Short-window spectral analysis using AMVAR and multitaper methods: a comparison

We compare two popular methods for estimating the power spectrum from short data windows, namely the adaptive multivariate autoregressive (AMVAR) method and the multitaper method. By analyzing a simulated signal (embedded in a background Ornstein–Uhlenbeck noise process) we demonstrate that the AMVAR method performs better at detecting short bursts of oscillations compared to the multitaper method. However, both methods are immune to jitter in the temporal location of the signal. We also show that coherence can still be detected in noisy bivariate time series data by the AMVAR method even if the individual power spectra fail to show any peaks. Finally, using data from two monkeys performing a visuomotor pattern discrimination task, we demonstrate that the AMVAR method is better able to determine the termination of the beta oscillations when compared to the multitaper method.     

Neural Activations during Visual Sequence Learning Leave a Trace in Post-Training Spontaneous EEG

Recent EEG studies have shown that implicit learning involving specific cortical circuits results in an enduring local trace manifested as local changes in spectral power. Here we used a well characterized visual sequence learning task and high density-(hd-)EEG recording to determine whether also declarative learning leaves a post-task, local change in the resting state oscillatory activity in the areas involved in the learning process. Thus, we recorded hd-EEG in normal subjects before, during and after the acquisition of the order of a fixed spatial target sequence (VSEQ) and during the presentation of targets in random order (VRAN). We first determined the temporal evolution of spectral changes during VSEQ and compared it to VRAN. We found significant differences in the alpha and theta bands in three main scalp regions, a right occipito-parietal (ROP), an anterior-frontal (AFr), and a right frontal (RFr) area. The changes in frontal theta power during VSEQ were positively correlated with the learning rate. Further, post-learning EEG recordings during resting state revealed a significant increase in alpha power in ROP relative to a pre-learning baseline. We conclude that declarative learning is associated with alpha and theta changes in frontal and posterior regions that occur during the task, and with an increase of alpha power in the occipito-parietal region after the task. These post-task changes may represent a trace of learning and a hallmark of use-dependent plasticity.     

Brain mechanisms of imagination in solving creative verbal tasks

The brain’s mechanisms of imagination were studied using electroencephalography (EEG) spectral analysis in student actors and student non-actors under three experimental conditions: when they generated coherent stories on the basis of art reproductions (STORY task); listed the details of art reproductions presented (DETAIL task); and performed simple arithmetic calculations while observing a neutral background (COUNT task). Statistical analysis showed that, in α₁ (7.5–10 Hz) and α₂ (10–12.5 Hz) frequency bands, in both groups, execution of the STORY task, in contrast to the DETAIL task, was accompanied by significantly higher spectral power (synchronization) in most of the cortical areas studied; while, the contrasts STORY-COUNT and DETAILS-COUNT, were associated with a decrease in the EEG’s power (desynchronization) in all of the areas studied. Topographic mapping of the EEG’s power showed that, in both groups, maximal differences between the STORY and DETAILS tasks were related to the central parietal area. Maximal differences between the STORY and COUNT tasks, as well as those between the DETAILS and COUNT tasks, were related mainly to the occipital areas. Based on these findings, we consider parietal areas to be stable elements of integrated brain mechanisms underlying verbal creativity in actors and nonactors. Comparing our data with previous studies, we suggest that the parietal areas are involved in the selective inhibition of visual information processing during the involvement of brain structures in the processes of imagination.     

Endogenous rhythms of locomotor activity in the high-shore limpet, Helcion pectunculus (Patellogastropoda)

Helcion pectunculus, a high-shore, crevice-dwelling limpet, is active during nocturnal low tides and during daytime low tides whilst in the shade. We examined whether this activity is controlled by an internal clock or purely by exogenous stimuli, such as light levels and tidal phase. Maximum entropy spectral analysis (MESA) revealed that the limpets possess a free-running endogenous rhythm of locomotor activity with both circadian (period 28.1 h) and circatidal (period 13.8 h) components. We suggest that this rhythm plays a role in allowing individuals to avoid unfavourable environmental conditions. The exogenous entrainment factor of the endogenous circatidal rhythm in H. pectunculus is the time of exposure to air, whilst the zeitgeber for the circadian component is not yet known. Copyright 1999 The Association for the Study of Animal Behaviour.     

