Extracallosal channels of interhemispheric transmission of visual information

Evoked potentials (EP) in response to light flashes were recorded in cats with different degree of optical tract disconnection. In intact and operated on animals, the latent period of the first component of these EP was the same as in the visual cortex. The different degree of disconnection of the classic and commissural optical tract brought about an increase in the amplitude of commissural potentials. The data obtained point to the existence of the effective callosal and extracallosal volleys of interhemispheric transmission of visual information, which are also likely to pay an essential part in compensatory processes of the optical system.     

Synaptic information transfer in computer models of neocortical columns

Understanding the direction and quantity of information flowing in neuronal networks is a fundamental problem in neuroscience. Brains and neuronal networks must at the same time store information about the world and react to information in the world. We sought to measure how the activity of the network alters information flow from inputs to output patterns. Using neocortical column neuronal network simulations, we demonstrated that networks with greater internal connectivity reduced input/output correlations from excitatory synapses and decreased negative correlations from inhibitory synapses, measured by Kendall’s τ correlation. Both of these changes were associated with reduction in information flow, measured by normalized transfer entropy (nTE). Information handling by the network reflected the degree of internal connectivity. With no internal connectivity, the feedforward network transformed inputs through nonlinear summation and thresholding. With greater connectivity strength, the recurrent network translated activity and information due to contribution of activity from intrinsic network dynamics. This dynamic contribution amounts to added information drawn from that stored in the network. At still higher internal synaptic strength, the network corrupted the external information, producing a state where little external information came through. The association of increased information retrieved from the network with increased gamma power supports the notion of gamma oscillations playing a role in information processing.     

Corticothalamic interactions in the transfer of visual information

Thalamic function does not stand apart, as a discrete processing step, from the cortical circuitry. The thalamus receives extensive feedback from the cortex and this influences the firing pattern, synchronization and sensory response mode of relay cells. A crucial question concerns the extent to which the feedback simply controls the state and transmission mode of relay cells and the extent to which the feedback participates in the specific processing of sensory information. Using examples from experiments examining the influence of feedback from the visual cortex to the lateral geniculate nucleus (LGN), we argue that thalamic mechanisms are selectively focused by visually driven feedback to optimize the thalamic contribution to segmentation and global integration. This involves effects on both the temporal and spatial parameters characterizing the responses of LGN cells and includes, for example, motion-driven feedback effects from MT (middle temporal visual area) relayed via layer 6 of V1 (primary visual cortex).     

Bilateral receptive fields in cortical area SII: contribution of the corpus callosum and other interhemispheric commissures

The corpus callosum contributes to the interhemispheric transfer of somatosensory information. Since the somatosensory pathways are essentially crossed, a number of studies have postulated that the corpus callosum may be responsible for the presence of bilateral receptive fields (RFs) in cortical area SII. Moreover, subcortical structures, as well as some of the other commissures, may also contribute to the bilateral nature of these cells. In order to assess the relative importance of the corpus callosum, this study compared the RF properties of cells in area SII of callosum-sectioned cats to normal cats, using single-cell recordings. Results showed that the corpus callosum makes an important contribution to the bilateral activation of cells in SII, since the proportion of cells with bilateral RFs found in callosum-sectioned cats was less than half that obtained in normal cats. The decrease in the proportion of bilateral RFs was found for all body regions with the exception of the face. However, the substantial number of bilateral RFs remaining in callosotomized cats indicates that this structure is not the sole contributor to the bilateral activation of cells in SII. In order to determine whether this residual bilateral activation might be mediated by the other interhemispheric commissures, a group of cats was subjected, besides the callosotomy, to the additional transection of their subcortical commissures, including the anterior, posterior, habenular, and intertectal commissures, as well as the massa intermedia. When this group of deep-split cats was compared to the callosotomized group, the results indicated that the contribution of the other commissures to bilateral activation is negligible, since approximately the same proportion of bilateral RFs was encountered in the two groups. The relative importance of the callosal contribution to bilateral RFs of different body regions is discussed with respect to the roles commonly attributed to this structure.     

Effect of psychostimulants on responses of neocortical neurons to afferent and subcortical stimuli

The effect of psychostimulants on unit responses of the pericruciate region of the cortex during sensory and subcortical stimulation was studied in experiments on 52 immobilized cats. Amphetamine (2 mg/kg) caused a definite increase in the number of spontaneously active cortical cells. Caffeine (40 mg/kg) had a weaker action. After administration of psychostimulants afferent stimuli more often induced tonic changes in the spontaneous unit activity. More polymodal neurons were found. Phasic responses were often facilitated but were recorded at the same frequency as in the control. Amphetamine and caffeine weakened inhibition of the unit discharges during stimulation of the caudate nucleus and potentiated activation caused by stimulation of the reticular formation. The character of interaction between sensory and reticular (caudate) stimuli was not modulated by the psychostimulants although its scale and intensity were varied. The possible role of the effects of amphetamine and caffeine in therapeutic psychostimulation is discussed.     

