Structure and properties of methacrylate based dental restorative materials

The chemistry and structure of the dimethacrylate resins and the nature of the filler systems in dental composite resins are reviewed in relation to their influence on the setting behaviour, dimensional stability, aesthetics, fracture behaviour and adhesive potential. It is clear that a deeper understanding of the structure of the polymeric matrix and the mechanism of clinical wear is required. As a result of ongoing research in this area and with the development of dentine adhesives, the future prospects of composite resins are encouraging.     

A small-animal activity-analysing system for behavioural studies

Automated recording and data analysis of the activity of small laboratory animals are often required for psychological and other forms of behavioural investigation. This paper describes such a system using an open field of 1·14×1·14 m. Three arrays of infrared-light-emitting diodes and phototransistors are used to locate the animal. Two of the arrays are used to generate an xy grid, while the third one is used to determine whether the animal is rearing. The position of the animal gives rise to both digital and analogue signals; so the equipment can be interfaced directly with a minicomputer, or coupled to an analogue recorder. Several activity parameters, such as the path length (absolute value of the line integral), the time spent at a predetermined area of the open field or the latency to move, are computed and displayed in digital form.     

Frequency-domain analysis of cerebral autoregulation from spontaneous fluctuations in arterial blood pressure

The dynamic relationship between spontaneous fluctuations of arterial blood pressure (ABP) and corresponding changes in crebral blood flow velocity (CBFV) is studied in a population of 83 neonates. Static and dynamic methods are used to identify two subgroups showing either normal (group A, n=23) or impaired (group B, n=21) cerebral autoregulation. An FFT algorithm is used to estimate the coherence and transfer function between CBFV and ABP. The significance of the linear dependence between these two variables in demonstrated by mean values of squared coherence >0.50 for both groups in the frequency range 0.02–0.50 Hz. However, group A has significanlty smaller coherences than group B in the frequency ranges 0.02–0.10 Hz and 0.33–0.49 Hz. The phase response of group A is also significantly more positive than that of group B, with slopes of 9.3±1.05 and 1.80±1.2 rad Hz⁻¹, respectively. The amplitude frequency response is also significantly smaller for group A in relation to group B for the frequency range 0.25–0.43 Hz. These results suggest that transfer function analysis may be able to identify different components of cerebral autoregulation and also provide a deeper understanding of recent findings by other investigators.     

The time-course of ribavirin-provoked changes of basal and AMPH-induced motor activities in rats

The time-course of changes of basal and amphetamine (AMPH)-induced locomotor and stereotypic activities in adult male Wistar rats after a single ribavirin injection was studied. In the first set of experiments, 10, 20 or 30 mg ribavirin/kg body weight (b.w.) were injected i.p. to rats and their basal motor activities were recorded every 10 min for 2 h and compared with those of saline-treated controls. In the second set of experiments, the animals were pretreated with ribavirin and 20 min later i.p. injected with AMPH (1.5 mg/kg b.w.). The controls received AMPH 20 min after the saline injection. Motor activity was recorded after the first injection and until 120 min after AMPH administration. Ribavirin did not significantly affect the time-course of either basal locomotor or stereotypic activities. Pretreatment with any of the applied ribavirin doses decreased the AMPH-induced hyperlocomotor response. However, the most pronounced effect was observed with ribavirin doses of 20 mg/kg and 30 mg/kg when administered during the first 10 min and 30 min after the AMPH injection respectively. In contrast, the stereotypic activities of these animals were only slightly changed. These results indicate a different susceptibility of regions in the basal ganglia to ribavirin.     

Adaptive motor unit action potential clustering using shape and temporal information

An adaptive algorithm is described that groups motor unit action potentials (MUAPs), detected in a composite EMG signal during signal decomposition, and creates partial motor unit action potential trains (MUAPTs). Data-driven MUAP shape and motor unit firing-pattern based criteria are used to form the clusters. An algorithm for estimating MUAPT temporal parameter, which provides accurate estimates even for partially defined trains, is used to obtain firing-pattern information. No a priori knowledge is required regarding the number of clusters or the distribution of their template shapes. The clustering algorithm when applied to real concentric-needle detected MUAP data provides accurate and useful clustering results. Compared to a classical leader-based algorithm, it provides more robust performance, is better able to estimate the true number of motor units represented in a set of detected MUAPs, and obtains more complete and accurate MUAPTs.     