Spectral kinetics ratiometry: a simple approach for real-time monitoring of fluorophore distributions in living cells.

BACKGROUND: Spectral Imaging Microscopy is gaining attention in biological research. Most of the commercial systems in vogue employ linear spectral un-mixing algorithms and/or spectral profile matching algorithms to extract the component spectral information from the measured specimen spectra. The need to accurately deconvolve multiple spectra with minimal cross-contamination is always accompanied by an increase in system complexity and cost. METHODS: We describe here a variant of the spectral waveform cross-correlation analysis (SWCCA) method where the master reference spectral library is constructed by composite spectra with varying ratios of component spectra, unlike the conventional spectral library where pure spectra form the components. We demonstrate that this spectral kinetics ratiometric approach gives realistic estimates of fluorophore distribution in living cells with a better spectral correlation as compared with pure component spectral libraries. RESULTS: Biological applications demonstrated in this article include acceptor photobleaching FRET, caspase activity during cell death and mitochondrial membrane polarization kinetics during substrate metabolism. CONCLUSIONS: Beyond the representative applications presented in this article, we think the proposed approach can be valuable in dynamic studies of a variety of other cellular processes such as pH oscillations, photobleaching and quenching kinetics. Besides giving better spectral correlation and real-time monitoring of biophysical processes in living cells, this method can serve as an economical solution for high-throughput spectral classification requirements.     

Meiotic sister chromatid cohesion in holocentric sex chromosomes of three heteropteran species is maintained in absence of axial elements

It has been suggested that in species with monocentric chromosomes axial element (AE) components may be responsible for sister chromatid cohesion during meiosis. To test this hypothesis in species with holocentric chromosomes we selected three heteropteran species with different sex-determining mechanisms. We observed in surface-spreads and sections using transmission electron microscopy that the univalent sex chromosomes form neither AEs nor synaptonemal complexes (SCs) during pachytene. We also found that a polyclonal antibody recognizing SCP3/Cor1, a protein present at AEs and SC lateral elements of rodents, labels the autosomal SCs but not AEs or SC stretches corresponding to the sex chromosomes. Cytological analysis of the segregational behaviour of the sex univalents demonstrates that although these chromosomes segregate equationally during anaphase I they never show precocious separation of sister chromatids during late prophase I or metaphase I. These results suggest that AEs are not responsible for sister cohesion in sex chromosomes. The segregational behaviour of these chromosomes during both meiotic divisions also indicates that different achiasmate modes of chromosome association exist in heteropteran species. Received: 22 September 1999; in revised form: 20 December 1999 / Accepted: 21 December 1999     

Spontaneous analogising caused by text stimuli in design thinking: differences between higher- and lower-creativity groups

Understanding the cognitive processes used in creative practices is essential to design research. In this study, electroencephalography was applied to investigate the brain activations of visual designers when they responded to various types of word stimuli during design thinking. Thirty visual designers were recruited, with the top third and bottom third of the participants divided into high-creativity (HC) and low-creativity (LC) groups. The word stimuli used in this study were two short poems, adjectives with similar meanings, and adjectives with opposing meanings. The derived results are outlined as follows: (1) the brain activations of the designers increased in the frontal and right temporal regions and decreased in the right prefrontal region; (2) the negative association between the right temporal and middle frontal regions was notable; (3) the differences in activations caused by distinct word stimuli varied between HC and LC designers; (4) the spectral power in the middle frontal region of HC designers was lower than that of LC designers during the short love poem task; (5) the spectral power in the bilateral temporal regions of HC designers was higher than that of LC designers during the short autumn poem task; (6) the spectral power in the frontoparietal region of HC designers was lower than that of LC designers during the similar concept task; and (7) the spectral power in the frontoparietal and left frontotemporal regions of HC designers was higher than that of LC designers during the opposing concept task.     

