Buildup Of Activity Research Articles

Epileptiform activity in the dentate gyrus during low-calcium perfusion and exposure to transient electric fields.

1. The dentate gyrus fails to develop epileptiform activity in many experimental models of epilepsy, including the in vitro low-Ca2+ model. Although manipulating the K+ concentration or osmolality of normal low-Ca2+ perfusion mediums can enhance the propensity of the dentate gyrus to develop seizure activity, the specific mechanisms contributing to this change are still under investigation. Identification of these mechanisms should improve our understanding of epileptogenesis and of the factors contributing to the propensity for seizure discharge in other tissues. 2. In the present experiments we used externally generated electric fields to depolarize the somata of large populations of dentate granule cells during exposure to a perfusion medium with no added Ca2+ (low-Ca2+ medium). Uniform electric fields were generated across an individual slice by passing current between two parallel AgCl-coated silver wires placed on the surface of the artificial cerebral spinal fluid. The wires were positioned to straddle the slice such that the current flow was parallel to the dendrosomatic axis of the cell population under investigation. 3. Under control conditions (low-Ca2+ medium, no applied field), stimulation of the dentate hilus evoked a single antidromic population spike in 89% of the slices studied (n = 27). During application of electric fields the same stimulus evoked epileptiform activity in all trials. Well-formed bursts first occurred at an average field intensity of +22.9 +/- 2.5 (SE) mV/mm (n = 24). The amplitude of individual spikes and the total number of spikes, within a burst increased in a graded fashion as the magnitude of the applied field was increased. 4. High field intensities evoked epileptiform activity in the absence of a synchronizing antidromic stimulus. These field-induced bursts occurred after a progressive buildup of rhythmic activity recorded in the extrasomatic space and could persist for the entire duration of an applied field, lasting for several seconds. The average field intensity required to produce a threshold burst was +84.6 +/- 3.6 mV/mm (n = 24). 5. In 11% of trials (3 of 27) the dentate gyrus exhibited poorly developed antidromic bursting without the application of depolarizing electric fields. These bursts were completely suppressed by hyperpolarizing fields in the range of -10 to -20 mV/mm. 6. The results of this investigation support the hypothesis that granule cell sensitivity to nonsynaptic interactions is adequate to support bursting in a normal low-Ca2+ medium, but bursting fails to occur because these cells are normally too hyperpolarized relative to their action potential threshold.(ABSTRACT TRUNCATED AT 400 WORDS)

Saccade-related activity in monkey superior colliculus. I. Characteristics of burst and buildup cells.

1. In the monkey superior colliculus (SC), the activity of most saccade-related neurons studied so far consists of a burst of activity in a population of cells at one place on the SC movement map. In contrast, recent experiments in the cat have described saccade-related activity as a slow increase in discharge before saccades followed by a hill of activity moving across the SC map. In order to explore this striking difference in the distribution of activity across the SC, we recorded from all saccade-related neurons that we encountered in microelectrode penetrations through the monkey SC and placed them in categories according to their activity during the generation of saccades. 2. When we considered the activity preceding the onset of the saccade, we could divide the cells into two categories. Cells with burst activity had a high-frequency discharge just before saccade onset but little activity between the signal to make a saccade and saccade onset. About two thirds of the saccade-related cells had only a burst of activity. Cells with a buildup of activity began to discharge at a low frequency after the signal to make a saccade and the discharge continued until generation of the saccade. About one third of the saccade-related cells studied had a buildup of activity, and about three fourths of these cells also gave a burst of activity with the saccade in addition to the slow buildup of activity. 3. The buildup of activity seemed to be more closely related to preparation to make a saccade than to the generation of the saccade. The buildup developed even in cases when no saccade occurred. 4. The falling phase of the discharge of these saccade-related cells stopped with the end of the saccade (a clipped discharge), shortly after the end of the saccade (partially clipped), or long after the end of the saccade (unclipped). 5. Some cells had closed movement fields in which saccades that were substantially smaller or larger than the optimal amplitude were not associated with increased activity. Other cells tended to have open-ended movement fields without any peripheral border; they were active for all saccades of optimal direction whose amplitudes were equal to or greater than a given amplitude.(ABSTRACT TRUNCATED AT 400 WORDS)

