Dreaming: The functional state-shift hypothesis. A neuropsychophysiological model

The different brain functional states during sleep and wakefulness are associated with differences in processing strategies, memory stores, and EEG patterns. Shifts of functional state occur spontaneously or as orienting reactions to processed information, and cause the formal characteristics of dreams. Forgetting of dreams is a function of the magnitude of the difference between states during storage and recall. Based on EEG similarities between sleep stages and developmental stages, brain states during sleep in adults are proposed to correspond functionally with waking states during childhood. Repeated functional regressions occur during sleep, with access to earlier memory material and cognitive strategies unavailable during waking life, so that earlier experiences can be used for current problems. This dream work constitutes the biological significance of sleep.

Spectral analysis of all-night sleep EEG in healthy adults

Power and coherence spectra were computed from all-night sleep EEG records in 6 healthy adult subjects. Derivations were from F3, F4, P3, P4, O1, O2, T3, and T4 to the vertex (Cz). Records were conventionally scored into sleep stages. Average power per sleep stage was maximal at frequencies 0.4-6 c/s in stage 4, at 6-10 c/s in either stage 3 or stage 4, at 12-14 c/s in stage 2 and at 14-30 c/s in stage 1. The average power range from highest values in the lowest frequency band to lowest values in the highest frequency band showed marked differences between sleep stages: It was lowest (12-14 dB) in stage 1, followed by stage 2 (20-22 dB), and stage 3 (16-28 dB), and largest in stage 4 (29-32 dB). REM sleep (15-16 sB) was between stage 1 and 2. The waking state showed an average power range of 11-15 dB. Alpha power at 8-10 c/s in occipital and parietal leads was remarkably constant during sleep, i.e. independent of sleep stage. Coherence showed maximal values at 2-8 c/s in REM sleep, at 8-12 c/s in stage 4, at 12-17 c/s in either stage 3 or 4, and at 17-30 c/s again in stage REM. There was significant coherence increase at 2-8 and 17-30 c/s from NREM to REM sleep, most pronounced between parietal to vertex derivations. Overall coherence between both occipital-to-vertex, or between occipital and parietal-to-vertex derivations, was essentially higher than in the other derivations. The results, essentially, give a comprehensive phenomenology of the dynamic spectral structure of all-night sleep EEG. They suggest that the different brain states during sleep (e.g. stage 1 NREM vs. REM) which are associated with different functions (e.g. hypnagogic hallucinations vs. dreams) differ in EEG spectral parameters if coherence is considered. Likewise, they suggest that studies of automatic sleep staging based exclusively on EEG spectral parameters appear promising.

Spatial principal components of multichannel maps evoked by lateral visual half-field stimuli

Multichannel records of responses to large and small hemiretinal stimuli were obtained from 6 healthy subjects. Scalp distribution maps were constructed for all conditions at all post-stimulus times and component latencies were objectively determined by computing a reference-independent measure of field power. This procedure identified 2 components (at 100 and 140 msec). The scalp distribution data at these latencies were entered into a spatial principal components analysis which further reduced the data set to three underlying spatial principal components. These components may be regarded as reflecting underlying processes and were related to experimental conditions. A component reflecting lateralized brain activity displayed a significant interaction between size and retinal location of the stimulus with large stimuli showing a more pronounced lateralization over the hemisphere contralateral to the stimulated hemiretina, and the scores on this component were low for upper hemiretinal stimuli. These findings are in agreement with intracranially recorded evoked potential data and theoretical dipole source computations, and confirm a model of cortical neuronal generator processes whose locations and orientations in the hemisphere ipsilateral to the hemiretina stimulated are influenced not only by retinal stimulus location but also by stimulus size.

[Visual evoked potentials and click-evoked brainstem potentials in early diagnosis of multiple sclerosis: statistics (author's transl)]

95 sequential unselected patients which had been referred to our lab as certain (31), probable (32) and possible (32) MS cases were examined using checkerboard (VEP) and click-brainstem (BAEP) average potentials. In VEPs, latency of the positive wave around 100 msec, and in BAEPs, latency differences between waves III-V, I-V and latency wave V was measured. Pathology was defined as values of more than 3 SD above mean of controls. VEPs were pathological in 68%/50%/41% and BAEPs were pathological in 32%/28%/9% of the certain/probable/possible cases. Eleven of the probable cases had spinal symptomatology only; 9 of these had pathological VEPs, 4 in addition pathological BAEPs. Ten of the possible cases had spinal symptomatology only; 5 of these had pathological VEPs, 2 in additional pathological BAEPs. - Improved diagnostic certainty was reached in 11 of the 32 probable cases because of pathological VEPs (4 of these in addition had pathological BAEPs). - 10 of the 32 possible cases could be classified as probable, 8 of these because of pathological VEPs and 2 because of pathological BAEPs (the latter 2 had normal VEPs). - Monaural stimulation was not significantly more effective than binaural stimulation. In general, VEPs were clearly more useful than BAEPs in the early diagnostics of MS, and for clarification of spinal symptomatology; however in occasional cases, BAEPs might contribute to the early diagnosis.