Trichromatic colour vision in the hummingbird hawkmoth, Macroglossum stellatarum L.

Hymenopterans have long been shown to choose colours by means of the spectral distribution and independently of the intensity (true colour vision). The same ability has only very recently been proven for two butterfly species. We present evidence for the existence of true colour vision in the European hummingbird hawkmoth, Macroglossum stellatarum. Moths were trained in dual-choice situations to spectral lights of a rewarding and an unrewarding wavelength. After training, unrewarded tests were performed during which the intensities of the lights were changed. The results confirm that the species has three spectral receptor types and uses true colour vision when learning the colour of a food source. If colour vision is not possible since only one receptor type is receiving input from both stimuli, the moths learn to associate some achromatic cue correlated to the receptor quantum catch, with the reward. The moths learn spectral cues rapidly and choose correctly after one to several rewarded visits even when trained to different colours in sequence. Accepted: 24 February 1999     

Children with well controlled epilepsy possess different spatio-temporal patterns of causal network connectivity during a visual working memory task

Using spectral Granger causality (GC) we identified distinct spatio-temporal causal connectivity (CC) patterns in groups of control and epileptic children during the execution of a one-back matching visual discrimination working memory task. Differences between control and epileptic groups were determined for both GO and NOGO conditions. The analysis was performed on a set of 19-channel EEG cortical activity signals. We show that for the GO task, the highest brain activity in terms of the density of the CC networks is observed in α band for the control group while for the epileptic group the CC network seems disrupted as reflected by the small number of connections. For the NOGO task, the denser CC network was observed in θ band for the control group while widespread differences between the control and the epileptic group were located bilaterally at the left temporal-midline and parietal areas. In order to test the discriminative power of our analysis, we performed a pattern analysis approach based on fuzzy classification techniques. The performance of the classification scheme was evaluated using permutation tests. The analysis demonstrated that, on average, 87.6 % of the subjects were correctly classified in control and epileptic. Thus, our findings may provide a helpful insight on the mechanisms pertaining to the cognitive response of children with well controlled epilepsy and could potentially serve as “functional” biomarkers for early diagnosis.     

Fruits, foliage and the evolution of primate colour vision

Primates are apparently unique amongst the mammals in possessing trichromatic colour vision. However, not all primates are trichromatic. Amongst the haplorhine (higher) primates, the catarrhines possess uniformly trichromatic colour vision, whereas most of the platyrrhine species exhibit polymorphic colour vision, with a variety of dichromatic and trichromatic phenotypes within the population. It has been suggested that trichromacy in primates and the reflectance functions of certain tropical fruits are aspects of a coevolved seed-dispersal system: primate colour vision has been shaped by the need to find coloured fruits amongst foliage, and the fruits themselves have evolved to be salient to primates and so secure dissemination of their seeds. We review the evidence for and against this hypothesis and we report an empirical test: we show that the spectral positioning of the cone pigments found in trichromatic South American primates is well matched to the task of detecting fruits against a background of leaves. We further report that particular trichromatic platyrrhine phenotypes may be better suited than others to foraging for particular fruits under particular conditions of illumination; and we discuss possible explanations for the maintenance of polymorphic colour vision amongst the platyrrhines.     

