Contrast modulated steady-state visual evoked potentials (CMSS VEPs): recording evoked potentials and related single cell responses in area 17 of the cat

(1) The functional characteristics of the neuronal substrate, responding to the CMSS VEP stimulus, were studied by recording CMSS VEPs and related single unit activity in area 17 of the anaesthetised and paralysed cat. CMSS VEPs use an 8 Hz phase reversing (i.e., 16 reversals/sec) grating stimulus with rapid contrast sweeping and allow the contrast thresholds and lag values to be measured as a function of the spatial frequency. (2) The CMSS VEPs of the anaesthetised cat have a wave form similar to those of humans but are shifted to lower spatial frequencies, higher contrast thresholds and longer lag values. (3) The cellular response to a sinusoidal grating, phase reversing at 8 Hz, was studied in order to identify the neuronal substrate generating the CMSS VEPs. Sixty percent of the area 17 cells respond to this stimulus. Cells responding at 8 Hz reversal comprise a distinct subpopulation of visual cortical cells selective for higher velocities and lower spatial frequencies. (4) Although the CMSS VEPs contain almost exclusively energy at 16 Hz, the temporal response pattern of striate cells is quite disparate, including first and second harmonic response patterns as well as an intermediate type. (5) There is a near-perfect correlation between the contrast thresholds of single cells, obtained with the contrast swept stimulus and those obtained with a static contrast test, validating the technique of rapid linear contrast sweeping. (6) The influence of the temporal parameters of the contrast sweeping on the calculated contrast threshold was investigated at the neuronal level. These parameters only marginally influence the responses. (7) CMSS VEP contrast thresholds and neuronal thresholds were compared. The sensitivity of VEPs corresponds to that of the most sensitive neuronal generators. CMSS VEP lag values are longer than the values for individual neurones.

Cardiovascular reactivity in isometric exercise and mental arithmetic in children

In children, we studied noninvasively the cardiovascular stress responses, including changes over time of systolic blood pressure (SBP), heart rate (HR), and stroke volume (SV) in isometric handgrip (IHG) and mental arithmetic. Specifically, we asked whether 1) these cardiovascular stress responses were different for the two stress conditions in children, 2) these responses differed in boys and girls, and 3) the anthropometric variables related to these stress responses. SV differed significantly between IHG and mental arithmetic over the entire stress period. This may reflect higher systemic vascular resistance during IHG. HR in boys was lower than in girls over the entire period of stress in both stress tests. This observation cannot be attributed to differences in conditioning, because this should not influence responses to isometric or mental stress. A larger left ventricular mass was related to higher SVs. A marked relationship was found between HR and SBP and between HR and SV. No relationship was found between SBP and SV.

Iatrogenic multiple pregnancies in East Flanders, Belgium

OBJECTIVE

To evaluate the specific contribution of artificial induction of ovulation to the increasing number of multiple gestations in East Flanders and the effects of this treatment on the frequencies of monozygotic and dizygotic twinning.

DESIGN

Since 1976 the East Flanders Prospective Twin Study has collected data on artificial induction of ovulation for all the multiple births listed in its registry.

SETTING

East Flanders Prospective Twin Survey.

PATIENTS

Between 1976 and 1992, 458 twin and 78 triplet pregnancies resulting from artificial induction of ovulation were analyzed.

MAIN OUTCOME MEASURES

Zygosity and frequency of iatrogenic multiple births.

RESULTS

Since 1985 there is an explosive increase in twin and triplet births in East Flanders. This increase has been caused mainly by the sole use of fertility-enhancing drugs and in the last few years by resorting to other technologies of assisted reproduction, such as IVF-ET, GIFT, or zygote intrafallopian transfer.

CONCLUSION

In view of the elevated risk inherent to multiple pregnancies in terms of perinatal mortality and morbidity, the over enthusiastic or improper use of fertility drugs should be curtailed.

Age-specific correlation analysis of longitudinal physical fitness levels in men

This study investigated the age-specific tracking of adult health- and performance-related fitness scores. In addition, the independent contribution of adolescent physical characteristics to the explanation of adult fitness scores was also studied. The sample consisted of 173 adults observed at age 30 years. These subjects had been followed at annual intervals from age 13 to age 18 years and were remeasured at age 30 years. At each age nine fitness tests were administered together with the recording of anthropometric dimensions, biological maturation, sports participation and family characteristics. Tracking was measured by the inter-age correlations at each age between 13 and 18 years and the performance scores at 30 years. The independent contribution of characteristics observed during adolescence to the explanation of adult fitness was investigated through stepwise multiple regression analysis and discriminant analysis with the adult fitness scores as the dependent variables and the fitness, maturation, anthropometric characteristics, sports participation and family background as the independent variables. Tracking between age 13 and age 30 years was moderately high (46% of variance explained) for flexibility, low to moderate (between 19% and 27% of variance explained) for the other fitness parameters and low for pulse recovery and static strength (7% to 11% of variance explained). Between age 18 and age 30 years the tracking was high for flexibility, moderately high for explosive and static strength, and moderate for the other fitness parameters except for pulse recovery. The amount of variance of adult fitness levels explained increased significantly when other characteristics observed during adolescence entered the regressions or discriminant functions.(ABSTRACT TRUNCATED AT 250 WORDS)