Propagation of photon noise and information transfer in visual motion detection

The extraction of the direction of motion from the time varying retinal images is one of the most basic tasks any visual system is confronted with. However, retinal images are severely corrupted by photon noise, in particular at low light levels, thus limiting the performance of motion detection mechanisms of what sort so ever. Here, we study how photon noise propagates through an array of Reichardt-type motion detectors that are commonly believed to underlie fly motion vision. We provide closed-form analytical expressions of the signal and noise spectra at the output of such a motion detector array. We find that Reichardt detectors reveal favorable noise suppression in the frequency range where most of the signal power resides. Most notably, due to inherent adaptive properties, the transmitted information about stimulus velocity remains nearly constant over a large range of velocity entropies. Action editor: Matthew Wiener     

Time-frequency analysis of visual evoked potentials for interhemispheric transfer time and proportion in callosal fibers of different diameters

This study is an extension of the experimental research of Nalçac et al., who presented 16 subjects with a reversal of checkerboard pattern as stimuli in the right visual field or left visual field and recorded EEG at O1, O2, P3, and P4. They applied the chosen bandpass filters (4–8, 8–15, 15–20, 20–32 Hz) to the VEPs of subjects and obtained four different components for each VEP. The first aim of this study is to improve the previous report using some methods in time-frequency domain to estimate interhemispheric delays and amplitudes in a time window. Using the improved estimates of interhemispheric delays, the second aim is to estimate the proportion of callosal fibers of different diameters that are activated by visual stimuli by comparing amplitudes of VEPs in different frequency bands. If the relation between frequency components of VEP and delays for callosal fibers of different dimension were reliable, it would give us an opportunity to deal with amplitude of bandpass-filtered VEPs in order to see approximately the proportion of these fibers activated by a certain stimulus. By using frequency-dependent shifts in time and maximizing the cross correlation of direct VEP (DVEP–VEP obtained from contralateral hemisphere)–indirect VEP (IVEP–VEP obtained from ipsilateral hemisphere) pairs in the time-frequency domain, we examined the delay not only at P100 and N160 peaks but along a meaningful time interval as well. Furthermore, by shifting back the IVEP according to the delay estimated at each time window, both the amplitudes and energies of the synchronized DVEP–IVEP pairs were compared at the chosen frequency bands. The percentages of IVEPs at each band was then examined further in conjunction with the distribution of axon diameters in the posterior pole of the CC, questioning the relation between the distributions of the axon diameters and activations at each band. We established an energy definition to express the activation in the fibers. When the energy percentages of IVEPs in theta and alpha were totaled, they were found to be between 76.2% and 81.6%, which is close to the value 74–77% for fibers of 0.4–1 m in diameter obtained from anatomical study of human CC. The sum of energy percentages in the beta1 and beta2 bands was between 20.1% and 24.2%, which probably reflects the proportion of activation of callosal fibers 1–3 m in diameter.     

Transthalamic conduction of visual impulses to the cortex and subcortical forebrain structures in turtles

The thalamic relays for the conduction of impulses arising during photic stimulation of the eyes and electrical stimulation of the tectum in the general cortex, hyperstriatum (the dorsal ventricular ridge), and the striatum proper were studied in the turtleEmys orbicularis. Acute experiments on immobilized animals showed that anodal polarization temporarily and destruction of n. rotundus irreversibly suppress the main negative wave of the responses to tectal stimulation and to flashes in the hyperstriatum, whereas the corresponding responses in the general cortex still persist. Polarization and destruction of the lateral thalamic region, including the lateral geniculate body, have the opposite effect: responses in the hyperstriatum to photic and tectal stimulation are virtually unchanged whereas those in the general cortex disappear, except their late components. Preceding single stimulation of the tectum or n. rotundus depresses responses in the hyperstriatum evoked by flashes. However, during stimulation of the lateral thalamic region, combined potentials and single unit responses appear in the hyperstriatum and interact with responses evoked by tectal stimulation. It is concluded that the main pathways in turtles which supply visual information to the general cortex and hyperstriatum differ: the former relay in the lateral thalamic region, the latter in n. rotundus, although some overlapping of their projections in the hyperstriatum and striatum is possible.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Leningrad. Translated from Neirofiziologiya, Vol. 9, No. 5, pp. 486–494, September–October, 1977.     

