Responses of mechanoreceptive afferent units in the glabrous skin of the human hand to sinusoidal skin displacements.

The impulse responses to perpendicular sinusoidal skin displacements were recorded from 4 different types of mechanoreceptive different units innervating the glabrous skin of the human hand. The cycle responses, defined as the number of impulses evoked per sine wave cycle, were studied at a wide range of frequencies (0.5-400 Hz) and amplitudes (0.001-1mm). The rapidly adapting units (RA) were most easily excited at stimulus frequencies between 8 and 64 Hz, whereas the corresponding frequencies for the Pacinian units (PC) were above 64 Hz. However, at high stimulus amplitudes, the RA and the PC units showed quite similar response profiles within the range of frequencies tested. The sensitivities of the slowly adapting unit types (SA I and SA II) were greatest at lower frequencies. A characteristic finding for all 4 types of units was that the higher the amplitude, the lower the frequency at which the cycle response was maximal.

Sensitivity to edges of mechanoreceptive afferent units innervating the glabrous skin of the human head.

One type of rapidly adapting (RA) and one type of slowly adapting (SA I) mechanoreceptive unit innervating the glabrous skin area of the human hand have small and well defined receptive fields. Their responses to perpendicular sinusoidal skin displacements were measured when the field was completely covered by a flat contact surface and when the edge of the contact surface was placed over the field. It was found that the majority of the RA and SA I units exhibited stronger responses when the edge of the contactor was placed over the receptive field. This edge sensitivity, which was greatest for the SA I units, may be of particular importance in improving the spatial analysis of the edges of objects in contact with the skin during manual manipulation and exploration.

Field studies on the effects of food content on wakefulness.

The investigation included six drivers engaged in day driving and six drivers engaged in night driving. Changes in wakefulness were analysed by means of a questionnaire where the drivers were asked to rate their wakefulness on a 100 mm rating scale. Changes in wakefulness were analysed during intake of food with higher and lower contents of fat. The day-drivers had their intakes as breakfast and lunch, the night-drivers as dinner and between meals. No significant difference was observed between the two types of intake, meaning that the balance between fat, protein and carbohydrate does not effect the development of drowsiness.

Laboratory studies of the effects of carbohydrate consumption on wakefulness.

Changes in wakefulness before and after exposure to carbohydrate intake were tested in 30 test persons. Changes in wakefulness were tested via EEG and subjective estimates. The intakes consisted of 400 ml glucose, 250 kcal (GI 100), 400 ml fructose, 209 kcal (GI 20), and 400 ml water. The study has indicated that intake of fructose, glucose and water had a similar stimulating effect on wakefulness in drowsy subjects immediately after intake. Our results also indicate that intake of fructose can lead to a delay in the development of drowsiness. Compared to water, a 20-30 minutes delay of the point in time when high-degree drowsiness developed, took place. There was no significant difference between glucose and water.

Onset of drowsiness and satiation after meals with different energy contents.

The investigation consisted of a laboratory study with 10 healthy subjects who were both sleep and food deprived prior to each experimental condition. The aim of the study was to investigate the importance of energy content and the bulk of food on wakefulness and satiation. Each subject was tested in four conditions, each with equal food composition but different energy amounts: 100, 500 and 1000 kcal and 100 kcal with low bulk content. Recordings and ratings of wakefulness and satiations were carried out throughout the investigation, starting 30 minutes before and continuing until 90 minutes after intake of the food alternatives. No differences in wakefulness could be observed after the four food alternatives. However, subjects rated themselves as more satiated after the food alternatives with higher energy content and higher bulk.

Noise, vibration and changes in wakefulness during helicopter flight.

The investigation was carried out in cooperation with the helicopter school AF 1 in Boden. Measurements were made in two different types of helicopter, Hkp 3 and Hkp 6. Three different parameters were recorded during the flights: noise, vibrations, and wakefulness. Noise and vibration exposures were mainly correlated to the main rotor energy and frequency. Both types of exposure were dominated by lower frequencies, below 10 Hz. Analyses of wakefulness during long-distance flights, about 4 h, and short-distance flights, less than 2 h, were based on EEG and EKG recordings. As expected the level of wakefulness was influenced by the stress upon the pilots. Take-offs and landings, as well as unexpected events during the flight, were correlated to an increased level of wakefulness. In some cases flying was correlated to a gradual increase of weariness. The correlation between weariness, types of flying, and the external environmental factors of noise and vibration, is also discussed.

Acceptable levels of tonal and broad-band repetitive and continuous sounds during the performance of nonauditory tasks.

