Memory trace in prefrontal cortex: theory for the cognitive switch

The dorsolateral prefrontal cortex in human and non-human primates functions as the highest-order executor for the perception-action cycle. According to this view, when perceptual stimuli from the environment are novel or complex, the dorsolateral prefrontal cortex serves to set consciously a goal-directed scheme which broadly determines an action repertory to meet the particular demand from the environment. In this respect, the dorsolateral prefrontal cortex is a short-term activation device with the properties of a cognitive switch', because it couples a particular set of perceptual stimuli to a particular set of actions. Here, I suggest that, in order for the organism to react systematically to the environment, neural traces for the switch function must be stored in the brain. Thus, the highest-order, perception-action interface function of the dorsolateral prefrontal cortex per se depends on permanently stored neural traces in the dorsolateral prefrontal cortex and related structures. Such a memory system may be located functionally between two of the well-documented memory systems in the brain: the declarative memory system and the procedural memory system. Finally, based on available neurophysiological data, the possible mechanisms underlying the formation of cognitive switch traces are proposed.     

The problem of reinforcement. From behavioural control to neurochemical background and the development of psychopathologies

At the first part of the paper a number of conceptions about psychophysiological mechanisms of reinforcement and its role in brain system activity is presented. At the second part, a significance of the mesolimbic and mesocortical dopaminergic systems in reinforcement process and the relationships between different components of behavioural control (signal, memory, actions, etc.) and intensity of dopamine transmission at the level of n. accumbens and frontal cortex are considered. At the final part of the paper the results of development of some psychopathologies and marginal conditions, related to a low or high content of dopamine in the above-mentioned structures, and possible neurophysiological mechanisms of their formation are presented.     

The human premotor cortex is 'mirror' only for biological actions

Previous work has shown that both human adults and children attend to grasping actions performed by another person but not necessarily to those made by a mechanical device. According to recent neurophysiological data, the monkey premotor cortex contains "mirror" neurons that discharge both when the monkey performs specific manual grasping actions and when it observes another individual performing the same or similar actions. However, when a human model uses tools to perform grasping actions, the mirror neurons are not activated. A similar "mirror" system has been described in humans, but whether or not it is also tuned specifically to biological actions has never been tested. Here we show that when subjects observed manual grasping actions performed by a human model a significant neural response was elicited in the left premotor cortex. This activation was not evident for the observation of grasping actions performed by a robot model commanded by an experimenter. This result indicates for the first time that in humans the mirror system is biologically tuned. This system appears to be the neural substrate for biological preference during action coding.     

Inverted micellar structures in bilayer membranes. Formation rates and half-lives.

Two sorts of inverted micellar structures have previously been proposed to explain morphological and 31P-NMR observations of bilayer systems. These structures only form in systems with components that can adopt the inverse hexagonal (HII) phase. LIP (lipidic particles) are intrabilayer structures, whereas IMI (inverted micellar intermediates) are structures that form between apposed bilayers. Here, we calculate the formation rates and half-lives of these structures to determine which (or if either) of these proposed structures is a likely explanation of the data. Calculations for the egg phosphatidylethanolamine and the Ca+-cardiolipin systems show that IMI form orders of magnitude faster than LIP, which should form slowly, if at all. This result is probably true in general, and indicates that "lipidic particle" electron micrograph images probably represent interbilayer structures, as some have previously proposed. It is shown here that IMI are likely intermediates in the lamellar----HII phase transitions and in the process of membrane fusion in some systems. The calculated formation rates, half-lives, and vesicle-vesicle fusion rates are in agreement with this observation.     

Formation of Central Mechanisms of Regulation of Mammalian Motor Functions: Dependence on Conditions of Embryonal Development

The paper summarizes results of studying the acute hypoxia model during pregnancy in rats. A relationship has been demonstrated between changes of conditions of embryonal development and formation in postnatal ontogenesis of molecular-cellular mechanisms of brain functioning and behavior of progeny. In animals exposed to hypoxia at the prenatal 13–14th day a delay of physiological development and formation of motor reactions has been revealed, which correlates with disturbances of structures of the sensorimotor brain system. Changes of properties of brain transmitter systems and signal transduction systems in the sensorimotor cortex and striatum as well as impairment of learning capability in adult animals were shown. The detected changes in development of an organism are due to disturbance of neurogenesis of the studied brain structures during the period of action of the pathological factor. The proposed model of acute hypoxia during pregnancy might also be effective for the search for, and testing of, new neuroprotective and nootropic drugs and for elaboration of strategy for treatment of pathology of the nervous system in children and adults submitted to prenatal hypoxia, as well as for correction of disturbances of nervous system functions, which develop in the process of aging.     

