A dynamic similarity hypothesis for the gaits of quadrupedal mammals

The dynamic similarity hypothesis postulates that different mammals move in a dynamically similar fashion whenever they travel at speeds that give them equal values of a dimensionless parameter, the Froude number. Thus, given information about one species, it could be possible to predict for others relationships between size, speed and features of gait such as stride length, duty factor, the phase relationships of the feet and the patterns of force exerted on the ground.
Data for a diverse sample of mammals have been used to test the hypothesis. It is found to be tenable in many cases when comparisons are confined to quadrupedal mammals of the type described by Jenkins (1971) as "cursorial". Most mammals of mass greater than 5 kg are of this type. Although the hypothesis applies less successfully to comparisons between cursorial and non-cursorial mammals it is shown to be a reasonable approximation even for such comparisons and for comparisons between quadrupedal mammals and bipedal mammals and birds.     

Psychophysiological monitoring under conditions of real and simulated microgravity.

Dynamics of indices characterizing the process of adaptation of operators to complicated conditions of vital activity was studied with psychophysiological monitoring. This technique is based on the complex analysis of subjective and objective estimations of the current psychoemotional state and physiological and biochemical indices. We analyzed the data obtained during the examination of three healthy volunteers, who participated in the HUBES experiment (135-day isolation in the ground-based model of the orbital station "Mir"), and during a biorhythmological study conducted by six Russian cosmonauts of the main expeditions on the station "Mir." It was shown that psychophysiological monitoring is an informative method for studying different parameters of the operator's state and regulatory processes, the dynamics of biological rhythms, and individual characteristics of adaptation. By means of the analysis of a population of the variation in the characteristics of the parameters under study the experimental period of isolation was divided into three stages. The first and third stages were characterized by a relatively high variability, which was minimized at the second stage. The phasic character of the adaptation processes with a phase duration of about 60 days was revealed and a correlation was shown between the dynamics of parameters obtained by means of psychophysiological monitoring and specific features of the system regulation in different phases of the space flight and its simulation. It is suggested that the phases of the minimal variability of the studied characteristics are related to the periods of the minimal reliability of an operator's work. [Translated from Fiziologiya Cheloveka, vol. 25, no. 5, 1999 Sep-Oct, p. 86-91]     

Cognitive processes and dynamic time structures. Introduction of a measuring instrument for studying the Micro-Vigilance-Shift-(MVS) hypothesis]

The psychophysiological measuring method for the determination of the auditory order threshold (OT) is steadily gaining in importance, both for the diagnosis and treatment of speech disorders. Observed intraindividual variability of (macro-) vigilance led to the hypothesis of discontinuous cognitive processing in the central nervous system. The base for the variability of microvigilance is hypothesized to be in the phase difference of the alpha rhythm. To test for this hypothesis, we developed an EEG-comparator, which allows for a phase-dependent triggering of external stimuli. In direct comparison with stochastic (i.e. non-phase-dependent) stimulus presentation, the threshold in phase-dependent OT-testing is distinctly lower. Optimal results occurred at phase angels of phi = 90 degrees and phi = 270 degrees. Our findings support the hypothesis of a correlation between alpha rhythm and vigilance processes. Furthermore, there seems to be evidence that memory processes go with changes in vigilance, and in this context the alpha phase correlation seems to be important.     

Neurochemical Oscillations in the Basal Ganglia

This work represents an attempt to elucidate the neurochemical processes in the basal ganglia by mathematical modelling. The correlation between neurochemistry and electrophysiology has been used to construct a dynamical system based on the basal ganglia’s network structure. Mathematical models were constructed for different physical scales to reformulate the neurochemical and electrophysiological behaviour from synapses up to multi-compartment systems. Transformation functions have been developed to transit between the different scales. We show through numerical simulations that this network produces oscillations in the electrical potentials as well as in neurotransmitter concentrations. In agreement with pharmacological experiments, a parameter sensitivity analysis reveals temporary changes in the neurochemical and electrophysiological systems after single exposure to antipsychotic drugs. This behaviour states the structural stability of the system. The correlation between the neurochemical dynamics and drug-induced behaviour provides the perspective for novel neurobiological hypotheses.     