The pathway of secretion of proteinases in Trichomonas vaginalis

Trichomonads secrete large amounts of hydrolytic enzymes into liquid growth medium. Proteinase release by Trichomonas vaginalis has been quantified after resuspension of the parasite in a simple buffered maltose medium. After 6 h incubation, 70–90% of each of two cysteine proteinase activities, one towards benzyloxycarbonyl-arginyl-arginine 4-nitroanilide (Z-RR-Nan) and the other active towards N-benzoyl-prolyl-phenylalanyl-arginine 4-nitroanilide (Bz-PFR-Nan), was extracellular. This release was insensitive to changes in pH within the range from 5.5 to 8.6 but was partially inhibited by chloride ions. The secretion of activity towards Bz-PFR-Nan was temperature-sensitive but was still detectable down to 14°C. Neither this nor other cysteine proteinase activities were detectable on the surface of parasites. Release was stimulated by various amines and monensin, suggesting that secretion was from or via acidic compartments. The intracellular activity towards Bz-PFR-Nan could be totally and irreversibly inhibited by treating the parasites with benzyloxycarbonyl-phenylalanyl-alanine diazomethylketone (Z-FA-DMK), without otherwise harming the cells. Regeneration and routing of the proteinases responsible for this activity was followed after removal of the inhibitor. There was a significant rise in the intracellular level of activity before it became detectable in the medium. The release of this activity was accelerated by amines and monensin, but the build-up of enzyme activity within cells was not prevented. Organelles containing cysteine proteinases banded as a single peak in Percoll density gradients. The density of these increased when cells were treated with dextran. The activity towards Bz-PFR-Nan which reappeared after Z-FA-DMK treatment has a similar distribution. The proteinase-containing fraction could be distinguished from an early (5 min) endosome fraction, suggesting that it was composed of late endosomes/lysosomes. Thus these results imply that the secretion pathway for proteinases necessarily involves lysosomes/late endosomes.

Complex Critical Exponents from Renormalization Group Theory of Earthquakes: Implications for Earthquake Predictions

Several authors have proposed discrete renormalization group models of earthquakes, viewing them as a kind of dynamical critical phenomena. Here, we propose that the assumed discrete scale invariance stems from the irreversible and intermittent nature of rupture which ensures a breakdown of translational invariance. As a consequence, we show that the renormalization group entails complex critical exponents, describing log-periodic corrections to the leading scaling behavior. We use the mathematical form of this solution to fit the time to failure dependence of the Benioff strain on the approach of large earthquakes. This might provide a new technique for earthquake prediction for which we present preliminary tests on the 1989 Loma Prieta earthquake in northern California and on a recent build-up of seismic activity on a segment of the Aleutian-Island seismic zone. The earthquake phenomenology of precursory phenomena such as the causal sequence of quiescence and foreshocks is captured by the general structure of the mathematical solution of the renormalization group

A realistic three-component planetary wave model, with a wave-breaking parametrization

A fairly simple stratospheric model of the three longest planetary waves is constructed, which includes interference terms between the three wave components, and a diffusive parametrization of wave breaking in regions where the local meridional potential vorticity gradient is negative. In order to allow comparison with the observed behaviour of planetary waves the model is forced near the tropopause with observed wave amplitudes and the model waves propagate over the observed zonal-mean state. the model is able to mimic the behaviour of the observed waves fairly accurately, with the thermal damping, interference and wave breaking terms all being important to its success. Good results are obtained with a value of local wave-breaking diffusion coefficient between 106 and 107m2s−1. It is shown that the deficiencies in Matsuno's (1970) model are probably due mainly to the neglect of wave-wave interactions and an over-simplified zonal-mean temperature structure. It is shown that Garcia's (1991) idea that wave breaking completely absorbs any build-up of zonal-mean wave activity is probably too severe, but that better results are obtained if the local nature of the wave-breaking is taken into account. The zonal-mean diffusion coefficient sometimes has large values within the vortex, as well as in the midlatitude surf zone, with the two regions of diffusion being separated by the vortex edge. The difficulty in estimating the diffusion coefficient required for a tracer is discussed, as well as the behaviour of the zonal-mean potential vorticity flux during a wave-breaking episode. the assumption of turbulent diffusion in reversed-gradient regions implies a positive diffusive contribution to the potential vorticity flux. It was also found that changes in the equatorial zonal wind result in a modulation of the extra-tropical potential vorticity flux similar to that found by Dunkerton and Baldwin (1991), but that the modulation did not depend strongly on a movement of the tropical zero-wind line.