The problems of evaluating the automatized and exploratory intellectual actions of man]

On the basis of psychological testing two groups of subjects have been formed: "automatizators" and "searchers". The incompatibility in the individual structure of the ability to automatized and searching actions, according to the data, are connected with the presence of the complex of alternative signs of cognitive styles. The neurophysiological organization of searching and automatized intellectual actions was studied by a method of computer toposcopy of the synchronous electrical processes. It has been shown that there are spatial-frequency interactions of electrical processes of the cerebral cortex, characteristic for each of the two above mentioned individuals groups, which are probably based on the functioning of neuronal networks with different lability levels.     

Congruent embodied representations for visually presented actions and linguistic phrases describing actions

The thesis of embodied semantics holds that conceptual representations accessed during linguistic processing are, in part, equivalent to the sensory-motor representations required for the enactment of the concepts described . Here, using fMRI, we tested the hypothesis that areas in human premotor cortex that respond both to the execution and observation of actions-mirror neuron areas -are key neural structures in these processes. Participants observed actions and read phrases relating to foot, hand, or mouth actions. In the premotor cortex of the left hemisphere, a clear congruence was found between effector-specific activations of visually presented actions and of actions described by literal phrases. These results suggest a key role of mirror neuron areas in the re-enactment of sensory-motor representations during conceptual processing of actions invoked by linguistic stimuli.     

The perception of inferred action

Our actions, and those of others, are often partly obscured from view. This complicates the sensory inputs that guide motor actions. In this issue of Neuron, Umilità and colleagues demonstrate that "mirror neurons" in ventral premotor cortex respond when monkeys observe hidden, but inferred, actions.     

A national fish passage barrier inventory to support fish passage policy implementation and estimate river connectivity in New Zealand

Fragmentation of river systems is a key driver of freshwater biodiversity loss. Instream structure inventories are an essential component of delivering a strategic approach to restoring river connectivity. We used a range of data sources to collate the best available information on fish passage barriers and instream structures across the whole of New Zealand. To support implementation of new national policy objectives to maintain and improve river connectivity, the structure inventory has been integrated with a new fish passage assessment mobile application that allows river managers and asset owners to ground-truth, update and add records to the database. The data are provided open access and are being used for environmental reporting and to support strategic prioritisation of barrier mitigation actions. We used these data to quantify river connectivity at regional and national scales and demonstrated that at least half of New Zealand's river network is upstream of fish migration barriers. Limitations to our calculation of upstream river connectivity included the unknown influence of unrecorded structures, particularly on private land, missing information within recorded data, the large number of instream structures that have been identified but not yet assessed for their risk to fish passage, and spatial errors in the automated pairing of structures to a digital river network. A critical challenge for river managers is understanding the consequences of these uncertainties in the data for prioritisation and decision-making regarding barrier removal or mitigation.     

The associative parietal cortex and spatial processing in rodents

It is widely acknowledged that the hippocampal formation has a central function in rodents' spatial memory and navigation. However, recent work has shown that other structures participate in specific spatial processing. That is so for the associative parietal cortex (APC). Although this neocortical region is far less developed in rodents than in humans and non-human primates, APC damage in rodents induces deficits which affect both egocentrically and allocentrically organized spatial behaviours. On the basis of behavioural (following parietal lesions) and neuroanatomical data, we propose that the APC could be at the interface between the level of perception of the physical world (egocentrically organized) and that of representations or maps (allocentrically organized) of this world. Reciprocally, the APC could also be involved in the transformation, in the opposite direction, of computations made on the basis of representations into motor actions necessary for the efficient execution of oriented behaviours within the physical world.     

Maternal effect mutations of the sponge locus affect actin cytoskeletal rearrangements in Drosophila melanogaster embryos

In the syncytial blastoderm stage of Drosophila embryogenesis, dome-shaped actin "caps" are observed above the interphase nuclei. During mitosis, this actin rearranges to participate in the formation of pseudocleavage furrows, transient membranous invaginations between dividing nuclei. Embryos laid by homozygous sponge mothers lack these characteristic actin structures, but retain other actin associated structures and processes. Our results indicate that the sponge product is specifically required for the formation of actin caps and metaphase furrows. The specificity of the sponge phenotype permits dissection of both the process of actin cap formation and the functions of actin caps and metaphase furrows. Our data demonstrate that the distribution of actin binding protein 13D2 is unaffected in sponge embryos and suggest that 13D2 is upstream of actin in cortical cap assembly. Although actin caps and metaphase furrows have been implicated in maintaining the fidelity of nuclear division and the positions of nuclei within the cortex, our observations indicate that these structures are dispensible during the early syncytial blastoderm cell cycles. A later requirement for actin metaphase furrows in preventing the nucleation of mitotic spindles between inappropriate centrosomes is observed. Furthermore, the formation of actin caps and metaphase furrows is not a prerequisite for the formation of the hexagonal array of actin instrumental in the conversion of the syncytial embryo into a cellular blastoderm.     

