Orientation anisotropies in macaque visual areas.

In mammals, a larger number of neurons in V1 are devoted to cardinal (horizontal and vertical) orientations than to oblique orientations. However, electrophysiological results from the macaque monkey visual cortex are controversial. Both isotropic and anisotropic orientation distributions have been reported. It is also unclear whether different visual areas along the visual hierarchy have different orientation anisotropies. We analyzed orientation maps in a large set of intrinsic signal optical imaging data and found that both V1 and V4 exhibited significant orientation anisotropies. However, their overrepresented orientations were very different: in V1, both cardinal and radial orientations were overrepresented, while in V4, only cardinal bias was presented. These findings suggest that different cortical areas have evolved to emphasize different features that are suitable for their functional purposes, a factor that needs to be considered when efforts are made to explain the relationships between the visual environment and the cortical representation and between the cortical representation and visual perception.

[Early diagnosis of diabetic polyneuropathy based on the results of corneal nerve fibers examination]. / Vozmozhnosti rannei diagnostiki diabeticheskoi polineiropatii na osnove issledovaniya nervnykh volokon rogovitsy.

Laser corneal confocal microscopy (CCM) is a method of objective visualization of thin corneal nerve fibers (CNF), the structure of which changes in patients with diabetes mellitus (DM). PURPOSE: To conduct comparative analysis of the results of CNF assessment using CCM and other known neurological instrumental techniques as well as evaluate their applicability to the early diagnosis of diabetic polyneuropathy (DPN). MATERIAL AND METHODS: We examined a total of 46 patients (85 eyes) with type 1 DM and either subclinical (24 patients), or clinical-stage DPN (22 patients) and 50 patients (87 eyes) with type 2 DM (subclinical DPN in 27 patients and clinical-stage DPN in 23 patients). The control group consisted of 34 healthy volunteers (68 eyes). All patients underwent standard ophthalmological examination, CCM with nerve tortuosity assessment (including calculation of coefficients of CNF orientation anisotropy, KΔL, and symmetry, Ksym) and interocular asymmetry, electroneuromyography (ENMG), and quantitative sensory testing (QST). RESULTS: Analysis of the CCM results revealed a reliable decrease in the average KΔL values in patients with type 1 and type 2 DM compared with the control group. In the group of patients with type 1 DM and subclinical DPN, correlations were revealed between the CNF tortuosity coefficients and a number of ENMG parameters, such as the M-response amplitude of the peroneal nerve (r=0.73, p≤0.02), M-response amplitude of the tibial nerve (r=0.58, p≤0.01), residual latency (r= -0.62, p≤0.05), and peroneal nerve conduction velocity (r=0.57, p≤0.01). Ksym values correlated with the warm sensitivity threshold (r=0.6, p≤0.008). Among patients with type 2 DM and subclinical DPN, the KΔL coefficient correlated with the peroneal nerve conduction velocity (r=0.46, p≤0.02), M-response amplitude of the tibial nerve (r=0.6, p≤0.04), and residual latency of the peroneal nerve (r=-0.56, p≤0.05). CONCLUSION: The state of thin corneal nerves correlates with functional changes in the peripheral nerves. Pathological changes in CNF in patients with DM can be detected at an early (subclinical) stage of DPN using laser CCM and a program for corneal nerve tortuosity analysis.

Radial bias for orientation and direction of motion modulates access to visual awareness during continuous flash suppression.

Two types of radial bias have been demonstrated in the primate visual cortex: for orientation and for direction of motion. Considering that a visual neuron's directional selectivity is generally perpendicular to its preferred orientation, it is counterintuitive that radial biases for orientation and direction of motion coexist in retinotopic cortex including primary visual cortex. The current study measured the influence of radial bias for orientation and direction of motion on the access to visual awareness during continuous flash suppression. Strength of static and moving target stimuli, inferred by time to breakup of suppression, was modulated by the orientation and motion direction of the suppressed target stimulus according to its spatial location, indicating radial biases for both orientation and motion direction. However, orientation dominated over direction of motion when they were perpendicular to each other. These results indicate that, first, orientation-specific neural responses may be stronger than direction-specific neural responses at the stage of visual processing where interocular suppression is resolved. Second, the preferential processing of both orientation and direction of motion may result from anisotropic distribution of orientation- and direction-selective cells. Third, the neural substrate of the radial direction bias may reflect an orientation-specific neural response induced by fast-moving random dot patterns.

The impact of head orientation with respect to B0 on diffusion tensor MRI measures.

Diffusion tensor MRI (DT-MRI) remains the most commonly used approach to characterise white matter (WM) anisotropy. However, DT estimates may be affected by tissue orientation w.r.t. B→0 due to local gradients and intrinsic T2 orientation dependence induced by the microstructure. This work aimed to investigate whether and how diffusion tensor MRI-derived measures depend on the orientation of the head with respect to the static magnetic field, B→0. By simulating WM as two compartments, we demonstrated that compartmental T2 anisotropy can induce the dependence of diffusion tensor measures on the angle between WM fibres and the magnetic field. In in vivo experiments, reduced radial diffusivity and increased axial diffusivity were observed in white matter fibres perpendicular to B→0 compared to those parallel to B→0. Fractional anisotropy varied by up to 20% as a function of the angle between WM fibres and the orientation of the main magnetic field. To conclude, fibre orientation w.r.t. B→0 is responsible for up to 7% variance in diffusion tensor measures across the whole brain white matter from all subjects and head orientations. Fibre orientation w.r.t. B→0 may introduce additional variance in clinical research studies using diffusion tensor imaging, particularly when it is difficult to control for (e.g., fetal or neonatal imaging, or when the trajectories of fibres change due to, e.g., space occupying lesions).

Spontaneous Emergence of Legibility in Writing Systems: The Case of Orientation Anisotropy.

Cultural forms are constrained by cognitive biases, and writing is thought to have evolved to fit basic visual preferences, but little is known about the history and mechanisms of that evolution. Cognitive constraints have been documented for the topology of script features, but not for their orientation. Orientation anisotropy in human vision, as revealed by the oblique effect, suggests that cardinal (vertical and horizontal) orientations, being easier to process, should be overrepresented in letters. As this study of 116 scripts shows, the orientation of strokes inside written characters massively favors cardinal directions, and it is organized in such a way as to make letter recognition easier: Cardinal and oblique strokes tend not to mix, and mirror symmetry is anisotropic, favoring vertical over horizontal symmetry. Phylogenetic analyses and recently invented scripts show that cultural evolution over the last three millennia cannot be the sole cause of these effects.