Tritium inventory prediction in a CANDU plant

The flow of tritium in a CANDU nuclear power plant was modeled to predict tritium activity build-up. Predictions were generally in good agreement with field measurements for the period 1983–1994. Fractional contributions of coolant and moderator systems to the environmental tritium release were calculated by least square analysis using field data from the Wolsong plant. From the analysis, it was found that: (1) about 94% of tritiated heavy water loss came from the coolant system; (2) however, about 64% of environmental tritium release came from the moderator system. Predictions of environmental tritium release were also in good agreement with field data from a few other CANDU plants. The model was used to calculate future tritium build-up and environmental tritium release at Wolsong site, Korea, where one unit is operating and three more units are under construction. The model predicts the tritium inventory at Wolsong site to increase steadily until it reaches the maximum of 66.3 MCi in the year 2026. The model also predicts the tritium release rate to reach a maximum of 79 KCi/yr in the year 2012. To reduce the tritium inventory at Wolsong site, construction of a tritium removal facility (TRF) is under consideration. The maximum needed TRF capacity of 8.7 MCi/yr was calculated to maintain tritium concentration effectively in CANDU reactors.

Long-Lived Radon Decay Products as a Long-Term Radon Exposure Indicator

Abstract The different members of the uranium decay series have distinct roles to play in the scenario of indoor radon. The 222Rn gas is the airborne carrier of the dose giving short-lived decay products. These transform into long-lived daughters (LRnD) of low activity, useful as retrospective radon tracers. Porous objects constitute volume traps for LRnD via radon diffusion, while surfaces trap LRnD through alpha recoil implantation. Only when the build-up of LRnD activity proceeds undisturbed over many years, do we have a system which is potentially useful for retrospective radon/radon daughter exposure studies. The feasibility of using LRnD in humans and in volume and surface traps as radon retrospective monitors is discussed. It is concluded that only surface implantation sinks are potentially well suited for long-term studies at radon levels met in dwellings.

Characteristics of medial temporal lobe epilepsy: II. Interictal and ictal scalp electroencephalography, neuropsychological testing, neuroimaging, surgical results, and pathology.

Sixty-seven patients with temporal lobe epilepsy without circumscribed, potentially epileptogenic lesions, who were studied with intracranial electrodes and who became seizure free following temporal lobectomy were retrospectively evaluated with regard to preoperative scalp electroencephalographic (EEG) findings, neuropsychological test results, neuroimaging findings, results of surgery, and pathology of resected tissue. Interictal scalp EEG showed paroxysmal abnormalities during prolonged monitoring in 64 patients (96%). These were localized in the anterior temporal region in 60 (94%) of these 64 patients. Bilateral independent paroxysmal activity occurred in 42% of the patients and was preponderant over the side of seizure origin in half. Ictal EEG changes were rarely detected at the time of clinical seizure onset, but lateralized buildup of rhythmic seizure activity during the seizure occurred in 80% of patients. In 13%, the scalp EEG seizure buildup was, however, contralateral to the side of seizure origin as subsequently determined by depth EEG and curative surgery. Lateralized postictal slowing, when present, was a very reliable lateralizing finding. Neuropsychological testing provided lateralizing findings concordant with the side of seizure origin in 73% of patients. When neuropsychological testing produced discordant results or nonlateralizing findings, those patients were usually found to have right temporal seizure origin. Intracarotid amobarbital (Amytal) testing demonstrated absent or marginal memory functions on the side of seizure onset in 63% of patients, but 26 patients (37%) had bilaterally intact memory. In those patients who had magnetic resonance imaging, it was very sensitive in detecting subtle medial temporal abnormalities. These abnormalities were present in 23 of 28 magnetic resonance images, and corresponded with mesial temporal sclerosis on pathological examination in all but 2 patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of synaptic excitation in the generation of bursting-induced epileptiform potentials in the endopiriform nucleus and piriform cortex

