Foveal pRF properties in the visual cortex depend on the extent of stimulated visual field

Previous studies demonstrated that alterations in functional MRI derived receptive field (pRF) properties in cortical projection zones of retinal lesions can erroneously be mistaken for cortical large-scale reorganization in response to visual system pathologies. We tested, whether such confounds are also evident in the normal cortical projection zone of the fovea for simulated peripheral visual field defects. We applied fMRI-based visual field mapping of the central visual field at 3 T in eight controls to compare the pRF properties of the central visual field of a reference condition (stimulus radius: 14°) and two conditions with simulated peripheral visual field defect, i.e., with a peripheral gray mask, stimulating only the central 7° or 4° radius. We quantified, for the cortical representation of the actually stimulated visual field, the changes in the position and size of the pRFs associated with reduced peripheral stimulation using conventional and advanced pRF modeling. We found foveal pRF-positions (≤3°) to be significantly shifted towards the periphery (p<0.05, corrected). These pRF-shifts were largest for the 4° condition [visual area (mean eccentricity shift): V1 (0.9°), V2 (0.9°), V3 (1.0°)], but also evident for the 7° condition [V1 (0.5°), V2 (0.5°), V3 (0.9°)]. Further, an overall enlargement of pRF-sizes was observed. These findings indicate the dependence of foveal pRF parameters on the spatial extent of the stimulated visual field and are likely associated with methodological biases and/or physiological mechanisms. Consequently, our results imply that, previously reported similar findings in patients with actual peripheral scotomas need to be interpreted with caution and indicate the need for adequate control conditions in investigations of visual cortex reorganization

Forests for the New Millennium - MAKING FORESTS WORK FOR PEOPLE AND NATURE

THE WAYS IN WHICH FORESTS ARE PERCEIVED AND USED HAVE CHANGED DRAMATICALLY OVER RECENT YEARS. FORESTS ARE NO LONGER SEEN SIMPLY AS A SOURCE OF TIMBER, BUT AS COMPLEX ECOSYSTEMS WHICH SUSTAIN LIVELIHOODS AND PROVIDE A RANGE OF PRODUCTS AND ENVIRONMENTAL SERVICES. IT IS NOW WIDELY RECOGNISED THAT FORESTS CAN CONTRIBUTE TO RURAL DEVELOPMENT AND POVERTY ALLEVIATION.Forest, economics, livelihoods

Structural changes to primary visual cortex in the congenital absence of cone input in achromatopsia

Autosomal recessive Achromatopsia (ACHM) is a rare inherited disorder associated with dysfunctional cone photoreceptors resulting in a congenital absence of cone input to visual cortex. This might lead to distinct changes in cortical architecture with a negative impact on the success of gene augmentation therapies. To investigate the status of the visual cortex in these patients, we performed a multi-centre study focusing on the cortical structure of regions that normally receive predominantly cone input. Using high-resolution T1-weighted MRI scans and surface-based morphometry, we compared cortical thickness, surface area and grey matter volume in foveal, parafoveal and paracentral representations of primary visual cortex in 15 individuals with ACHM and 42 normally sighted, healthy controls (HC). In ACHM, surface area was reduced in all tested representations, while thickening of the cortex was found highly localized to the most central representation. These results were comparable to more widespread changes in brain structure reported in congenitally blind individuals, suggesting similar developmental processes, i.e., irrespective of the underlying cause and extent of vision loss. The cortical differences we report here could limit the success of treatment of ACHM in adulthood. Interventions earlier in life when cortical structure is not different from normal would likely offer better visual outcomes for those with ACHM

Structural differences across multiple visual cortical regions in the absence of cone function in congenital achromatopsia

Most individuals with congenital achromatopsia (ACHM) carry mutations that affect the retinal phototransduction pathway of cone photoreceptors, fundamental to both high acuity vision and colour perception. As the central fovea is occupied solely by cones, achromats have an absence of retinal input to the visual cortex and a small central area of blindness. Additionally, those with complete ACHM have no colour perception, and colour processing regions of the ventral cortex also lack typical chromatic signals from the cones. This study examined the cortical morphology (grey matter volume, cortical thickness and cortical surface area) of multiple visual cortical regions in ACHM (n=15) compared to normally sighted controls (n=42) to determine the cortical changes that are associated with the retinal characteristics of ACHM. Surface-based morphometry was applied to T1-weighted MRI in atlas-defined early, ventral and dorsal visual regions of interest. Reduced grey matter volume in V1, V2, V3 and V4 was found in ACHM compared to controls, driven by a reduction in cortical surface area as there was no significant reduction in cortical thickness. Cortical surface area (but not thickness) was reduced in a wide range of areas (V1, V2, V3, TO1, V4 and LO1). Reduction in early visual areas with large foveal representations (V1, V2 and V3) suggests that the lack of foveal input to the visual cortex was a major driving factor in morphological changes in ACHM. However, the significant reduction in ventral area V4 coupled with the lack of difference in dorsal areas V3a and V3b suggest that deprivation of chromatic signals to visual cortex in ACHM may also contribute to changes in cortical morphology. This research shows that the congenital lack of cone input to the visual cortex can lead to widespread structural changes across multiple visual areas