Growth and menarcheal status of elite female gymnasts

The growth and maturity status of 201 elite female gymnasts was considered. The subjects were participants at the 24 World Championship Artistic Gymnastics in 1987. In addition to age at menarche, weight, stature, biacromial, and bicristal breadths, the sitting height/stature ratio, and the Health-Carter anthropometric somatotype of gymnasts 13-20 yr of age were compared with reference data for a nationally representative sample of Flemish girls. Median age at menarche (probit analysis) in gymnasts is 15.6 +/- 2.1 yr compared with 13.2 +/- 1.2 yr in Flemish girls. Anthropometric dimensions increase with age until about 16 yr and then tend to plateau. In contrast to body size, there is little variation in somatotype with age. Compared with adolescent girls, elite gymnasts are considerably shorter and lighter with narrower shoulders and hips, but the differences are more apparent after 17 yr. Elite gymnasts do not differ from nonathletes in relative leg length, but they have proportionally broader shoulders relative to hips. Differences in somatotype occur primarily in endomorphy (especially lower in gymnasts) and to a lesser extent in mesomorphy (higher in gymnasts).

First-order analysis of optical flow in monkey brain

Optical flow is a rich source of information about the three-dimensional motion and structure of the visual environment. Little is known of how the brain derives this information. One possibility is that it analyzes first-order elementary components of optical flow, such as expansion, rotation, and shear. Using a combination of physiological recordings and modeling techniques, we investigated the contribution of the middle superior temporal area (MST), a third-order cortical area in the dorsal visual pathway that receives inputs from the medial temporal area (MT). The results show (i) that MST cells, but not MT cells, are selective for elementary flow components (EFCs) alone or their combination with translation, (ii) that MST cells selective for an EFC do not extract this component from a more complex motion pattern, and (iii) that position invariance as observed in MST is compatible with an input arrangement from MT cells matching the selectivity of MST neurons.

Anthropometric characteristics of outstanding male and female gymnasts

Anthropometric data of outstanding gymnasts were gathered on the occasion of the 24th World Championship Artistic Gymnastics, held at Rotterdam, The Netherlands, in October 1987. In total 165 males and 201 females were investigated, constituting 84% of the total number of participants. The data of these gymnasts were descriptively compared with both reference data and data reported in previous studies on gymnasts competing at international events. Also, based on the data obtained, 'gymnastic-specific' anthropometric reference values (i.e. profile charts), were established for both male and female gymnasts. Finally, the maturational characteristics (skeletal age and menarche) of the 'Rotterdam' female gymnasts were described.

Temporal integration in cat visual cortex: a test of Bloch's law

Some units in the cat visual cortex fail to respond to a briefly flashed bar and it has been suggested that such neurons function as visual integrators with a long time constant. To test this integrator hypothesis, a study was made using presentations of a bar, flashed over the receptive field for various durations and at different luminances. Some cortical cells indeed showed an increase in the time to peak latency and in the response amplitude when stimulus duration was prolonged up to 320 msec. Such units obeyed Bloch's law for durations over 100 msec.

Selectivity of cat area 18 neurons for direction and speed in depth

1. Fifty-eight area 18 cells recorded in anesthetized and paralyzed cats were tested for selectivity for direction in depth after their monocular velocity characteristics and static disparity profile were determined. 2. Direction in depth was produced by changing the speed and direction in the two eyes, but keeping the speed along axes in depth constant. 3. Forty-two cells were completely investigated, which means that direction in depth selectivity was tested at least at two different position disparities and two different bar speeds. Seven out of the 42 cells were accepted as direction in depth selective. 4. The 16 remaining cells were incompletely tested. Only one of them was direction in depth selective at the disparity and speed tested and shared all the properties of the seven completely tested direction in depth selective cells. Therefore we estimated that 8/58, i.e., 14% of the area 18 cells are direction in depth selective. 5. The direction in depth selective cells are a very homogeneous class: they all belong to the S family, are velocity tuned, monocular, prefer orientations close to vertical, and have a broad inhibitory or an unmodulated position disparity profile. 6. Direction in depth selectivity arises both from monocular properties and binocular interactions. These binocular interaction profiles can be symmetric or asymmetric. The change of these interaction profiles with changes in base speed can be summarized as changes in level of inhibition for the axes corresponding to equal speed in the two eyes on one hand and changes in the slope of the inhibition gradient centered on these axes of equal speed on the other hand. 7. Nineteen of the 58 cells were tested for selectivity for speed along trajectories in depth. All five direction in depth selective cells tested were also tuned to speed in depth. This suggests that area 18 contributes to the elaboration of a 3D velocity map. 8. A wiring diagram that accounts for the binocular interactions underlying direction selectivity in depth is presented.