Stages of motor skill learning

Successful learning of a motor skill requires repetitive training. Once the skill is mastered, it can be remembered for a long period of time. The durable memory makes motor skill learning an interesting paradigm for the study of learning and memory mechanisms. To gain better understanding, one scientific approach is to dissect the process into stages and to study these as well as their interactions. This article covers the growing evidence that motor skill learning advances through stages, in which different storage mechanisms predominate. The acquisition phase is characterized by fast (within session) and slow learning (between sessions). For a short period following the initial training sessions, the skill is labile to interference by other skills and by protein synthesis inhibition, indicating that consolidation processes occur during rest periods between training sessions. During training as well as rest periods, activation in different brain regions changes dynamically. Evidence for stages in motor skill learning is provided by experiments using behavioral, electrophysiological, functional imaging, and cellular/molecular methods.     

Stress and drug dependence (animal studies)

This review describes a role of stress in formation of the primary drug-taking behaviour and the effects of stress on a drug-seeking behaviour after withdrawal of drugs. The psychophysiological and neurochemical mechanisms of the rewarding and aversive states during a drug taking and after its withdrawal are considered. A role of separate neurotransmitters and their interactions in formation of drug dependence and the effects of stress on neuroadaptive changes in these neurotransmitter systems are described. A review of the structures involved in mediation of the stress effects and a drug-seeking behaviour is also discussed.     

Changes in the color sensitivity of operators during modelling of different forms of emotional stress

The dynamics is considered of absolute changes of differential color sensibility of operators at modelling of different psychophysiological states with the original method of the work at teletraining in combination with the complex of distracting factors. A possibility is suggested of diagnostics of operator's different psychophysiological states by absolute changes of differential color sensibility.     

A hypothetico-deductive analysis of the environmental factors involved in the current reptile distribution pattern in the Canary Islands

Aim We analyse the influence of different factors on the inter‐insular colonization processes that yielded the current distribution pattern of endemic reptile species in the Canary Islands. Location The seven main islands of the Canary Islands. Methods We tested 11 hypotheses about factors that might have affected the colonization processes. We used Mantel and partial Mantel tests to establish the statistical significance of the relationship between the islands predicted by each hypothesis, and a parsimony analysis to detect the most parsimonious hypothesis. Results The only significant relationships were those predicted by inter‐island distance, also taking area into account, and habitat similarity, considering current vegetation in the islands. The latter was the best hypothesis according to the parsimony criterion. Main conclusions Our results support the hypothesis that habitat similarity between islands is the main factor affecting the colonization processes of the whole group, although inter‐insular distance seems to play a separate role in colonization events.     

Electromyogram of pericranial muscles in frequency bands β and γ comparing various cognitive and emotional states

Results of comparison of power of electromyogram (EMG) of six pericranial muscles in electroencephalographic frequency bands β₁, β₂ and γ are presented corresponding to performances of the tasks bound to inductions of affective experiences. The external induction was implemented by means of presentation of images and the internal induction by means of autobiographical memoirs revived. The tasks were focused on an induction of affective experiences with different emotional valences—positive, negative and neutral. The EMG was derived, registered and processed by means of computer electroencephalography techniques. Self-assessments of signs and intensities of experienced emotions were recorded as well. The study involved two groups of healthy subjects—students-actors (N = 39), and students of other specialties (N = 32). Statistically reliable, reproducible and diverse differences of mean EMG power of the pericranial muscles took place in comparisons of psychophysiological states with different valences of emotions, and certain differences in comparisons of states without expressed emotional differences, but differing in the direction of attention took place also. Therefore it is obviously necessary for an assessment of a degree of muscular contamination in records of high-frequency scalp electroencephalograms (EEG) to supplement psychophysiological EEG methods with EMG registration and statistical analysis and to do such registration for several facial muscles.     

