Search PubMed⌕ Search

Biomedical subjects

D Lehmann

Publications and source records attributed to D Lehmann.

At least 199 records · Page 11Linked to original sources
PubMed1979

Right/left differences of median nerve evoked scalp potentials in multiple sclerosis.

Scalp potentials evoked by electrical stimulation of the median nerve at the wrist were examined in multiple sclerosis patients and healthy controls. The latencies of the first negative peak (about 18 ms latency) of the response to right and to left-sided stimulation were compared. Forty-eight of 60 measured latency differences in 15 suspected or certain MS patients were more than 3 standard deviations beyond the average difference in controls (arbitrary norm limit), whereas none of the 56 results of the 14 controls was in that range. Fifteen of 24 latency differences in 6 patients without anamnestic or clinical sensory disturbances in the arms were above the limit. On the other hand, conduction velocity between wrist, neck and scalp did not differentiate controls from patients. We suggest using latency differences of the early components of right and left median nerve-evoked scalp potentials as a mean for the early detection of functional disturbances in multiple sclerosis.

Adult↗
PubMed1979

Multichannel evoked potential fields show different properties of human upper and lower hemiretina systems.

Scalp potential fields in human subjects were evoked by checkerboard reversals to the upper and lower hermiretinae, using 1.6 and 3.2 reversals/s. Averaged fields were sampled along a saggital midline row of electrodes (field profiles) in 20 subjects, and from a 47 electrode array (field maps) in five subjects. In five subjects, profile peaks and troughs between 84 and 128 ms latency resided within the recorded electrode row surrounded by lesser potential values, and thus met the evaluation criteria. Response latency defined as maximal voltage difference between two electrodes within the profiles was significantly shorter (medians 12 and 11 ms, respectively) for upper than for lower hemiretina stimuli at both frequencies. There was a significant difference between latencies to 3.2 and 1.6 stimuli/s in the upper but not in the lower hemiretina system, suggesting different system behavior of the two retinal halves. Pertinent anatomical, electrophysiological, and behavioral data are reviewed.

Adult↗
PubMed1979

Nalidixic acid and lactic acidosis.

Nalidixic acid may cause severe acidosis and we report a fatal case of lactic acidosis assocaited with nalidixic acid therapy. Studies in normal volunteers showed drug related impairment of lactate metabolism. We question whether the drug should be used in patients who may accumulate the drug or be predisposed to lactic acidosis.

Acidosis↗
PubMed1978

Correlations between cannabis-induced psychopathology and EEG before and after drug ingestion.

The study investigates EEG characteristics in relation to psychopathology. Tetrahydro-Cannabinol (THC) was taken orally by 12 volunteers. The EEG was recorded continuously, and THC-induced psychopathology was assessed by pre- and post-experiment questionnaires. Subjects had to signal THC experiences. EEG measurements (distribution means of frequency bands derived from EEG frequency analysis) before and after THC were correlated with THC induced psychopathology. High correlations were found before THC ingestion, and after THC during periods without experiences. Thus, the pre-drug EEG indicates predisposition to THC induced body image disturbances and euphoria, and the drug-influenced EEG in periods without experiences indicates the tendency to drug-induced experiences. The predicting EEG parameters were different for THC induced visual experiences and for body image disturbances.

Adult↗
PubMed1977

Theta bursts: an EEG pattern in normal subjects practising the transcendental meditation technique.

In a survey of the EEG characteristics of persons practising the Transcendental Meditation technique, 21 of 78 people demonstrated intermittent prominent bursts of frontally dominant theta activity. On the average across subjects, the theta bursts occurred about every 2 min, had an average duration of 1.8 sec, and an average maximal amplitude of 135 muV. Typically, the bursts were preceded and followed by alpha rhythm. Subject reports elicited during theta bursts indicated pleasant states with intact situational orientation and no subjective experiences related to sleep. Fifty-four non-meditating controls showed no theta bursts during relaxation and sleep onset. It is hypothesized that theta burst may be the manifestation of a state adjustment mechanism which comes into play during prolonged low-arousal states, and which may be related to EEG patterns of relaxation in certain behavioural conditions.

