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Is imitation learning the route to humanoid robots?

This review investigates two recent developments in artificial intelligence and neural computation: learning from imitation and the development of humanoid robots. It is postulated that the study of imitation learning offers a promising route to gain new insights into mechanisms of perceptual motor control that could ultimately lead to the creation of autonomous humanoid robots. Imitation learning focuses on three important issues: efficient motor learning, the connection between action and perception, and modular motor control in the form of movement primitives. It is reviewed here how research on representations of, and functional connections between, action and perception have contributed to our understanding of motor acts of other beings. The recent discovery that some areas in the primate brain are active during both movement perception and execution has provided a hypothetical neural basis of imitation. Computational approaches to imitation learning are also described, initially from the perspective of traditional AI and robotics, but also from the perspective of neural network models and statistical-learning research. Parallels and differences between biological and computational approaches to imitation are highlighted and an overview of current projects that actually employ imitation learning for humanoid robots is given.

Journal Article↗

[Long-term changes in the physiologic and biochemical status of the body through immunization with endogenous regulators].

Immunization with protein and oligopeptide, and low-molecular weight nonpeptide compounds demonstrated a possibility for selective decrease in the level (activity) of several endogenous compounds, and consequently, for a significant prolonged changes is physiological functions connected with these compounds. The method opens possibilities for directed regulation of physiological status of organism, correction of pathological changes, and creation of relatively stable functional systems with new properties.

Animals↗

Neurophysiological architecture of functional magnetic resonance images of human brain.

We investigated large-scale systems organization of the whole human brain using functional magnetic resonance imaging (fMRI) data acquired from healthy volunteers in a no-task or 'resting' state. Images were parcellated using a prior anatomical template, yielding regional mean time series for each of 90 regions (major cortical gyri and subcortical nuclei) in each subject. Significant pairwise functional connections, defined by the group mean inter-regional partial correlation matrix, were mostly either local and intrahemispheric or symmetrically interhemispheric. Low-frequency components in the time series subtended stronger inter-regional correlations than high-frequency components. Intrahemispheric connectivity was generally related to anatomical distance by an inverse square law; many symmetrical interhemispheric connections were stronger than predicted by the anatomical distance between bilaterally homologous regions. Strong interhemispheric connectivity was notably absent in data acquired from a single patient, minimally conscious following a brainstem lesion. Multivariate analysis by hierarchical clustering and multidimensional scaling consistently defined six major systems in healthy volunteers-- corresponding approximately to four neocortical lobes, medial temporal lobe and subcortical nuclei- - that could be further decomposed into anatomically and functionally plausible subsystems, e.g. dorsal and ventral divisions of occipital cortex. An undirected graph derived by thresholding the healthy group mean partial correlation matrix demonstrated local clustering or cliquishness of connectivity and short mean path length compatible with prior data on small world characteristics of non-human cortical anatomy. Functional MRI demonstrates a neurophysiological architecture of the normal human brain that is anatomically sensible, strongly symmetrical, disrupted by acute brain injury, subtended predominantly by low frequencies and consistent with a small world network topology.

Adult↗

[State of the urea-producing function of the liver in gamma-irradiated rats].

The investigations of some metabolites and enzymes of ornithine cycle in irradiated rats were performed. It was shown that ionizing radiation furthered the intensification of liver ammonium-connecting function. It took place without visible enzyme activation during the first period of defeat. It was shown also the increasing of enzyme activity at the top of pathological process development. The definite dose-dependence was observed in this period. The month after irradiation the liver function wasn't normal.

Animals↗

A HRP qualitative and quantitative study of the intra-hemispheric connections of kittens.

In post-natal kittens which were given injections of HRP in the suprasylvian gyrus (polysensory cortex), the cortico-cortical connections were studied qualitatively and quantitatively. These connections originate essentially from cortical cells localized in cortices of the upper part of the hemisphere. They are formed preferentially with cortices involved in the visual function. Connections between the cingulate, prefrontal and area 19 cortices, have been described here. Layers III and V are quantitatively the most highly involved in these connections. The number of connections is related to axon length: the connections are more numerous the shorter the neuron axons, and thus the nearer they lie to the cortex injected. The HRP+ cells appear first in the cell layers which will subsequently be most marked quantitatively. The cortico-cortical connections appear in the following order: connections of medium length, then short, then long. The system of cortico-cortical connections of the injected cortex forms chronologically during the first 3 weeks following birth in the following order: 1st week: Connections of primary nuclei to primary cortex, 2nd week: Connections of non-primary cortex to non-primary cortex, 3rd week: Connections of primary cortex to non-primary cortex.

