The selectively distributed theta system: functions

The present paper provides three interwoven or interrelated approaches: (1) the dependence of frontal theta response from the spontaneous activity will be pointed out. This helps in understanding that 'frontal theta' is a major oscillation of the human frontal cortex and has a response-controlling function; (2) it will be shown that complex stimulations such as bimodal stimulation enhances the theta response; and by bringing together the results outlined in a number of previous reviews the so-called 'selectively distributed theta system of the brain' is described.

Event-related oscillations are 'real brain responses'--wavelet analysis and new strategies

The EEG consists of the activity of an ensemble of generators producing rhythmic activity in several frequency ranges. These oscillators are active usually in a random way. However, by application of sensory stimulation these generators are coupled and act together in a coherent way. This synchronization and enhancement of EEG activity gives rise to 'evoked' or 'event-related oscillations'. The compound evoked potential manifests as superimposition of evoked rhythms in the EEG frequencies ranging from delta to gamma ('natural frequencies of the brain'). The superimposition principle is described with efficient strategies and by utilization of an efficient algorithm. The wavelet analysis confirms the results of the combined analysis procedure obtained by using the amplitude frequency characteristics (AFCs) and digital filtering. The AFC and adapted digital filtering methods are based on the first approach to analyze average evoked potentials. In contrast, the wavelet analysis is based on signal retrieval and selection among a large number of sweeps recorded in a given physiological or psychological experiment. By combining all these results and concepts, it can be stated that the wavelet analysis underlines and extends the expression that alpha-, theta-, delta-, and gamma-responses described in this report are the most important brain responses related to psychophysiological functions. The wavelet analysis confirms once more the expression 'real signals' which we attribute to EEG frequency responses of the brain. It will be demonstrated that the delta, theta, and alpha responses (i.e. the rhythms 'predicted' by digital filtering) are real brain oscillations. The frequency components of the event-related potential vary independently of each other with respect to: (a) their relation to the event; (b) their topographic distribution; and (c) with the mode of the physiological measurements.

Delta responses and cognitive processing: single-trial evaluations of human visual P300

Visual P300 responses were recorded by using checkerboard-type stimuli. (1) High amplitude P300-delta responses were visible even in single trial ERPs. (2) An algorithm for efficient selection of P300 single trials (based on evaluation of delta responses) is introduced. (3) The 'universal' character of the P300-delta response demonstrated in this report may open new avenues for the understanding of functional ERP components.

Angiotensin-converting enzyme (ACE) gene polymorphisms and familial occurrence of sarcoidosis

OBJECTIVES

The aim of this study was to test for genetic linkage and association between polymorphisms of the angiotensin-converting enzyme (ACE) gene and familial occurrence of sarcoidosis.

DESIGN, SETTING AND SUBJECTS

German families with more than one member suffering from sarcoidosis were contacted and a DNA bank was established. Sixty-two families (140 patients, 77 females and 63 males, and 104 unaffected relatives) were genotyped for the ACE gene insertion/deletion (I/D) polymorphism and for two flanking variable sites (ACE A-5466C and ACE 4656(CT)2/3). As controls, 100 DNAs from unrelated resident Caucasians (50 females, 50 males) were analysed. ACE allele and genotype frequencies were determined, and parametric linkage and affected sib pair analyses and transmission disequilibrium tests were performed.

RESULTS

There was a striking over-representation of the ACE I/D genotype DD in patients with sarcoidosis and their families as compared with controls of the study and well founded genotype frequencies from the literature. The same was evident for the accompanying genotypes CC and 2,2 of the flanking polymorphisms. Linkage between the segregation of ACE alleles and the disorder within families was clearly excluded for simple models of inheritance. However, there was a suggestive but not significant (P = 0.06) excess of allele sharing amongst affected siblings. There was no transmission disequilibrium for any ACE allele or haplotype.

CONCLUSIONS

ACE is involved in the pathogenesis of sarcoidosis, but the ACE polymorphisms are not an inherited main cause of the disease. They are more likely to modify the development of the disorder, and the ACE I/D genotype DD might be a promoter to clinical manifestation.

Topological distribution of oddball 'P300' responses

This report describes the frequency response of the oddball paradigm upon auditory stimuli. Other reports related to wavelet analysis of the same ERPs (Demiralp et al., 1999) and the application of visual signals (Schürmann et al., this volume) indicate that the P300 response has a dominant delta response oscillation, independent of the modality of the stimulation. Moreover, the adaptive digital filtering and the wavelet analysis lead to very similar results, confirming that delta responses are real brain responses as already mentioned, by Başar et al. (this volume). The theta response has a second late response window in comparison to auditory evoked potentials. Moreover, the functional significance of the selectively distributed theta and delta systems of the brain will be clearly demonstrated. Signal detection, short-term memory, and decision-making processes are discussed.

