Spatial integration of cold pressor pain sensation in humans

Spatial integration of cold pressor pain (CPP) in the hand was studied in healthy human subjects by measuring the latency to the ice water-induced first pain sensation with and without conditioning CPP. CPP alone showed a marked spatial summation effect. When conditioning and test CPP were applied at the same time, conditioning CPP suppressed test CPP both in an adjacent and a distant site. When test CPP was applied after the conditioning CPP (i.e. pain induced by conditioning CPP was considerably stronger than that evoked by test CPP) conditioning CPP suppressed the test CPP only in a distant site but enhanced it in an adjacent site. A decrease in the test stimulus area increased the suppressive effect by conditioning CPP. Thus, CPP shows spatial summation or inhibition depending on experimental parameters.     

Spatial orientation in humans: perception of angular whole-body displacements in two-dimensional trajectories

Vestibular perception of whole-body passive rotation in the horizontal plane was studied by applying two-dimensional (2D) motion to eight blindfolded healthy volunteers: pure rotations in place, corner-like trajectories and arcs of a circular trajectory were randomly applied by means of a remotely controlled robot. Angles embedded in the 2D trajectories were 45°, 90°, 135° and 180°. Stimulation of semicircular canals was the same for all trajectories but was accompanied by concurrent otolith stimulation during circular motion. Subjects participated in two successive experimental sessions. In the first session they were instructed to use a pointer to reproduce the total angular displacement after the motion (REPRODUCTION); in the second session they had to keep pointing towards a remote (15 m) memorised target during the motion (TRACKING). In REPRODUCTION subjects tended to overestimate their rotation angle by 28 ± 11% (mean ± SD). There was no systematic effect of the trajectory. Overestimation also occurred when subjects were required to rotate in darkness by 180° (by controlling a joystick). In TRACKING there was virtually no overestimation (6 ± 17%) and the movement of the pointer matched the dynamics of angular motion. We conclude that (a) the brain can separate and memorise the angular component of complex 2D motion; however, a large inter-individual variability in estimating its amplitude exists; (b) in the range of linear accelerations used in the study, no appreciable effect of otolith-canal perceptual interaction was shown; (c) angular displacements can be dynamically transformed into matched pointing movements; (d) overestimation seems to be typical of delayed judgements of angular displacement and of self-controlled rotations in place. This could be due to the characteristics of the physiological calibration of the vestibular input. Received: 30 October 1996 / Accepted: 18 June 1997     

Spatial working memory performance after high-frequency repetitive transcranial magnetic stimulation of the left and right posterior parietal cortex in humans

The effects of high-frequency repetitive transcranial magnetic stimulation (rTMS) at the left or right posterior parietal cortex were studied using a spatial working memory task. Eight subjects were stimulated over the P3 and P4 electrode site at 115% of the motor threshold (frequency 25 Hz, trains of 200 ms) during the 1000-ms delay of the spatial working memory task, or received sham stimulation. It was found that the reaction times were slower during right-parietal rTMS than during left-parietal rTMS. No differences were found between the percentages correct responses. These results are in line with recent neuroimaging findings and data from patients with cerebral lesions, suggesting that the posterior parietal cortex is especially involved in spatial processing, and provide converging evidence for recent theories on hemispheric specialization.     

Building artificial humans to understand humans

If we could build an android as a very humanlike robot, how would we humans distinguish a real human from an android? The answer to this question is not so easy. In human–android interaction, we cannot see the internal mechanism of the android, and thus we may simply believe that it is a human. This means that a human can be defined from two perspectives: one by organic mechanism and the other by appearance. Further, the current rapid progress in artificial organs makes this distinction confusing. The approach discussed in this article is to create artificial humans with humanlike appearances. The developed artificial humans, an android and a geminoid, can be used to improve understanding of humans through psychological and cognitive tests conducted using the artificial humans. We call this new approach to understanding humans android science.     

Antipyretic system in humans

The elevation of body temperature during fever reaction and endogenous antipyretic effect reflects the existing balance between 2 components directed to the maximal positive use of the fever effects and simultaneous prevention of their side effects. The mechanisms involved in the control of balance between factors known as the fever triggers and endogenous antipyretic factors. The possible mechanisms of action of various endogenous antipyretic system components (glucocorticoids, neuropeptides, cytokines etc.) capable to regulate the duration and quantity of fever reaction are discussed in this review.     