Features of the spectral power of the EEG rhythms in autistic children and their relation with the progress of different symptoms in schizophrenia

Right hemispheric dominance of the baseline alpha-band spectral power was revealed in 5-7 years boys with autism. This feature persisted during performance of a cognitive task (counting). Also, boys with autism showed lowered level of the alpha spectral power as compared with healthy children. In healthy children, the gamma spectral power increased during performance of the cognitive task as compared to baseline state. Autistic persons showed higher values of the gamma spectral power as compared with normal boys. Boys with autism showed less expressed changes in the gamma spectral power during the cognitive task than healthy children. The reduced spectral power of the alpha band in autistic boys may serve as a precursor of conversion from autism to schizophrenia. Higher level of the gamma spectral power in autistic boys is characteristic also of schizophrenic patients with positive symptoms. Lowered levels of fast rhythms reactivity revealed in autistic boys and the same effect earlier described in schizophrenic adults probably have the similar nature.     

Assessment of brain interactivity in the motor cortex from the concept of functional connectivity and spectral analysis of fMRI data

Functional magnetic resonance imaging (fMRI) was used to assess the contributions of movement preparation and execution of a visuomotor task in a cerebral motor network. The functional connectivity of the voxel time series between brain regions in the frequency space was investigated by performing spectral analysis of fMRI time series. The regional interactivities between the two portions of the supplementary motor area (pre-SMA and SMA-proper) and the primary motor cortex (M1), defined as a seed region, were evaluated. The spectral parameter of coherence was used to describe a correlation structure in the frequency domain between two voxel-based time series and to infer the strength of the functional interaction within our presumed motor network of connections. The results showed meaningful differences of the functional interactions between the two portions of the SMA and the M1 area depending on the task conditions. This approach demonstrated the existence of a functional dissociation between the pre-SMA and SMA-proper subregions. We therefore conclude that spectral analysis is useful for identifying functional interactions of brain regions and might provide a powerful tool to quantify changes in connectivity profiles associated with various components of an experimental task.     

Search for seasonal rhythmicity of pineal melatonin production in rats under constant laboratory conditions: spectral chronobiological analysis, and relation to solar and geomagnetic variables

Earlier we reported that in a number of experiments pineal melatonin production in rats under constant laboratory conditions displayed seasonal rhythms but subsequently were not always able to confirm this. Since there was no indication under which conditions such rhythms may be present, we performed four consecutive identical experiments with untreated female Sprague-Dawley rats within the same animal room during 1997-2006. Nocturnal urine samples (19-23, 23-3, 3-7?h) were collected at monthly intervals over 494-658?d with 12 animals each in experiments I and II (1997-1999, 1999-2000), 30 animals in experiment III (2002-2004), and 15 in experiment IV (2005-2006). 6-Sulfatoxymelatonin (aMT6s) was measured by ELISA. The excreted aMT6s at each time interval as well as total nocturnal aMT6s-excretion (19-7?h) was submitted to standard statistical analyses as well as to a spectral chronobiological analysis to determine the period lengths of the components involved which was followed by processing with the single cosinor method. Seasonal rhythm components (circannual period length: 360 ± 60?d) were detected in experiment III (2002-2004) for the overall nocturnal excretion as well as for two sub-intervals (23-3 and 3-7?h) and in one night interval of experiment II (23-3?h). Multiple components with mostly short period lengths of around 100?d and some long ones of 500-650?d were found in the other experiments. Systematic MESOR and amplitude variations were observed during the experiments, being highest in experiment II (19-7?h, also 23-3?h and 3-7?h) and lowest in experiments I and IV. These results illustrate that seasonal melatonin rhythms are not a general phenomenon in female laboratory rats indicating an involvement of unknown environmental cues. As an extension of our earlier hypothesis regarding a seasonal Zeitgeber function of the horizontal intensity H of the geomagnetic field showing circannual variations, we assume further modulation by the 11-yrs' sunspot cycle which leads to geomagnetic disturbances and could facilitate seasonal aMT6s rhythmicity during specific years. (Author correspondence: christian.bartsch@uni-tuebingen.de ).     

