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PubMed1989

Kinetic depth effect and optic flow--I. 3D shape from Fourier motion.

Fifty-three different 3D shapes were defined by sequences of 2D views (frames) of dots on a rotating 3D surface. (1) Subjects' accuracy of shape identifications dropped from over 90% to less than 10% when either the polarity of the stimulus dots was alternated from light-on-gray to dark-on-gray on successive frames or when neutral gray interframe intervals were interposed. Both manipulations interfere with motion extraction by spatio-temporal (Fourier) and gradient first-order detectors. Second-order (non-Fourier) detectors that use full-wave rectification are unaffected by alternating-polarity but disrupted by interposed gray frames. (2) To equate the accuracy of two-alternative forced-choice (2AFC) planar direction-of-motion discrimination in standard and polarity-alternated stimuli, standard contrast was reduced. 3D shape discrimination survived contrast reduction in standard stimuli whereas it failed completely with polarity-alternation even at full contrast. (3) When individual dots were permitted to remain in the image sequence for only two frames, performance showed little loss compared to standard displays where individual dots had an expected lifetime of 20 frames, showing that 3D shape identification does not require continuity of stimulus tokens. (4) Performance in all discrimination tasks is predicted (up to a monotone transformation) by considering the quality of first-order information (as given by a simple computation on Fourier power) and the number of locations at which motion information is required. Perceptual first-order analysis of optic flow is the primary substrate for structure-from-motion computations in random dot displays because only it offers sufficient quality of perceptual motion at a sufficient number of locations.

Depth Perception↗
PubMed1991

Ultrastructure of giant and small thalamic terminals of cortical origin: a study of the projections from the barrel cortex in mice using Phaseolus vulgaris leuco-agglutinin (PHA-L).

By means of tracing with the lectin Phaseolus-vulgaris leucoagglutinin (PHA-L), we examined in the thalamus of the mouse, the axon terminals of fibers originating in the barrel cortex. Vibratome sections of the brain were subjected to PHA-L immunocytochemistry and processed for light and electron microscopy. We observed small (0.5-0.8 microns in diameter) varicosities of labeled fibers in the nucleus ventrobasalis (VB) and the nucleus posterior (PO) as well as labeled giant terminals (3-5 microns in diameter) in PO. The analysis involved examination of serial sections and computer-aided reconstruction of several terminals. The small varicosities in VB appear to be small axon terminals forming distinct asymmetric synapses with small dendritic profiles. Some labeled terminals are apposed to, but not synaptically related with, the cell bodies of neurons in VB that are retrogradely labeled with PHA-L. The small varicosities seen with the light microscope in PO are terminals forming asymmetric synapses with dendritic shafts. The giant terminals in PO appear as large, vesicle-filled profiles forming part of synaptic glomeruli, i.e. complexes of one corticothalamic terminal engulfing several excrescences of a single dendrite. A giant terminal forms several asymmetric synapses (about 8) with these excrescences, as well as numerous (up to 15) puncta adhaerentia. The glomeruli are enveloped in glial lamellae, and they are often found at the bifurcations of primary dendritic segments. We suggest that the small terminals in VB are in the service of feedback signalling from the barrel cortex to its principal thalamic relay nucleus; the functional importance of this projection may reside in increased spatio-temporal discrimination. We interpret the giant terminals in PO as elements serving feed-forward processing, allowing the barrel cortex to influence, via PO, parts of the motor pathway modulating the animal's ongoing behavior.

Animals↗
PubMed1992

Expression of various NCAM isoforms in human embryonic muscles: correlation with myosin heavy chain phenotypes.

