Line fragments and their intersections are the basic properties of most objects in the visual world [3]; therefore, their rapid and reliable detection is important for image recognition. It is obvious that identification of lines (properties of the first order) and their intersections (properties of the second order) in images occurs in cats and monkeys already in the primary visual cortex where half of neurons detect the orientation of single lines and the other half of neurons more rapidly and strongly respond to their intersections or branching nodes [11, 12]. There is no information on the location of the mechanism responsible for identifying lines and their intersections in the human brain. Our previous study [1] demonstrated differences in the temporal and amplitude characteristics and regional specificity of the components of visual evoked potentials (EPs) in the human brain after presentation of images consisting of lines and crosses. However, the location of the dipole sources of these EP components has not been studied. Nevertheless, such information is important for assessing more precisely the involvement of different zones of the visual cortex in the identification of image properties. Therefore, we studied threedimensional location of dipole sources of the early component of visual EPs (wave P1) in the spherical and real model of the head in 12 subjects during presentation of images consisting of lines and crosses. The P1 component was selected because, first, it is associated with early stages of the processing of simple image features in the visual cortex, and, second, according to fMRT data, the location of the current dipole of the P1 wave coincides with the activation focus in the visual cortex [4]. METHODS The EEG was recorded in the electrophysiological experiments on 12 healthy subjects using a NeocortexPro 40-channel recording system (Neurobotics, Russia) according to the 10‐10 scheme with a sampling rate of 1000 Hz/channel. The right-ear electrode was used as an indifferent electrode. The upper limit of the frequency band of amplifiers was 100 Hz, the lower limit was 0.1 Hz, and the characteristic slope was 12 dB/octave. The subjects studied sat in a chamber isolated from light with a background illumination of 6 cd/m 2 . The images containing sets of lines or crosslike figures were shown for 100 ms on a monitor in a random order with various intervals [1]. The angular size of the image was 18.8° , and the size of its single element (cross or line) was 0.6° . Each experiment included 50 stimuli of each type. The average optical densities of the stimuli were equalized. A short sound warning was given 1 s before the beginning of the stimulus exposition. The subject focused the gaze at the fixation point in the screen center after the signal and watched the appearing image.

Location of the dipoles of the P1 wave of visual evoked potential in the human brain

Brain mapping: The methods. Arthur W. Toga and John C. Mazziotta, San Diego, CA, Academic Press, 1996 471 pp, illustratred, $145.00

The effects of systemic administration of the anesthetic propofol on the amplitude of the optical signal recorded from the neuron population of the primary visual cortex of the cat were studied. The study included development of an anesthesia protocol allowing maintenance of the required depth of anesthesia without introducing artefacts into the experimental data. Optical access to the cerebral cortex was gained at the beginning of the experiment. The effects of propofol on the functional responses of the neuron population were evaluated in the experiments by optical mapping using intrinsic signals. The study addressed the stability of the population response of the brain during the whole experiment and after single doses of propofol. The results showed that prolonged administration of propofol at a constant rate had no effect on the amplitude of the optical signal recorded from the cortical surface. On this background, single concentrated doses induced transient suppression of signal amplitude. Practical recommendations are provided for long-lasting acute neurophysiological experiments using propofol anesthesia.

Changes in the Functional Population Response of the Cat Primary Visual Cortex after Short-Term Injections of Propofol on the Background of Continuous Propofol Infusion

