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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↗

PubMed1996

Spatio-temporal correlations in human gamma band electrocorticograms.

Animal electrocorticogram (ECoG) studies have shown that spatial patterns in the gamma band (>20 Hz) reflect perceptual categorization. Spatio-temporal correlations were investigated in the 20-50 Hz range in search for similar phenomena in human ECoG. ECoGs were recorded in a somatosensory discrimination task from 64-electrode subdural grid arrays, with inter-electrode spacing of 1 cm, overlying somatosensory, motor and superior temporal cortices in 2 patients with intractable epilepsy. Bootstrap techniques were devised to analyze the spatial and temporal characteristics of the correlations. Despite an extensive search, no evidence was found for globally correlated activity related to behavior either in narrow (1.e., 35-45 Hz) or broad (i.e., 20-50 Hz) bands. Spatial patterns, extracted using principal component analysis, could not be classified with respect to stimulus type in any time interval. Instead, spatially and temporally intermittent synchronization was observed between pairs of electrodes in 1 cm X 1 cm regions with high variability within and across trials. The distribution of correlation coefficients differed substantially from background levels at inter-electrode distances of 1 cm and 1.4 cm but not 2 cm or more. The minimum duration of correlation, the decorrelation time, of the ECoG was about 50 msec; the average correlation duration at 1 cm inter-electrode distance was about 150 msec; and the recurrence rate of significant correlation peaks was about 1.3/sec. The findings suggest that the surface diameters of domains of spatially correlated activity underlying perceptual categorization in human gamma band ECoG are limited to less than 2 cm and that the intermittent synchronization observed across separations of 1 cm and 1.4 cm is not solely due to volume conduction. Thus, if such gamma band spatial patterns exist in the human brain, no existing technology would be capable of measuring them at the scalp, and subdural electrode arrays for cortical surface recording would have to have spacings under 5 mm.

Adult↗

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↗

PubMed1996

Differential activation of the primary auxin response genes, PS-IAA4/5 and PS-IAA6, during early plant development.

The plant growth hormone auxin typified by indoleacetic acid (IAA) transcriptionally activates early genes in pea, PS-IAA4/5 and PS-IAA6, that are members of a multigene family encoding short-lived nuclear proteins. To gain first insight into the biological role of PS-IAA4/5 and PS-IAA6, promoter-beta-glucuronidase (GUS) gene fusions were constructed and their expression during early development of transgenic tobacco seedlings was examined. The comparative analysis reveals spatial and temporal expression patterns of both genes that correlate with cells, tissues, and developmental processes known to be affected by auxin. GUS activity in seedlings of both transgenic lines is located in the root meristem, sites of lateral root initiation and in hypocotyls undergoing rapid elongation. In addition, mutually exclusive cell-specific expression is evident. For instance, PS-IAA4/5-GUS but not PS-IAA6-GUS is expressed in root vascular tissue and in guard cells, whereas only PS-IAA6-GUS activity is detectable in glandular trichomes and redistributes to the elongating side of the hypocotyl upon gravitropic stimulation. Expression of PS-IAA4/5 and PS-IAA6 in elongating, dividing, and differentiating cell types indicates multiple functions during development. The common and yet distinct activity patterns of both genes suggest a combinatorial code of spatio-temporal co-expression of the various PS-IAA4/5-like gene family members in plant development that may mediate cell-specific responses to auxin.

Cell Differentiation↗

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↗

PubMed1997

Controlling locomotion during the acceleration phase in sprinting and long jumping.

The production of a stabilized locomotor pattern is crucial in sporting activities such as the run-up in long jumping, a task which is characterized by high spatio-temporal constraints. The aims of this study were as follows. First, we wished to investigate how athletes stabilize their stride patterns so as to strike the take-off board accurately. Previous studies have argued that during the initial accelerative phase of the run-up, athletes attempt to produce a stereotyped stride pattern. We investigated this initial phase in more detail by examining the kinematic parameters of long jumpers' strides and their spatial consequences. These data were then compared with the stride patterns observed in a sprinting task, which did not impose the same spatio-temporal constraints. Our second aim was to compare the stride patterns of skilled and unskilled jumpers. Kinematic stride parameters were measured in two ways. The temporal parameters (flight time, stance time) were recorded by a microcomputer attached to the athlete, whereas the spatial parameters (stride length) were measured directly from the footprints the subjects made on the track. The results confirmed those of previous studies, showing that long jumpers initiate locomotor adjustments in the last 3-4 strides before take-off, but a more detailed analysis revealed that long jumping is characterized by adjustments during the first few strides. These adjustments were not seen in the sprinting task, where systematic variations of accumulated error were observed. These stride adjustments differed from those seen in previous studies and thus permit a more comprehensive understanding of the control involved in the tasks studied. The patterns exhibited by the skilled and unskilled subjects were very similar overall, but differed in that variations in accumulated error were less marked for the skilled subjects, who tended to make early stride adjustments sooner than the unskilled subjects. These results are discussed in relation to the cognitive and ecological approaches to movement coordination.

