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NO2 foliar deposition through the stomata of leaves has been identified as a significant sink of NOx within a forest canopy. In this study, we investigated NO2 and NO exchange between the atmosphere and the leaves of the native California oak tree Quercus agrifolia using a branch enclosure system. NO2 detection was performed with laser-induced fluorescence (LIF), which excludes biases from other reactive nitrogen compounds and has a low detection limit of 5–50 ppt. We performed both light and dark experiments with concentrations between 0.5 and 10 ppb NO2 and NO under constant ambient conditions. Deposition velocities for NO2 during light and dark experiments were 0.123±0.009 and 0.015±0.001 cm s−1, respectively. Much slower deposition was seen for NO, with deposition velocities of 0.012±0.002 and 0.005±0.002 cm s−1 measured during light and dark experiments, respectively. This corresponded to a summed resistance of the stomata and mesophyll of 6.9±0.9 s cm−1 for NO2 and 140±40 s cm−1 for NO. No significant compensation point was detected for NO2 uptake, but compensation points ranging from 0.74 to 3.8 ppb were observed for NO. NO2 and NO deposition velocities reported here are comparable both with previous leaf-level chamber studies and inferences from canopy-level field measurements. In parallel with these laboratory experiments, we have constructed a detailed 1-D atmospheric model to assess the contribution of leaf-level NOx deposition to the total NOx loss and NOx canopy fluxes. Using the leaf uptake rates measured in the laboratory, these modeling studies suggest that loss of NOx to deposition in a California oak woodland competes with the pathways of HNO3 and RONO2 formation, with deposition making up 3 %–22 % of the total NOx loss. Additionally, foliar uptake of NOx at these rates could account for ∼ 15 %–30 % canopy reduction of soil NOx emissions.

The causes of the interindividual differences (IDs) in how we perceive and control spatial orientation are poorly understood. Here, we propose that IDs partly reflect preferred modes of spatial referencing and that these preferences or "styles" are maintained from the level of spatial perception to that of motor control. Two groups of experimental subjects, one with high visual field dependency (FD) and one with marked visual field independency (FI) were identified by the Rod and Frame Test, which identifies relative dependency on a visual frame of reference (VFoR). FD and FI subjects were tasked with standing still in conditions of increasing postural difficulty while visual cues of self-orientation (a visual frame tilted in roll) and self-motion (in stroboscopic illumination) were varied and in darkness to assess visual dependency. Postural stability, overall body orientation and modes of segmental stabilization relative to either external (space) or egocentric (adjacent segments) frames of reference in the roll plane were analysed. We hypothesized that a moderate challenge to balance should enhance subjects' reliance on VFoR, particularly in FD subjects, whereas a substantial challenge should constrain subjects to use a somatic-vestibular based FoR to prevent falling in which case IDs would vanish. The results showed that with increasing difficulty, FD subjects became more unstable and more disoriented shown by larger effects of the tilted visual frame on posture. Furthermore, their preference to coalign body/VFoR coordinate systems lead to greater fixation of the head-trunk articulation and stabilization of the hip in space, whereas the head and trunk remained more stabilized in space with the hip fixed on the leg in FI subjects. These results show that FD subjects have difficulties at identifying and/or adopting a more appropriate FoR based on proprioceptive and vestibular cues to regulate the coalignment of posturo/exocentric FoRs. The FI subjects' resistance in the face of altered VFoR and balance challenge resides in their greater ability to coordinate movement by coaligning body axes with more appropriate FoRs (provided by proprioceptive and vestibular co-variance)., (Copyright (c) 2010 IBRO. Published by Elsevier Ltd. All rights reserved.)

Static roll head tilt induces bias in the trajectory of upper limb voluntary movements. The aim of the experiment was to investigate whether this bias is dependant on the perception of body configuration rather than on its actual configuration. We used the 'return' phenomenon as a method to produce dissociation between perceived and actual head tilt. Static roll head tilt in supine subjects was sustained for 15 min during which subjects were periodically required to estimate verbally the tilt of their head respective to their trunk and draw, with their right index finger, straight lines aligned with their trunk. After 15 min, subjects' head were realigned with the trunk, and subjects continued to give verbal estimate of head position and perform the motor task. Results showed that the initial angular deviation of the lines in the direction opposite to head tilt gradually diminished. The adaptation was noticeable within the first 3-5 min of tilt and subsequently diminished. Verbal estimates confirmed the return phenomenon, i.e. subjects perceived their head as slowly returning towards its neutral position after a few minutes of sustained tilt. When realigned with the trunk, subjects experienced the illusion that their head was tilted in the opposite direction to the initial head tilt and a line deviation in the opposite direction to those made on initial exposure was observed (after-effect). These results indicate that the angular deviation in motor production observed in condition of static head tilt were largely related to the perceived body configuration and therefore favour the hypothesis that the conscious perception of body configuration plays a key role in organising sensorimotor tasks.

