The retrocalcarine sulcus maps different retinotopic representations in macaques and humans

Opposite asymmetry in visual perception of humans and macaques

In human adults, visual perception varies throughout the visual field. Performance decreases with eccentricity1,2 and varies around polar angle. At isoeccentric locations, performance is typically higher along the horizontal than vertical meridian (horizontal-vertical asymmetry [HVA]) and along the lower than the upper vertical meridian (vertical meridian asymmetry [VMA]).3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23 It is unknown whether the macaque visual system, the leading animal model for understanding human vision,24,25 also exhibits these performance asymmetries. Here, we investigated whether and how visual field asymmetries differ between these two groups. Human adults and adult macaque monkeys (Macaca nemestrina) performed a two-alternative forced choice (2AFC) motion direction discrimination task for a target presented among distractors at isoeccentric locations. Both groups showed heterogeneous visual sensitivity around the visual field, but there were striking differences between them. Human observers showed a large VMA-their sensitivity was poorest at the upper vertical meridian-a weak horizontal-vertical asymmetry, and lower sensitivity at intercardinal locations. Macaque performance revealed an inverted VMA-their sensitivity was poorest in the lower vertical meridian. The opposite pattern of VMA in macaques and humans revealed in this study may reflect adaptive behavior by increasing discriminability at locations with greater relevance for visuomotor integration. This study reveals that performance also varies as a function of polar angle for monkeys, but in a different manner than in humans, and highlights the need to investigate species-specific similarities and differences in brain and behavior to constrain models of vision and brain function.

Expansion of a conserved architecture drives the evolution of the primate visual cortex

Human brain evolution is marked by a disproportionate expansion of cortical regions associated with advanced perceptual and cognitive functions. While this expansion is often attributed to the emergence of novel specialized brain areas, modifications to evolutionarily conserved cortical regions also have been linked to species-specific behaviors. Distinguishing between these two evolutionary outcomes has been limited by the ability to make direct comparisons between species. Here, we addressed this limitation by examining the expansion of the human visual cortex relative to macaques using a common functional architecture: retinotopy. Our findings revealed that human visual cortex expansion is primarily driven by increases in the surface area of a visual map architecture present in macaques rather than an increase in the number of individual areas. This expansion was not uniform, with higher-order areas, particularly in the parietal cortex, exhibiting the largest growth. Comparisons between neonate and adult humans revealed that these relative areal size differences were already established at birth. A meta-analysis of neuroimaging studies indicated that the most expanded areas are associated with advanced cognitive functions beyond visual processing. These results suggest that human perceptual and cognitive adaptations may be rooted in the expansion of evolutionarily conserved cortical architecture, with modifications even in the sensory cortex contributing to the broader cognitive functions characteristic of human behavior.

An intrinsic hierarchical, retinotopic organization of visual pulvinar connectivity in the human neonate

The thalamus plays a crucial role in the development of the neocortex, with the pulvinar being particularly important for visual development due to its involvement in various functions that emerge early in infancy. The development of connections between the pulvinar and the cortex constrains its role in infant visual processing and the maturation of associated cortical networks. However, the extent to which adult-like pulvino-cortical pathways are present at birth remains largely unknown, limiting our understanding of how the thalamus may support early vision. To address this gap, we investigated the organization of pulvino-cortical connections in human neonates using probabilistic tractography analyses on diffusion imaging data. Our analyses identified white matter pathways between the pulvinar and areas across occipital, ventral, lateral, and dorsal visual cortices at birth. These pathways exhibited specificity in their connections within the pulvinar, reflecting both an intra-areal retinotopic organization and a hierarchical structure across areas of visual cortical pathways. This organization suggests that even at birth, the pulvinar could facilitate detailed processing of sensory information and communication between distinct processing pathways. Comparative analyses revealed that while the large-scale organization of pulvino-cortical connectivity in neonates mirrored that of adults, connectivity with the ventral visual cortex was less mature than other cortical pathways, consistent with the protracted development of the visual recognition pathway. These findings advance our understanding of the developmental trajectory of thalamocortical connections and provide a framework for how subcortical structures may support early perceptual abilities and scaffold the development of cortex.

Altered functional connectivity within the primary visual networks and neurotransmitter activity in male smokers: A group ICA study

Smoking puts patients at high risk for cognitive and psychiatric disorders. The aim of this study was to explore the effects of nicotine use on primary visual network (PVN) and its association with neurotransmitters. A total of 59 tobacco use disorder (TUD) patients and 51 healthy controls (HC) participated in this study and underwent resting state functional magnetic resonance imaging scans. Functional connectivity (FC) within the network was explored using independent component analysis. In addition, the spatial correlations of PVN changes with neurotransmitters and their correlations with clinical characteristics of patients were evaluated using the JuSpace toolbox and SPSS. We found reduced FC within the PVN in patients with TUD compared with HC. In terms of relevant analysis, there is a spatial correlation between FC changes in the patient's PVN and a higher distribution of dopamine receptor and gamma-aminobutyric acid receptor. This study revealed changes in the FC and neurotransmitters of the PVN in patients with TUD, expanding the potential neural mechanisms underlying sensory perception and psychiatric disorders.

Effects of early monocular enucleation on cortical spreading depression in well-nourished and malnourished adult rats

Sensory development is a complex process that can influence physiological and pathological factors. In laterally-eyed mammals, monocular enucleation (ME) during development and the subsequent lack of external sensory stimuli can result in permanent morphological and physiological changes. Malnutrition, especially in early life, also can cause permanent morphofunctional changes due to inadequate nutrient intake in both hemispheres. This study investigated the effects of early (postnatal day 7) ME and malnutrition during the suckling period on cortical excitability in adulthood (110-140 days of life). For this, we compared the speed propagation of cortical spreading depression in the occipital and parietal cortex of malnourished and well-nourished adult rats, previously suckled small-sized litters with three pups (L3/dam) medium-sized litters with six pups (L6/dam), and large-sized litters with twelve pups (L12/dam). The CSD velocity was augmented by the ME in the contralateral side of the removed eye in the parietal and occipital cortex. These findings suggest that visual sensory input deprivation is associated with permanent functional changes in the visual pathways, which can alter cortical excitability and lead to modifications in CSD propagation.

A Whole-Brain Topographic Ontology

It is a common view that the intricate array of specialized domains in the ventral visual pathway is innately prespecified. What this review postulates is that it is not. We explore the origins of domain specificity, hypothesizing that the adult brain emerges from an interplay between a domain-general map-based architecture, shaped by intrinsic mechanisms, and experience. We argue that the most fundamental innate organization of cortex in general, and not just the visual pathway, is a map-based topography that governs how the environment maps onto the brain, how brain areas interconnect, and ultimately, how the brain processes information.