Publications by authors named "Mark Eldridge"

The Hoary Bat Chalinolobus nigrogriseus is the only species of the genus known from the island of New Guinea. A new species of Chalinolobus from Papua New Guinea is described based on DNA sequence and morphological criteria using material previously assigned to C. nigrogriseus.

View Article and Find Full Text PDF

In real-world vision, objects may appear for a short period, such as in conjunction with visual search. Presumably, this puts a premium on rapid categorization. We designed a visual categorization task cued by briefly presented images to study how visual categorization is processed in an ethologically relevant context.

View Article and Find Full Text PDF

Cholinergic projection neurons of the nucleus basalis and substantia innominata (NBM/SI) densely innervate the basolateral amygdala (BLA) and have been shown to contribute to the encoding of fundamental and life-threatening experiences. Given the vital importance of these circuits in the acquisition and retention of memories that are essential for survival in a changing environment, it is not surprising that the basic anatomical organization of the NBM/SI is well conserved across animal classes as diverse as teleost and mammal. What is not known is the extent to which the physiology and morphology of NBM/SI neurons have also been conserved.

View Article and Find Full Text PDF

Area TE is required for normal learning of visual categories based on perceptual similarity. To evaluate whether category learning changes neural activity in area TE, we trained two monkeys (both male) implanted with multielectrode arrays to categorize natural images of cats and dogs. Neural activity during a passive viewing task was compared pre- and post-training.

View Article and Find Full Text PDF

Primates must adapt to changing environments by optimizing their behavior to make beneficial choices. At the core of adaptive behavior is the orbitofrontal cortex (OFC) of the brain, which updates choice value through direct experience or knowledge-based inference. Here, we identify distinct neural circuitry underlying these two separate abilities.

View Article and Find Full Text PDF

Cholinergic projection neurons of the nucleus basalis and substantia innominata (NBM/SI) densely innervate the basolateral amygdala (BLA) and have been shown to contribute to the encoding of fundamental and life-threatening experiences. Given the vital importance of these circuits in the acquisition and retention of memories that are essential for survival in a changing environment, it is not surprising that the basic anatomical organization of the NBM/SI is well conserved across animal classes as diverse as teleost and mammal. What is not known is the extent to which the physiology and morphology of NBM/SI neurons have also been conserved.

View Article and Find Full Text PDF

In recent years, we and others have identified a number of enhancers that, when incorporated into rAAV vectors, can restrict the transgene expression to particular neuronal populations. Yet, viral tools to access and manipulate fine neuronal subtypes are still limited. Here, we performed systematic analysis of single cell genomic data to identify enhancer candidates for each of the cortical interneuron subtypes.

View Article and Find Full Text PDF

Genetic management is a critical component of threatened species conservation. Understanding spatial patterns of genetic diversity is essential for evaluating the resilience of fragmented populations to accelerating anthropogenic threats. Nowhere is this more relevant than on the Australian continent, which is experiencing an ongoing loss of biodiversity that exceeds any other developed nation.

View Article and Find Full Text PDF

Positron emission tomography (PET) reporter systems are a valuable means of estimating the level of expression of a transgene in vivo. For example, the safety and efficacy of gene therapy approaches for the treatment of neurological and neuropsychiatric disorders could be enhanced via the monitoring of exogenous gene expression levels in the brain. The present study evaluated the ability of a newly developed PET reporter system [F]fluoroestradiol ([F]FES) and the estrogen receptor-based PET reporter ChRERα, to monitor expression levels of a small hairpin RNA (shRNA) designed to suppress choline acetyltransferase (ChAT) expression in rhesus monkey brain.

View Article and Find Full Text PDF

Increased sampling of genomes and populations across closely related species has revealed that levels of genetic exchange during and after speciation are higher than previously thought. One obvious manifestation of such exchange is strong cytonuclear discordance, where the divergence in mitochondrial DNA (mtDNA) differs from that for nuclear genes more (or less) than expected from differences between mtDNA and nuclear DNA (nDNA) in population size and mutation rate. Given genome-scale data sets and coalescent modeling, we can now confidently identify cases of strong discordance and test specifically for historical or recent introgression as the cause.

View Article and Find Full Text PDF

In assessments of skeletal variation, allometry (disproportionate change of shape with size) is often corrected to examine size-independent variation for hypotheses relating to function. However, size-related trade-offs in functional demands may themselves be an underestimated driver of mammalian cranial diversity. Here, we use geometric morphometrics alongside dental measurements to assess craniodental allometry in the rock-wallaby genus (all 17 species, 370 individuals).

View Article and Find Full Text PDF

Opioid receptors within the CNS regulate pain sensation and mood and are key targets for drugs of abuse. Within the adult rodent hippocampus (HPC), μ-opioid receptor agonists suppress inhibitory parvalbumin-expressing interneurons (PV-INs), thus disinhibiting the circuit. However, it is uncertain if this disinhibitory motif is conserved in other cortical regions, species, or across development.