Animals↗

Effects of parabrachial stimulation on angiotensin and blood pressure sensitive area postrema neurons.

Subpopulations of neurons in the area postrema (AP) and commissural nucleus tractus solitarius (NTS) have been identified according to their responses to systemic angiotensin-II (ANG-II) and increases in blood pressure (BP). In order to further define the functional connections of these subpopulations of cells, electrophysiological single unit recording studies have been done to determine the orthodromic effects of parabrachial nucleus (PBN) stimulation on these functionally defined cell groups. Orthodromic effects were seen in a similar proportion of ANG-II sensitive neurons in the AP (31.5%) and NTS (31%). PBN stimulation influenced a similar percentage of BP sensitive neurons in the AP (35%), although a larger proportion of this group of NTS cells was affected (55.5%). Twenty-five percent of ANG-II/BP sensitive neurons in the AP were orthodromically influenced, and 71.5% of this group of NTS neurons were affected by PBN stimulation. Small proportions of the neurons in the unaffected subpopulation of AP (10%) and NTS (27%) were also orthodromically affected by PBN stimulation. The remaining neurons in each group were not affected. This study suggests that there is no apparent preferential distribution of excitatory or inhibitory PBN efferents to any of the identified subpopulations of AP and NTS neurons.

Angiotensin II↗

A prominent role for amygdaloid complexes in the Variability in Heart Rate (VHR) during Rapid Eye Movement (REM) sleep relative to wakefulness.

Rapid eye movement sleep (REMS) is associated with intense neuronal activity, rapid eye movements, muscular atonia and dreaming. Another important feature in REMS is the instability in autonomic, especially in cardiovascular regulation. The neural mechanisms underpinning the variability in heart rate (VHR) during REMS are not known in detail, especially in humans. During wakefulness, the right insula has frequently been reported as involved in cardiovascular regulation but this might not be the case during REMS. We aimed at characterizing the neural correlates of VHR during REMS as compared to wakefulness and to slow wave sleep (SWS), the other main component of human sleep, in normal young adults, based on the statistical analysis of a set of H(2)(15)O positron emission tomography (PET) sleep data acquired during SWS, REMS and wakefulness. The results showed that VHR correlated more tightly during REMS than during wakefulness with the rCBF in the right amygdaloid complex. Moreover, we assessed whether functional relationships between amygdala and any brain area changed depending the state of vigilance. Only the activity within in the insula was found to covary with the amygdala, significantly more tightly during wakefulness than during REMS in relation to the VHR. The functional connectivity between the amygdala and the insular cortex, two brain areas involved in cardiovascular regulation, differs significantly in REMS as compared to wakefulness. This suggests a functional reorganization of central cardiovascular regulation during REMS.

Adult↗

Specificity of novel allosterically trans- and cis-activated connected maxizymes that are designed to suppress BCR-ABL expression.

Chronic myelogenous leukemia (CML) is associated with the presence of the Philadelphia chromosome, which is generated by the reciprocal translocation of chromosomes 9 and 22. In the case of L6 (b2a2) mRNA, it is difficult to cleave the abnormal mRNA specifically because the mRNA includes no sequences that can be cleaved efficiently by conventional hammerhead ribozymes near the BCR-ABL junction. We recently succeeded in designing a novel maxizyme, which specifically cleaves BCR-ABL fusion mRNA, as a result of the formation of a dimeric structure. As an extension of our molecular engineering of maxizymes, as well as to improve their potential utility, we examined whether an analogous conformational change could be induced within a single molecule when two maxizymes were connected via a linker sequence. An active conformation was achieved by binding of the construct to the BCR-ABL junction in trans, with part of the linker sequence then acting as an antisense modulator in cis (within the complex) to adjust the overall structure. Results of studies in vitro in the presence of cetyltrimethylammonium bromide (CTAB) (but not in its absence) suggested that a certain kind of connected maxizyme (cMzB) might be able to undergo a desired conformational change and, indeed, studies in vivo confirmed this prediction. Therefore, we successfully created a fully functional, connected maxizyme and, moreover, we found that the activity and specificity of catalytic RNAs in vivo might be better estimated if their reactions are monitored in vitro in the presence of CTAB.

