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Biomedical subjects

W Sommer

Publications and source records attributed to W Sommer.

At least 55 records · Page 3Linked to original sources
PubMed1994

The lateralized readiness potential preceding brief isometric force pulses of different peak force and rate of force production.

Previous studies have reported that the lateralization of the readiness potential is unaffected by force amplitude of brief unimanual responses. However, because those studies did not specify rate of force production, response force probably was mainly controlled by force unit duration rather than by recruitment of force units, which may explain this negative finding. To enforce recruitment control, we factorially combined peak force (10% or 50% of maximal voluntary finger force) and time to peak force (100 or 200 ms). A precue provided advance information about the responding index finger (left vs. right). After 1 s, the imperative stimulus followed, requiring a brisk isometric flexion of the specified index finger. Symmetric effects, maximal at the vertex, of both force and rate of force production were observed 200-100 ms before the imperative stimulus in stimulus-synchronized averages and 200-100 ms before response onset in response-synchronized averages. However, neither force nor rate of force production affected the lateralized readiness potential. We conclude that this measure does not reflect movement parameters but appears to indicate an abstract preparation of lateralized response channels.

Adult↗
PubMed1993

Antisense oligonucleotide to c-fos induces ipsilateral rotational behaviour to d-amphetamine.

The immediate-early genes, especially c-fos, have been suggested to have an important role in neuronal plasticity and memory. However, it has been difficult to determine if in fact c-fos can participate in control of behaviour. Here we can report that direct unilateral infusion into the rat neostriatum of an antisense phosphothioate oligodeoxynucleotide to c-fos mRNA leads to the rapid induction of ipsilateral rotational behaviour after d-amphetamine administration. This is associated with an elimination of the in vivo expression of Fos-like immunoreactivity within the infused region of neostriatum. Following infusion of these oligodeoxynucleotides labelled with fluorescein isothiocyanate they appear with a nuclear and cytoplasmic location in a large number of nerve cells, many of which are immunoreactive for dopamine and cyclic AMP regulated phosphoprotein. The present findings suggest that the immediate-early gene c-fos has a role also in control of behavioural activity, as illustrated in D1 receptor containing striatal neurones.

Animals↗
PubMed1993

Reaction time improvements with practice in brain-damaged patients.

This study investigated practice effects on reaction time (RT) in patients with unilateral brain damage and age-matched controls. Subjects performed a Sternberg-type stimulus recognition task. Both RT and RT variability decreased in all subjects from a short initial session to a second session, 1 to 3 days later. Within the second session, however, RT remained constant in the controls, whereas it was further reduced in the patients. These findings argue against the assumption that brain-damaged patients generally show smaller practice effects on RT than controls, and instead suggest that it may be essential to provide patients with sufficient practice opportunities. To locate the processing stage where practice is effective, analyses were performed also on the intercept and slope parameters of the RT function. It is argued that the differential practice effects were due to the speeding of perceptual and/or response-related stages, rather than gains in memory search speed.

Brain Damage, Chronic↗
PubMed1993

Stimulus presentation rate dissociates sequential effects in event-related potentials and reaction times.

The present study explored the impact of the stimulus presentation rate on sequential effects in event-related potentials (ERPs) and reaction times (RTs). Random series of equiprobable tones were presented at interstimulus intervals (ISIs) of 1.3, 2.1, and 2.9 s. Fast and accurate choice responses to the tones were required. Although sequential effects in RTs were stable across all ISIs, the common first-order repetition effect in P300 amplitude was only observed at the 1.3-s ISI and not at the slower presentation rates. This dissociation between the first-order effects in RTs and ERPs speaks against an explanation of both effects by a common expectancy mechanism. In addition, sequential effects were observed as early as about 100 ms after stimulus onset in the lateralized readiness potential. Together with similar sequential effects in P300 latency, this finding supports a continuous flow model of information processing.

Acoustic Stimulation↗
PubMed1993

Covert effects of alcohol revealed by event-related potentials.

Contradictory evidence as to the effects of alcohol on early information processing stages has been obtained from behavioral and psychophysiological investigations. In the present study, choice reaction times, error rates, and event-related potentials (ERPs) were recorded in a task in which variations in stimulus discriminability and of the (task irrelevant) correspondence between stimulus location and response location were orthogonally combined. Both discriminability and stimulus-response correspondence affected reaction time and electrophysiological chronometric measures as expected. However, no behavioral effects of alcohol were observed, possibly because of strategic adjustments. Psychophysiological chronometric measures indicated that alcohol leaves the initial flow of perceptual evidence to motor stages unimpaired, whereas it appears to increase the duration of stimulus evaluation. Interestingly, a number of alcohol effects appeared in the ERP amplitudes. Decrements in early ERP components indicate alcohol-induced impairments of involuntary visual attention and/or the automatic stimulus location-dependent activation of response channels. In contrast, a strong enhancement of a late slow-wave component under alcohol may reflect the investment of processing resources in order to maintain normal performance levels.