Effects of sialoadenectomy and castration in female rats

Previous work on the role of the submaxillary glands in the control of the oestrous cycle in rats has been extended to castrated rats in order to avoid the overlapping between sexual and salivary hormones. Animals were sacrificed 30 days after sialadectomy or pseudosialadectomy. The data show that simultaneous castration and sialadectomy increases significantly the glucaemia level and decreases the weight of the adrenal glands. Non-simultaneous castration and removal of the submaxillary glands decreases the weight of the parotid glands. This effect decreases when both actions are simultaneous. On the other hand, castration produces an important decrease in QO2 uptake in tested structures. Removal of submaxillary glands produces a significant increase of QO2 in hypothalamus and thyroid glands. Simultaneous castration and sialadectomy at the anterior cortex, posterior cortex and parotid gland level shows similar results with respect to desalivated rats; other structures show results similar to the castrated group values. From these results, the role played by submaxillary glands in the control of the sexual cycle of the rat and the possible relation to other structures is discussed.     

Analysis of the level of cyclic adenosine-3',5'-monophosphate in structures of the 'informational' and 'motivational' system of the rat brain during active conditioning

The content of cyclic adenosine-3',5'-monophosphate (cAMP) was studied in structures of the "motivational" and "infromational" systems of rat brain after the active avoidance conditioning procedure in rats. Three groups of animals were examined: naive rats, trained (conditioned) rats, and group of the active control presented with uncombined conditioned (light) and unconditioned (electric footshock) stimuli. The content of cAMP was determined in the frontal cortex, hippocampus, amygdala, and hypothalamus of both hemispheres immediately after the retrieval of conditioned reaction one day after conditioning. A significant increase in cAMP level was bilaterally observed in the hypothalamus in the group of active control, and in both hippocampi and the right frontal cortex in the conditioned animals. Positive correlations between the cAMP levels in symmetrical regions of the frontal cortex, amygdala, and hypothalamus were revealed in all the examined groups. Additionally, intra- and interhemispheric correlations were found in the active control and conditioned rats. Patterns of correlation were specific for each of these groups. The observed phenomenon is discussed in term of involvement of "informational" and "motivational" brain structures in the mechanisms of adaptive behavior.     

The typological characteristics of higher nervous activity in dogs and the maxima of the cross-correlation function between the electrical activities of the frontal cortex and the brain limbic systems]

Electrical activity of the frontal cortex, dorsal hippocampus, basolateral amygdala and lateral hypothalamus was recorded in eight dogs with chronically implanted electrodes. Mean values of the maxima of crosscorrelation function (MCCF) between electrical potentials in the theta, alpha and beta-2 ranges were used as a basis for assessment of conditions for interaction between these structures. Typological features of the higher nervous activity were assessed by the animal performance under conditions of free choice of the reinforcement mode of a conditioned stimulus: either high probable but of low alimentary quality or with low probability but more valuable. The mean MCCF values in the theta range were higher than in the other ranges. The brain structure which had the high MCCF in the theta-range, at least, with two of the structures under study was considered as "dominant". It was shown that hippocampus was the dominant structure for melancholic dogs, the frontal cortex was in phlegmatics. The hypothalamus was shown to be the "dominant structure" in both sanguine and choleric animals, but, for the most part, its activity was correlated with different structures. Thus, conditions for interaction between the frontal cortex, hippocampus, amygdala and hypothalamus seem to be an important factor, which determines typological features of the higher nervous activity of dogs.     

Peculiarities of Formation of the Wakefulness—Sleep Cycle in Ontogenesis of Rats

Electrophysiological changes in the wakefulness—sleep cycle were studied in early postnatal ontogenesis of rat pups. EEG was recorded and its spectral power was determined, as well as spatial-temporal synchronization between the brain cortex zones (visual and sensomotor) and hippocampus in the process of sleep at various periods of ontogenesis. These data were compared with the literature data on studying of cytoarchitectonics and ultrastructure of rat neocortex as well as on formation of neuronal activity and maturation of transmitter systems at the same periods. Based on time of formation of interneuronal and interstructural connections and of maturation of transmitter systems, 3 stages of functional development of sleep in ontogenesis were identified: the first stage—undifferentiated sleep, the interneuronal connections are absent; the second stage—partially differentiated sleep, interneuronal connections function and control from subcortical structures appears; the third stage—differentiated sleep, clear division into sleep phase, additional control from all three transmitter systems: noradrenergic, cholinergic, and serotoninergic, action of the latter providing inhibitory mechanisms in CNS.__________Translated from Zhurnal Evolyutsionnoi Biokhimii i Fiziologii, Vol. 41, No. 2, 2005, pp. 154–159.Original Russian Text Copyright © 2005 by Titkov, Aristakesyan, Oganesyan.     

