Cognitive, perceptual and action-oriented representations of falling objects

We interact daily with moving objects. How accurate are our predictions about objects' motions? What sources of information do we use? These questions have received wide attention from a variety of different viewpoints. On one end of the spectrum are the ecological approaches assuming that all the information about the visual environment is present in the optic array, with no need to postulate conscious or unconscious representations. On the other end of the spectrum are the constructivist approaches assuming that a more or less accurate representation of the external world is built in the brain using explicit or implicit knowledge or memory besides sensory inputs. Representations can be related to naive physics or to context cue-heuristics or to the construction of internal copies of environmental invariants. We address the issue of prediction of objects' fall at different levels. Cognitive understanding and perceptual judgment of simple Newtonian dynamics can be surprisingly inaccurate. By contrast, motor interactions with falling objects are often very accurate. We argue that the pragmatic action-oriented behaviour and the perception-oriented behaviour may use different modes of operation and different levels of representation.     

Keeping with the beat: movement trajectories contribute to movement timing

Previous studies of paced repetitive movements with respect to an external beat have either emphasised (a) the form of movement trajectories or (b) timing errors made with respect to the external beat. The question of what kinds of movement trajectories assist timing accuracy has not previously been addressed. In an experiment involving synchronisation or syncopation with an external auditory metronome we show that the nervous system produces trajectories that are asymmetric with respect to time and velocity in the out and return phases of the repeating movement cycle. This asymmetry is task specific and is independent of motor implementation details (finger flexion vs. extension). Additionally, we found that timed trajectories are less smooth (higher mean squared jerk) than unpaced ones. The degree of asymmetry in the flexion and extension movement times is positively correlated with timing accuracy. Negative correlations were observed between synchronisation timing error and the movement time of the ensuing return phase, suggesting that late arrival of the finger is compensated by a shorter return phase and conversely for early arrival. We suggest that movement asymmetry in repetitive timing tasks helps satisfy requirements of precision and accuracy relative to a target event.     

Kv1 currents mediate a gradient of principal neuron excitability across the tonotopic axis in the rat lateral superior olive

Principal neurons of the lateral superior olive (LSO) detect interaural intensity differences by integration of excitatory projections from ipsilateral bushy cells and inhibitory inputs from the medial nucleus of the trapezoid body. The intrinsic membrane currents active around firing threshold will form an important component of this binaural computation. Whole cell patch recording in an in vitro brain slice preparation was employed to study conductances regulating action potential (AP) firing in principal neurons. Current-clamp recordings from different neurons showed two types of firing pattern on depolarization, one group fired only a single initial AP and had low input resistance while the second group fired multiple APs and had a high input resistance. Under voltage-clamp, single-spiking neurons showed significantly higher levels of a dendrotoxin-sensitive, low threshold potassium current (ILT). Block of ILT by dendrotoxin-I allowed single-spiking cells to fire multiple APs and indicated that this current was mediated by Kv1 channels. Both neuronal types were morphologically similar and possessed similar amounts of the hyperpolarization-activated nonspecific cation conductance (Ih). However, single-spiking cells predominated in the lateral limb of the LSO (receiving low frequency sound inputs) while multiple-firing cells dominated the medial limb. This functional gradient was mirrored by a medio-lateral distribution of Kv1.1 immunolabelling. We conclude that Kv1 channels underlie the gradient of LSO principal neuron firing properties. The properties of single-spiking neurons would render them particularly suited to preserving timing information.     

Three-dimensional navigator coronary MRA with the aid of a blood pool agent in pigs: improved image quality with inclusion of the contrast agent first-pass

PURPOSE: To evaluate the effect of including the first-pass of a blood pool agent (BPA) on the image quality of three-dimensional navigator coronary MRA. MATERIALS AND METHODS: A pig model was used to perform: 1) T1 simulation of the BPA, based on actual blood samples, and 2) BPA-enhanced three-dimensional navigator coronary MRA, with or without inclusion of the first-pass of the BPA. The acquisitions with inclusion of the first-pass were timed with the use of a test bolus. The acquisitions without first-pass were started one minute after bolus injection (steady-state). A gradient echo acquisition technique with centric k-space sampling was applied. Comparison of both acquisitions was based on determination of contrast-to-noise ratio (CNR), signal-to-noise ratio (SNR), and vessel length. RESULTS: T1 simulation shows a distinct T1 reduction during first-pass (to a level below 50 msec), increasing to 190 msec during steady-state. Images obtained with first-pass inclusion showed improved CNR (8.6 +/- 1.7 vs. 4.5 +/- 1.8), SNR (11.9 +/- 1.6 vs. 7.4 +/- 2.0), and vessel length (99.2 +/- 10.9 mm vs. 60.5 +/- 21.8 mm) as compared to the acquisitions during steady-state only (all: P< 0.05). CONCLUSION: The image quality of three-dimensional navigator coronary MRA combined with a gadolinium BPA in pigs is improved when starting the image acquisition during first-pass of the bolus.     