Allosteric Regulation↗

[Micropolarization of the brain: a noninvasive method for correction of morphological and functional disturbances in acute focal brain lesions and their consequences].

The paper is devoted to the use of small direct current in correction of morphological and functional disturbances of the human brain. Two hundred and one patients aged from 7 to 82 years have been studied. In patients with focal brain damages at the acute stage (1-2 days after stroke), the anode and cathode were placed in the projection of a damaged center. In patients in "autonomic status" condition, the anode was placed both in frontal and parietal projection of the right hemisphere cortex and the cathode--on a mastoid of the right hemisphere. Strength of the current used was 300-500 mcA, time of one procedure--30-40 min. The whole treatment course involved no more than 15 procedures. Before the treatment, after 3-5 procedures of micropolarization and at the end of the treatment course, patients underwent computer tomography and electroencephalographic study. Transcranial micropolarization exerts a cerebroprotective effect and has a selective-systemic character due to an increase of neuronal structures activity boht directly in the area of the impact that manifests with the absence of brain edema and the reduction of the destruction locus by 10-15% just after three procedures and as in the other brain regions that results in the decrease of intensity of general cerebral symptoms. The micropolarization promotes restoration of the broken functional connections in central regulatory systems caused by improvement of interaction between neurons, structures and systems the results finally in restoration of central regulation of body's functions.

Adult↗

[Effect of arousing and somnogenic effects on the hypothalamus on the space-time organization of the internal connections of the somatosensory cortex].

Evoked potentials arising in the somatosensory cortex in response to single local stimulation of a forepaw, were recorded in cats in a state of slow-wave sleep and strained alertness elicited by electric activation of the basal preoptic area and posterior hypothalamus. Structure of connections between cortical points was studied by values of responses' amplitudes by means of correlation and factor analyses. It has been found that the organization of functional connections within the somatosensory cortex is determined by several factors, sensitive to hypothalamic influences. The most specific organization for each state is revealed at the stage of completion of the positive-negative complex of the primary response, which combines with the highest plasticity of connection formation.

Animals↗

[Outflow pathways of venous blood from the myocardium in the dog and structures participating in their regulation].

The intramural pathways of the venous blood outflow from the cardiac wall have been studied histologically, histochemically and micrometrically in 20 control and 84 experimental dogs with an artificially produced circulatory disturbances, peculiar for congenital heart disease (open arterial canal, coarctation of the aorta and stenosis of the pulmonary trunk). The experimental animals have been observed for 6-12 months. In the venous line of the coronary basin several morphologically differed parts, anatomically and functionally connected between themselves and ensuring blood outflow from the myocardium, are distinguished: coronary sinus, subepicardial veins, paired sinusoid veins, myocardial sinusoids and endocardial cushions. In each of them there are their own adaptive structures, participating in regulation of the venous blood stream. In the cardial sinus, in the subepicardial and paired sinusoid veins--these are valves of various complexity. In the myocardial sinusoids, the regulatory function, together with the valves, are performed by the intimal and muscle cushions, connective tissue and muscle bridges. In the endocardial cushions they are realized by the valves, muscle sphincters, bundles of obliquely and longitudinally oriented leiomyocytes. All the adaptive structures mentioned are also found in the hearts of the control animals. Under modelling various hemodynamic disturbances, the degree of their development increases sharply. The latter ensures the maintenance of an optimal regimen of blood circulation in the myocardium of a functionally loaded heart and prevents development of decompensation in the organ.

Adaptation, Physiological↗

Experience-dependent mechanism of binocular map plasticity in Xenopus: incongruent connections are masked by retinal input.

When one eye in larval Xenopus is rotated to change the orientation of its visual map on the contralateral tectum, the map from the other eye to the same tectum can subsequently alter its orientation to match the rotated input. This plasticity re-establishes binocular congruence between the two maps and involves an experience-dependent reorganization of functional connections in the crossed isthmotectal projection, which delivers the ipsilateral eye's map to the tectum. Here, recordings were made at the same tectal sites in 8 eye-rotated frogs immediately before and after removing the rotated retina. All had congruent binocular maps prior to enucleation, with matching receptive fields in the two eyes at each recording site. In 5 frogs, eye removal unmasked additional, incongruent receptive fields in the ipsilateral eye, recorded from previously undetectable crossed isthmotectal connections occupying their original positions in the tectum. This result suggests that the plasticity also involves functional suppression of binocularly-incongruent inputs from the ipsilateral eye by retinotectal afferents.