Adult↗
PubMed1992

Operant conditioning of P300.

This study demonstrates that operant conditioning may increase the P300 component of the event-related potential above a level obtained without contingent training. An experimental group of subjects was rewarded for producing large P300 amplitudes and was compared with a yoked control group which was rewarded on a random basis. During training the experimental subjects increased both the amplitude of the P300 and of a subsequent frontal negative slow wave relative to the control group. These training effects were independent of prestimulus potential shifts and occurred likewise for target and nontarget stimuli.

Adult↗
PubMed1992

Differential effects of voluntary expectancies on reaction times and event-related potentials: evidence for automatic and controlled expectancies.

Expectancy has been used to explain the effects of stimulus sequences both on reaction times (RTs) and on the P300 component of the human event-related potential. However, there are conflicting views about the control obtainable over these underlying expectancies. We compared the effects of voluntary expectancies for stimulus changes or repetitions in random tone series on RTs and the P300. Ss responded according to either stimulus identity (Experiment 1) or stimulus sequence (Experiment 2). In both experiments RTs were strongly affected by event expectedness. P300 amplitude, on the other hand, was affected (as a trend) only in Experiment 2. The results suggest that there are at least 2 types of "expectancy", one that is largely automatic and inflexible, reflected in P300 amplitude, and a second, controlled process that is reflected mainly in RT. The latter type of expectancy appears to affect processing stages beyond stimulus evaluation and classification.

Arousal↗
PubMed1992

Memory search for faces and digits in patients with unilateral brain lesions.

To clarify whether the impairment of right-brain-damaged (RBD) patients in face recognition is related to perceptual or mnestic processing stages, we tested unilaterally lesioned patients and controls in a Sternberg-type memory search task. Subjects had to memorize sets of 1, 2, or 3 faces (or, in a control condition, digits) and were then to recognize these memorized stimuli among new ones by speeded choice reactions. In this task, deficits in stimulus encoding and memory search should show up in increased intercepts and slopes, respectively, of the RT function over memory set size. A face-specific impairment of the RBD patient group, consisting in longer reaction times and higher error rates, was confirmed but could not be unequivocally attributed to either stimulus encoding or memory search. However, inspection of individual data suggested that (1) some RBD patients are virtually unimpaired in face recognition and (2) if impairment after right hemisphere damage is present, it may selectively affect either stimulus encoding or memory search.

Adult↗
PubMed1992

Student mental health needs: survey results and implications for service.

In preparation for planning counseling and mental health services at Columbia University, the authors conducted a mental health needs assessment survey that sampled representative numbers of students. Respondents were most concerned about academic and school-related issues, followed by concerns in the area of love relationships. Multiple regression analysis revealed certain subgroups that were more likely to have these concerns and certain health and mental health problems that were significantly associated with these concerns. The study identified serious psychological problems, including suicidal/homicidal thoughts and sexual abuse, and surveyed respondents' treatment preferences. Finally, the authors discuss how the study findings contributed to sharpening and expanding focus on different aspects of program development in the collaboration between mental health and health education.

Adult↗
PubMed1992

Bioavailability of vinpocetine and interference of the time of application with food intake.

In a pilot study based on an open cross-over design involving four phases, the relative bioavailability of the eburnamenine derivative vinpocetine (CAS 42971-09-5) was investigated in 8 healthy volunteers in relation to different times of drug administration relative to food intake. The substance was applied orally as 10 mg film tablets. The areas under the plasma concentration-time curves (AUC) amounted to 27.3 +/- 18.1 ng.h/ml (fasting) and 42.8 +/- 27.4 up to 54.3 +/- 38.4 ng.h/ml (non-fasting, intake before and after meal, resp.). The relative bioavailability under non-fasting conditions was found to be approx. 60 to 100% higher than under fasting conditions.

Adult↗
PubMed1991

Power spectral analysis of EEG during sufentanil infusion in humans.

The purpose of this study was to examine the relationship of continuous sufentanil infusion (0.71 micrograms.kg-1.min-1 for 14 min) and the response of the power spectrum of the electroencephalogram (EEG) performed during the induction of anaesthesia in 12 patients undergoing CABG surgery. Data were collected at various times including the preinduction period, every minute during the infusion period (minute 0 to 14), and 15, 20 and 25 min after the start of the infusion (1, 6 and 11 min respectively after completion of the infusion). Within three minutes of the sufentanil infusion, the total power and the relative power of delta increased to near maximum, while the 95% spectral edge and the mean frequency decreased markedly. In spite of the continued infusion of sufentanil, there were very little further changes in the EEG activity. This ceiling effect for the EEG changes appear to coincide with the failure to respond to verbal command. We conclude that the power spectrum of the EEG failed to respond to increasing doses of sufentanil during its infusion after the rapid initial changes.

