A framework for three-dimensional navigation research

We have argued that the neurocognitive representation of large-scale, navigable three-dimensional space is anisotropic, having different properties in vertical versus horizontal dimensions. Three broad categories organize the experimental and theoretical issues raised by the commentators: (1) frames of reference, (2) comparative cognition, and (3) the role of experience. These categories contain the core of a research program to show how three-dimensional space is represented and used by humans and other animal

Navigating in a three-dimensional world

The study of spatial cognition has provided considerable insight into how animals (including humans) navigate on the horizontal plane. However, the real world is three-dimensional, having a complex topography including both horizontal and vertical features, which presents additional challenges for representation and navigation. The present article reviews the emerging behavioral and neurobiological literature on spatial cognition in non-horizontal environments. We suggest that three-dimensional spaces are represented in a quasi-planar fashion, with space in the plane of locomotion being computed separately and represented differently from space in the orthogonal axis-a representational structure we have termed "bicoded.” We argue that the mammalian spatial representation in surface-travelling animals comprises a mosaic of these locally planar fragments, rather than a fully integrated volumetric map. More generally, this may be true even for species that can move freely in all three dimensions, such as birds and fish. We outline the evidence supporting this view, together with the adaptive advantages of such a schem

Mehanohemijska sinteza nikal i nikal-cink feritnih prahova sa Nicolson-Ross analizom absorpcionih koeficijenata

The interest in finding new methods for the preparation of nickel ferrite (NiFe2O4) and nickel-zinc ferrite (NixZn1-xFe2O4) powders has recently increased, because the physical and chemical properties of these soft magnetic materials depend strongly on the preparation conditions. In this study, powder samples of ferrites were obtained by: 1) a classic sintering procedure (NixZn1-xFe2O4, x = 0.9) and 2) planetary mill synthesis (both NiFe2O4 and the NixZn1-xFe2O4). The mechano-chemical reaction leading to the formation of the spinel phase of NixZn1-xFe2O4 (x = 1 or 0.9) was monitored by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD) analysis. The values of the real and imaginary parts of the permittivity and permeability were measured for the obtained nickel and nickel-zinc ferrite samples in the 7-12 GHz frequency range. Based on the obtained results, the electromagnetic radiation (EMR) absorption coefficients were calculated for all three types of sample. It was concluded that the method of preparation and the final particle size influence the EMR absorption coefficient of nickel and nickel-zinc ferrites.U novije vreme povećan je interes za pronalaženje novih metoda za sintezu nikal-ferita (NiFe2O4) i nikal-cink-feritnih (NixZn1-xFe2O4) prahova, zbog činjenice da fizička i hemijska svojstva ovih 'mekih' magnetnih materijala u mnogome zavise od uslova pripreme. Dobijeni feritni prahovi, opisani u ovom radu, sintetisani su: 1) klasičnom procedurom sinterovanja (NixZn1-xFe2O4, x = 0,9 ili 2) sintezom u planetarnom mlinu (NiFe2O4 i NixZn1-xFe2O4). Prosečna veličina čestica dobijenih prvom metodom iznosi 3-5 μm, dok druga metoda daje čestice veličine 10-12 nm. Karakterizacija uzoraka praćena je skenirajućom elektronskom mikroskopijom (SEM), transmisionom elektronskom mikroskopijom (TEM), kao i difrakcionom analizom X-zracima (XRD). Realni i imaginarni delovi koeficijenata permitivnosti i permeabilnosti su mereni na dobijenim uzorcima nikal i nikal-cink-ferita u frekventnom opsegu 7-12 GHz. Na osnovu dobijenih rezultata, izračunati su EMR apsorpcioni koeficijenti za sve dobijene uzorke. Zaključeno je da je način pripreme, kao i dobijena veličina čestica, utiču na EMR apsorpcione koeficijente nikal i nikal-cink-ferita

Place field repetition and purely local remapping in a multicompartment environment

Hippocampal place cells support spatial memory using sensory information from the environment and self-motion information to localize their firing fields. Currently, there is disagreement about whether CA1 place cells can use pure self-motion information to disambiguate different compartments in environments containing multiple visually identical compartments. Some studies report that place cells can disambiguate different compartments, while others report that they do not. Furthermore, while numerous studies have examined remapping, there has been little examination of remapping in different subregions of a single environment. Is remapping purely local or do place fields in neighboring, unaffected, regions detect the change? We recorded place cells as rats foraged across a 4-compartment environment and report 3 new findings. First, we find that, unlike studies in which rats foraged in 2 compartments, place fields showed a high degree of spatial repetition with a slight degree of rate-based discrimination. Second, this repetition does not diminish with extended experience. Third, remapping was found to be purely local for both geometric change and contextual change. Our results reveal the limited capacity of the path integrator to drive pattern separation in hippocampal representations, and suggest that doorways may play a privileged role in segmenting the neural representation of space