Selectively distributed gamma band system of the brain

Experiments from the cat brain demonstrate that gamma responses can be recorded in cortex, hippocampus, cerebellum, formatio reticularis and thalamus, independent of the mode of sensory stimulation. These results support the hypothesis of a selectively distributed gamma system of the brain.

Increased frontal phase-locking of event-related alpha oscillations during task processing

Recent findings substantiate the view that electroencephalographic (EEG) alpha rhythm (7-13 Hz) is functionally involved in cognitive stimulus processing. Our previous results have shown that enhanced alpha responses to auditory task stimuli can be well synchronized with stimulus until 800-1000 ms. The present study analyzed the effect of perceptual uncertainty and difficulty in decision making on event-related alpha oscillations in single auditory event-related brain potentials (ERPs). EEG was recorded from Fz, Cz and Pz electrodes in 10 subjects participating in two experimental sessions, in which auditory stimuli with equal physical parameters were presented under passive and task instructions. Separate measurements of single alpha response amplitude and phase-locking were performed and statistically analyzed for consecutive time windows in the post-stimulus epoch. Major results show that, during the cognitive task, the phase-locking of alpha oscillations at the frontal site is significantly increased in the time window of 500-1000 ms after stimulation. Thus, the involvement of enhanced and synchronized frontal alpha activity in higher brain processes is strongly emphasized.

Gamma, alpha, delta, and theta oscillations govern cognitive processes

The increased interest in gamma oscillations, now widely regarded as functionally relevant signals of the brain, underlines the importance of the concept of event-related oscillations for bridging the gap between single neurons and neural assemblies. Taking this concept further, we review experiments showing that oscillatory phenomena such as alpha, theta, and delta responses to events are, just as the gamma band, strongly interwoven with sensory and cognitive functions. This review argues that selectively distributed delta, theta, alpha and gamma oscillatory systems act as resonant communication networks through large populations of neurons. Thus, oscillatory processes might play a major role in functional communication in the brain in relation to memory and integrative functions.

Functional aspects of alpha oscillations in the EEG

Experimental evidence suggests a functional significance of EEG alpha rhythms. Event-related, evoked, and induced alpha rhythms may have functional correlates in primary sensory processing and preparatory processes. These results are in accordance with the view that spontaneous and induced EEG alpha rhythms have quasi-deterministic properties.

EEG responses to combined somatosensory and transcranial magnetic stimulation

OBJECTIVES

To investigate a possible interaction between sensory processing and transcranial magnetic stimulation (TMS), an experimental set-up permitting multichannel EEG measurements was used.

METHODS

A somatosensory stimulus was delivered to the right wrist, while single-pulse TMS was applied to the contralateral somatosensory cortex, either concurrent with the somatosensory stimulus or 10 ms after it. A control condition served to mimic the sound of TMS without actually resulting in brain stimulation.

RESULTS

An enhancement of the P25 component of the somatosensory-evoked potential (SEP) was consistently observed for TMS concurrent with somatosensory stimulus. The effect was topographically specific to the EEG recording sites below the TMS coil, i.e. above the somatosensory cortex contralateral to the stimulated peripheral nerve.

CONCLUSIONS

The results can be interpreted (1) as an indication of local interaction between the somatosensory-evoked cortical activity and TMS-evoked activity or (2) as support of a relationship between the background EEG and the evoked potential (EP), this relationship being 'disrupted' by TMS.

Peripheral sympathetic function as a predictor of complex regional pain syndrome type I (CRPS I) in patients with radial fracture