Neural cell adhesion molecules (NCAM) are known to play a pivotal role in regulating cell-cell interactions in various tissues. The diversity of NCAM is made by alternative splicing of a single gene and by post-translational modifications. The spatio-temporal expression of the various isoforms is developmentally regulated and may modulate cell interactions. We investigated the expression of NCAM isoforms, in particular polysialylated and phosphatidylinositol-anchored isoforms, in developing psoas and quadriceps human muscle from 15 weeks of gestation to term. In parallel, we examined the expression of the myosin heavy chain phenotype (another developmentally regulated system) to determine whether polysialylated-NCAM molecules (the so-called embryonic NCAM) and developmental myosin heavy chains are coexpressed. Our results showed an expression of polysialylated-NCAM and phosphatidylinositol-anchored isoforms during the early stages of myotube maturation. The expression of polysialylated-NCAM on developing myotube was always associated with the expression of developmental myosin heavy chains. However, the loss of polysialylated-NCAM from maturing myotubes was not correlated with the disappearance of the developmental myosin heavy chains, but rather with the appearance of an adult myosin heavy chain phenotype. The relationship between polysialylated-NCAM and myosin heavy chain phenotype was similar in psoas and in quadriceps muscles. We observed that maturation of quadriceps muscle takes place earlier than psoas. Biochemical analysis showed that phosphatidylinositol-anchored molecules were never polysialylated; this indicates different roles of these isoforms in muscle development.

Aging↗
PubMed1983

Spatio-temporal recoding of rapid eye movement signals in the monkey paramedian pontine reticular formation (PPRF).

The integrity of the paramedian pontine reticular formation (PPRF) is necessary for the generation of rapid eye movements. The main saccade-related population is of the burst type with latencies between 0 and 40 ms preceding a saccade, and they can be divided into medium- and long-lead burst neurons. Burst neurons have predominantly spatially coded movement fields in the rostral PPRF, while in the caudal PPRF they increase their burst strength in temporal coding approximately in the pulling directions of extraocular eye muscles (i.e. almost horizontal or vertical). Both neuronal populations have ipsilateral on-directions and contain long-lead burst neurons. In a quantitative analysis the firing patterns of long-lead burst neurons are compared to those of medium-lead burst neurons, which form the predominant output of the saccadic pulse generator to the motoneurons. The firing patterns of temporally coded long-lead bursters are similar to those of medium-lead bursters, except for earlier on-latencies, larger statistical fluctuations, and specializations for small or large saccades in oblique directions. The spatially coded burst neurons form a motor map of saccadic vectors. The diameter of their movement field is often about the size of the saccade vector, and they encode saccadic onset and duration. These results are consistent with a model for visual saccades in eye displacement coordinates, where the spatio-temporal recording of horizontal eye movements is effected by long-lead burst neurons in the PPRF.

Animals↗
PubMed1984

Cell adhesion and morphogenesis: the regulator hypothesis.

A sequence for the genetic and molecular regulation of morphogenesis is proposed in terms of the regulator hypothesis which is intended to provide a specific molecular framework relating developmental genetics to evolution. The hypothesis derives from an analysis of the interactive morphogenetic roles of the primary processes of cell adhesion, cell movement, and embryonic induction during regulative development. According to the regulator hypothesis, the genes for cell adhesion molecules (CAMs) are expressed in schedules that are prior to and largely independent of those for cytodifferentiation. The expressed CAMs act as regulators of the overall patterns of those morphogenetic movements that are essential for inductive sequences or early milieu-dependent differentiations. It is proposed that, during evolution, natural selection eliminates those organisms in which variants of CAM gene expression or of morphogenetic movements or of both result in interruptions in the inductive sequence. Under this assumption, more than one (but not all) combinations of these two variables will lead to stabilization of the order of inductive sequences and of the body plan in a variety of species. Moreover, small variations in the pattern of action of regulatory genes for CAMs in those organisms that are not selected against could lead to large changes in animal form within relatively short periods of evolutionary time. The experimental bases for the regulator hypothesis are reviewed here in terms of the molecular properties of CAMs and their known spatio-temporal sequences of expression during early embryogenesis.

Animals↗
PubMed1995

Comparison of Z and multivariate statistical brain electromagnetic maps for the localization of brain lesions.

Conventional Z maps provide probability statements about the deviation of observed values from the norm. Galán et al. (1994) introduced Simultaneous Significance Probability Scales to detect abnormalities over the whole map, making use of the information provided by the topographic structure of dependencies. They also described multivariate brain electromagnetic (MBE) maps for compact presentation of complex spatio-temporal information. In this paper, using the distance-based localization receiver operating characteristic curves (DL-ROC curves), we compare the localization provided by computed tomography with that provided by Z and MBE maps in 61 patients with brain lesions. Maps were calculated for absolute power and relative power in delta, theta, alpha and beta bands for voltage and current source densities (CSD). In each patient, all maps were compared and the map with the highest value of the area of the DL-ROC curve was considered to be the "best map." Z maps of CSD were the "best maps" in 24 patients. In the voltage montage, we observed that multivariate maps add some information not contained in the Z maps. However, for CSD, Z maps were more accurate than multivariate maps. A very consistent finding was the observation that lesions were better detected by maps analyzing the delta band, while edema was better represented by maps in the theta range.