The purpose of the present study was to examine the influence of submaximal aerobic exercise duration on simple and complex cognitive performance. Eight well-trained male subjects agreed to participate in this study (trial group). A control group of eight regularly trained male subjects was included for comparative purposes. For the trial group, the experiment involved a critical flicker fusion test (CFF) and a map recognition task performed before, every 20 min during, and immediately after, a 3-h cycling task at an intensity corresponding to approximately 60 % of VO2max. Data were obtained over two experimental sessions with fluid ingestion (F) or no fluid (NF) ingestion. For the control group the experiment was the same but without exercise and fluid ingestion. In the trial group, a significant effect of hydration status was observed on physiological parameters (p <0.05). No effect was found on cognitive performance. A significant decrease in CFF performance was observed after 120 min of exercise when compared with the first 20 min (respectively for CFFmdi: 2.6 vs. 3.8 Hz), irrespective of experimental condition. A significant improvement in speed of response (respectively: 3291 vs. 3062 msec for 20 and 120 min, respectively) and a decrease in error number (21.5 % vs. 6.0 % for 20 and 120 min, respectively) during the map recognition task were recorded between 80 min and 120 min when compared with the first 20 min of exercise. After 120 min the number of recorded errors was significantly greater indicating a shift in the accuracy-speed trade-off (6.0 % vs. 14.1 % for 120 and 180 min, respectively). These results provide some evidence for exercise-induced facilitation of cognitive function. However this positive effect disappears during prolonged exercise--as evidenced within our study by an increase in errors during the complex task and an alteration in perceptual response (i.e. the appearance of symptoms of central fatigue).

Body sway was studied in standing with eyes closed during quiet breathing and apnoea. The hypothesis was that absence of ventilation improved balance. Performance and control of balance were assessed by centre of gravity and centre of pressure motions respectively. Eight healthy male subjects participated in the study. The analysis was performed for the first 20s when no activity of the diaphragm and no force variation at thoracic and abdominal levels were observed in apnoea condition. Performance and control were significantly improved in apnoea from 17 to 26% for the planar parameters; this improvement was only observed along the medio-lateral axis (around 34%), probably due to upper body asymmetry and diminution of the number of degrees of freedom that can be mobilised along this axis. In conclusion, ventilation in quiet breathing is a perturbing factor in human standing.

The present paper addresses the question of the possible links between perceptive visual field dependence-independence and the visual contribution to postural control. In our differential approach, visual field dependent (FD) and independent (FI) subjects were selected on the basis of their score in the Rod and Frame Test (subjective vertical). The hypothesis that we have tested is that the FD subjects use mainly visual cues for estimating not only their subjective vertical but also their body orientation and stability. Moreover, we have postulated that these subjects use mainly dynamic visual cues to control their postural stability. In the postural test, the selected subjects were instructed to stand in the sharpened Romberg position in darkness and under normal or stroboscopic illumination, in front of either a vertical or a tilted frame. Lateral head and body orientation and stability were measured. We found that: (1) all subjects leaned slightly towards the tilted frame (postural frame effect), and this was obtained on the basis of the static visual cues alone; (2) FD subjects were less stable than FI subjects, and their stability required the use of dynamic visual cues, mainly extracted from the vertical frame. In FI subjects, static visual cues may act as a complementary regulation, enhancing stability even with a strobe tilted frame. We thus demonstrate that visual field dependence interacts with the visual contribution to postural control.

The choice of swimming as locomotor behaviour was justified by the fact that it could be elicited from birth to adult age. We have recorded electromyographic activities during swimming movements, on flexor muscles in front legs and hind legs (Spinodeltoidus and Gluteus superficialis). The mean frequency of activity of each limb during swimming, for animals aged from 0 to 20 or 30 days was then computed. The results showed an increase in frequency between 0 and 20 days from 1 to 4 Hz. This increase was not linear, but composed of different successive phases. After a first period of increase between 0 and 6 days (slope 0.25), for the hind limbs and the fore-limbs, we noted a plateau between 6 and 12 days during which the frequency was stable. This plateau was followed by another increase in the frequency values between 12 and 16 days (slope 0.30), followed by another plateau that corresponded to the adult frequency.

Rhythmic motor activities were studied in two rat spinal cord preparations; in the first one, the spinal cord was completely isolated and the ventral roots activity was recorded; in the other, spinal cord and hindlimbs were kept in order to record muscle activities. Motor patterns were therefore recorded in ventral roots and/or hindlimb muscles. Two kinds of specific patterns were elicited by neurochemicals. The first which was induced by N-methyl-D,L-aspartate (NMDA) and serotonin (5-HT) was a slow rhythm (0.5-0.2 Hz) of left and right alternating bursts of spikes. The second one which was induced by NMDA, 5-HT and norepinephrine (NE), was a high frequency rhythm (5-10 Hz). One particularity observed was that these two rhythms could occur simultaneously. The relationship between the two in vitro rhythms is discussed and they are compared with those reported in other rhythmic systems.

Classical experiments on the ability of cats to turn in the air during a free fall, the air righting reflex, have shown that vestibular and visual cues can play a role in this behavior. The development of this air righting reflex in kittens blinded since birth has been studied. The results show that the development in the blinded kittens is the same as in normal kittens with vision: mature by 33 days. This result and the comparison with other studies confirm that the air righting reflex is primarily a vestibular controlled reaction.