Horizontal biases in rats' use of three-dimensional space

Rodent spatial cognition studies allow links to be made between neural and behavioural phenomena, and much is now known about the encoding and use of horizontal space. However, the real world is three dimensional, providing cognitive challenges that have yet to be explored. Motivated by neural findings suggesting weaker encoding of vertical than horizontal space, we examined whether rats show a similar behavioural anisotropy when distributing their time freely between vertical and horizontal movements. We found that in two- or three-dimensional environments with a vertical dimension, rats showed a prioritization of horizontal over vertical movements in both foraging and detour tasks. In the foraging tasks, the animals executed more horizontal than vertical movements and adopted a “layer strategy” in which food was collected from one horizontal level before moving to the next. In the detour tasks, rats preferred the routes that allowed them to execute the horizontal leg first. We suggest three possible reasons for this behavioural bias. First, as suggested by Grobety and Schenk [5], it allows minimisation of energy expenditure, inasmuch as costly vertical movements are minimised. Second, it may be a manifestation of the temporal discounting of effort, in which animals value delayed effort as less costly than immediate effort. Finally, it may be that at the neural level rats encode the vertical dimension less precisely, and thus prefer to bias their movements in the more accurately encoded horizontal dimension. We suggest that all three factors are related, and all play a part

Navigating in a three-dimensional world

The study of spatial cognition has provided considerable insight into how animals (including humans) navigate on the horizontal plane. However, the real world is three-dimensional, having a complex topography including both horizontal and vertical features, which presents additional challenges for representation and navigation. The present article reviews the emerging behavioral and neurobiological literature on spatial cognition in non-horizontal environments. We suggest that three-dimensional spaces are represented in a quasi-planar fashion, with space in the plane of locomotion being computed separately and represented differently from space in the orthogonal axis – a representational structure we have termed “bicoded.” We argue that the mammalian spatial representation in surface-travelling animals comprises a mosaic of these locally planar fragments, rather than a fully integrated volumetric map. More generally, this may be true even for species that can move freely in all three dimensions, such as birds and fish. We outline the evidence supporting this view, together with the adaptive advantages of such a scheme

New protein deposition tracers in the pipeline

Abstract Traditional nuclear medicine ligands were designed to target cellular receptors or transporters with a binding pocket and a defined structure–activity relationship. More recently, tracers have been developed to target pathological protein aggregations, which have less well-defined structure–activity relationships. Aggregations of proteins such as tau, α-synuclein, and β-amyloid (Aβ) have been identified in neurodegenerative diseases, including Alzheimer’s disease (AD) and other dementias, and Parkinson’s disease (PD). Indeed, Aβ deposition is a hallmark of AD, and detection methods have evolved from coloured dyes to modern 18F-labelled positron emission tomography (PET) tracers. Such tracers are becoming increasingly established in routine clinical practice for evaluation of Aβ neuritic plaque density in the brains of adults who are being evaluated for AD and other causes of cognitive impairment. While similar in structure, there are key differences between the available compounds in terms of dosing/dosimetry, pharmacokinetics, and interpretation of visual reads. In the future, quantification of Aβ-PET may further improve its utility. Tracers are now being developed for evaluation of tau protein, which is associated with decreased cognitive function and neurodegenerative changes in AD, and is implicated in the pathogenesis of other neurodegenerative diseases. While no compound has yet been approved for tau imaging in clinical use, it is a very active area of research. Development of tau tracers comprises in-depth characterisation of existing radiotracers, clinical validation, a better understanding of uptake patterns, test-retest/dosimetry data, and neuropathological correlations with PET. Tau imaging may allow early, more accurate diagnosis, and monitoring of disease progression, in a range of conditions. Another marker for which imaging modalities are needed is α-synuclein, which has potential for conditions including PD and dementia with Lewy bodies. Efforts to develop a suitable tracer are ongoing, but are still in their infancy. In conclusion, several PET tracers for detection of pathological protein depositions are now available for clinical use, particularly PET tracers that bind to Aβ plaques. Tau-PET tracers are currently in clinical development, and α-synuclein protein deposition tracers are at early stage of research. These tracers will continue to change our understanding of complex disease processes

A framework for three-dimensional navigation research

We have argued that the neurocognitive representation of large-scale, navigable three-dimensional space is anisotropic, having different properties in vertical versus horizontal dimensions. Three broad categories organize the experimental and theoretical issues raised by the commentators: (1) frames of reference, (2) comparative cognition, and (3) the role of experience. These categories contain the core of a research program to show how three-dimensional space is represented and used by humans and other animals

Mechanochemical synthesis of stoichiometric MgFe2O4 spinel

The influence of long-term milling of a mixture of (1) MgO and alpha-Fe2O3, (2) MgCO3, and alpha-Fe2O3, and (3) Mg(OH)(2) and alpha-Fe2O3 powders in a planetary ball mill on the reaction synthesis of nanosized MgFe2O4 ferrites was studied. Mechanochemical reaction leading to formation of the MgFe2O4 spinel phase was followed by electron microscopy, (SEM and TEM), X-ray diffraction and magnetization measurements. The spinel phase was observed first in cases (1) and (2) after 5 h of milling, and its formation was observed in all cases after 10 h. The synthesized MgFe2O4 ferrite has a nanocrystalline structure with a crystallite size of about 11, 10, and 12 nm, respectively for cases (1)-(3). Magnetic measurements after 10 h of milling show magnetization values of 19.8 J/(Tkg), 23.5 J/(Tkg) and 13.8 J/(Tkg), respectively for the cases (1)-(3)