Intracortical Directed Connectivity for Information Retention in Visual-Spatial Working Memory.

A group of 27 healthy young adults solved a task involving the working memory (WM) activation, consisting of the comparison between the spatial orientations of two sequentially presented square-wave luminance gratings. We investigated the effective (directed) connectivity patterns between the frontal and postcentral cortical regions related to the visual system. The connectivity was assessed using vector autoregression modeling of EEG. It was shown that the strength of the top-down right-hemispheric connectivity patterns directed from the frontal cortex to the visual areas in θ frequency was significantly lower at the stage of stimulus retention in the WM than at the stage of stimulus anticipation. On the contrary, in the α band the descending influences were slightly more intense. The results of the study showed the frequency-dependent dynamics of the descending influences of the frontal cortex on visual areas and confirm that the frontal cortex plays the role of a controlling and modulating center in the brain system underlying WM.

Working Memory for Low-Level Visual Features: Sensory Mechanisms for Detecting the Mismatch between the Current Orientations and Those Stored in Memory.

The amplitudes of the P100 and N150 early components of evoked potentials in the visual cortex have been analyzed on 33 volunteers with normal vision during matching between the current orientation and that stored in memory. An increase in the P100 response in the occipital and parietal cortical areas was identified as an informative indicator of mismatch between the current and stored-in-memory orientations. This effect was not found for more complex stimuli, namely, spatial patterns. The N150 component demonstrated a similar effect, but in contrast to P100 it was not stimulus specific. Thus, in the first 100 ms, a signal of mismatch between the current and stored-in-memory orientations arises in the early visual areas that represents a mechanism for early implicit response to changes in the basic characteristics of the visual space.

[The Mechanisms of Orientation Sensitivity of Human Vision System. Part II: Neural Patterns of Early Processing of Information about Line Orientation].

The high density EEG was registered in 41 healthy subjects (20 males, 21 females) in the cardinal (horizontal and vertical) and oblique (45 and 135 deg) line orientation identification task. The analysis of the adaptive amplitude maximum (4 ms averaging) of P1 and N1 evoked potentials in the symmetrical occipital, parietal and inferior temporal areas and dipole source modelling showed the anisotropy of cortical responses in the 80-150 ms interval. The amplitude is higher on the oblique orientations as comparison with cardinal ones. The temporal and regional features of cortical answers were discovered. The earlier selective response (~90 ms latency) is registered.in the parietal areas, while the later (~145 ms latency) is found in the occipital ones. We discovered a number of sex-related differences in the early stages of line orientation detection. In males, the amplitude of components is higher; they have broader area of localisation of their dipole sources: in addition to the occipital and parietal regions, cortex of the temporal regions is involved. Theobtained data are discussed in the context of the idea of effective neural coding (Barlow, 1959) and the features of spatial information processing in the visual system of males and females.

[The Modeling of Human Visual ERPs Sources in the Task of Line Orientation Identification].

The high-resolution EEG was taken from 35 healthy subjects (16 males, 19 females) in the task of identification of cardinal (horizontal, vertical) and oblique (45°, 135°) orientations. The integrated approach was developed and used for the ERPs analysis. It includes the modeling of the distributed intracranial dipole sources of the ERPs' components by the weighted Minimum Norm Estimates (wMNE) method, the combination of distributed intracranial dipole sources with the M RI data and the statistical analysis of the current density. It was shown that a multiple network of brain structures was active during the early stage of analysis of line orientation. It includes not only primary striate visual area, but also the parietal, temporal and prefrontal corticies. The new data was obtained about the participation of structures, responsible for navigation (parahippocampal gyrus and entorhinal area) in the line orientation detection. For the first time the gender-related differences in the organization ofthe line detection network were described. The obtained data provides a significant supplement to the knowledge of the mechanisms of the orientation sensitivity and assumes that orientation sensitivity plays an important role in the navigation.

Gender differences in the recognition of spatially transformed figures: behavioral data and event-related potentials (ERPs).

The gender differences in accuracy, reaction time (RT) and amplitude of the early P1 and N1 components of ERPs during recognition of previously memorized objects after their spatial transformation were examined. We used three levels of the spatial transformation: a displacement of object details in radial direction, and a displacement in combination with rotation of the details by ±0° to 45° and ±45° to 90°. The accuracy and the RT data showed a similarity of task performance in males and females. The effect of rotation was significantly greater than the effect of simple displacement, and the accuracy decreased, and the RT increased with the rotation angle in both genders. At the same time we found significant sex differences in the early stage of visual processing. In males the P1 peak amplitude at the P3/P4 sites increased significantly during the recognition of spatially transformed objects, and the wider the angle of rotation the greater the P1 peak amplitude. In contrast, in females the P1 peak amplitude did not depend on the rotation of figure details. The N1 amplitude revealed no gender differences, although the object transformation evoked somewhat greater changes in the N1 at the O1/O2 sites in females compared to males. This new fact that only males demonstrated the sensitivity of early perceptual stage to the transformation of objects adds information about the neurobiological basis of different strategies in the visual processing used by each gender.

Effect of PAR1 agonist on acetylcholine secretion in a newly formed neuromuscular synapse in mice.

Peptide agonist of PARI in a concentration of 10 microM significantly facilitated neuromuscular transmission in newly formed synapses in mice. The absence of changes in the amplitude of miniature end-plate potentials attests to presynaptic mechanism of the effect of PAR1 agonist. The effect of the peptide was blocked by protein kinase A inhibitor H89 (1 microM). Blockade of inositol-1,4,5-trisphosphate receptors with 2-amino-ethoxydiphenylborate (30 microM) did not prevent the effects of PARI agonist. Inhibition of protein kinase C with bisindolylmaleimide (1 microM) facilitated neuromuscular transmission in newly formed synapses. Protein kinase C inhibition was associated with reversal of the object of PARI agonist: transmission inhibition instead of facilitation.

Study of neurotrophic activity of thrombin on the model of regenerating mouse nerve.

Experiments demonstrated a dose-dependent facilitating effect of thrombin and peptide thrombin receptor agonist PAR1 (TRAP6) on regeneration of mouse peripheral nerve after its crushing. The maximum neurotrophic effect was observed at low concentrations of thrombin (10 nM) and TRAP6 (10 microM).