1. The mechanism of generation of epileptiform excitatory postsynaptic potentials (e-EPSPs) induced by bursting activity in vitro was examined in slices of piriform cortex. 2. Previous study revealed that e-EPSPs in piriform cortex are generated in the subjacent endopiriform nucleus, perhaps with a contribution from the claustrum and deep part of layer III of piriform cortex. A puzzling feature of these e-EPSPs was their abrupt origin at long latency with little sign of preceding abnormal activity. 3. Systematic mapping revealed that within spatially restricted regions of the endopiriform nucleus there is an irregular buildup in extracellularly recorded multiunit activity and intracellularly recorded depolarization that precedes the onset of e-EPSPs. Analysis of latency revealed that these "slow-onset" e-EPSPs precede the more widely distributed "abrupt-onset" e-EPSPs, suggesting that they occur at sites of initiation. 4. The hypothesis was tested that the buildup associated with slow-onset e-EPSPs is dependent on synaptically mediated excitation. According to this hypothesis, all-or-none e-EPSPs originate when mutually excitatory (positive feedback) interactions within a population of cells in the endopiriform nucleus become self-regenerative. 5. Predictions from the regenerative positive feedback hypothesis that were successfully verified include the presence of excitatory synaptic connections between cells in the endopiriform nucleus; the consistent prediction of a subsequent e-EPSP from the occurrence of the accelerating buildup in population activity; the occurrence of inhibitory postsynaptic potentials (IPSPs) together with EPSPs during the buildup period; and the blockage of the buildup and e-EPSP by a low concentration of a specific excitatory amino acid antagonist 6,7-dinitroquinoxaline-2,3-dione (DNQX). 6. Blockage of e-EPSPs by a concentration of DNQX that was much less than that required to block monosynaptic EPSPs in the endopiriform nucleus indicates that synaptic reverberation is mediated by alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) type excitatory amino acid receptors. 7. D-2-amino-5-phosphonovaleric acid (D-APV) reduced the duration and amplitude of e-EPSPs but did not block their occurrence, indicating that N-methyl-D-aspartate (NMDA) receptors have a boosting effect on e-EPSPs but are not required for their generation. This is in contrast to the induction of e-EPSPs by bursting activity for which NMDA receptor activation is required. 8. Outside the region of initiation e-EPSPs propagated through the endopiriform nucleus at a velocity of 0.1 m/s.(ABSTRACT TRUNCATED AT 400 WORDS)

On-line monitoring for further corrosion reduction and better understanding of the activity build-up in LWR primary coolant systems

Uniform corrosion rates of materials in contact with the coolant in boiling water reactors (BWRs) and pressurized water reactors (PWRs) are low and this kind of material degradation is very unlikely to compromise the integrity of the primary pressure boundary. In a properly controlled environment the initial corrosion rates decrease reaching the low corrosion rate, typical for the steady state between the outer oxide surface and the environment. The water chemistry practice modifications can be used to decrease fuel corrosion, improve material integrity and slow down activity build-up in the primary circuit. Therefore, on-line water chemistry monitoring at high temperatures should be conducted to obtain local, reliable and thus useful information over long measurement periods at a specific loop site. In this paper, the effect of water chemistry on the corrosion product formation, activation, transport and redeposition on out-of-core surfaces is discussed.

Surface analytical characterization of chromium-stabilized protecting oxide layers on stainless steel referring to activity buildup

Surface analytical methods were used to characterize both protecting oxide layers formed by hydrothermal chromate treatment (HTCT) on stabilized austenitic stainless steel and hydrothermally grown corrosion product layers (CPL) within the scope of lowering the activity buildup in the primary circuit of nuclear power plants. Morphology, thickness and chromium depth distribution of the layers proved to be considerably different from each other. According to Raman microspectrometry, there were also alterations in the chemical nature of the oxide species. Preceding electropolishing gave rise to particular properties of the respective layers. Prerequisites for an optimal corrosion behaviour of the protecting layers are discussed. Titanium-containing precipitations were oxidatively transformed by HTCT.

Locust marching: A mathematical model

A mathematical model is described that simulates the sequences of behaviour that make up the marching behaviour of the African migratory locust, Locusta migratoria migratorioides . The “model locust” was developed using the results from behavioural experiments in which locusts walked in continuous light and the predictive value of the model was tested against results of behavioural experiments obtained under a variety of other conditions. The model locust consists of two reciprocally inhibitory systems—one controlling walking, the other controlling all non-walking activities—that form a switch mechanism that prevents both systems from being active at the same time. Real locusts switch spontaneously between different behavioural activities, they will also switch from walking behaviour to non-walking activities in response to pulses of 3-kHz sound. In the model locust the spontaneous alternations in behaviour occur because the inhibitory input from the active system to the suppressed system “habituates” over time, whilst the switch from walking to non-walking induced by sound stimuli occurs when the excitatory input to non-walking is increased by a stimulus to a level higher than the inhibitory input it receives from the walking activity. The stopping threshold to sounds does not remain constant however, but falls exponentially through a bout of continuous walking. In the model this is simulated by an exponential fall in the rate at which the inhibition imposed on the non-walking activity by walking habituates. During marching the strength of the component behaviours changes over time. The observed build-up of walking activity of locusts placed in continuous light was simulated accurately by the model locust by the mechanism of post-inhibitory rebound, for when the non-walking system is active it not only inhibits the walking system, but as an after-effect it also increases its excitatory input as well. The behaviour of the model locust is consistent with these results.