Sonic phase delay from trachea to chest wall: spatial and inhaled gas dependency

A parametric phase delay estimation technique is used to determine the spatial and inhaled gas composition dependencies of sound propagation time through an intact human lung at frequencies of 150–1200 Hz. Noise transmission measurements from the mouth to the extrathoracic trachea and six sites on the posterior chest wall are performed in 11 healthy adult subjects at resting lung volume after equilibration with air, an 80% helium-20% oxygen mixture, and an 80% sulfurhexafluoride-20% oxygen mixture. The phase delay, τ(f), exhibits a bilateral asymmetry with relatively decreased delays to the left posterior chest as compared with the right. The phase delay to lower lung sites is greater than to upper sites at frequencies below 300 Hz; yet the opposite is found at higher frequencies, indicating changing propagation pathways with frequency. There is no measurable effect of inhaled gas composition on τ(f) below 300 Hz. At higher frequencies, changes in τ(f) that reflect the relative sound speed of the particular inhaled gas are observed. These findings support and extend previous measurements and hypotheses concerning the strong frequency dependence of the acoustical properties of the intact respiratory system.     

Phase shifts of circadian rhythms in activity entrained to food access

Rats anticipate daily 2 hr meals with a sharp increase in activity several hours prior to food availability. The present experiment examined the response to phase shifts of food access in rats with lesions of the suprachiasmatic nuclei (SCN). Following entrainment of activity to 2 hr of food per day, food access was phase delayed or phase advanced by 4, 6, or 8 hr. All rats responded to phase delays of 4 or 6 hr with an increase in the duration of anticipatory activity so that transients appeared mostly in activity onset. Following 8 hr phase delays, clear delaying transients in both activity onset and end were observed. Only a few rats showed advancing transients in activity after phase advances of food access. In response to 6 hr and 8 hr phase advances, 3 different responses occurred: (a) activity re-entrained to food access by the 2nd or 3rd day without clear intervening transients, (b) activity phase shifted by means of distinct delaying transients and (c) delaying transients occurred in one component of activity while a second component of activity appeared at the new phase position by the second or third day. These results provide further evidence that anticipation of food access is mediated by a circadian mechanism which is functionally independent of the SCN and illustrate some similarities as well as considerable differences between circadian rhythms entrained by feeding and those entrained by light-dark cycles.     

Monocular and binocular control of human interceptive movements

Previous work in our laboratory has demonstrated that binocular vision makes an important contribution to skilled reaching and grasping movements directed at static targets. In the present study we examine the contribution of binocular vision to interceptive reaching movements. We monitored such movements using a high-resolution, opto-electronic recording device (WATSMART), while subjects attempted to catch balls projected at them. No differences were found between monocular and binocular viewing conditions using this paradigm – either with respect to the velocity profiles or trajectories of the reaches. Moreover, the grasp was not affected by the type of vision available. It appears, then, that the moving targets provide adequate monocular depth and direction information (on the basis of optic flow) for the control of skilled interceptive movements directed at them. In addition, the time to achieve maximum grip aperture was constant across the trials – a finding consistent with the use of a time-to-contact variable derived from optic flow information. Finally, the transport component of prehension was found to be affected by certain variables that have, in the past, been thought to exclusively affect the grasp component of prehension, whereas the grasp component of prehension was affected by factors that have traditionally been thought to affect only the transport component. Received: 12 August 1996 / Accepted: 1 September 1997     

Effects of frustration on behaviour and plasma corticosteroid levels in pigs

Frustration was elicited in pigs by not rewarding the operant response of subjects having learnt to press a panel with their snout to get a food reward. When pigs were exposed singly to this situation, they extinguished their operant responding. Plasma corticosteroid levels increased during frustration and the number of responses emitted was correlated negatively with the initial plasma corticosteroid levels. When two pigs were submitted together to the frustration situation, they developed aggressive behaviour accompanied by increases of plasma corticosteroid levels. These experiments demonstrate that pigs are sensitive to the effects of frustration elicited by the omission of an expected reward.