Presynaptic inhibition in humans

Presynaptic inhibition plays an important role in controlling sensory processing of information in humans, as in other animals. However, because of experimental constraints the methods for measuring presynaptic inhibition are necessarily more indirect in humans. The most common method uses the modulation of the H-reflex by vibratory or electrical inputs. However, these stimuli can produce postsynaptic as well as presynaptic changes so it is important to use very short periods of stimulation and measure changes at a latency where presynaptic changes predominate. In addition, the stimuli should be superimposed upon a steady background of EMG activity, preferably in a single motor unit, to maintain the postsynaptic state at a constant level.

Recent studies indicate that presynaptic inhibition is used as part of the program for voluntary movement and that it can be rapidly and dramatically adapted to the task being carried out. This task-dependent modulation is produced by pattern generators within the central nervous system as well as sensory feedback from the periphery, but the relative importance of the two remains uncertain. Clinical disorders, such as spasticity, affect the ability of humans to modulate presynaptic inhibition, and contribute to the deficits observed. Improved methods for treating the symptoms pharmacologically and electrically can improve function in these patients.     

Eye-head coupling in humans

Summary One component of the dynamic response of muscle spindles is characterized by a phase lead and frequency dependent sensitivity in response to sinusoidal stretches at frequencies around 1 Hz. Possible mechanisms producing this component, designated the mid-frequency dynamics, were investigated by testing the hypotheses that they arise from the mechanical behavior of the intrafusal muscle and alternatively from within the sensory terminals. Destruction of the myofibrillar structure of the intrafusal muscle fibers did not alter the mid-frequency dynamics, indicating that they do not arise from viscoelastic properties of the intrafusal muscle. An Arrhenius plot of the temperature dependence of the mid-frequency dynamics yielded an equivalent activation energy of 6.5 Kcal/M in the temperature range 23–42° C and a 3-fold higher activation energy at lower temperatures. These observations are consistent with a dynamic process associated with a membrane-bound bio-chemical process. The addition of Ca⁺⁺ and Ca⁺⁺-activated-K⁺ (K(Ca)) channel blockers (ZnCl₂, Apamin and TEA) to the bathing solution altered the response dynamics by reducing the mid-frequency phase lead. The results suggest a negative feedback on the membrane potential generated by K⁺⁺ efflux following a Ca⁺⁺ influx that opens K(Ca) channels. A quantitative model fit to the experimental data yields a time constant of about 80 ms representing the limiting process associated with activation of the K(Ca) channels in this system. The results indicate that the mechanism underlying the mid-frequency dynamics includes at least two processes: one, not identified in this study, generates the phase lead and another, involving Ca⁺⁺ and K(Ca) channels, provides a negative feedback that modifies the phase lead.     

Recurrent inhibition in humans

Methods have been developed to investigate recurrent inhibition (RI) in humans. A conditioning reflex discharge is used to evoke in motoneurones (MNs) supplying homonymous and synergistic muscles, an inhibition the characteristics of which are consistent with RI: it appears and increases with the conditioning motor discharge, has a short latency and a long duration, and is enhanced by an agonist of acetylcholine. As in the cat, homonymous RI exists in all explored motor nuclei of the limbs except those of the digits and the pattern of distribution of heteronymous RI closely matches that of monosynaptic Ia excitation. However, striking inter-species differences exist concerning the distribution of heteronymous RI since it is much more widely extended in the human lower limb than in the cat hindlimb, whereas it is more restricted in the upper limb than in the cat forelimb. Changes in transmission in the recurrent pathway have been investigated during various voluntary or postural contractions involving different (homonymous, synergistic, antagonistic) muscles and it has been found that the activation of Renshaw cells (RCs) by the voluntary motor discharge via recurrent collaterals was powerfully controlled by descending tracts: for example, during homonymous contraction, RI evoked by a given conditioning reflex discharge is much smaller during strong than during weak contraction, which suggests that the descending control of RCs might contribute to the regulation of muscle force. The finding that RC inhibition is more marked during phasic than during tonic contraction of similar force of the homonymous muscle is discussed in relation with the projections of RCs to Ia interneurones mediating reciprocal inhibition. Only in patients with progressive paraparesis is there evidence for decreased RI at rest which may contribute to the exaggeration of the passively-induced stretch reflex underlying spasticity. However, despite the seemingly normal RI at rest in most patients, the control of RCs during voluntary movements is disturbed in these patients, which probably contributes to their motor disability.     