Psychophysiological mechanisms of cognition disorders and optimization of their correction: I. Psychophysiological effects of transcranial micropolarization used as a corrective therapy for different disturbances in the control of wakefulness,emotions, and cognition in schoolchildren aged 10–12 years with learning difficulties

We have summarized the results of psychophysiological studies in schoolchildren aged 10–12 years with cerebral functional disturbances of hypoxic-ischemic or traumatic origin with learning difficulties. We have differentiated three types of disintegration of ultraslow information-controlling systems that reflect specific disturbances in the interaction of cortical-brainstem, limbic-reticular, and suprasegmental mechanisms of regulation of the wakefulness level and are characterized by emotional and cognitive disturbances typical of each type of disintegration. Adolescents with moderately and strongly decreased resistance to transitory hypoxia differed in psychological and psychophysiological effects of corrective and recovery therapy, which included transcranial micropolarization (TCMP) and psychological-pedagogical sessions during and between TCMP sessions and during the intervals between repeated TCMP courses. We discuss the psychophysiological mechanisms of the corrective effect of low-intensity direct currents with parameters close to the native ultraslow processes of the brain and the body systems regulated by these parameters.     

Psychophysiological Parameters of the Functional State in Adolescents at Different Stages of Puberty under Intense Informational Loading

A study of the psychophysiological reactivity of boys aged 13–14 years during mental performance at optimal and maximum rates showed that informational loading caused marked functional strain. The physiological cost of working at a comfortable rate was lower than at the maximum rate. Excessive psychophysiological reactivity was observed at the initial stages of puberty during intense mental loading. Such reactivity was responsible for a high physiological cost of adaptation and low functional capabilities of adolescents at puberty stages (PSs) II and III. Moreover, personality traits that contribute to mental strain were expressed to a greater extent in these adolescents. Comparisons indicated a tendency towards higher emotional stability and lower anxiety and frustration for the transition from PS II to PS IV. Excessive psychophysiological reactivity during intense mental work and a high psychophysiological cost of activity in adolescents at PSs II and III may decrease working efficiency, worsen the efficiency of learning, and cause adverse deviations in the state of health. This circumstance should be taken into account during elaboration of effective prophylactic measures aimed at optimizing the functional state of schoolchildren in puberty.     

Composite structural motifs of binding sites for delineating biological functions of proteins

Most biological processes are described as a series of interactions between proteins and other molecules, and interactions are in turn described in terms of atomic structures. To annotate protein functions as sets of interaction states at atomic resolution, and thereby to better understand the relation between protein interactions and biological functions, we conducted exhaustive all-against-all atomic structure comparisons of all known binding sites for ligands including small molecules, proteins and nucleic acids, and identified recurring elementary motifs. By integrating the elementary motifs associated with each subunit, we defined composite motifs that represent context-dependent combinations of elementary motifs. It is demonstrated that function similarity can be better inferred from composite motif similarity compared to the similarity of protein sequences or of individual binding sites. By integrating the composite motifs associated with each protein function, we define meta-composite motifs each of which is regarded as a time-independent diagrammatic representation of a biological process. It is shown that meta-composite motifs provide richer annotations of biological processes than sequence clusters. The present results serve as a basis for bridging atomic structures to higher-order biological phenomena by classification and integration of binding site structures.     

Age-related changes in the psychophysiological structure of intelligence and characteristics of its formation in young schoolchildren differing in academic progress

The psychophysiological structure of the verbal and nonverbal intelligence of children differing from one another in academic progress has been studied at the initial (six to seven years of age) and the last (nine to ten years of age) stages of studying at primary school. The age-related characteristics of the development and formation of a system of cognitive functions determining the efficiency of verbal and nonverbal activities in schoolchildren differing in academic progress have been determined. It has been demonstrated that the psychophysiological structure of intelligence in six-to seven-year-old and nine-to ten-year-old schoolchildren may characterize the cognitive strategy of their activity and is a criterion for early prediction of learning difficulties and a basis for developing individually oriented approaches to teaching and effective correction programs.     