Brain Damage, Chronic↗
PubMed1991

Training-stage related neuronal plasticity in limbic thalamus and cingulate cortex during learning: a possible key to mnemonic retrieval.

This study is part of an ongoing project concerned with the analysis of the neural substrates of discriminative avoidance learning in rabbits. Multi-unit activity was recorded in 5 anterior and lateral thalamic nuclei and in 4 layers of 2 posterior cingulate cortical areas (29c/d and 29b) during learning. The rabbits learned to step in response to a warning tone to avoid a foot-shock, and to ignore a different tone not followed by shock. Excitatory training-induced unit activity (TIA, increased tone-elicited activity during training relative to a pretraining session with unpaired tone-shock presentations) and/or discriminative TIA (greater discharges to the warning than to the safe tone) developed during training in 11 of the 13 areas. Discriminative TIA in the thalamic nuclei increased monotonically as learning occurred. Anterodorsal (AD) thalamic excitatory TIA peaked in an early stage (the first session of training), laterodorsal thalamic and parvocellular anteroventral (AVp) excitatory TIA peaked in an intermediate stage (the session of the first behavioral discrimination), and magnocellular anteroventral (AVm) and anteromedial (AM) thalamic excitatory TIA peaked in a late stage (the session in which asymptotic behavioral discrimination first occurred). The excitatory TIA in these nuclei declined as training continued beyond the stage in which the peak occurred. Peaks of excitatory TIA developed in area 29c/d of posterior cingulate cortex in the early (layer IV), intermediate (layers I-III and V) and late (layer IV) training stages, as just defined. Only layer IV in area 29b of posterior cingulate cortex exhibited a peak of excitatory TIA, which occurred in the early and intermediate training stages. As in limbic thalamus, discriminative TIA increased monotonically over training stages in layers V and VI of areas 29c/d and in layer VI of area 29b. However, layers I-III and IV in area 29c exhibited peak discriminative TIA in the intermediate and late training stages, respectively. Lesion studies indicate that limbic thalamus and cingulate cortex are essential for learning. The peaks represent a unique topographic pattern of thalamic and cortical excitation elicited by the CS+. It is proposed that the peaks constitute a retrieval pattern, i.e. a unique topographic array of excitation. This pattern encodes the spatio-temporal context which defines the learning situation and is necessary for recall and output of the learned response.

Animals↗
PubMed1991

Axial responses in visual cortical cells: spatio-temporal mechanisms quantified by Fourier components of cortical tuning curves.

The responses of 81 cells from area 17 in paralysed and anaesthetized cats were studied with moving spots and moving bars of different lengths. Tuning curves were measured and plotted as polar-plots. The strongest response of visual cortical cells to a moving bar occurs when the stimulus trajectory crosses the long axis of the receptive field (Hubel and Wiesel 1962). The optimal orientation for a moving and a flashing bar are identical, so that this response-type has been called the orientational component. For a moving spot, however, in most cases the strongest response occurs for motion along the receptive field long axis (axial component). Thus, the axial and orientational components are orthogonal (Wörgötter and Eysel 1989). It is shown that orientational and axial components can display direction selectivity and for short bar stimuli a superposition of the two orthogonal components is demonstrated. Such a superposition in general, resulted in a polar-plot with four peaks 90 degrees apart from each other (four-symmetrical polar-plot). Polar-plots with three or two response peaks were also found; the actual number of response peaks depending on the direction selectivity of the components. In many cells pure axial responses could be elicited with a light spot which stimulates only motion dependent mechanisms. Thus, it was concluded that temporal facilitation is strongly involved in the generation of axial responses. Fourier analysis of polar-plots (SDO-analysis, Wörgötter and Eysel 1987; Wörgötter et al. 1990) was applied to determine the tuning strengths of the different components.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Source analysis of generalized spike-wave complexes.

