch negativity, i.e., MMN) to obtain access to attention dependent and pre-attentive processing of sensory stimuli applied in VE. The MMN is known to be correlated with the ability of subjects to react to an unexpected event. The aim of the present study was to investigate cognitive responses to distracting auditory stimuli in two different age groups in a virtual environment (VE) and in a real environment ("real reality"), and to compare characteristic neurophysiological response patterns. Data show that stimulus detection as given by the N100 amplitude and latency does not differ in both age groups and task conditions. In contrast, the pre-attentive processing as given by the MMN is altered in the VR such as the non-VR condition in an age-related manner. A relevant finding of the present study was that the age related differences seen in the non-VR condition were not strengthened in VR.

Adult↗

PubMed2005

Cognitive ergonomics in virtual environments: development of an intuitive and appropriate input device for navigating in a virtual maze.

For patients suffering from mild cognitive impairments, the navigation through a virtual maze should be as intuitive and efficient as possible in order to minimize cognitive and physical strain. This paper discusses the appropriateness of interaction devices for being used for easy navigation tasks. Information gained from human centered evaluation was used to develop an intuitive and ergonomic interaction device. Two experiments examined the usability of tracked interaction devices. Usability problems with the devices are discussed. The findings from the experiments were translated into general design guidance, in addition to specific recommendations. A new device was designed on the basis of these recommendations and its usability was evaluated in a second experiment. The results were used to develop a lightweight interaction device for navigation in the virtual maze.

Cognition Disorders↗

PubMed2003

Safety of injectable opioid maintenance treatment for heroin dependence.

BACKGROUND: There is a growing debate about injectable opioid treatment programs in many Western countries. This is the first placebo-controlled study of the safety of injectable opioids in a controlled treatment setting. METHODS: Twenty-five opioid-dependent patients on intravenous (IV) heroin or IV methadone maintenance treatment were randomly assigned to either their individual prescribed IV maintenance dose or placebo. Acute drug effects were recorded, focusing on electrocardiography, respiratory movements, arterial blood oxygen saturation, and electroencephalography (EEG). RESULTS: After heroin injection, marked respiratory depression progressing to a Cheyne-Stokes pattern occurred. Peripheral arterial blood oxygenation decreased to 78.9 +/- 8.7% (mean +/- SD) ranging from 52%-90%. During hypoxia, 7 of the 16 subjects experienced intermittent and somewhat severe bradycardia. Five subjects exhibited paroxysmal EEG patterns. After methadone injection, respiratory depression was less pronounced than after heroin injection. No relevant bradycardia was noted. CONCLUSIONS: Opioid doses commonly prescribed in IV opioid treatment induce marked respiratory and circulatory depression, as well as occasionally irregular paroxysmal EEG activity. Further studies are needed to optimize the clinical practice of IV opioid treatment to prevent serious complications. Moreover, the extent of the observed effects raises questions about the appropriateness of IV opioid treatment in the present form.

Adult↗

PubMed1992

Different Types of Potassium Outward Current in Relay Neurons Acutely Isolated from the Rat Lateral Geniculate Nucleus.

Different classes of potassium (K+) outward current activated by depolarization were characterized in relay neurons acutely isolated from the rat lateral geniculate nucleus (LGN), using the whole-cell version of the patch-clamp technique. A fast-transient current (IA), activated at around - 70 mV, declined rapidly with a voltage-dependent time constant (tau=6 ms at + 45 mV), was 50% steady-state inactivated at - 70 mV, and rapidly recovered from inactivation with a monoexponential time course (tau=21 ms). IA was blocked by 4-aminopyridine (4-AP, 2 - 8 mM) and was relatively insensitive to tetraethylammonium (TEA, 2 - 10 mM). After elimination of IA by a conditioning prepulse (30 ms to - 50 mV), a slow-transient K+ current could be studied in isolation, and was separated into three components, IKm, IKs and a calcium (Ca2+)-dependent current, IK[Ca]. The slow-transient current was not consistently affected by 4-AP (up to 8 mM), while TEA (2 - 10 mM) predominantly blocked IKs and IK[Ca]. The component IKm persisted in a solution containing TEA and 4-AP, activated at around - 55 mV, declined monoexponentially during maintained depolarization (tau=98 ms at + 45 mV), was 50% inactivated at - 39 mV, and recovered with tau=128 ms from inactivation. IKs activated at a similar threshold, but declined much slower with tau=2662 ms at + 45 mV. Steady-state inactivation of IKs was half-maximal at - 49 mV, and recovery from inactivation occurred relatively fast with tau=116 ms. From these data and additional current-clamp recordings it is concluded that the K+ currents, due to their wide range of kinetics and dependence on membrane voltage or internal Ca2+ concentration, are capable of cooperatively controlling the firing threshold and of shaping the different states of electrophysiological behaviour in LGN relay cells.

Journal Article↗