Complex regional pain syndrome type I (CRPS I) is a frequent complication after injuries of the upper limbs. The pathophysiology of this disease remains unclear, although disturbances of the sympathetic nervous system have been detected in several clinical studies, and sympathetic blocks resolve the symptoms in many of the cases. To investigate the meaning of sympathetic dysfunction at the beginning of the disease, 27 patients with distal radial fracture were examined prospectively during the course of the disease with regard to their clinical symptoms and their peripheral sympathetic nervous function. Sympathetic nervous function was examined by testing the vasoconstrictor response to sympathetic stimuli--recorded with laser Doppler fluxmetry--of the fingertips of both hands. Four patients developed CRPS I during the 12-week observation time and two patients presented an incomplete clinical CRPS I picture ('borderline patients'). The complaints of all patients (normal fracture patients, CRPS I patients, borderline patients) were similar during the first week after trauma with focus on pain, motoric disturbances and autonomic symptoms. After 1 or 2 weeks, a larger clinical difference developed between normal fracture patients and CRPS I or 'borderline patients'. In CRPS I patients and 'borderline patients', the sympathetic vasoconstrictor response was diminished or absent from the first posttraumatic day throughout the observation time, whereas the normal fracture patients revealed slightly impaired sympathetic nervous function on the first posttraumatic day and normal results during the rest of the observation time. With regard to the unaffected contralateral hand, CRPS I patients also showed impaired sympathetic nervous function. The results of the present study suggest that the disturbances in the sympathetic nervous system in CRPS I patients are systemic and not limited to the affected limb. Their occurrence before the clinical breakout of the disease may serve as a marker that might be useful for early therapy and lead to further understanding of the pathophysiology of CRPS I.

Clinical and finite element analysis of a modular femoral prosthesis consisting of a head and stem component in the treatment of pertrochanteric fractures

OBJECTIVE

To determine the biomechanical characteristics and potential clinical efficacy of a cementless modular femoral prosthesis consisting of a variable head (50 to 80 millimeters) and stem (length 120 to 280 millimeters, diameter 10 to 20 millimeters) component in patients with pertrochanteric femoral fracture.

DESIGN

Finite element analysis (FEA) of different lengths and diameters of prosthesis components and first clinical prospective study in pertrochanteric femoral fracture.

METHOD

Using a 3D-CAD program, a model of femoral cortical bone with a pertrochanteric fracture was created and combined with a model of the prosthesis. This model was transferred into an FEA program. After applying a torsion-bending load of 2,000 N (25 degrees, 45 degrees) on the prosthesis, stress distribution in the cortical bone was determined for different lengths (160 to 240 millimeters) and diameters (10 and 12 millimeters) of stem.

PATIENTS

Twenty-eight patients with pertrochanteric fractures (very unstable or osteoarthritis) were treated with a modular hip arthroplasty. Complications, fracture healing, and results at first follow-up (average 13 months) were determined.

RESULTS

FEA analysis indicated that reduction in stress was less when a prosthesis with a short stem was used. Shear stress in the interface bone/prosthesis was not affected by stem length. Prostheses with thin stems produced higher sheer stresses than those with thick stems. Results of FEA were used as the basis for clinical application of the device. None of the patients died, and all patients were able to walk, although some needed a cane or walker after surgery. There was no increase in thigh pain compared with reported pretrauma levels. Radiographs showed subsidence of up to 5 millimeters in 20 percent of patients. However, all but one prosthesis was stable at follow-up. Fracture healing was achieved in all patients.

CONCLUSIONS

If proximal fixation of a femoral uncemented stem cannot be achieved, stem diameter should provide maximum cortical contact to reduce sheer stress. Longer stems do not necessarily provide additional stability. By using this prosthesis and selection method, a good outcome at first follow-up was observed.

Metastatic lesions of the humerus treated with the isoelastic diaphysis prosthesis

Between January 1, 1987, and December 31, 1997, an isoelastic polyacetal resin prosthesis was used in 50 patients with metastatic bone disease to reconstruct pathologic or impending fractures of the humeral diaphysis. Fifty-seven operations were performed, including seven revision surgeries. The patients were assessed before and after surgery for limb function and quality of life using a modified Karnofsky scale. The mean survival time was 440 days. Ninety-one percent of the operations resulted in restoration or improvement of quality of life. Limb function was good or excellent in more than 80% of the patients after surgery. Breaking of the implant (n = 3), loosening of the implant (n = 2), periprosthetic fracture (n = 1), hematoma (n = 2), infection (n = 1), and one radial nerve paralysis were the main complications. In the cases of implant failure, the prosthesis broke at the site of a locking screw that was inserted across the prosthetic shaft in the cementless implantation technique. This kind of complication could be avoided by using bone cement for implantation or additional plate osteosynthesis between the prosthesis and humeral shaft. The isoelastic diaphyseal prosthesis offers a promising method of treating patients with metastatic lesions of the humeral shaft.

Electroencephalogram alpha (8-15 Hz) responses to visual stimuli in cat cortex, thalamus, and hippocampus: a distributed alpha network?

To investigate possible functional correlates of alpha (8-15 Hz) oscillations in the electroencephalogram (EEG) intracranial recordings in cats (from thalamus, occipital cortex, and hippocampus) were performed. In response to visual stimuli, event-related alpha oscillations were observed. Such alpha responses were found not only in a specific sensory (visual) pathway but also in the hippocampus, hinting at a possible distributed alpha response system.