Acceleration↗

PubMed1997

Face and shape repetition effects in humans: a spatio-temporal ERP study.

The neural bases of repetition effects for faces and non-significant shapes was studied using Mooneys' faces presented upright (face) or upside down (shape) with a repetition interval of 8 min 30 s-1. Scalp potentials and current density maps on 30 electrodes were compatible with an involvement of the infero-temporal and fusiform gyri (from 50 to at least 250 ms), mainly on the right, for both faces and shapes; the hippocampus and adjacent areas (around 300 ms), specifically for faces; the medial temporal lobes (450-650 ms) again independent of stimulus meaning. These results suggest that the facilitation of perception due to repetition involves both neocortical specialized areas and the medial temporal lobe, with different timings of activation. They further suggest that memory updating takes place more rapidly for faces than for meaningless shapes and that face recognition may be, at least partly, functionally encapsulated.

Adult↗

PubMed1997

Human cortico-hippocampal activity related to auditory discrimination revealed by neuromagnetic field.

We carried out multi-dipole estimation and pursued spatio-temporal brain activity on a time scale of several milliseconds during an auditory discrimination task using a whole-cortex type SQUID system. Neuronal activities were estimated in the medial (hippocampus, parahippocampal gyrus, etc.) and lateral temporal cortices (superior and middle temporal gyri, etc.), the dorsolateral prefrontal cortex (middle and inferior frontal gyri, etc.) and the parietal cortex (supramarginal gyrus, etc.) in the 280-400 ms latency range. The activity in the posterior hippocampal region was the most prominent and long-lasting in parallel with the activities in the other regions. Therefore, the posterior hippocampal region is a central structure engaged in auditory discrimination. The whole-cortex neuromagnetic measurements provided the possibility of imaging the time-varying activities of the human cortico-hippocampal neural networks.

Adult↗

PubMed1997

The epidemiology of BSE in cattle herds in Great Britain. I. Epidemiological processes, demography of cattle and approaches to control by culling.

This paper explores the key epidemiological processes and demographic factors that determined the pattern of transmission of the aetiological agent of bovine spongiform encephalopathy (BSE) in cattle herds in Great Britain (GB). The analyses presented utilize data from published and unpublished experimental studies and from the GB central database of confirmed BSE cases. We review the experimental and epidemiological evidence that has both confirmed indirect horizontal transmission via the consumption of infectious material as the major transmission route and provided information on the duration and variability of the dose-dependent incubation period of BSE in cattle. The epidemiological and genetic data pertaining to the possible existence of maternal transmission and/or genetically variable susceptibility to infection is discussed. The demography of British cattle is characterized and the impacts of key demographic features on the observed epidemic profile are discussed. In the main BSE case database, analyses reveal that BSE cases cluster significantly at both the holding and county scale. Furthermore, analysis of longitudinal patterns reveal substantial temporal within-holding correlation. Such clustering of cases suggests a highly heterogeneous infection process. The paper ends with a discussion of how analyses of spatio-temporal clustering inform the design of targeted culling programmes aimed at reducing future disease incidence. We show how the retrospective implementation of culling policies on the BSE case database allows the qualitative evaluation of policy performance, but that model predictions of future trends in case incidence are required to estimate the precise impact of any current or future programme.

Age Factors↗

PubMed1993

GABA-ergic control of visual perception in healthy volunteers: effects of midazolam, a benzodiazepine, on spatio-temporal contrast sensitivity.

1. We studied the effects of midazolam (MDZ), a benzodiazepine, on spatio-temporal contrast sensitivity, choice reaction time, and mood visual analogue scales in healthy volunteers. 2. Eight extensively trained, healthy volunteers were included in a placebo-controlled cross-over double-blind trial of MDZ (0.15 mg kg-1). Treatments were injected intramuscularly and evaluations were performed before and 0.5, 1, 2, 3 and 4 h after drug administration. Spatio-temporal contrast sensitivity was measured using a micro-computer with appropriate software. Stimuli were vertical gratings with adjustable contrast, with spatial frequencies of 0.25, 1 and 4 cpd. Four conditions of temporal modulation were used: the grating was either static or drifting laterally with temporal frequencies of 1, 3 and 9 Hz. 3. An analysis of variance was performed on the data. As compared with placebo, MDZ induced an increase in choice reaction time and sedation (as assessed on visual analogue scales). From 0.5-4 h after the injection, MDZ produced an overall decrease in visual sensitivity, as compared with placebo. More specifically, MDZ preferentially affected medium to high spatial frequencies and low temporal frequencies. Several non-exclusive hypotheses may account for the results: 1) an increase in the size of the receptive fields, 2) a preferential effect on the visual parvocellular pathways which mediate the sensitivity to high spatial and low temporal frequencies.

Adult↗

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↗