Adolescent↗
PubMed1977

Pattern evoked average EEG potentials and dichoptic visual percepts.

Monocular xenon flashes were used to evoke average EEG potentials while blank, dot or grid targets were shown simmultaneously in ten dichoptic stimulus conditions, either continuously illuminated (added to the flashes, or contraocularly), or presented only by the flashes. Mean evoked-EEG-potential waveforms over repeated conditions were computed from average evoked potentials (EPs) for each stimulus condition and each hemisphere. Correlation coefficients were computed between mena-EP waveforms of all stimulus condition for each subject. Mean correlation coefficients over subjects were treated in a cluster analysis to diagnose conditions associated with similar EP waveforms. Data from the two hemispheres yielded identical cluster results. Presence or absence of continuous target illumination for the flashed eye was the most powerful descriptor. Next important was continuously visible structure (regardless whether seen by the flashed or the nonflashed eye) in conditions with continuous illumination seen by the flashed eye, and flashed structure in conditions without continuous illumination for the flashed eye. It was concluded that a visual percept which enters the processor as non-EP-evoking information nevertheless is reflected by the EP waveform. However, the waveforms are different if the flashes carry the perceptual information exclusively. More powerful than visual structure is the mode of flash presentation (with or withoug continuous target illumination) for the EP waveform.

Adult↗
PubMed1976

[Methods and evaluation of visually evoked EEG potentials in cases of suspected multiple sclerosis (author's transl)].

In multiple sclerosis, average EEG potentials which are monocularly evoked by checkerboard pattern reversal frequently show increased latencies of the dominant, occipitally positive peak (more than 110 ms), and latency differences of more than 6--7 ms between responses to right and left eye stimulation. Fixation of the stimulus field at the lower border causes significantly longer latencies and smaller amplitudes than fixation at the upper border. With lower border fixation, the increase of response latency may suggest a reversal of response polarity in extreme cases. Central fixation often but not always results in responses similar to upper border fixation. In order to have minimal variability of the results, fixation of the stimulus field at the upper border is preferred over central fixation.

Electroencephalography↗
PubMed1976

[Controlled EEG alpha feedback training in normals and headache patients (author's transl)].

Headache patients and healthy controls underwent alpha-EEG feedback training in 12 sessions. The present study does not support the literature which reports alpha increase by feedback training. The study included a patient group receiving feedback, a patient control group receiving pseudofeedback, and a volunteer group receiving feedback. Increase of alpha EEG was observed under feedback and pseudofeedback. However, there was always more alpha during baseline times than during training times. Alpha increase over time is suggested to be a habituation effect. Headache pain decreased with training (within the boundaries of a placebo effect), and there was no difference in headache decrease between feedback and pseudofeedback patients.

Adult↗
PubMed1976

Human EEG spectra before and during cannabis hallucinations.

EEG correlates of subjective experiences induced by delta9-trans-tetrahydrocannabinol (THC) and EEG correlates of individual disposition to such experiences were investigated. Twelve normal volunteers took 200 mug/kg THC orally. The subjects were asked to signal subjective experiences. The EEG was analyzed (period analysis) before and repeatedly after THC injestion, during resting, attention, eye closure, visual hallucinations, and body image disturbances. EEG frequency spectra differed significantly between resting and visual hallucinations and body image disturbances. The differences included slower alpha and more theta during THC experiences, reminiscent of initial drowsiness EEG, and of some results in schizophrenia. The differences between spectra during visual hallucinations and during body image disturbances indicate different functional brain states. Subjects with a high tendency to cannabinol induced experiences exhibited resting spectra before and after THC with higher modal alpha frequences (reminiscent of subjects with high neuroticism scores) than subjects with a low tendency.

Adult↗
PubMed1975

Depth perception and location of brain lesions.

Depth perception was examined in 50 patients with brain lesions and in 16 controls using a polaroid test (Titmus). Error percentage and response time were measured. Intellectually impaired patients performed significantly worse than intellectually normal patients. On the other hand, location of the cerebral lesion (right, left, or generalized) had no significant effect; zero error percentages were observed among intellectually normal patients even with right or left parietal lesions. Intellectually normal patients did not differ from healthy controls.

Brain Diseases↗