Local blood supply to the brain is known to depend on the changes in neuronal activity. The functional brain imaging methods developed in recent decades made it possible to study the fine organization of brain functions on the basis of changes in local circulation (positron emission tomography, functional magnetic resonance imaging, and mapping by intrinsic signal). Optical mapping of the cerebral cortex [2, 3, 11] is based on differences in optical characteristics between oxyhemoglobin and its reduced form, deoxyhemoglobin. Local decrease in the concentration of oxyhemoglobin and increase in the concentration of deoxyhemoglobin in the cerebral tissue results from the activation of neurons accompanied by an increase in their oxygen consumption. These changes in the concentrations of two hemoglobin forms can be measured using a sensitive CCD camera. Recording this intrinsic signal, one can construct functional maps of the brain surface where activated regions look darker. Mapping upon visual stimulation of different types allowed the arrangement of different functional modules of the cerebral cortex (orientation columns and hypercolumns and eye dominance bands) [5]. Earlier electrophysiological experiments showed that about half of neurons of area 17 of the cat visual cortex were most sensitive to intersections and branching of line segments [7–10] rather than their orientation [4]. It remains unknown whether the detectors of cruciform figures are included in the classic orientation columns or in other cortical modules. Therefore, the purpose of our study was to analyze the tangential package of neuron detectors of second-order shapes (grids, crosses, and corners) in the cat primary visual cortex with the use of optical mapping of the cerebral cortex by intrinsic signal. We performed 12 acute experiments with anesthetized adult cats immobilized with a myorelaxant. The animals were under artificial ventilation and were intraarterially or intravenously infused with Ringer solution containing glucose. The degree of anesthesia and the general state of the animals were monitored by measuring body temperature, arterial pressure, and CO 2 content of the expired air. The optical access to the cortex was ensured as follows. After trephination and the removal of the dura mater, a cylindrical chamber was fixed over area 17 (Fig. 1a), filled with silicon oil, and hermetically covered with glass to preclude respiratory and pulse shifts of the cortex. A highly sensitive CCD camera (Fig. 1b) with a small depth of focus, equipped with a light source (Fig. 1c), was focused at a depth of 700 μ m from the cortex surface to reduce artifacts related to the blood flow through large vessels on the brain surface.

Anesthesia and tangential package of neurons sensitive to cruciform figures in the cat striate cortex.

We report here the first studies of optical maps in the primary visual cortex of the cat constructed using internal signals and reflecting the population activity of detector neurons for first- and second-order image features on presentation of grids consisting of bars and crosses. Superimposition of maps of responses to the bars making up the crosses on maps of responses to crosses allowed assessment of overlapping cortical regions producing responses to these stimuli, as well as areas without overlap, i.e., those activated by only one of the stimuli. Overlapping is evidence of the packing of detector neurons in the corresponding orientation columns. Responses to straight and inclined crosses differed not only topographically, but also in terms of the extent of overlap. It is suggested that this results from different contributions being made by the detectors of bands of different types.

Overlapping of Zones Producing Optical Responses to Cross-Shaped Figures and Segments of Lines in Different Orientations in the Primary Visual Cortex of the Cat

We report here studies of orientational tuning and its dynamics during generation of responses in neurons located in orientation columns and the centers of orientation pinwheels in the primary visual cortex of the cat. Intrinsic signal optical mapping was used to define the position of the working module on functional and vascular maps of the cortical surface. Both maps were used for targeted implantation of microelectrodes. The dynamics of orientational tuning were studied using a time slice method. Neurons whose preferred orientations were stable during response generation were observed in pinwheel centers and in orientation columns, accounting for 14.5% of cells, along with neurons in which the preferred orientation sequentially shifted by an average of 102 ± 5° (40.8%) and neurons with mixed-type dynamics (44.7%). Neurons with stable tuning in pinwheel centers differed from neurons with unstable tuning by producing greater responses to the preferred orientation, while those in orientation columns were characterized by later onset of responses to all orientations, including the preferred and non-preferred orientations. The orientational qualities of detection in stable neurons in these functional modules were better than those of cells with unstable tuning. Comparison of neurons with the same type of preferred orientation dynamics but different locations showed that stable neurons in pinwheel centers had shorter latent periods and larger responses than neurons in orientation columns. The width and selectivity of orientation tuning in these cells showed no differences. In unstable neurons, the characteristics of orientation tuning and responses to the preferred orientation were independent of location and were essentially identical. The functional significance of neurons with stable and unstable tuning during response generation in pinwheel centers and orientation columns in the primary visual cortex is discussed

https://link.springer.com/content/pdf/10.1007%2Fs11055-014-9938-x.pdf

R. S. Ivanov

Papers

Changes in the Functional Population Response of the Cat Primary Visual Cortex after Short-Term Injections of Propofol on the Background of Continuous Propofol Infusion

Anesthesia and tangential package of neurons sensitive to cruciform figures in the cat striate cortex.

Overlapping of Zones Producing Optical Responses to Cross-Shaped Figures and Segments of Lines in Different Orientations in the Primary Visual Cortex of the Cat

Comparison of Orientational Tuning and Its Dynamics in Neurons in Different Functional Domains of the Primary Visual Cortex