Current measures for distance decay in similarity of species composition are influenced by study extent and grain size

Aim The relationship between geographic distance and similarity in species composition is regularly used as a measure of species turnover and beta diversity. Distance–decay analyses are applied, cited and compared despite the variable extent, and different grain sizes of records (e.g. plots, islands, states) are regularly used within such analyses. Currently, differences among distance–decay relationships that cover different grain sizes and extents are attributed to ecological processes that are suspected to operate differently over varying extents and grain sizes. We assess whether the implicit assumption that the distance–decay relation is independent of grain size and study extent is valid, or whether sampling design could be the underlying cause for observed differences. Location An artificial one‐dimensional ‘landscape’. Methods The distance–decay relationship was quantified in simulated communities. Grain and study extent were varied systematically. In each sampled data set the linear relation of Simpson and Sørensen similarity to geographic distance (on both log‐transformed and original scales) between 100 even‐sized equidistant plots was assessed using linear regression and generalized linear regression with a log‐link function. Regressions were applied either including or removing zero similarities from the data. Results Both the slope (measuring turnover) and the goodness of fit measure r² (quantifying the influence of space on species composition) of the distance–decay relationship were strongly influenced by grain and study extent. Approaches that are able to cope with zero similarity values of large distance comparisons were less dependent on grain and extent. Main conclusions Reported differences between landscapes detected by current distance–decay measures cannot be explicitly traced back to ecological scale‐specific processes. Instead, they can largely be attributed to sampling design and are highly sensitive to grain size and study extent. More appropriate approaches for the study of distance–decay and the understanding of scale‐specific processes are required.     

Karyotypic evolution in Aotus

Great karyotypic diversity exists within the platyrrhine genus Aotus. Primarily by comparing banded karyograms of different forms of Aotus, the pattern of karyotypic evolution can be assessed. Out-group comparisons are used to establish primitive and derived states of particular chromosomes, and a parsimonious cladogram is constructed. Other karyotypic changes are then positioned at appropriate nodes of the cladogram. The resulting phylogenetic hypothesis is entirely self-consistent, is in accord with out-group comparisons, does not invoke hybridization between ancestral forms, and, importantly, indicates a single origin for each rearrangement of euchromatic segments. Moreover, it is consistent with the hypothesis, derived from pelage studies, that the more southerly Aotus taxa constitute a holophyletic group. The reconstructed ancestral karyotype had a diploid number of 54. There has been little loss of euchromatic material during Aotus evolution.     

Local similarity in evolutionary rates extends over whole chromosomes in human-rodent and mouse-rat comparisons: implications for understanding the mechanistic basis of the male mutation bias

The sex chromosomes and autosomes spend different times in the germ line of the two sexes. If cell division is mutagenic and if the sexes differ in number of cell divisions, then we expect that sequences on the X and Y chromosomes and autosomes should mutate at different rates. Tests of this hypothesis for several mammalian species have led to conflicting results. At the same time, recent evidence suggests that the chromosomal location of genes on autosomes affects their rate of evolution at synonymous sites. This suggests a mutagenic source different from germ cell replication. To correctly interpret the previous estimates of male mutation bias, it is crucial to understand the degree and range of this local similarity. With a carefully chosen randomization protocol, local similarity in synonymous rates of evolution can be detected in human-rodent and mouse-rat comparisons. However, the synonymous-site similarity in the mouse-rat comparison remains weak. Simulations suggest that this difference between the mouse-human and the mouse-rat comparisons is not artifactual and that there is therefore a difference between humans and rodents in the local patterns of mutation or selection on synonymous sites (conversely, we show that the previously reported absence of a local similarity in nonsynonymous rates of evolution in the human-rodent comparison was a methodological artifact). We show that linkage effects have a long-range component: not one in a million random genomes shows such levels of autosomal heterogeneity. The heterogeneity is so great that more autosomes than expected by chance have rates of synonymous evolution comparable with that of the X chromosome. As autosomal heterogeneity cannot be owing to different times spent in the germ line, this demonstrates that the dominant determiner of synonymous rates of evolution is not, as has been conjectured, the time spent in the male germ line.     