Dipole source analysis was carried out in three adults and four children with 3 c/s generalized spike-wave (SW) discharges and absence seizures. Eighty-seven SW complexes were investigated. When one regional source was used the equivalent location was always near the baso-frontal area close to the midline. It explained on the average 89% of the variance in the adults and 82% in the children. When two regional sources were used and initially constrained for symmetry, the residual variance (RV) was reduced to 7% in the adults and 9% in the children. The sources remained in the frontal areas and were on the average 2 cm from the midline. When the mirror source was freed it remained contralateral in 76% of the complexes but moved ipsilaterally to various locations in the rest. To reduce the RV to between 2 and 3% one or two additional regional sources were required. These were located in the temporal or parietal areas in the adults and occasionally one occipital region in the children. The study showed that widespread and repetitive EEG events, like the generalized SW, can lend themselves to spatio-temporal multiple dipole modeling. More precise anatomic correlates may become possible with an expanded electrode array and the verification of their locations against the patient's MRI scan.

Adolescent↗
PubMed1995

Kinetic images of neuronal activity of the human brain based on the spatio-temporal MNLS inverse: a theoretical study.

Prior work proved that it is possible to find a unique solution to the problem of defining the configuration of electric current underlying observed extracranial magnetic fields, if sufficient priori knowledge of the source configuration is available. This minimum-norm least-squares (MNLS) inverse solution for a magnetic source image (MSI) is extended here to include temporal as well as spatial parameters of the underlying current pattern. This capitalizes on the temporal resolution of magnetoencephalography (MEG), which is on the order of milliseconds. Other forms of functional brain imaging are far less sensitive to the rate of change of states of the brain. Influences on the quality of the resulting MSI by measurement noise and errors in determining the image surface are characterized. A new technique for reducing noise in the inverse problem is developed by taking into consideration the spatial and time-dependence of the noise detected by the sensors. This new approach to regularization reduces the contribution from noisy measurements to the inverse calculation, and therefore improves the stability of the inverse.

Brain Mapping↗
PubMed1994

A spatio-temporal dipole model of the readiness potential in humans. II. Foot movement.

Readiness potentials (RP) have been recorded in 9 subjects who performed voluntary unilateral plantar flexions with the right or left foot. These show a paradoxical ipsilateral dominance. Spatio-temporal dipole models were obtained for these data, by iterative parameter estimation. The non-uniqueness of the inverse problem leads to several models which describe the data almost equally well, and which all pass orthogonality tests for the individual residuals and source waves. In these dipole models the ipsilateral preponderance is attributed to generators in the contralateral hemisphere, which agrees with results from MEG recording. According to these models the main generators of the RP are in the primary motor cortex, one bilaterally in its posterior wall and the other in the contralateral crown. This agrees with earlier results for finger RPs. However, for foot RPs, it was difficult to distinguish individual sub-components in both the observed scalp potentials and the estimated temporal activation patterns of the dipoles. Some of the presented models include a fronto-central dipole which possibly represents activity of the supplementary motor area. It is concluded that this finding is at best suggestive and needs further investigation.

Adult↗
PubMed1995

Spatio-temporal dynamics of the primary epileptogenic area in temporal lobe epilepsy characterized by neuronal complexity loss.

Neurons involved in the epileptic processes exhibit high frequency discharges scarcely modulated by physiological brain activity. This behaviour should be accompanied by a loss of complexity in the corresponding electrographic signal. From the theory of non-linear dynamics it is known that the correlation dimension allows a quantitative description of complexity in terms of the number of degrees of freedom. To test whether a relationship exists between spatio-temporal alterations of neuronal complexity and spatial extent and temporal dynamics of the epileptogenic area, a moving-window correlation dimension analysis was applied to intracranially recorded electrocorticograms of 20 patients with unilateral temporal lobe epilepsy. Dimension as a function of time was calculated for interictal activity (n = 98) and seizure activity including the pre- and postictal phase (n = 28) from recording locations within the epileptogenic area, in adjacent areas and in homologous contralateral sites. Pronounced changes of the dimension in time were found, gradually decreasing with increasing distance from the focal area. Extraction of a single value quantifying the dimension variance of interictal activity allowed the primary epileptogenic area to be laterized in exact agreement with the results of the presurgical work-up and the confirmation of the postoperative outcome, without the necessity of observing actual seizure activity.