Three groups of 24 subjects were exposed to a 1000-Hz tone or broad band noise in a sound chamber. During the exposures subjects were engaged in an easy reaction time test or a difficult grammatical reasoning test. For each exposure and work subjects adjusted the noise to a tolerance level defined by its interference with task performance. During the simple reaction-time task significantly higher sound-pressure levels were accepted than during the reasoning test. At the tonal exposure, much lower levels were accepted than during the exposure to broad-band noise. For continuous sound exposures much higher levels were accepted than for noncontinuous exposures. For tonal exposures the difference was approximately 5 dB, for the broad-band exposures approximately 9 dB. In a separate study the effects of the noncontinuity of the noise and pauses were analysed. The raised annoying effect of the noncontinuous noise was not more affected by the noncontinuity of the noise periods than by the noncontinuity of the pauses. The results imply that the annoying reactions to the sound will be increased for repetitive noise and that the reaction is highly influenced by the over-all noncontinuity of the exposure.

Annoyance and discomfort during exposure to high-frequency noise from an ultrasonic washer.

Annoyance and discomfort during exposure to high-frequency noise from an ultrasonic washer have been examined in the experiments carried out with 10 subjects. After a short exposure during which the subjects rated their annoyance and discomfort, a broad-band noise was matched to the ultrasound. The subjects were exposed to three different levels of ultrasound on three different occasions. Analyses showed that ultrasound causes considerable annoyance and discomfort even for the lowest exposure levels. No significant difference between annoyance and discomfort was observed. The matchings indicated, however, that the A-weighting, i.e., the traditional rating technique used for noise evaluations, overestimated the high-frequency sound when evaluating annoyance and discomfort.

Laboratory studies of a sound system that maintains wakefulness.

Two studies investigated the effects of a waking sound that enhances wakefulness. Study I investigated the effect of the sound level and Study 2 the effect of time and frequency variability of the sound. The recordings of EEG and subjective ratings were analysed to study the effect upon wakefulness. The waking effect increased when sound varied in duration and frequency. A number of specific conditions necessary for the waking effect are described. The exposure should be based on high frequency sounds and several tones chosen to produce disharmony. The exposure should be loud enough to be heard over the masking background noise. The duration and tonal quality should be variable from one presentation to another.

Laboratory studies on the effects of temperature variations on drowsiness.

20 subjects were analysed in a laboratory study investigating the inhibition of drowsiness by altering air temperature. The EEGs of the subjects were used to measure the effect of sequences of temperature lowerings of 10 degrees for 2- and 4-min. periods. The effect upon wakefulness was analysed through EEG recordings and subjective ratings. Results indicated that reductions of the air temperature of 10 degrees during repeated 2- and 4-min. periods significantly increased wakefulness.

On the differentiation of prospective ectoderm to a ciliated cell pattern in embryos of Ambystoma mexicanum.

The differentiation of the ectoderm in Ambystoma mexicanum (Harrison stage 26--27) was examined under in vivo and in vitro conditions by scanning electron microscopy under different experimental conditions. About one out of three flank epidermal cells was found to be ciliated in the undistrubed or control embryos. The shape of ciliated cells in the explants from the animal region was only slightly affected. In no case was it possible to find two adjacent ciliated cells, implying that these cells prevent the appearance of cilia in the cells in direct contact. Transformation to ciliated cells is suppressed by hypertonicity but favoured in a hypotonic medium. The differentiation of epidermis is also dependent upon the synthesis of RNA and some kind of sulphated glucosaminoglycan, corroborated by the inhibitory effect of actinomycin and selenate. The differences between the test series and the controls are discussed with regard to factors controlling embryonic epidermal differentiation.

Changes in wakefulness during exposure to whole body vibration.

Thirty subjects were exposed to low frequency sinusoidal and random whole body vibration in the vertical direction, 0.3 m/sec2 (rms). Changes in wakefulness during 15 min vibration were compared to changes occurring during corresponding pauses without exposure. Measurements were made on EEG and ECG. Exposure to whole body vibration was found to be correlated with reduction in wakefulness. This effect, verified by an increase of theta and decrease of alpha activity, was greater during sinusoidal than random vibration.

Blood pressure changes in man during infrasonic exposure. An experimental study.

Twenty healthy male volunteers were exposed to infrasound in a pressure chamber especially designed for the experiments. The effects on blood pressure, pulse rate and serum cortisol levels of acute infrasonic stimulation were studied in a series of different experiments. Varying frequencies (6, 12, 16 Hz) and pressure levels (95, 110, 125 dB(lin)) were tested. Significantly increased diastolic and decreased systolic blood pressures were recorded without any rise in pulse rate. The increase in diastolic blood pressure reached a maximal mean of about 8 mmHg after 30 min exposure. The results suggest that acute infrasonic stimulation induces a peripheral vasoconstriction with increased blood pressure, previously shown to occur in conjunction with industrial noise. Chronic long-term exposure to environmental infrasound may be of importance for the development of essential hypertension in predisposed individuals.

Fate maps and cell differentiation in the amphibian embryo--an experimental study.