Alpha Rhythm↗
PubMed1991

Human brain potential correlates of face encoding into memory.

ERPs elicited by photographs of unfamiliar faces were shown to be predictive for their later recognition. We established that these ERP differences were unrelated to fluctuations of attention or other non-specific factors during perceptual processing. Therefore they may be interpreted as manifestations of brain processes that correlate with memory encoding. The scalp topography of this ERP difference was bipolar with greater electrical positivity at frontal and greater negativity at parieto-temporal scalp sites. This topography appears to contrast with the more uniformly positive differences reported for verbal stimuli but is in accord with what might be expected for faces and complex visual stimuli.

Adult↗
PubMed1991

Contributions of stimulus encoding and memory search to right hemisphere superiority in face recognition: behavioural and electrophysiological evidence.

The relative contributions of stimulus encoding and memory search to right hemisphere (RH) superiority in face recognition were investigated in a memory search task with lateralized probe stimulus presentation. RH superiority in reaction time and latency of a late positive ERP component was independent of stimulus degradations, but increased as a function of memory set size. These results suggest equal efficiency of the hemispheres in stimulus encoding, but RH superiority in memory search. In addition, a long-lasting ERP negativity contralateral to the stimulated hemifield is discussed with reference to models of hemispheric processing in hemifield studies.

Adult↗
PubMed1991

Influence of food on the bioavailability of theophylline from a sustained-released theophylline preparation.

In a single-dose cross-over study with 12 healthy male volunteers the relative bioavailability of theophylline (CAS 58-55-9) in a dosage of 700 mg (sustained-release preparation) under fasting- and non-fasting conditions was investigated. The areas under the plasma concentration-time curves AUC amounted to 184.2 +/- 42.7 micrograms.h/ml (fasting) and 157.9 +/- 32.9 micrograms.h/ml (non-fasting, p = 0.031). The bioavailability was reduced by approx. 15% by concomitant food intake. The 95% confidence intervals for AUC and Cmax were 76-99% and 78-105%, respectively, and therefore narrowly outside the usual 80-120% limits. There were no therapeutically relevant changes with regard to the parameters Cmax, tmax and MRT. The MRT values of 13.4 and 13.9 h respectively showed furthermore that theophylline represents a twice-daily formulation. No "dose-dumping effect" was observed.

Administration, Oral↗
PubMed1990

Consciousness of attention and expectancy as reflected in event-related potentials and reaction times.

The effects of conscious expectancies and attention on event-related potentials (ERP) and choice reaction times (RT) and their modulation by stimulus sequence were studied. Subjects retrospectively reported their expectancy of, and attention to, the terminal tones of short series. ERPs and RTs showed the usual sequential effects that were modulated by practice. As ratings were affected by only a few of the stimulus sequence, conscious access to sequence-based expectancy or attention appears to be fragmentary. Increased P300 amplitude with attention indicates conscious access to processing capacity. RTs and P300 latencies suggest stimulus processing time to decrease with sequence-based and consciously accessible expectancy. Differential effects of stimulus sequences and conscious expectancies on P300 amplitude indicate influences of two varieties of expectancy.

Arousal↗
PubMed1990

Evidence for the role of spinal cord systems in Parkinson's disease-associated pain.

A patient with Parkinson's disease had severe levodopa-associated leg pain in a beginning-of-dose and peak-dose pattern. Local anesthetic block of the lumbar sympathetic chain or differential epidural block did not alter the pain. Spinal anesthesia abolished the pain. We postulate that levodopa-associated pain in Parkinson's disease either originates in or is mediated by spinal cord dopaminergic systems.

Aged↗
PubMed1990

Awareness of P300-related cognitive processes: a signal detection approach.

Although the P300 component of the human event-related potential is purported to indicate consciousness of an event, it is unclear which of the P300-related processes, if any, are accessible to awareness. This study explored awareness of such processes in Bernoulli series of auditory stimuli using signal detection theory and selective averaging of ERPs according to the subjects' classifications. Following targets eliciting appropriate P300 amplitudes, the subject was requested to classify his brain response as small, medium, or large, whereupon visual feedback was given about the correctness of the response. Averaging the ERPs according to the subjects' classifications showed P300 amplitudes to increase with the classification category, whereas the prestimulus and post-P300 event-related potentials were unrelated to the category. Signal detection analysis revealed non-zero sensitivity measures for the P300 amplitude categories. Although no conclusive suggestion can be made at present as to the basis of the P300 discrimination ability found here, it was possible to rule out electro-ocular and electromyographic activity, the preceding auditory stimulus, and the prior feedback given, as cues for discrimination.

Adult↗