Adolescent↗
PubMed1989

Influence of spatial frequency and handedness on hemispheric asymmetry in visually steady-state evoked potentials.

Recent suggestions on the involvement of the spatial frequency of visual stimuli in the hemispheric lateralization were investigated by recording steady-state evoked potentials in two groups of subjects: five right-handers and five left-handers. Sinusoidal gratings at spatial frequency of 0.5, 1, 3, 4, 6, 8, 10, 12 or 16 cpd were phase reversed at 4 Hz or 12 Hz. Evoked potentials recorded from temporal leads over each hemisphere were submitted to a FFT analysis. Results concern the amplitude of the fundamental component. In right-handers, the temporal frequency was the deciding factor of the lateralization: the evoked activities were greatest in the RH at 4 Hz and in the LH at 12 Hz. This effect was obvious for the range of spatial frequencies from 3-12 cpd. Results, discussed in terms of global/local information, suggested the existence of two transient and sustained systems. In left-handers, both the spatial and temporal parameters were relevant to the lateralization. A spatio-temporal interaction was observed which was reversed at 6 cpd.

Adult↗
PubMedDate not supplied

Spatio-temporal source modeling of evoked potentials to acoustic and cochlear implant stimulation.

Spatio-temporal source modeling (STSM) of event-related potentials was used to estimate the loci and characteristics of cortical activity evoked by acoustic stimulation in normal hearing subjects and by electrical stimulation in cochlear implant (CI) subjects. In both groups of subjects, source solutions obtained for the N1/P2 complex were located in the superior half of the temporal lobe in the head model. Results indicate that it may be possible to determine whether stimulation of different implant channels activates different regions of cochleotopically organized auditory cortex. Auditory system activation can be assessed further by examining the characteristics of the source wave forms. For example, subjects whose cochlear implants provided auditory sensations and normal hearing subjects had similar source activity. In contrast, a subject in whom implant activation evoked eyelid movements exhibited different source wave forms. STSM analysis may provide an electrophysiological technique for guiding rehabilitation programs based on the capabilities of the individual implant user and for disentangling the complex response patterns to electrical stimulation of the brain.

Acoustic Stimulation↗
PubMed1994

Spatially regulated expression of retrovirus-like transposons during Drosophila melanogaster embryogenesis.

Over twenty distinct families of long terminal direct repeat (LTR)-containing retrotransposons have been identified in Drosophila melanogaster. While there have been extensive analyses of retrotransposon transcription in cultured cells, there have been few studies of the spatial expression of retrotransposons during normal development. Here we report a detailed analysis of the spatial expression patterns of fifteen families of retrotransposons during Drosophila melanogaster embryogenesis (17.6, 297, 412, 1731, 3S18, blood, copia, gypsy, HMS Beagle, Kermit/flea, mdg1, mdg3, opus, roo/B104 and springer). In each case, analyses were carried out in from two to four wild-type strains. Since the chromosomal insertion sites of any particular family of retrotransposons vary widely among wild-type strains, a spatial expression pattern that is conserved among strains is likely to have been generated through interaction of host transcription factors with cis-regulatory elements resident in the retrotransposons themselves. All fifteen families of retrotransposons showed conserved patterns of spatially and temporally regulated expression during embryogenesis. These results suggest that all families of retrotransposons carry cis-acting elements that control their spatial and temporal expression patterns. Thus, transposition of a retrotransposon into or near a particular host gene-possibly followed by an excision event leaving behind the retrotransposon's cis-regulatory sequences-might impose novel developmental control on such a host gene. Such a mechanism would serve to confer evolutionarily significant alterations in the spatio-temporal control of gene expression.

Animals↗
PubMed1995

Chemical signals in the marine environment: dispersal, detection, and temporal signal analysis.