Interactive effects of task difficulty and personality on mood and heart rate variability

Susceptibility to stress would presumably be different from person to person and be affected by the cause of the given stress. The purpose of this study was to investigate the interactive effects of task difficulty and subject's personality on mood and autonomic nervous function when stress was induced experimentally by tasks involving 3 degrees of difficulty: easy (Task A), difficult but controllable (Task B), and very difficult and uncontrollable (Task C). Twelve healthy female subjects volunteered for the experiment. We assessed their personalities using the Minnesota Multiphasic Personality Inventory (MMPI) questionnaire. Mood states were evaluated by a profile of mood states and a frontal alpha laterality ratio (FALR). Autonomic nervous function was estimated by a spectral analysis of heart rate variability (HRV). Repeated measures analysis of variance applied to two groups (low- and high-) divided by a median split of MMPI clinical scales, revealed significant interactions of time course x task difficulty x Hs (hypochondriasis) in FALR and time course x task difficulty x Pt (psychasthenia) in a low-frequency component and in a high-frequency component of HRV, and in FALR. The differences between low- and high-Hs, and low- and high-Pt were more obvious in Task B session. High-Hs group, whose members tend to place overemphasis on existing physical disorders, showed more negative FALR throughout the session, which would indicate prolonged negative mood possibly due to the task. High-Pt group, whose members tend to be susceptible to stress, showed sympathetic predominance during task period and parasympathetic predominance after task period, which would imply a tendency to overreact. These results suggest that task difficulties would affect mood states assessed by FALR and/or autonomic nervous function differently depending on the subject's personality, especially on Hs and Pt.     

Nonlinear time-course of lumbar muscle fatigue using recurrence quantifications

 Isometric skeletal muscle fatigue is usually assumed to be a linear process based upon the monotonic decrease in spectral frequency of the EMG. Since spectral analysis by fast Fourier transform (FFT) constitutes a linear transformation of the data, the present study was designed to reevaluate the time-course of muscle fatigue with a nonlinear tool, recurrence quantification analysis (RQA). Surface EMG recordings were obtained from the multifidus muscle of 17 human subjects during isometric posture-holding of the upper torso. The process of muscle fatigue was found to be linear for 59% of the subjects by FFT criteria, but nonlinear for 76% by RQA criteria. As a demonstrative control, both slow and fast transients occurring within a nonlinear mathematical process could be accurately depicted by RQA, but not by FFT. It is concluded that assessment of EMG patterns by nonlinear techniques can give insight into the time-course of fatiguing muscles attributed to the summation of several nonlinear and competing processes. Received: 12 November 1998 / Accepted in revised form: 29 November 1999     

Induced cortical electrical activity during different time-spans between warning and target stimuli

A certain alpha-band EEG dynamics was revealed in healthy adults (n = 16) at the interval between a warning and a target stimulus in a simple visuospatial task (subjects were instructed to locate a specific letter in the table of letters). Two series of experiment--either with a 2-sec or a 9-sec inter-stimulus interval were conducted, each consisting of 60 trials. In both series, we observed an induced desynchronization of low alpha (8-10 Hz) at the first second after the warning stimulus and its desynchronization just before the target stimulus. In series with a 9-sec inter-stimulus interval at the 4-6 s of it we observed an alpha-band synchronization, especially distinct in high alpha (10.5-13 Hz). This synchronization gradually reduced towards the end of the inter-stimulus interval. We consider the above changes in alpha-band spectral power during the inter-stimulus interval to be induced by "inner impulsations" caused by an internal representation (set) of the stimuli time-sequence. Changes in the level of cognitive control during the inter-stimulus interval cause increases and decreases in fronto-thalamic system activity, which are manifested in changes of alpha-band spectral power. Analysis of theta-band dynamics suggests that cortico-hippocampal system doesn't participate in this process.     

