Changes in potential are known to occur in the orbital area during saccades. The sign of these changes depends on the position of the electrode and the direction of eye rotation, while their amplitude depends on the rotation angle. The patterns of potentials can be used to resolve the reverse task, i.e., that of describing the gaze trajectory, such that the eye can be used to control a computer in an on-line regime. This requires a screen cursor to be placed at the calculated gaze fixation point, i.e., the point at which the observer is looking. Electrodes beneath the eyes were used to assess the vertical component of gaze displacement, while side electrodes at the corners of the orbit were used to assess the horizontal component. Sharp unipolar changes in potential occurring on saccades were apparent as steps which could be detected and measured. The signal was digitally filtered using a complex filter constructed by ourselves. The ratio of the amplitudes at the four points was then used to calculate the direction and angle of eye rotation. Characteristic changes in potential during spontaneous blinking were identified and ignored. Voluntary blinks of one eye were used to simulate mouse clicks. Subjects were initially told to make changes in gaze through specified angles in eight directions. This allowed calibration of standard saccades (in microV). Calibration curves were used to resolve the reverse task - changes in potential (in microV) were used to calculate the point on the screen (the pixel) to which the cursor was to be moved. Subjects were then trained to control the cursor using their eyes, and control of the computer was then completely handed over to the subject. The apparatus described here provides a brain-computer interface. Some interesting data on eye coordination were obtained during these studies: saccades were preceded by short negative electrooculogram (EOG) potentials lasting 10-15 msec. With age, the amplitude of saccade-related EOG potentials decreased. When gaze was shifted to the left, deviation of the eyes was more significant than when gaze was shifted to the right, while on shifting of gaze to the right, the lateral deviations of the eyes were similar. On diagonal right-down and left-up movements, right eye skew was greater than left eye skew, while on right-up and left-down movements, left eye skew was greater than right eye skew. Differences in eye coordination between genders were minor.
The amyloid concept of Alzheimer’s disease (AD) assumes the β-amyloid peptide (Aβ) as the main pathogenic factor, which injures neural and other brain cells, causing their malfunction and death. Although Aβ has been documented to exert its cytotoxic effect in a solitary manner, there is much evidence to claim that its toxicity can be modulated by other proteins. The list of such Aβ co-factors or interactors includes tau, APOE, transthyretin, and others. These molecules interact with the peptide and affect the ability of Aβ to form oligomers or aggregates, modulating its toxicity. Thus, the list of potential substances able to reduce the harmful effects of the peptide should include ones that can prevent the pathogenic interactions by specifically binding Aβ and/or its partners. In the present review, we discuss the data on Aβ-based complexes in AD pathogenesis and on the compounds directly targeting Aβ or the destructors of its complexes with other polypeptides.
The state of cortical activation during visual symbol shape and position selection tasks was assessed in humans in terms of the magnitude of prestimulus negativity (contingent negative variation, CNV) and the amplitude of the N1-P3 complex in evoked potentials (EP). Evoked potentials in the frontal parietal, occipital, and temporal leads were recorded in 18 young healthy subjects in two sets of experimental conditions: in a screened chamber and in an "open field" beside the experimenter, who communicated the results to the subjects and guided them towards quicker and more precise responses to the target stimuli. The maximum magnitudes of CNV and evoked potentials during selective attention were seen in the parietal areas, and additional increases of activation indexes were observed in the "open field," where subjects' motivation was enhanced. The state of readiness (CNV) was an informative measure of cortical activation, as it determined the parameters of subsequent evoked potentials; the more marked the readiness, themore marked and stable were EP. Comparison of the situations of passive observation and selective reactions to stimuli revealed a reciprocal relationship between CNV in these conditions: the greater the magnitude of CNV in "passive" conditions, the smaller the difference between CNV in "passive" conditions and during selective attention and vice versa. We termed this "additivity of involuntary and voluntary attention." The fact that activation indexes were greatest in the parietal areas suggests that the occipital-parietal system is dominant in visual selection tasks in humans.
The state of cortical activation in the parietal and temporal areas of the right and left hemispheres was evaluated using evoked potentials (EP) during tasks consisting of selection of visual stimuli lateralized in the right and left visual fields and needing three different types of attention: to stimulus shape, to stimulus position, and simultaneously to stimulus shape and position. EP were recorded in 15 young healthy experimental subjects using six cortical leads: P3, P4, T3, T4, T5, and T6; the following endogenous EP components (in standard terminology) were analyzed: contingent negative variation (CNV), N1, P3, and the N1-P3 complex. Asymmetry in evoked potentials was assessed in terms of differences to contra-and ipsilateral stimuli in the right and left hemispheres. EP asymmetry was detected in the right hemisphere in all types of selection of lateralized stimuli. The magnitude of asymmetry in the right hemisphere depended on the level (or intensity) of attention: the degree of asymmetry increased with increases in the need for attention to analyze the stimuli. There was a significant relationship between the magnitude of asymmetry and the latent periods of the subjects' responses. The functional significance of these data demonstrating asymmetry may be that it provides better spatial differentiation of visual signals in the right hemisphere, along with dominance of the right hemisphere in attention tasks.
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