Genetic and environmental variation in the birth weight of twins

Two novel approaches to the analysis of twin data are illustrated with data from birth weight in twins. First, two possible covariates of birth weight are fitted to the data simultaneously, allowing for linear effects of these variables, and their correlation. Second, information on chorionicity is used to estimate the effects of chorion type on birth weight. The data were collected from a large sample of twins born in East Flanders, Belgium. Variation and covariation in twins were considered as a function of sex, chorionicity, maternal age, gestational age, and genotype. No evidence for sex differences in causes of variation was found. As expected, the largest source of variation in bith weight was associated with gestational age. Other common environmental influences were non-significant. Heritability was significant, constituting approximately 40% of variation not associated with maternal and gestational age. A small but significant effect of chorionicity was found, such that dichorionic twins show a greater similarity than monochorionic.

CMSS-VEPs: contrast modulated steady state visual evoked potentials: its neuronal origin and clinical use

CMSS-VEPs are presented as a sensitive, non-invasive functional investigation technique of the visual function, applicable in clinical practice. New improvements of the technique are presented. The underlying neuronal mechanisms are discussed. The clinical use is illustrated in a case of optic neuritis.

The suppressive influence of moving textured backgrounds on responses of cat striate neurons to moving bars

The suppressive action of a moving textured background on responses to moving bars was investigated in 118 striate neurons, 19 dorsal lateral geniculate neurons, and 5 perigeniculate neurons in paralyzed and anesthetized cats. In standard conditions the background was a two-dimensional (2D) noise pattern, the bar moved at optimal speed, and its contrast level was adjusted to yield 50% of the maximum response. Neuronal responses to the moving bar were suppressed when the background moved at the same speed or faster than the bar. The direction of motion of the bar had little influence. This suppressive effect was equally strong in all three experimental samples. The suppressive effect of the moving background was uniformly distributed among the cortical population, being equally strong in all layers, in all parts of the visual field representation, and for different categories of cortical cells. The suppressive effect of the moving background depended little on the structure of the background or on the speed of the bar. The suppression increased with decreasing contrast of the bar. Many (80%) cortical cells and all geniculate neurons responded to the movement of the 2D noise on its own. Most of these cells responded to isolated features ("grains") in the pattern rather than to movement of the whole pattern. There was no difference in strength of suppression between cortical neurons responsive and unresponsive to the moving 2D noise. The possible origins of this suppressive influence of moving backgrounds and its significance for the processing of visual scenes, more complicated than a single stimulus, are discussed.

The velocity dependence of direction selectivity of visual cortical neurones in the cat

1. The range of velocities, yielding direction-selective responses, was investigated in a total of 167 direction-selective cells from areas 17 and 18 of the cat, using a high-contrast light bar moving at velocities ranging from 0.6 to 900 deg s-1. 2. 11% of the cells were direction selective over the full range of velocities tested. Most cells (66%) gave only responses at low velocities and thus were not direction selective at high velocities. The remaining cells gave responses over a broad range of velocities but the direction selectivity was limited to either high or intermediate velocities (18 and 5% of the cells, respectively). Cells with direction selectivity at high but not at low velocities had large receptive fields with non-overlapping 'on' and 'off' subregions and they responded quickly and phasically to stationary flashes. This suggests that the latter cells relied on fast and brief interactions over large distances. 3. In thirty cells the spatial and temporal limits of direction selectivity were investigated using a stroboscopically illuminated moving light bar. In all cells direction selectivity depended both on the interflash distance and the interflash time interval. Area 17 cells with large receptive field at high eccentricity tolerated much larger interflash spacings than area 17 cells with small receptive fields near the area centralis. For eleven of the thirty cells the effective interflash distance could be larger than the width of the receptive field. The largest effective interflash time interval varied between 35 and 250 ms. 4. Eight of the thirty cells were direction selective at high but not at low velocities. These eight cells all remained direction selective over large interflash distances and they required brief interflash intervals (less than or equal to 65 ms). 5. Responses to single stroboscopic flashes within the sequence were observed in ten cells, which all responded well at high apparent velocities. While most cells (eight out of ten) showed both response increments in the preferred direction and response decrements in the non-preferred, the decrements constituted the dominant element in the direction selectivity of six out of ten cells while the remaining four cells relied mainly on response increments. 6. It is concluded that the range of direction-selective velocities of some cat visual cortical cells can be predicted from a knowledge of the spatial extent and the time course of the direction-selective interactions.(ABSTRACT TRUNCATED AT 400 WORDS)