Conservation of the WD-repeat, microtubule-binding protein, EMAP, in sea urchins, humans, and the nematode C. elegans

The echinoderm microtubule-associated protein (EMAP) is the most abundant microtubule-binding protein in the first cleavage mitotic apparatus in sea urchin embryos. The first goal of this study was to determine whether there is sufficient EMAP in the egg and embryo to modify microtubule dynamics during the early cleavages divisions and whether EMAP functions at a specific time or place in the embryo. To accomplish this goal, we examined the relative abundance, tissue distribution, and temporal pattern of EMAP expression during embryonic development. The second goal of this study was to identify important functional domains within the EMAP coding sequence. A conserved sequence might reveal a potential microtubule-binding domain. We cloned, sequenced and compared overlapping EMAP cDNAs from two different sea urchin species that diverged approximately 80 million years ago, and compared these with cDNA sequences from a vertebrate and nematode species. From quantitative immunoblots, we determined the EMAP concentration in eggs to be 4 μM. The steady-state levels of EMAP mRNA and protein accumulated during development, and all three germ layers expressed EMAP. During the early stages of development, EMAP and tubulin were both abundant in the ectoderm, mesoderm and endoderm. However, during late gastrulation and the formation of the early pluteus larvae, EMAP was enriched in the mesoderm, while tubulin staining was most abundant in the archenteron. These results indicate that EMAP may have tissue-specific functions in the late stage embryo. To identify conserved functional domains, we compared the predicted amino acid sequence encoded by Strongylocentrotus purpuratus and Lytechinus variegatus EMAP cDNAs, and determined that these two sea urchin EMAPs were 95% conserved and shared an identical domain organization. A parsimonious analysis of these sea urchin protein sequences, as well as human and C. elegans EMAP sequences was used to construct a gene tree. Together these results suggest that EMAP is an important microtubule protein required at all developmental stages of sea urchins, and whose cellular function may be conserved amongst metazoans. Received: 2 March 1999 / Accepted: 28 June 1999     

Hydrophobic and Hydrophilic Radio-Iodination, Crosslinking, and Differential Extraction of Cell Surface Proteins in Paramecium tetraurelia Cells

We combined widely different biochemical methods to analyze proteins of the cell surface of P. tetraurelia since so far one can isolate only a subfraction of cell membrane vesicles enriched in the GPI-anchored surface antigens (``immoblization' or ``i-AGs'). We also found that i-AGs may undergo partial degradation by endogenous proteases. Genuine intrinsic membrane proteins were recognized particularly with lipophilic 5-[¹²⁵I]-iodonaphthalene-1-azide (INA) labeling which reportedly ``sees' integral proteins and cytoplasmic cell membrane-associated proteins. With INA (+DTT), bands of ≤55 kDa were similar as with hydrophilic iodogen (+DTT), but instead of large size bands including i-AGs, a group of 122, 104 and 94 kDa appeared. Several bands of the non i-AG type are compatible with integral (possibly oligomeric) or associated proteins of the cell membrane of established molecular identity, as we discuss. In summary, we can discriminate between i-AGs and some functionally important minor cell membrane components. Our methodical approach might be relevant also for an analysis of some related protozoan parasites. Received: 5 April 1999/Revised: 19 July 1999     

A computational model of rapid task-related plasticity of auditory cortical receptive fields

Receptive field properties of neurons in A1 can rapidly adapt their shapes during task performance in accord with specific task demands and salient sensory cues (Fritz et al., Hearing Research, 206:159–176, 2005a, Nature Neuroscience, 6: 1216–1223, 2003). Such modulatory changes selectively enhance overall cortical responsiveness to target (foreground) sounds and thus increase the likelihood of detection against the background of reference sounds. In this study, we develop a mathematical model to describe how enhancing discrimination between two arbitrary classes of sounds can lead to the observed receptive field changes in a variety of spectral and temporal discrimination tasks. Cortical receptive fields are modeled as filters that change their spectro-temporal tuning properties so as to respond best to the discriminatory acoustic features between foreground and background stimuli. We also illustrate how biologically plausible constraints on the spectro-temporal tuning of the receptive fields can be used to optimize the plasticity. Results of the model simulations are compared to published data from a variety of experimental paradigms.