View Article and Find Full Text PDF

Chemogenetic tools are designed to control neuronal signaling. These tools have the potential to contribute to the understanding of neuropsychiatric disorders and to the development of new treatments. One such chemogenetic technology comprises modified Pharmacologically Selective Actuator Modules (PSAMs) paired with Pharmacologically Selective Effector Molecules (PSEMs).

View Article and Find Full Text PDF

We trained two monkeys implanted with multi-electrode arrays to categorize natural images of cats and dogs, in order to observe changes in neural activity related to category learning. We recorded neural activity from area TE, which is required for normal learning of visual categories based on perceptual similarity. Neural activity during a passive viewing task was compared pre- and post-training.

View Article and Find Full Text PDF

To be the most successful, primates must adapt to changing environments and optimize their behavior by making the most beneficial choices. At the core of adaptive behavior is the orbitofrontal cortex (OFC) of the brain, which updates choice value through direct experience or knowledge-based inference. Here, we identify distinct neural circuitry underlying these two separate abilities.

View Article and Find Full Text PDF
Article Synopsis
  • The study investigates the properties of hippocampal mossy fiber (MF) synapses in humans, comparing them to findings in rodent models.
  • Human MFs exhibit similar features to rodent MFs, including the dominance of AMPA receptors, significant frequency facilitation, and independent presynaptic long-term potentiation.
  • A reduction in GABAergic inhibition in human MFs is linked to increased excitability in epilepsy, highlighting potential implications for understanding and treating the disorder.
View Article and Find Full Text PDF

Positron emission tomography (PET) can be used as a noninvasive method to longitudinally monitor and quantify the expression of proteins in the brain in vivo. It can be used to monitor changes in biomarkers of mental health disorders, and to assess therapeutic interventions such as stem cell and molecular genetic therapies. The utility of PET monitoring depends on the availability of a radiotracer with good central nervous system (CNS) penetration and high selectivity for the target protein.

View Article and Find Full Text PDF

Translocation programmes are increasingly being informed by genetic data to monitor and enhance conservation outcomes for both natural and established populations. These data provide a window into contemporary patterns of genetic diversity, structure and relatedness that can guide managers in how to best source animals for their translocation programmes. The inclusion of historical samples, where possible, strengthens monitoring by allowing assessment of changes in genetic diversity over time and by providing a benchmark for future improvements in diversity via management practices.

View Article and Find Full Text PDF

Impulsivity, the tendency to react quickly and without consideration of consequences, is correlated with asymmetry in the volume of the caudate nucleus in human patients. In this study, we sought to determine whether the induction of functional asymmetry in the caudate nucleus of monkeys would produce phenomenologically comparable behavior. We found that unilateral suppression of the ventral caudate nucleus increases impulsive behavior in rhesus monkeys.

View Article and Find Full Text PDF

Genetically encoded synthetic receptors, such as the chemogenetic and optogenetic proteins, are powerful tools for functional brain studies in animals. In the primate brain, with its comparatively large, intricate anatomical structures, it can be challenging to express transgenes, such as the hM4Di chemogenetic receptor, in a defined anatomical structure with high penetrance. Here, we compare parameters for lentivirus vector injections in the rhesus monkey amygdala.

View Article and Find Full Text PDF

Decades of neuroscientific research has sought to understand medial temporal lobe (MTL) involvement in perception. Apparent inconsistencies in the literature have led to competing interpretations of the available evidence; critically, findings from human participants with naturally occurring MTL damage appear to be inconsistent with data from monkeys with surgical lesions. Here, we leverage a 'stimulus-computable' proxy for the primate ventral visual stream (VVS), which enables us to formally evaluate perceptual demands across stimulus sets, experiments, and species.

View Article and Find Full Text PDF

In the canonical view of visual processing the neural representation of complex objects emerges as visual information is integrated through a set of convergent, hierarchically organized processing stages, ending in the primate inferior temporal lobe. It seems reasonable to infer that visual perceptual categorization requires the integrity of anterior inferior temporal cortex (area TE). Many deep neural networks (DNNs) are structured to simulate the canonical view of hierarchical processing within the visual system.

View Article and Find Full Text PDF
Article Synopsis
  • Optogenetics enables precise control of brain neuron activity using light-sensitive proteins delivered through engineered viruses, but challenges arise with large brains like those of nonhuman primates.
  • The Opto-Array device simplifies light delivery to extensive areas of the cortex, allowing for high-throughput optogenetic studies, with detailed surgical protocols provided for installation in a rhesus monkey.
  • The approach demonstrated effective stimulation detection in the animal, proving reliable light delivery and establishing a method for chronic experimentation, potentially paving the way for future applications in restoring vision for humans.
View Article and Find Full Text PDF

Artificial activation of neurons in early visual areas induces perception of simple visual flashes. Accordingly, stimulation in high-level visual cortices is expected to induce perception of complex features. However, results from studies in human patients challenge this expectation.

View Article and Find Full Text PDF