重症胰腺炎外科治疗84例临床分析

目的 探讨重症胰腺炎外科治疗的手术时机和手术方式。方法 回顾分析1990-2001年间84例重症胰腺炎患者的外科治疗资料。结果46例手术治疗,其中有16例发现胰腺弥漫性肿胀,胰腺被膜张力增高,并有部分发黑,周围有散在“皂化斑”。46例均有血性腹水或淡黄色混浊液体(1000-2000ml),手术均行坏死胰腺组织清除加充分引流,胆源性胰腺炎同时行胆管切开取石加“T”管引流。结论 为了提高生存率,减少术后并发症,合理选择手术时机和手术方式是手术成功关键。     

Impact of oestradiol and inhibin A concentrations on pregnancy rate in in-vitro oocyte maturation

The purpose of the present study was to analyse the results of maturation of oocytes obtained in unstimulated normal women after a leading follicle of 10 mm diameter and an endometrium of at least 5 mm thickness were observed at ultrasound. The serum concentrations of oestradiol and inhibin A were analysed from day 3 to the day of aspiration and retrospectively evaluated. A total of 75 normal regular cycling women referred for IVF/intracytoplasmic sperm injection (ICSI) because of male factor and/or tubal disease was included (n = 87 consecutive cycles). The oocytes were aspirated transvaginally and matured for 28-36 h. ICSI was performed on all metaphase II oocytes and they were cultured to day 2 or 3 after insemination, at which time suitable embryos (maximum two) were replaced into the women. Eleven singleton pregnancies with a live fetus were obtained after transfer in 63 cycles (pregnancy rate of 13% per aspiration and 17% per transfer). Nine healthy children have been born and the remaining two pregnancies miscarried in the eighth to ninth gestational week. The serum concentrations of oestradiol on day 3 and on the day of aspiration were available in 85 cycles, and in 57 of these an increase of 100% was detected on the day of aspiration. Significantly more pregnancies were observed in these cycles compared with cycles without an increase in the concentration of oestradiol (19 versus 0% per aspiration, 24 versus 0% per transfer, P < 0.02). Further improvement in pregnancy rate was obtained if aspiration was performed after increase in inhibin A concentration (24 versus 0% per aspiration and 33 versus 0% per transfer, P < 0.02) (n = 83 cycles, where inhibin concentrations were available, and n = 42 cycles, where an increase of 80% was detected on the day of aspiration compared with day 3). Timing of aspiration may improve the developmental potential of immature oocytes.     

Acute and convalescent changes in plasma homocysteine concentrations in acute coronary syndromes

BACKGROUND—Raised plasma homocysteine is a risk factor for coronary artery disease. Patients with myocardial infarction or unstable angina show greater activation of coagulation, greater troponin release, and a worse outcome.OBJECTIVE—To examine variations in plasma homocysteine concentration in relation to C reactive protein (CRP) in patients presenting with acute coronary syndromes.METHODS—Consecutive patients presenting with acute myocardial infarction (22) and unstable angina pectoris (12) were studied. Plasma samples were obtained on admission (before clinical intervention), on days 2, 7, and 28, and again six months after admission. Plasma homocysteine, assayed by high performance liquid chromatography, and CRP were both determined at the same time points. Changes were assessed by analysis of variance.RESULTS—CRP concentrations showed a classical rise on day 2, followed by a gradual decline to normal values taken at six months from admission in both myocardial infarction (p < 0.0001) and unstable angina (p = 0.02). Homocysteine concentrations in myocardial infarction (median, 25th to 75th interquartile range) were: 11.9 (10.7 to 12.6), 11.5 (9.1 to 13.4), 12.1 (11.4 to 14.1), 12.4 (11.1 to 14.4), and 12.1 (11.2 to 14.0) µmol/l, for days 1, 2, 7, 28, and 180, respectively (p = 0.02). Significant differences were observed only between day 2 and day 7 (p < 0.05). The final homocysteine measurement was not different from the admission level. Homocysteine concentrations in unstable angina did not differ between admission and convalescence (12.5 (9.1 to 14.5) µmol/l and 12.3 (7.7 to 14.9) µmol/l, respectively).CONCLUSIONS—Plasma homocysteine concentrations are minimally influenced by acute phase variations with reliable measurements obtained on admission in patients with myocardial infarction and unstable angina.     

36例前房出血继发青光眼的临床分析

目的 探讨前房积血引起继发性青光眼的治疗原则及手术时机。方法 对36例前房积血的继发性青光眼，据出血时间的长短、眼压的情况，采取不同的治疗方法。结果1例行小梁切除术，其余均用药物或前房冲洗术控制眼压至正常，出院时8眼视力〈0．05，14眼0．05～0．1，6眼0．2～0．5，8眼0．6～1．0。结论前房积血继发青光眼经积极适当的治疗，选择好手术时机可以更好的挽救视功能。     

Regional right ventricular function and timing of contraction in healthy volunteers evaluated by strain‐encoded MRI

Purpose

To prospectively determine the feasibility and accuracy of strain‐encoded (SENC) magnetic resonance imaging (MRI) for the characterization of the right ventricular free wall (RVFW) strain and timing of contraction at 3.0 Tesla (3T) MRI.

Materials and Methods

In 12 healthy volunteers the RVFW was divided into three segments (anterior, lateral, and inferior) in each of three short‐axis (SA) slices (apical, mid, and basal) and into three segments (apical, mid, and basal) in a four‐chamber view. The study was repeated on a different day and interobserver and interstudy agreements were evaluated.

Results

Maximal systolic longitudinal strain values were highest at the apex and base, with a pronounced decrease in the medial segments (apex: –19.1% ± 1.4; mid: –17.4% ± 2; base: –19.4% ± 2.4, P < 0.001), and maximal systolic circumferential strain showed the highest values at the apex (apex: –18.1% ± 1.7; mid: –17.6% ± 1.2; base: –16.6% ± 0.9, P < 0.001). Peak systolic longitudinal and circumferential shortening occurred earliest at the apex compared to the mid‐ventricle and base. Excellent interobserver and interstudy correlation and agreement were observed.

Conclusion

The use of SENC MRI for the assessment of normal RV contraction pattern is feasible and accurate in 3T MRI. J. Magn. Reson. Imaging 2008;28:1379–1385. © 2008 Wiley‐Liss, Inc.