Animals↗

The concept of chemical neurotransmission--variations on the theme.

The present concept of chemical neurotransmission occurring purely through synaptic transmission has dominated neurobiological thinking for about the last 40 years. According to this conventional view neurotransmitters are substances that are synthesized within the neurones, liberated into the synaptic cleft after stimulation of the nerve, and that finally elicit a biologically plausible response in the postsynaptic target cell or the nerve terminal itself. This concept undoubtedly comprises the main body of interneuronal chemical signalling. However, a large amount of evidence, obtained during the last two decades, suggests that there are a number of parallel mechanisms, which may essentially participate in neuronal signalling, or at least modulate it. Thus, the recent progress of research has provided the following compelling evidence: 1) a large variety of substances, some of them synthesized in non-neuronal cells, actually participate actively in neuronal signalling; 2) functional connections in brain are not determined by the synaptic connections only; 3) glial cells have an active and fundamental role in signal transmission; and 4) the signalling properties and mechanisms of each neurone are constantly under functional and structural regulation. The aim of this review is to present shortly some of the central concepts and/or mechanisms that have risen during the last two decades. Also the functional and/or clinical relevance of these mechanisms is addressed briefly.

Animals↗

Recombinant expression of N-terminal truncated mutants of the membrane bound mouse, rat and human flavoenzyme dihydroorotate dehydrogenase. A versatile tool to rate inhibitor effects?

Mammalian dihydroorotate dehydrogenase, the fourth enzyme of pyrimidine de novo synthesis is an integral protein of the inner mitochondrial membrane that faces the intermembrane space and is functionally connected to the respiratory chain via ubiquinone. Here, we describe the first cloning and analyzing of the complete cDNA of mouse dihydroorotate dehydrogenase. Based on our recent functional expression of the full-length rat and human dihydroorotate dehydrogenase, here we expressed N-terminal-truncated C-terminal-histidine-tagged constructs of the mouse, rat and human enzymes in Escherichia coli. These proteins were devoid of the N-terminal bipartite sequence consisting of the mitochondrial targeting sequence and adjacent hydrophobic domain necessary for import and proper location and fixation of the enzyme in the inner mitochondrial membrane. By employing metal-chelate affinity chromatography under native conditions, the enzymes were purified without detergents to a specific activity of more than 100 micromol x min(-1) x mg(-1) at pH optimum of 8.0--8.1. Flavin analyses by UV-visible spectrometry of the native enzymes gave fairly stoichiometric ratios of 0.6--1.2 mol flavin per mol protein. The kinetic constants of the truncated rat enzyme (K(m) = 11 microM dihydroorotate; K(m) = 7 microM ubiquinone) and human enzyme (K(m) = 10 microM dihydroorotate; K(m) = 14 microM ubiquinone) were very close to those recently reported for the full-size enzymes. The constants for the mouse enzyme, K(m) = 26 microM dihydroorotate and K(m) = 62 microM ubiquinone, were slightly elevated in comparison to those of the other species. The three truncated enzymes were tested for their efficacy with five inhibitors of topical clinical relevance against autoimmune disorders and tumors. Whereas the presence of the N-terminus of dihydroorotate dehydrogenase was essentially irrelevant for the efficacy of the malononitrilamides A77-1726, MNA715 and MNA279 with the rat and human enzyme, the N-termini were found to be important for the efficacy of the dianisidine derivative redoxal. Moreover, the complete N-terminal part of the human enzyme seemed to be of crucial importance for the 'slow-binding' features of the cinchoninic acid derivative brequinar, which was suggested to be one of the reasons for the narrow therapeutic window reported from clinical trials on its anti-proliferative and immunosuppressive action.

Amino Acid Sequence↗

Trigeminal transition zone/rostral ventromedial medulla connections and facilitation of orofacial hyperalgesia after masseter inflammation in rats.