The aim of this paper is to test two different fate maps for the amphibian blastula with respect to their predictions concerning the process of cell differentiation. The first of these fate maps is the one proposed by Vogt, according to which all three germ layers can be projected on to the surface of the embryo. The second is a revision which claims that only endoderm and ectoderm are located in the surface, while the mesoderm is represented by free cells in the interior of the embryo. The testing has been performed by observing the differentiation of small explants of cells taken from various regions of the embryo. It was found that the spontaneous cell differentiation comprises three patterns: undifferentiated cells (free interior cells and circumpolar endodermal cells), fibroblast-like cells (the remaining endodermal cells) and epidermis (ectodermal cells). Further differentiation occurs only through induction, exerted either by the fibroblast-like endodermal cells or by heparan sulphate. When induced, the equatorial ectodermal cells give rise to swollen, hyaline cells (chordocytes), while the remaining ectodermal cells form a sequence of cell differentiation patterns, mesenchyme cells, nerve cells, melanophores and xanthophores. The free interior cells differentiate into striated muscle cells and elongated collagen-producing fibroblasts. Our results thus confirm the revised fate map, and they also give an insight into the mechanisms of the initial cell differentiations in the amphibian embryo.

On the determination of the dorso-ventral polarity in Xenopus laevis embryos.

When embryos, or dorsal or ventral half-embryos, of Xenopus laevis are subjected to unilateral restriction of oxygen supply, the posterior end will always appear at the aerobic side, while the development of the anterior end, oriented towards the anaerobic side, will be partly suppressed. The shorter the time treatment lasts, the more normal the development will be. When the restriction of oxygen effects an inversion of the dorso-ventral polarity, development is retarded, otherwise not. Measurements of oxygen consumption show a substantial reduction in the experimental embryos, as compared with normal ones. The change in oxygen consumption in inverted embryos is delayed relative to non-inverted ones, but there is no significant difference in the total consumption of oxygen. Our results support the idea that the dorso-ventral polarity is associated with a gradient in oxygen consumption, and various kinds of evidence suggest that oxygen consumption is, in part, required for the formation of Ruffini's flask-cells, responsible for the initiation of invagination. It is suggested that the basic mechanisms involved in the determination of the normal, and the inverted, dorso-ventral polarity are fundamentally different, the latter being in fact an induction of a new polarity.

Sound exposure as a measure against driver drowsiness.

Twelve lorry drivers participated in a field study, including in total 110 tests of a waking sound system. The system was based on a time and frequency varied sound, generated at intervals between 1 and 15 min for periods of 3-7 s. The waking effect of the sound was analysed through subjective ratings. Exposure to the sounds was correlated to improvements of the immediate as well as the long-term self-reported changes in wakefulness. The results of the study show consistently positive assessments concerning the applied waking system, both regarding the system as a measure for raised wakefulness, increased road safety and the interest in having the system installed in the vehicle. The waking sounds were in no case felt to be annoying. Analyses of the wakefulness and other factors and the interaction related to fatigue and driving are included in the investigation.

On the determination of the dorso-ventral polarity in the amphibian embryo: suppression by lactate of the formation of Ruffini's flask-cells.

Cells isolated from the vegetal hemisphere of the blastula of Ambystoma mexicanum differentiate spontaneously into fibroblast-like cells. Similar cells may be formed from animal cells, provided they are induced either by vegetal cells or by Li+. We have found that lactate and various inhibitors of RNA synthesis suppress the spontaneous cell differentiation. The effect of lactate differs from that of the other agents in so far as lactate must be present before the second day of culture to suppress the outgrowth of fibroblasts on the third day; the other inhibitors are active also when added on the second day. An explanation of this difference may possibly be found in the fact that lactate suppresses incorporation of RNA but only by 40%. The effect on the differentiation of various substances supposed to interfere with the metabolism of lactate was established. The results obtained were suggestive, but not conclusive. It is concluded that the effect of anaerobiosis may be explained as a lactate inhibition. The amounts of lactate under aerobic conditions are so slight that it is unlikely, but not impossible, that lactate is directly involved in the control of differentiation.

Control of cell division and cell differentiation by deoxynucleotides in the early embryo of Xenopus laevis.

It is proposed that the deoxyriboside triphosphates present in the egg of Xenopus laevis support the synchronous cell divisions occurring during the earliest phase of embryonic development and that, as long as synchrony prevails, the cells are prevented from undergoing differentiation. This hypothesis has been tested by injecting deoxyribonucleotides into fertilized eggs. The following effects were observed: 1) the duration of synchrony is prolonged, 2) the morphological development is suppressed, an effect which is greatest when four nucleotides are injected together and 3) the synthesis of all kinds of RNA is inhibited, including the mRNA required for differentiation to occur.

Lactate--a suppressor of differentiation in embryonic cells.

All kinds of visible differentiation in cultured amphibian embryonic cells are suppressed in the presence of lactate. This effect differs in certain respects from that observed with actinomycin, but like the latter lactate inhibits RNA synthesis. In this communication we present some further observations on the effect of lactate.