The directional flow of visual information transfer between pedestrians

Close behavioural coupling of visual orientation may provide a range of adaptive benefits to social species. In order to investigate the natural properties of gaze-following between pedestrians, we displayed an attractive stimulus in a frequently trafficked corridor within which a hidden camera was placed to detect directed gaze from passers-by. The presence of visual cues towards the stimulus by nearby pedestrians increased the probability of passers-by looking as well. In contrast to cueing paradigms used for laboratory research, however, we found that individuals were more responsive to changes in the visual orientation of those walking in the same direction in front of them (i.e. viewing head direction from behind). In fact, visual attention towards the stimulus diminished when oncoming pedestrians had previously looked. Information was therefore transferred more effectively behind, rather than in front of, gaze cues. Further analyses show that neither crowding nor group interactions were driving these effects, suggesting that, within natural settings gaze-following is strongly mediated by social interaction and facilitates acquisition of environmentally relevant information.     

Sexual and interhemispheric differences in the involvement of serotonin from the hippocampus and amygdaloid body in the processing of new and repeatedly presented information in rats]

Effects of novel or relevant (a single exposure to experimental chamber) and irrelevant (20 exposures to experimental chamber) stimuli on the levels of serotonin (5-HT) and its metabolite 5-hydroxyindoleacetic acid (5-HIAA) in the left and right hippocamp and amygdala were studied in male and female rats. It was found that hemispheric specificity of 5-HT metabolism in hippocampus and amygdala depended on sex and novelty of information. In male rats, the hippocampal level of 5-HT in response to the novel stimulus increased in the left hemisphere, and the 5-HIAA hippocampal level increased bilaterally in response to irrelevant stimulus. In females, an increase in 5-HT and/or 5-HIAA levels was observed only in the left hippocampus in response both to relevant and irrelevant stimuli. In the amygdala, a hemispheric asymmetry of the 5-HT involvement, due to right-hemispheric changes in 5-HT metabolism, was observed only in male rats. In females, an increase in 5-HT level was found in the left and right amygdalas in response to irrelevant stimulus. These data suggest that serotonergic neurotransmitter mechanisms are an important factor which determines hemispheric and sex differences in selective attention.     

The topography of functional interhemispheric asymmetry in the visual cortex]

Functional interhemispheric asymmetry was investigated by evoked potentials method in experiments on ten cats under ethaminal anaesthesia at 200 points of the visual cortex during the action of binocular and monocular photic flashes of submaximal intensity. Topographic maps have been plotted of the functional interhemispheric asymmetry. In most of the animals a hemisphere dominant and non-dominant at the given moment can be singled out. Section of the callosal body leads to reduction of the functional interhemispheric asymmetry due to a decrease of the focus of maximum activity in the dominant hemisphere and its increase in the non-dominant one. A mozaic pattern of functional interhemispheric asymmetry has been demonstrated, as expressed in the existence of zones of inverse dominance along with prevailing zones of direct dominance. Section of the callosal body produced a decrease in the area of direct dominance and an increase in that of inverse dominance. Absolute interhemispheric asymmetry was most pronounced in the central part of the visual cortex (field 18 and its medial boundary) and the relative one, on the periphery of the visual area (fields 17 and 19).     

A novel interhemispheric interaction: modulation of neuronal cooperativity in the visual areas

Background

The cortical representation of the visual field is split along the vertical midline, with the left and the right hemi-fields projecting to separate hemispheres. Connections between the visual areas of the two hemispheres are abundant near the representation of the visual midline. It was suggested that they re-establish the functional continuity of the visual field by controlling the dynamics of the responses in the two hemispheres.

Methods/Principal Findings

To understand if and how the interactions between the two hemispheres participate in processing visual stimuli, the synchronization of responses to identical or different moving gratings in the two hemi-fields were studied in anesthetized ferrets. The responses were recorded by multiple electrodes in the primary visual areas and the synchronization of local field potentials across the electrodes were analyzed with a recent method derived from dynamical system theory. Inactivating the visual areas of one hemisphere modulated the synchronization of the stimulus-driven activity in the other hemisphere. The modulation was stimulus-specific and was consistent with the fine morphology of callosal axons in particular with the spatio-temporal pattern of activity that axonal geometry can generate.

Conclusions/Significance

These findings describe a new kind of interaction between the cerebral hemispheres and highlight the role of axonal geometry in modulating aspects of cortical dynamics responsible for stimulus detection and/or categorization.