Analysis and restitution of visual function in a case of cerebral amblyopia

In a patient suffering from a severe bilateral dysfunction in both occipital and parietal areas we have found: (1) A loss of contrast-sensitivity, being strongest in the range of spatial frequencies where the normal eye is most sensitive; (2) Virtually normal grating resolution, a severe loss in letter acuity (about 15-fold), and a very strong loss in vernier acuity (about 100-fold); (3) Rapid partial recovery of contrast sensitivity due to stimulation; (4) Slow partial recovery of letter acuity due to CAM rotating grating treatment; (5) No improvement of a 10-fold temporal retardation in the speed of reading. Evidence is presented that the residual impairment of vision depends upon improper synthesis of spatial frequency components originating from a heavy loss in processing speed and abnormally long store duration for high spatial frequency information.

Sleep deprivation: effect on sleep stages and EEG power density in man

Sleep was analysed in 8 young adults subjects during two baseline nights and two recovery nights following 40.5 h sleep deprivation. Sleep stages were scored from the polygraph records according to conventional criteria. In addition, the EEG records of the entire nights were subjected to spectral analysis to compute the frequency distribution of the power density in the 0.25-25 Hz range for 0.5 Hz or 1.0 Hz bins. In the first recovery night, the power density in the delta band was significantly higher than baseline for total sleep time as well as for sleep stages 2, 3 and 4, 4 and REM. These changes were not restricted to the delta band, but extended to higher frequency bands. Minor, but significant, effects of sleep deprivation were seen in the power density distribution of the second recovery night. In the baseline nights, a progressive reduction of power density in the delta/theta range was present for successive non-REM-REM sleep cycles for total sleep time and stages 2, 3 and 4, and 4. The results show that effects of sleep deprivation as well as trends within the sleep periods are readily apparent from spectral analysis, but are inadequately reflected by conventional sleep scoring. When the power density values were integrated over the entire frequency range (0.75-25 Hz) for each non-REM-REM sleep cycle, an exponential decline from cycle 1 to cycle 3 was suggested. The present findings support the hypothesis that the EEG power density in the low frequency range is an indicator of a progressively declining process during sleep whose initial value is determined by the duration of prior waking.

EEG power and coherence during non-REM and REM phases in humans in all-night sleep analyses

All-night spectral power and coherence analysis of six channels of EEG data from 6 healthy volunteers was performed. Integrated power and integrated coherence for the frequency bands of 0.1-7 and 7-12 Hz in 20 s epochs was plotted over the entire nights. Power and coherence increased with deepening slow wave sleep. With the onset of REM periods, power expectedly decreased, whereas coherence showed a further increase or maintained levels. With post-REM phase awakenings, power showed further reductions, and coherence decreased. The REM coherence results were most pronounced in interhemispheric right to left parietal comparisons (recorded vs. a Cz reference) in the 0.1-7 Hz band. It is hypothesized that the high interhemispheric coherence facilitates or reflects right-left transfer of information.

Reference-free identification of components of checkerboard-evoked multichannel potential fields

A method is proposed to determine components of evoked scalp potentials, in terms of times of occurrence (latency) and location on the scalp (topography). The scalp field distributions were evoked by checkerboard reversal and were recorded simultaneously in 47 channels. Component latencies are defined as times of maximal values of the electrical power of the evoked field (a measure of the amount of field relief); this measurement is independent of the choice of the reference electrode. In 10 subjects, two evoked components were found consistently: at 100 and at 140 msec. Plots of scalp locations of the extreme field values (i.e., reference-free data) at the occurrence times of the components showed occipitally positive and anteriorly negative extreme values at 100 msec, and vice versa at 140 msec. The occipital extreme values were surrounded by steep field gradients suggesting occipital generator processes. The polarity reversal of the evoked field distributions between 100 and 140 msec was a quick, jump-like location change of the extreme values in the field. The locations of the extreme field values were stable for long periods around peak times of the power curve. During these periods, the shape of the field remained constant (assessed by the average standard deviation of voltages per electrode between successive field distributions), suggesting also a stable localization of the generating process in depth. The field distributions tended to be concentric around the extreme field values. The major characteristics of the observed scalp fields showed no wave fronts, and no continuous 'traveling' of extreme values over larger distances.

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.

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.

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.

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.

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.

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.

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.

[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.

[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.

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.