Familial sarcoidosis is linked to the major histocompatibility complex region

Sarcoidosis is a systemic granulomatous disorder associated with high CD4+ cell activity, but no pathogen is detectable. Clustering in families occurs, and the existence of a genetic predisposition to sarcoidosis is widely accepted. The major histocompatibility complex (MHC) is believed to contribute to this susceptibility. Many studies testing this hypothesis have produced conflicting results. We have genotyped 122 affected siblings from 55 families for seven DNA polymorphisms that flank and cover the MHC region on chromosome 6, and for HLA-DPB1, a candidate gene for granulomatous disorders. Multipoint nonparametric linkage (NPL) analysis showed linkage (NPL score > 2.5; p < 0.006) for the entire MHC region with a maximum NPL score of 3.2 (p = 0.0008) at marker locus D6S1666 in the Class III gene cluster. There was a significant excess of marker haplotype sharing among affected siblings. However, the frequency of HLA-DPB1 alleles on 104 shared chromosomes did not differ from that of a control group of founders from the family panel. Transmission disequilibrium was found for allele DPB1*0201, but only nine families contributed to this result. We conclude that genes of the MHC are involved in the genetic predisposition to sarcoidosis, but HLA-DPB1 alone does not sufficiently explain this fact.

Endoscopic osteosynthesis after thoracic spine trauma: a report of two cases

Modern concepts of treating thoracic diseases suggest more and more the use of minimally invasive thoracoscopic techniques to reduce morbidity and save costs. For treatment of specific lesions at the thoracic spine, several thoracoscopic procedures have been performed successfully. The present report examines the feasibility of thoracoscopic osteosynthesis in two patients with ventral hyperextension injuries and anterior instability of the thoracic spine. After initial correction of the anatomical deformity, autologous bone was harvested from the anterior iliac crest. Using a ventral, thoracoscopic approach, the main location of the ventral, damaged spinal segment was identified by the covering pleural haematoma. After endoscopic ventral bone grafting, osteosynthesis was performed, using dynamic compression plates, cardan drills and screw drivers. The perioperative course was uneventful, and follow up examinations after 3 years and 9 months, respectively, revealed an unchanged stable spinal segment. Our results show thoracoscopic osteosynthesis to be technically possible, with a potential for yielding satisfying long-term results.

(1R*,11R*)-Bicyclo[9.4.1]hexadecane-12,16-dione

The title compound, C(16)H(26)O(2), (I), prepared by oxidation of (1R*,11R*)-12-hydroxybicyclo[9.4.1]hexadecan-16-one using pyridinium dichromate, has a trans configuration of the two fused rings and represents an interesting precursor for the synthesis of macrocyclic structures.

Oscillatory frontal theta responses are increased upon bisensory stimulation

OBJECTIVES

To investigate the functional correlation of oscillatory EEG components with the interaction of sensory modalities following simultaneous audio-visual stimulation.

METHODS

In an experimental study (15 subjects) we compared auditory evoked potentials (AEPs) and visual evoked potentials (VEPs) to bimodal evoked potentials (BEPs; simultaneous auditory and visual stimulation). BEPs were assumed to be brain responses to complex stimuli as a marker for intermodal associative functioning.

RESULTS

Frequency domain analysis of these EPs showed marked theta-range components in response to bimodal stimulation. These theta components could not be explained by linear addition of the unimodal responses in the time domain. Considering topography the increased theta-response showed a remarkable frontality in proximity to multimodal association cortices. Referring to methodology we try to demonstrate that, even if various behavioral correlates of brain oscillations exist, common patterns can be extracted by means of a systems-theoretical approach.

CONCLUSIONS

Serving as an example of functionally relevant brain oscillations, theta responses could be interpreted as an indicator of associative information processing.

Brain oscillations in perception and memory

Gamma oscillations, now widely regarded as functionally relevant signals of the brain, illustrate that the concept of event-related oscillations bridges the gap between single neurons and neural assemblies. Taking this concept further, we review experiments showing that oscillatory phenomena such as alpha, theta, or delta responses to events are strongly interwoven with sensory and cognitive functions. This review argues that selectively distributed delta, theta, alpha, and gamma oscillatory systems act as resonant communication networks through large populations of neurons. Thus, oscillatory processes might play a major role in relation with memory and integrative functions. A new 'neurons-brain' doctrine is also proposed to extend the neuron doctrine of Sherrington.