Recent studies have implicated a role for the trigeminal interpolaris/caudalis (Vi/Vc) transition zone in response to orofacial injury. Using combined neuronal tracing and Fos protein immunocytochemistry, we investigated functional connections between the Vi/Vc transition zone and rostral ventromedial medulla (RVM), a key structure in descending pain modulation. Rats were injected with a retrograde tracer, FluoroGold, into the RVM 7 days before injection of an inflammatory agent, complete Freund's adjuvant, into the masseter muscle and perfused at 2 hours postinflammation. A population of neurons in the ventral Vi/Vc overlapping with caudal ventrolateral medulla, and lamina V of the trigeminal subnucleus caudalis (Vc), exhibited FluoroGold/Fos double staining, suggesting the activation of the trigeminal-RVM pathway after inflammation. No double-labeled neurons were found in the dorsal Vi/Vc and laminae I-IV of Vc. Injection of an anterograde tracer, Phaseolus vulgaris leucoagglutinin, into the RVM resulted in labeling profiles overlapped with the region that showed FluoroGold/Fos double labeling, suggesting reciprocal connections between RVM and Vi/Vc. Lesions of Vc with a soma-selective neurotoxin, ibotenic acid, significantly reduced inflammation-induced Fos expression as well as the number of FluoroGold/Fos double-labeled neurons in the ventral Vi/Vc (P<0.05). Compared with control rats, lesions of the RVM (n=6) or Vi/Vc (n=6) with ibotenic acid led to the elimination or attenuation of masseter hyperalgesia/allodynia developed after masseter inflammation (P<0.05-0.01). The present study demonstrates reciprocal connections between the ventral Vi/Vc transition zone and RVM. The Vi/Vc-RVM pathway is activated after orofacial deep tissue injury and plays a critical role in facilitating orofacial hyperalgesia.

Animals↗

Insights into the pathophysiology of neuropathic pain through functional brain imaging.

We present here an example case of neuropathic pain with heat allodynia as a major symptom to illustrate how the functional imaging of pain may provide new insights into the pathophysiology of painful sensory disorders. Tissue injury of almost any kind, but especially peripheral or central neural tissue injury, can lead to long-lasting spinal and supraspinal re-organization that includes the forebrain. These forebrain changes may be adaptive and facilitate functional recovery, or they may be maladaptive, preventing or prolonging the painful condition, and interfering with treatment. In an experimental model of heat allodynia, we used functional brain imaging to show that: (1) the forebrain activity during heat allodynia is different from that during normal heat pain, and (2) during heat allodynia, specific cortical areas, specifically the dorsolateral prefrontal cortex, can attenuate specific components of the pain experience, such as affect, by reducing the functional connectivity of subcortical pathways. The forebrain of patients with chronic neuropathic pain may undergo pathologically induced changes that can impair the clinical response to all forms of treatment. Functional imaging, including PET, fMRI, and neurophysiological techniques, should help identify brain mechanisms that are critical targets for more effective and more specific treatments for chronic, neuropathic pain.

Adult↗

Behavioral and functional MRI study of attention shift in human verbal working memory.

The tripartite model of memory proposed the requirement of attentional switching when accessing different items in working memory [J. Exp. Psychol. Learn. Mem. Cogn. 27 (2001) 817]. This internal focus of attention is limited to just one item and the switching process is time-consuming [Mem. Cogn. 26 (1998) 263]. In the current study, given a three-digit list stored in working memory, we found that it took longer to shift attention in the direction of "Upstream" than "Downstream", and that each shift was a "single step" process. To investigate the neural basis of this type of attention switching, we performed a functional MRI study. The results revealed that at least three important brain areas are involved, including the left dorsal lateral prefrontal cortex, the cingulate gyrus, and the medial occipital cortex. These areas all showed greater activation in the attention shift condition compared to control conditions of no (or decreased) attention shift requirements. In addition, the hemodynamic activities in these areas are highly correlated, suggesting a strong functional connectivity between them. Taken together with evidence from several recent investigations, our results suggest that these areas each play an important and specific role in collaboratively supporting the function of attention shift in working memory.

Adolescent↗

Environment matters: synaptic properties of neurons born in the epileptic adult brain develop to reduce excitability.

Neural progenitors in the adult dentate gyrus continuously produce new functional granule cells. Here we used whole-cell patch-clamp recordings to explore whether a pathological environment influences synaptic properties of new granule cells labeled with a GFP-retroviral vector. Rats were exposed to a physiological stimulus, i.e., running, or a brain insult, i.e., status epilepticus, which gave rise to neuronal death, inflammation, and chronic seizures. Granule cells formed after these stimuli exhibited similar intrinsic membrane properties. However, the new neurons born into the pathological environment differed with respect to synaptic drive and short-term plasticity of both excitatory and inhibitory afferents. The new granule cells formed in the epileptic brain exhibited functional connectivity consistent with reduced excitability. We demonstrate a high degree of plasticity in synaptic inputs to adult-born new neurons, which could act to mitigate pathological brain function.

Animals↗