Involvement of Wound and Climacteric Ethylene in Ripening Avocado Discs

Avocado (Persea americana Mill. cv Hass) discs (3 mm thick) ripened in approximately 72 hours when maintained in a flow of moist air and resembled ripe fruit in texture and taste. Ethylene evolution by discs of early and midseason fruit was characterized by two distinct components, viz. wound ethylene, peaking at approximately 18 hours, and climacteric ethylene, rising to a peak at approximately 72 hours. A commensurate respiratory stimulation accompanied each ethylene peak. Aminoethoxyvinyl glycine (AVG) given consecutively, at once and at 24 hours following disc preparation, prevented wound and climacteric respiration peaks, virtually all ethylene production, and ripening. When AVG was administered for the first 24 hours only, respiratory stimulation and softening (ripening) were retarded by at least a day. When AVG was added solely after the first 24 hours, ripening proceeded as in untreated discs, although climacteric ethylene and respiration were diminished. Propylene given together with AVG led to ripening under all circumstances. 2,5-Norbornadiene given continuously stimulated wound ethylene production, and it inhibited climacteric ethylene evolution, the augmentation of ethylene-forming enzyme activity normally associated with climacteric ethylene, and ripening. 2,5-Norbornadiene given at 24 hours fully inhibited ripening. When intact fruit were pulsed with ethylene for 24 hours before discs were prepared therefrom, the respiration rate, ethylene-forming enzyme activity buildup, and rate of ethylene production were all subsequently enhanced. The evidence suggests that ethylene is involved in all phases of disc ripening. In this view, wound ethylene in discs accelerates events that normally take place over an extended period throughout the lag phase in intact fruit, and climacteric ethylene serves the same ripening function in discs and intact fruit alike.

An investigation of photonuclear reactions in Cerrobend eutectic material with an 18 MV linac

Under normal operating conditions, a patient undergoing radiotherapy will receive a total dose of approximately=5 Gy per treatment in terms of monitor units. Since the overall half-life of the activity is of the order of 49 minutes, and the radiation shielding blocks are usually customized for the patient, there would be no further build-up of activity with daily treatments. This implies a dose equivalent rate of the order of 3 mu Sv h-1 will be received by the hands of radiographers handling the blocks. However the activity can and would be expected to increase with greater accelerator voltages. Even so, it is unlikely that dose equivalent rates will pose a radiation hazard. It is concluded that photonuclear reactions in Cerrobend do not result in significant exposure to radiographers and other staff in a radiation oncology facility (at least for photon beam energies up to 18 MV).

Neutron emission and the tritium content associated with deuterium-loaded palladium and titanium metals

An experimental investigation has been conducted on samples of palladium and titanium metals which have been loaded with deuterium through the electrolysis of D2O and by absorption of D2 gas. In approximately 200 experiments on 25 cells, statistically significant evidence for neutron emission was obtained in three separate experiments from one palladium cathode. Observed rates are 3–4 times the background rate and correspond to source strengths up to 50 neutrons/min. The pulse height response of the NE213 liquid scintillator-based detectors corresponds to that expected for 2.45 MeV neutrons. Tritium has been identified in nine Pd−Ni electrolytic cells, at levels corresponding 1012–1016 atoms. Activity buildup curves indicate that the apparent production occurs over a time period as short as a few hours.

Effect of sleep deprivation on EEG slow wave activity within non-REM sleep episodes in the rat

Recordings of 10 rats were obtained during the first 8 h of the light period under control conditions and after 24 h of sleep deprivation (SD). Non-rapid eye movement sleep (non-REMS) and EEG spectra in the range of 0.5–4.0 Hz were analyzed for 4 sec epochs. The time course of EEG slow wave activity within non-REMS episodes was closely approximated by a saturating exponential function. The time constant of approx. 50 sec varied little over consecutive 2 h periods and was not significantly changed by SD. The maximal level of EEG slow wave activity attained within non-REMS episodes (corresponding to the asymptote level of the fitted function) decreased over consecutive 2 h periods and was massively enhanced after SD. The study documents both the invariant and the homeostatically regulated aspect of the intraepisodic build-up of EEG slow wave activity.