Variation in the floral fragrance of Epidendrum ciliare (Orchidaceae)

Variation in floral fragrance compounds might be a pollination strategy that disrupts associative learning processes and inhibits pollinator's ability to recognize non-rewarding flowers. Floral fragrances of the nectarless, moth-pollinated Epidendrum ciliare (Orchidaceae) were obtained from plants of Puerto Rico and the Virgin Islands. Fragrances were collected by passive diffusion on tenax adsorbent and analyzed using gas chromatography and mass spectrometry (GUMS). The analysis was performed at six different levels: 1) by flower position on the same inflorescence; 2) by flower age on the same plant; 3) by position and age of the flower in the same plant; 4) by different shoots of the same plant; 5) by flowers from different plants; 6) and by plants from different populations. At no level of analyses were fragrances of sample pairs identical. The greatest similarity among fragrances was between flowers of the same plant. The most notable differences were between flowers of different populations. High levels of floral fragrance variation were consistent with the hypothesized deception pollination syndrome, but comparisons with reward-producing flowers remain to be done.     

Vocal Learning in Songbirds and Humans: A Retrospective in Honor of Peter Marler

Peter Marler made a number of significant contributions to the field of ethology, particularly in the area of animal communication. His research on birdsong learning gave rise to a thriving subfield. An important tenet of this growing subfield is that parallels between birdsong and human speech make songbirds valuable as models in comparative and translational research, particularly in the case of vocal learning and development. Decades ago, Marler pointed out several phenomena common to the processes of vocal development in songbirds and humans—including a dependence on early acoustic experience, sensitive periods, predispositions, auditory feedback, intrinsic reinforcement, and a progression through distinct developmental stages—and he advocated for the value of comparative study in this domain. We review Marler's original comparisons between birdsong and speech ontogeny and summarize subsequent progress in research into these and other parallels. We also revisit Marler's arguments in support of the comparative study of vocal development in the context of its widely recognized value today.     

Mathematical models of eye movements in reading: a possible role for autonomous saccades

 An efficient method for the exact numerical simulation of semi-Markov processes is used to study minimal models of the control of eye movements in reading. When we read a text, typical sequences of fixations form a rather complicated trajectory – almost like a random walk. Mathematical models of eye movement control can account for this behavior using stochastic transition rules between few discrete internal states, which represent combinations of certain stages of lexical access and saccade programs. We show that experimentally observed fixation durations can be explained by residence-time-dependent transition probabilities. Stochastic processes with this property are known as semi-Markov processes. For our numerical simulations we use the minimal process method (Gillespie algorithm), which is an exact and efficient simulation algorithm for this class of stochastic processes. Within this mathematical framework, we study different forms of coupling between eye movements and shifts of covert attention in reading. Our model lends support to the existence of autonomous saccades, i.e., the hypothesis that initiations of saccades are not completely determined by lexical access processes. Received: 21 March 2000 / Accepted in revised form: 10 January 2001     

The molecular neurobiology of early learning,development, and sensitive periods,with emphasis on the avian brain

The subcellular processes that correlate with early learning and memory formation in the chick and sensitive periods for this learning are discussed. Imprinting and passive avoidance learning are followed by a number of cellular processes, each of which persists for a characteristic time in certain brain regions, and may culminate in synaptic structure modification. In the chick brain, the NMDA subtype of glutamate receptor appears to play an important role in both memory formation and sensitive periods during development, similar to its demonstrated role in neural plasticity in the mammalian brain. Two important findings have emerged from the studies using chickens. First, memory formation appears to occur at multiple sites in the forebrain and, most importantly, it appears to “flow” from one site to another, leaving neurochemical traces in each as it moves on. Second, the memory is laid down either in different sites or in different subcellular events in the left and right forebrain hemispheres. Hence, we are alerted to the possibility of similar asymmetrical processes occurring in memory consolidation in the mammalian brain. The similarities between early memory formation and experience-dependent plasticity of the brain during development are discussed.