Chemical signals connect most of life's processes, including interorganismal relationships. Detection of chemical signals involves not only recognition of a spectrum of unique compounds or mixtures of compounds but also their spatial and temporal distribution. Both spectral and temporal signal processing determine what is a signal and what is background noise. Each animal extracts its unique information from the chemical world and uniquely contributes to it. Lobsters have provided important information on temporal signal processing. Marine chemical signals can be measured with high spatio-temporal resolution giving us a novel view of the lobster's environment. Lobster chemoreceptor cells have flicker fusion frequencies of 4 Hz and can integrate stimuli over 200 ms, closely corresponding to odor sampling behavior with 4-Hz "sniffs." Using this information, spatial odor gradients can be determined from temporal analysis of odor patches typical of turbulent dispersal. Lobsters appear to use this information to locate odor sources. Lobster social behavior depends greatly on chemical signals. Urine carries important information for courtship, dominance, and individual recognition. A novel gland in the nephropore is strategically located to release its products into the urine. Urine, in turn, is injected into the gill current, which jets water 1-2 m ahead of the animal. Lobsters control three different currents that carry chemical signals to and from them. The study of odor dynamics has only just begun. It will be exciting to see how signal dispersal, receptor temporal tuning, neural processing, and animal behavior interact to enhance signals for communication and detection and to reduce signals for chemical camouflage.

Aggression↗
PubMed1984

Control of sequential movements: evidence for generalized motor programs.

The neuromotor processes underlying the control of rapid sequential limb movements were investigated. Subjects learned to pronate and supinate their forearms rapidly to four target locations in a specific spatio-temporal pattern under two movement-time conditions. The response sequence was first performed in a total movement time of 600 ms. Subjects were then told to produce the movement as quickly as possible while ignoring any timing pattern that they had previously learned. Electromyographic (EMG) signals were recorded from the biceps brachii and pronator teres muscles. Kinematic and EMG analyses were performed to investigate the temporal characteristics underlying the two movement-time conditions. When subjects produced the response as quickly as possible, average movement time to perform each reversal movement decreased while average peak velocity increased. Average total movement time was reduced by approximately 100 ms. Although movement time decreased, the proportion of total time to perform each movement of the sequence remained essentially invariant between movement-time conditions. Similar results were obtained for velocity. The time at which peak velocity was achieved occurred earlier in absolute time, although when normalized to the proportion of total movement time, the time to reach peak velocity was also invariant. Thus subjects proportionally compressed the entire movement sequence in time. The EMG analysis demonstrated that total EMG time decreased 89 ms on the average when subjects sped up the movement sequence. Thus average burst durations for both the biceps and pronator teres muscles decreased when movement speed increased. When burst durations were normalized to a proportion of total EMG time, the average proportion of time each muscle was active remained invariant. Therefore, the temporal pattern of activity for the biceps and pronator teres muscles were also proportionally compressed. The present experiment provided additional evidence for the structure of generalized motor programs consisting of invariant and variant features. Movement speed was considered a variant feature, which is specified each time the program is executed. Relative timing, the proportion of total time to produce each segment of the response, was considered to be an invariant feature and inherent in the structure of the motor program. Support for the invariance of relative timing was observed at both the kinematic and neuromuscular levels of analyses. Alternative models (9-11, 24) were found inadequate to account for the invariance of relative timing with the variation in movement time observed in the present experiment.

Electromyography↗
PubMed1987

[Retinotopic organization in the development of the young trout Salmo gairdneri Rich].

The progression of the retinotopic organization in the optic nerve projections to the contralateral thalamus and tectum was studied in Salmo gairdneri from hatching stage to 3 month old stage. After quadratic lesions of the temporal, dorsal, nasal, or ventral retina, the animals were separated in two groups: one used for Fink and Heimer method or electron microscopic observation and the other one for radioautography after injection in the operated eye of 14C or 3H proline. The analysis of the projections of each retinal quadrant shows that: Projections to thalamus and pretectum are ignorganized and appear progressively during development. On the contrary in tectum and corpus geniculatum, the visual projections are retinotopically organized since hatching. In the whole retino-tectal system, two subsystems develop differently: the naso-ventral retina reaches precociously its permanent target (the posterior tectum), the temporo-dorsal part of the retina links to the anterior tectum and shifts laterally during the first month after hatching, from medial to antero-lateral tectum for temporal projections. The shifting of projections is correlated with development of the medial fascicle of the optic tract. So it appears that the pathways play an important role in the spatio-temporal ordered pattern of terminations of retinal fibers on the tectal surface during development.

Aging↗