The Millimeter- and Submillimeter-Wave Spectra of Acetaldehyde: Centrifugal Distortion and Internal Rotation Analysis

141 internal rotation doublets (282 transitions, among which 174 new measurements) of acetaldehyde in its ground torsional state have been measured up to 600 GHz (J ≦ 32). An overall fit of the measurements (including the lines identified by previous workers) using the Internal Axis Method has allowed us to accurately determine the rotational, centrifugal distortion and internal rotation constants. The quality of the fit is good enough to permit the accurate prediction of transition frequencies of possible astrophysical interest.

Velocity discrimination in the cat

After considerable training (over 2 years) we measured the just noticeable differences (JNDs) in velocity as a function of reference velocity in three cats. The velocity discrimination curve plotting JNDs in velocity, expressed as Weber fractions as a function of reference velocity is U-shaped with optimal performance at reference speeds between 25 and 60 degrees/sec. The discrimination curve changed little with a tenfold change in slit width. Compared to the human velocity discrimination curve determined with the same test apparatus, the feline curve is narrower and shifted towards faster velocities and larger Weber fractions. These results support our specific linking hypothesis between velocity tuned cells as observed in cortical areas 17 and 18 of the cat, and velocity discrimination.

Velocity selectivity in the cat visual system. III. Contribution of temporal factors

In 149 units from area 17 and 48 units from area 18 the responses to stationary stimulation of different durations were compared with the responses to the same stimulus (a 0.3 degrees-wide light or dark bar) moving at different velocities. The aim was to test the hypothesis that the range of effective velocities depends on the time needed for the bar to cross the receptive field. Forty-two percent of the area 17 cells and 8% of the area 18 cells responded poorly or not at all to briefly presented stationary stimulation. These cells were unable to respond at high velocities, and for these "duration-sensitive" cells the velocity characteristics are well predicted on the basis of responses to stationary stimulation of different durations. Cells that responded equally well to periods of stationary stimulation ranging from 12.5 to 3,200 ms ("duration-insensitive cells") were found to be able to respond at all equivalent velocities, but their preference for either high, low, or intermediate velocities was not reflected in differences in responsiveness to the different durations tested. Duration-sensitive cells in area 17 tended to have a receptive field near the area centralis, and 73% of them were classified as S-family cells, one third being end-stopped S-cells. In contrast only 18% of the duration-insensitive cells were of the S family, and these S-family cells were rarely end-stopped (1/12) or rarely had receptive fields within 5 degrees of the fovea (3/12). Duration-sensitive cells had very long latencies (median 285 ms) in response to a stationary flashed light bar of 1 s duration but much shorter latencies (median 91 ms) when tested with a slowly moving light bar. This difference was not seen in duration-insensitive cells (median latencies = 61 and 59 ms). The ability to respond at high velocity was contrast dependent. At a low contrast level all cells failed to respond to brief stimulation, whether moving or stationary. At high contrast levels only the duration-insensitive cells showed an increased responsivity to brief stimuli. The absence of responses in duration-sensitive cells to brief stimuli of high contrast may depend upon suppressive influences reaching these cells before the excitatory influences. We conclude that the velocity upper cutoff of most S-family cells with a central receptive field can be predicted from a knowledge of the minimum duration of stationary presentation required for their activation (median ON duration threshold, 200 ms).(ABSTRACT TRUNCATED AT 400 WORDS)

Visual cortical correlates of visible persistence

In order to evaluate their possible role in visible persistence, cortical cells from area 17 of the cat were investigated with a stationary light bar flashed for different durations. Thirteen out of 72 cells with non-overlapping On and Off subregions were able to respond to the briefest On stimulus (12.5 msec) for low and moderate contrasts. The responses of these cells outlasted brief On stimuli and this neural persistence increased as the On duration was shortened, mimicking the inverse duration effect of visible persistence. The 30 cells with overlapping On and Off subregions were all able to respond to brief stimuli but their neural persistence was independent of stimulus duration. At very high contrast levels, the inverse duration effect, observed in cells with non-overlapping subregions, disappeared since the On responses were followed by Off rebound discharges regardless of stimulus duration. It is suggested that the latter responses are a possible cortical equivalent of positive afterimages.