Des Forêts pour le Nouveau Millénaire - DES FORÊTS À GÉRER DANS L’INTÉRÊT DES GENS ET DE LA NATURE

LA FAÇON DONT LES FORÊTS SONT PERÇUES ET LEURS UTILISATIONS ONT BEAUCOUP CHANGÉ AU COURS DES DERNIÈRES ANNÉES. LES FORÊTS NE SONT PLUS CONSIDÉRÉES COMME ÉTANT UNIQUEMENT DES SOURCES DE BOIS MAIS DES ÉCOSYSTÈMES COMPLEXES QUI PERMETTENT À DES COMMUNAUTÉS DE SE DÉVELOPPER ET OFFRENT TOUTE UNE GAMME DE PRODUITS ET DE SERVICES ENVIRONNEMENTAUX. ON RECONNAÎT AUJOURD’HUI QUE LES FORÊTS PEUVENT CONTRIBUER AU DÉVELOPPEMENT RURAL ET À LA LUTTE CONTRE LA PAUVRETÉ.Forêt, économie

Bosques para el Nuevo Milenio - BOSQUES QUE BENEFICIEN A LA GENTE Y SUSTENTEN LA NATURALEZA

LAS MANERAS DE PERCIBIR Y USAR LOS BOSQUES HAN CAMBIADO DRAMÁTICAMENTE DURANTE LOS ÚLTIMOS AÑOS. YA NO SE CONSIDERA MÁS A LOS BOSQUES SÓLO COMO UNA FUENTE DE MADERA, SINO COMO ECOSISTEMAS COMPLEJOS QUE SUSTENTAN LAS FORMAS DE VIDA HUMANA Y SUMINISTRAN UNA GAMA DE PRODUCTOS Y SERVICIOS AMBIENTALES. AHORA ES AMPLIAMENTE RECONOCIDO QUE LOS BOSQUES PUEDEN CONTRIBUIR AL DESARROLLO RURAL Y AYUDAN A ALIVIAR LA POBREZA.Forest, economics, livelihoods

Carbon sequestration and biodiversity following 18 years of active tropical forest restoration

Vast areas of degraded tropical forest, combined with increasing interest in mitigating climate change and conserving biodiversity, demonstrate the potential value of restoring tropical forest. However, there is a lack of long-term studies assessing active management for restoration. Here we investigate Above-Ground Biomass (AGB), forest structure, and biodiversity, before degradation (in old-growth forest), after degradation (in abandoned agricultural savanna grassland), and within a forest that is actively being restored in Kibale National Park, Uganda. In 1995 degraded land in Kibale was protected from fire and replanted with native seedlings (39 species) at a density of 400 seedlings ha-1. Sixty-five plots (50 m × 10 m) were established in restoration areas in 2005 and 50 of these were re-measured in 2013, allowing changes to be assessed over 18 years. Degraded plots have an Above Ground Biomass (AGB) of 5.1 Mg dry mass ha-1, of which 80% is grass. By 2005 AGB of trees ≥10 cm DBH was 9.5 Mg ha-1, increasing to 40.6 Mg ha-1 by 2013, accumulating at a rate of 3.9 Mg ha-1 year-1. A total of 153 planted individuals ha-1 (38%) remained by 2013, contributing 28.9 Mg ha-1 (70%) of total AGB. Eighteen years after restoration, AGB in the plots was 12% of old-growth (419 Mg ha-1). If current accumulation rates continue restoration forest would reach old-growth AGB in a further 96 years. Biodiversity of degraded plots prior to restoration was low with no tree species and 2 seedling species per sample plot (0.05 ha). By 2005 restoration areas had an average of 3 tree and 3 seedling species per sample plot, increasing to 5 tree and 9 seedling species per plot in 2013. However, biodiversity was still significantly lower than old-growth forest, at 8 tree and 16 seedling species in an equivalent area. The results suggest that forest restoration is beneficial for AGB accumulation with planted stems storing the majority of AGB. Changes in biodiversity appear slower; possibly due to low stem turnover. Overall this restoration treatment is an effective means of restoring degraded land in the area, as can be seen from the lack of regeneration in degraded plots, which remain low-AGB and diversity, largely due to the impacts of fire and competition with grasses

The Cape York tree-kangaroo: myth or reality

During the 1999 community survey of Australian tree-kangaroos by the Tree Kangaroo and Mammal Group of the Atherton Tablelands, the well-known naturalist, John Young, submitted a detailed account of watching a tree-kangaroo for half an hour in the Iron Range rainforest of Cape York Peninsula in 1979. At the time this was treated by hard-nosed scientists as "needing confirmation", particularly as numerous earlier collecting expeditions had worked the area without the hint of a tree-kangaroo. John's report triggered a flurry of interest and has resulted in the collation of numerous "sightings" from the Peninsula and some targeted searches for the animal, but as yet no concrete evidence. So does the animal exist? Tantalising leads, but no hard evidence, have been found for the occurrence of tree-kangaroos in the region. We discuss the possibility that such a creature exists and what might be necessary to find it, and if it does occur what level of evidence is required