Giardia infections in humans

A short report is given on the importance of the infections of people by Giardia lamblia with special consideration of epidemiological and immunological aspects. Results of the investigations of children from different day-care centres in large town also proved interactions with pathogenic and apathogenic bacteria. The prevalence in children with diarrhoea was up to 50% contrary to children without diarrhoea (up to 14%). Adults were infected with Giardia lamblia up to 3%. Environmental investigations of the sources of infection had negative results.     

X-radiation carcinogenesis in humans

Using a two hit theory of x-irradiation damage to DNA in ankylosing spondylitis treated patients (in a course of 10 treatments), I have found that a dose squared theory can approximately yield results which are in agreement with observation. The first hit inactivates premutational repair, while the second hit causes a mutation in an operator region which controls cell division. And average value of the immunological efficiency is used for the removal of incipient tumor cells.     

Cryptosporidium detection in humans

Cryptosporidium is known as an important cause of gastroenteritis in several animal species, especially in newborn calves and lambs. In our investigations we tested faeces samples of 78 diarrhoeic patients by the method of Ziehl-Neelsen modified after Henriksen. We could find Cryptosporidium oocysts in a boy of one and a half year. Cryptosporidia also should be considered as a cause of diarrhoeas in man.     

Immunological memory in humans

Specificity and memory are the defining characteristics of adaptive immune responses. Vaccines are predicated on the existence of immune memory, and the robustness of immune memory is a primary determinant of vaccine efficacy. How is immune memory maintained? Much progress has been made in this area over the past several years, and new human studies have added key insights into the longevity of B and T cell immune memory in the absence of antigen.     

Duodenogastric reflux in humans

Human duodenogastric reflux (DGR) was comprehensively studied via measurement of gastric juice bile acid levels, manometric, endoscopic and X-ray study in health and benign gastrointestinal diseases and during exercise. DRG is shown to fall in the physiological events that have a biologically determined circadian rhythm. There was an association of DGR with gastric secretion. The "refluctant dilution effect" was established which along with elimination provides a relative constancy of the concentrations of bile ACIDS FROM 0.025 TO 0.422 NG/ML. DGR regulation is effected by the coordinated motor and evacuatory performance of the gastroduodenal junction and duodenum which is described as a lock two-way system. It is concluded that DGR is involved in the formation of the internal gastric environment and hence plays a role in gastric digestion. The findings may be used in studies of the physiology of digestion and in clinical practice.     

Intrathymic lymph nodes in humans

An unusual lymph node exists in the centre of the human thymus. This lymph node, which we call an intrathymic lymph node (ITLN), possesses some interesting morphological characteristics. In ontogeny, this node seems to appear at the latter half of fetal period. The function of the ITLN is still unknown, but it is assumed that it may play a different role in the immune system than other peripheral lymph nodes by its characteristics.     

Oral tolerance induction in humans

Oral tolerance designates the status of systemic hyporesponsiveness against an antigen that makes contact with the immune system via the mucosa of the gastrointestinal tract. In various animal models of autoimmune disease the feeding of the particular autoantigen has been shown to tolerize the animal, thereby ameliorating the course of disease. In contrast, effectivity has not been found in human trials to induce oral tolerance in patients suffering from autoimmune disease. However, the underlying mechanisms of tolerance in rodents, in particular the induction of anti-inflammatory cytokines, seem to be functional in humans as well. Studies using the human neoantigen keyhole limpet hemocyanin (KLH) offer experimental access to examine cellular and molecular basics of oral tolerance in humans required to raise the efficiency of oral tolerance induction in clinical trials.