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)

We have compared responses of cat visual cortical cells of area 17 to continuously illuminated moving slits and to moving slits illuminated stroboscopically at different rates (70-2 Hz) using quantitative multihistogram techniques. At strobe rates over 30 Hz response characteristics of cortical cells are almost identical under both conditions, except for a lower response level under stroboscopic illumination. As strobe rates decrease below 30 Hz, direction selectivity and velocity tuning are severely impaired and some cells start responding to the individual strobe flashes rather than to the motion of the slit.

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.

Cells which respond only to slowly moving bars (velocity low-pass, or VLP cells) are numerous in area 17 whereas they are lacking in the LGN. The suggestion that this preference for low stimulus velocity is linked to the presence of S cells (equivalent of simple cells) in area 17 was critically evaluated by correlating S cell characteristics (subregion overlap, receptive field width and presence of inhibitory zones) with velocity preference. It was found that VLP cells generally respond only to relatively long durations of stationary stimulation and that this need of temporal summation best explains the preference for slow movement in area 17.

The effect of deprivation of visual perception of movement in a visuo-motor task has been tested in cats reared in stroboscopic light since birth. Three cats were reared in light of fixed (2 flash/sec, flash duration 2 msec) and three in light of random (between 0.5 and 3.5 flash/sec) frequency. These 6 animals, together with 6 control cats, underwent (as adults) a test of visual control of reaching for a target with a paw, with operant conditioning. While the cats raised in fixed frequency stroboscopic conditions (FFS) showed no deficit, those raised in random frequency condition (RFS) exhibited significantly less precise guidance than FFS and control animals.

The response properties of 196 area 17 cells were studied qualitatively in seven cats reared from birth in a stroboscopically illuminated environment (frequency, 2/s; duration, 200 microseconds). Quantitative testing with the multihistogram technique was carried out in 115 cells. As control population, 453 neurons recorded in area 17 of the normal adult cat and tested qualitatively (of which 301 neurons were tested quantitatively) were available. In area 17 of strobe-reared cats, a number of spatial characteristics of receptive fields investigated with hand-held stimuli were found to be abnormal. There was a strong reduction in the encounter frequency both of end-stopped cells and of binocularly driven cells in the strobe-reared cats. Central receptive fields in strobe-reared cats were wider than in normal cats, but the increase in receptive-field width with eccentricity was still observed. More cells than in normal cats showed either no selectivity or only a weak bias for stimulus orientation, but the orientation tuning of orientation-selective cells was similar in strobe-reared and normal cats. Quantitative testing revealed that the velocity preference of cells in area 17 subserving central vision was different in strobe-reared cats from that of normal cats, due to a reduction in the encounter frequency of cells showing a preference for low velocities. There was no difference in velocity preference between strobe-reared and normal cats in the parts of area 17 that subserve peripheral vision, the proportion of neurons responding to fast velocities showing a similar increase in both groups of animals. Fewer cells were direction selective in strobe-reared cats than in normal cats. Most of the remaining direction-selective cells had peripheral receptive fields and the synergism between leaving an OFF subregion and entering an ON subregion contributed to their direction selectivity. Latency of neurons in area 17 of strobe-reared cats was slightly higher than in normal cats, but the response strength of neurons was the same in the two groups. The proportion of cells failing to respond to briefly flashed stationary stimuli was significantly lower in strobe-reared than in normal animals. Qualitative and quantitative testing showed that strobe rearing has a stronger effect on the parts of area 17 that subserve central vision than on those that subserve peripheral vision. Comparing the present results with those of Kennedy and Orban (37) shows that strobe rearing has less effect on area 17 than on area 18 and that the functional differences between areas 17 and 18 in strobe-reared cats are smaller than in normal cats.

To investigate the dependence of velocity characteristics on spatiotemporal interactions the velocity selectivity of 15 geniculate and 72 cortical cells (areas 17 and 18) was examined with light and dark bars before and after masking all but the most sensitive part of the receptive field. The use of a 0.3 degree window proved effective in eliminating enough spatiotemporal interactions to abolish cortical direction selectivity. The same window improved the responsiveness at high velocities in only 26% of the cortical cells preferring low velocities and having a receptive field with nonoverlapping ON and OFF subregions. The remaining 74% showed various degrees of velocity-independent decrease in response amplitude. The only two geniculate cells that had a velocity upper cutoff lost this cutoff when tested with the mask. Cortical units preferring high velocities lost their responsiveness at high velocities in the mask condition, provided that their receptive fields contained nonoverlapping ON and OFF subregions. Cortical units, which responded best at intermediate velocities and which had receptive fields with nonoverlapping subregions, lost their sharp velocity tuning when tested with a mask. We conclude that inhibitory spatiotemporal interactions can account for the preference for low velocities in at most a quarter of the cells with nonoverlapping subregions. In contrast, facilitatory interactions seem to be important for cortical cells preferring high or intermediate velocities and having receptive fields with nonoverlapping subregions.

Spectacle refraction of eyes of strobe-reared animals was compared to that of normal cats. Strobe reared cats were found to be significantly more myopic than normal cats.