The role of preparation in tuning anticipatory and reflex responses during catching

The pattern of muscle responses associated with catching a ball in the presence of vision was investigated by independently varying the height of the drop and the mass of the ball. It was found that the anticipatory EMG responses comprised early and late components. The early components were produced at a roughly constant latency (about 130 msec) from the time of ball release. Their mean amplitude decreased with increasing height of fall. Late components represented the major build-up of muscle activity preceding the ball's impact and were accompanied by limb flexion. Their onset time was roughly constant (about 100 msec) with respect to the time of impact (except in wrist extensors). This indicates that the timing of these responses was based on an accurate estimate of the instantaneous values of the time-to-contact (time remaining before impact). The mean amplitude of the late anticipatory responses increased linearly with the expected momentum of the ball at impact. The reflex responses evoked by the ball's impact consisted in a short-latency coactivation of flexor and extensor muscles at the elbow and wrist joints. Their mean amplitude generally increased with the intensity of the perturbation both in the stretched muscles and in the shortening muscles. We argue that both the anticipatory and the reflex coactivation are centrally preset in preparation for catching and are instrumental for stabilizing limb posture after impact. A model with linear, time-varying viscoelastic coefficients was used to assess the neural and mechanical contributions to the damping of limb oscillations induced by the ball's impact. The model demonstrates that (1) anticipatory muscle stiffening and anticipatory flexion of the limb are synergistic in building up resistance of the hand to vertical displacement and (2) the reflex coactivation produces a further increment of hand stiffness and viscosity which tends to offset the decrement which would result from the limb extension produced by the impact.

Initial studies on leucine metabolism in the rumen of sheep.

1. [3H]leucine infused directly into the rumen of sheep labelled microbial protein and, when compared with the specific activity of the rumen free-leucine pool, indicated that 50% of the bacterial protein leucine originated from the rumen free-leucine pool. 2. The lower limit for bacterial protein turnover in the rumen was 0.37/d when calculated as the difference between the specific rate of disappearances of labelled bacteria from the rumen and the liquid-phase dilution rate. 3. Intravenously infused leucine also labelled the rumen bacteria. The build-up of specific activity in the rumen bacteria was sigmoidal and did not resemble that of the salivary protein which suggested that the rumen epithelium was a major endogenous protein input to the rumen. Additionally, bacteria isolated from the rumen epithelium had high radioactivity indicating that they were ingesting the rumen epithelial cells.

Age-related differences in lexical access, spreading activation, and simple pronunciation.

An experiment was conducted to address age-related differences in lexical access, spreading activation, and pronunciation. Both young and older adults participated in a delayed pronunciation task to trace the time course of lexical access and a semantic priming task to trace the time course of spreading activation. In the delayed pronunciation task, subjects were presented a word and then, after varying delays, were presented a cue to pronounce the word aloud. Older adults benefited considerably more from the preexposure to the word than did the younger adults, suggesting an age-related difference in lexical access time. In the semantic priming pronunciation task, semantic relatedness (related vs. neutral), strength of the relationship (high vs. low), and prime-target stimulus onset asynchrony (200 ms, 350 ms, 500 ms, 650 ms, and 800 ms) were factorially crossed with age to investigate age-related differences in the buildup of semantic activation across time. The results from this task indicated that the activation pattern of the older adults closely mimicked that of the younger adults. Finally, the results of both tasks indicated that older adults were slower at both their onset to pronounce and their actual production durations (i.e., from onset to offset) in the pronunciation task. The results were interpreted as suggesting that input and output processes are slowed with age, but that the basic retrieval mechanism of spreading activation is spared by age.

Building the organisation: Structure, programmes and activities

In this part of the 25-year history of the International Academy of Astronautics, the build-up of programmes and activities and the structure put together to carry them out are followed. In turn, the following areas are covered: (1) awards, (2) committees, (3) publications, and (4) the World Forum initiative, which was still under development at the time of the Academy's 25th birthday in 1985.still under development at the time of the Academy's