Factors influencing velocity coding in the human visual system

Differential velocity detection in the fovea was measured over a wide range of velocities (0.25-256 degrees/sec). Differential thresholds were minimum (about 6%) for intermediate velocities (4-32 degrees/sec). Velocity judgements were shown not to depend on duration judgments. The U-shaped curve relating differential velocity detection and velocity was preserved at different background levels and different contrasts. The physiological correlates of these observations are discussed.

Receptive field structure of area 19 as compared to area 17 of the cat

A total of 139 cells from area 19 along with a comparison sample of 172 cells from area 17 were classified using a system proposed by Orban and Kennedy, following Henry and consisting of 4 basic cell 'families', namely S, C, A and B, each having an end-stopped member: HS, HC, HA and HB. The two basic parameters separating the 4 families are firstly spatial overlap of ON and OFF subregions and secondly receptive field (RF) width. Spatial overlap was studied quantitatively in a number of these cells using multiple presentations of stationary slits or moving light and dark edges. RF width was determined quantitatively using bars moving at different velocities across the RF. It was found that cells with spatially nonoverlapping and overlapping subregions are present in both areas. S and HS cells, which show similarities with simple cells, were encountered in area 19 but they constituted only 18% of the population as opposed to 55% in area 17. C and HC cells, reminiscent of complex cells, were about as common in area 19 as in area 17. In both areas C cells were the only group which consistently discharged equally well or better in response to diffuse light turned on and off than when presented with light bars. A and B families formed a minority in both areas. Area 19 contained a larger proportion of nonoriented and undriveable units, as well as a special category of cells preferring stimuli with a width larger than the length ('rectangle cells'). RF width was generally larger in area 19 than in area 17 and its distribution in area 19 showed distinct peaks. In the part of area 19 subserving central vision these peaks appeared with a periodicity of 0.8 degrees, suggesting that cells in this zone are supplied by one or more rows of a uniform set of afferents having a RF center diameter of about 0.8 degrees. The identification of this population as W-relay cells is supported by the long latencies found in cells from this part of area 19. It is concluded that basic principles underlying the structure of the RF are similar in both areas 19 and 17.

Velocity sensitivity of areas 17 and 18 of the cat

Velocity sensitivity of areas 17 and 18 of the cat has been evaluated by preparing neuronal velocity-response (VR) curves in paralyzed and anaesthetized cats. VR curves suggest two possible mechanisms for neuronal coding of stimulus velocity as well as criterion for distinguishing between cells involved in analysis of stationary or moving objects. VR curves differ between cortical areas and with retinal eccentricity. Neurones with larger receptive fields (RFs) become, on the average, sensitive to faster velocities. Parallels with human psychophysics are pointed out as support of the suggestion that the present results are relevant for our insights in human motion perception.

Time course of feeding induced by pentobarbital-injections into the rat's VMH

Chemical blockade of the ventromedial hypothalamus (VMH) by single microinjections of pentobarbital in ad lib fed male Wistar rats induced a meal that did not outlast a 10-min postinjection period. When food was presented only after this period, feeding was nearly absent. Repeating the injection after 10 and 20 min led each time to eating, although the amount consumed decreased. Scanning behaviour was drastically depressed during the 4-min postinjection period but then recovered within 6-11 min. Sniffing into the litter was enhanced for about the same interval (8-10 min). Fixed-ratio lever pressing for food upon pentobarbital-blockade of the VMH also tended to disappear after this period, whether many (low ratios) or few (high ratios) food pellets were obtained. The limited meal size after VMH-blockade therefore presumably resulted from the waning of the anaesthetic effect (e.g. diffusion) in this brain site.

Functional changes across the 17-18 border in the cat

Changes in velocity sensitivity, receptive field (RF) position, and RF size were investigated in long oblique penetrations crossing the 17-18 border. The penetrations were histologically reconstructed and the border determined by cytoarchitectonics. In cortex subserving central and paracentral vision change in velocity sensitivity allowed a reasonable physiological identification of the 17-18 border. The physiological border correlates well with the histological border zone, best with its medial edge. Changes in RF position and RF size are of little use for physiological identification of the border in this region. In this cortical region area 18 representation of the vertical meridian (VM) has a high magnification factor. In cortex subserving peripheral vision, the change in velocity sensitivity was small and the change in RF position coincided with the cytoarchitectonics.