Neuronal Circuits with Whisker-Related Patterns

Neuronal circuits with whisker-related patterns, such as those observed in the rodent somatosensory barrel cortex, have been widely used as a model system for investigating the anatomical organization, development and physiological roles of functional neuronal circuits. Whisker-related patterns exist not only in the barrel cortex but also in subcortical structures along the trigeminal neuraxis from the brainstem to the cortex. Here, we briefly summarize the organization, formation, and function of each neuronal circuit with whisker-related patterns, including the novel axonal trajectories that we recently found with the aid of in utero electroporation. We also discuss their biological implications as model systems for the studies of functional neuronal circuits.     

Volition and conflict in human medial frontal cortex

Controversy surrounds the role of human medial frontal cortex in controlling actions. Although damage to this area leads to severe difficulties in spontaneously initiating actions, the precise mechanisms underlying such "volitional" deficits remain to be established. Previous studies have implicated the medial frontal cortex in conflict monitoring and the control of voluntary action, suggesting that these key processes are functionally related or share neural substrates. Here, we combine a novel behavioral paradigm with functional imaging of the oculomotor system to reveal, for the first time, a functional subdivision of the pre-supplementary motor area (pre-SMA) into anatomically distinct areas that respond exclusively to either volition or conflict. We also demonstrate that activity in the supplementary eye field (SEF) distinguishes between success and failure in changing voluntary action plans during conflict, suggesting a role for the SEF in implementing the resolution of conflicting actions. We propose a functional architecture of human medial frontal cortex that incorporates the generation of action plans and the resolution of conflict.     

The brain mechanism of error detection: the P.E.T. study

In present research, the brain maintenance of the error detection mechanism was studied in resting condition and while subjects consciously implemented incorrect actions (i.e. deception). Assessment of the regional cerebral blood flow revealed involvement of anterior cingulated cortex in deception. The obtained data indicate that it is impossible to consciously control the activity of the error detection mechanism. PET study of patients with obsessive compulsive disorder in resting condition revealed a decrease of brain glucose metabolism in the anterior cingulated cortex in comparison with healthy subjects. These data pointed to malfunctioning of the error detection mechanism. The findings support the formerly proposed hypothesis about the impact of the error detection mechanism in formation and support of obsessive compulsive disorder.     

Evidence for a higher glycolytic than oxidative metabolic activity in white matter of rat brain

Different values exist for glucose metabolism in white matter; it appears higher when measured as accumulation of 2-deoxyglucose than when measured as formation of glutamate from isotopically labeled glucose, possibly because the two methods reflect glycolytic and tricarboxylic acid (TCA) cycle activities, respectively. We compared glycolytic and TCA cycle activity in rat white structures (corpus callosum, fimbria, and optic nerve) to activities in parietal cortex, which has a tight glycolytic-oxidative coupling. White structures had an uptake of [(3)H]2-deoxyglucose in vivo and activities of hexokinase, glucose-6-phosphate isomerase, and lactate dehydrogenase that were 40-50% of values in parietal cortex. In contrast, formation of aspartate from [U-(14)C]glucose in awake rats (which reflects the passage of (14)C through the whole TCA cycle) and activities of pyruvate dehydrogenase, citrate synthase, alpha-ketoglutarate dehydrogenase, and fumarase in white structures were 10-23% of cortical values, optic nerve showing the lowest values. The data suggest a higher glycolytic than oxidative metabolism in white matter, possibly leading to surplus formation of pyruvate or lactate. Phosphoglucomutase activity, which interconverts glucose-6-phosphate and glucose-1-phosphate, was similar in white structures and parietal cortex ( approximately 3 nmol/mg tissue/min), in spite of the lower glucose uptake in the former, suggesting that a larger fraction of glucose is converted into glucose-1-phosphate in white than in gray matter. However, the white matter glycogen synthase level was only 20-40% of that in cortex, suggesting that not all glucose-1-phosphate is destined for glycogen formation.     

Learning of animals during adaptation to altitude and its relations with serotonin metabolism in the brain

The influence of high altitude (3 200 m) on learning was studied on 104 non-linear male rats weighing 120 to 140 g, along with biochemical analysis of serotonin content (5-HT) and noradrenaline (NA) in brain structures. A drastic deterioration in the animals' learning has been established in conditions of high altitude, both with alimentary and pain reinforcement attended with a considerable suppression of the 5-HT and NA brain systems activity. Systematic administration of 5-HTP resulting in an enhanced serotonin level in the cortex and the caudal part of the brainstem, improved the learning process, regardless of the emotional sign of the reinforcing stimulus. The prospect, is being substantiated, of evolving methods preventing pathological implications of external influences of high altitudes on the organism by means of pharmacological actions on monoamines' metabolism.