Translating the Timing of Developmental Benchmarks in Short-Tailed Opossums (Monodelphisdomestica) to Facilitate Comparisons with Commonly Used Rodent Models.

Introduction: The gray short-tailed opossum, Monodelhis domestica (M. domestica), is a widely used marsupial model species that presents unique advantages for neurodevelopmental studies. Notably their extremely altricial birth allows manipulation of postnatal pups at timepoints equivalent to embryonic stages of placental mammals.

Reversible deactivation of motor cortex reveals that areas in parietal cortex are differentially dependent on motor cortex for the generation of movement.

Primates are characterized by specializations for manual manipulation, including expansion of posterior parietal cortex (PPC) and, in Catarrhines, evolution of a dexterous hand and opposable thumb. Previous studies examined functional interactions between motor cortex and PPC in New World monkeys and galagos, by inactivating M1 and evoking movements from PPC. These studies found that portions of PPC depend on M1 to generate movements.

Comparing the development of cortex-wide gene expression patterns between two species in a common reference frame.

Advances in sequencing techniques have made comparative studies of gene expression a current focus for understanding evolutionary and developmental processes. However, insights into the spatial expression of genes have been limited by a lack of robust methodology. To overcome this obstacle, we developed methods and software tools for quantifying and comparing tissue-wide spatial patterns of gene expression within and between species.

Coevolution of motor cortex and behavioral specializations associated with flight and echolocation in bats.

Bats have evolved behavioral specializations that are unique among mammals, including self-propelled flight and echolocation. However, areas of motor cortex that are critical in the generation and fine control of these unique behaviors have never been fully characterized in any bat species, despite the fact that bats compose ∼25% of extant mammalian species. Using intracortical microstimulation, we examined the organization of motor cortex in Egyptian fruit bats (Rousettus aegyptiacus), a species that has evolved a novel form of tongue-based echolocation.

Functional characterization of the fronto-parietal reaching and grasping network: reversible deactivation of M1 and areas 2, 5, and 7b in awake behaving monkeys.

In the present investigation, we examined the role of different cortical fields in the fronto-parietal reaching and grasping network in awake, behaving macaque monkeys. This network is greatly expanded in primates compared to other mammals and coevolved with glabrous hands with opposable thumbs and the extraordinary dexterous behaviors employed by a number of primates, including humans. To examine this, we reversibly deactivated the primary motor area (M1), anterior parietal area 2, and posterior parietal areas 5L and 7b individually while monkeys were performing two types of reaching and grasping tasks.

Phenotypic Alterations in Cortical Organization and Connectivity across Different Time Scales.

In the following review, we describe the types of phenotypic changes to the neocortex that occur over the longer time scale of evolution, and over the shorter time scale of an individual lifetime. To understand how phenotypic variability emerges in the neocortex, it is important to consider the cortex as part of an integrated system of the brain, the body, the environment in which the brain and body develops and evolves, and the affordances available within a particular environmental context; changes in any part of this brain/body/environment network impact the neocortex. We provide data from comparative studies on a wide variety of mammals that demonstrate that body morphology, the sensory epithelium, and the use of a particular morphological structure have a profound impact on neocortical organization and connections.

Kinematic analysis of sensorimotor behavior during variable ladder rung walking in short-tailed opossums (.

This protocol presents a workflow for detecting differences in kinematics between experimental conditions. It is tailored for short-tailed opossums but can be applied to any species capable of completing the ladder rung task. There are four phases of this protocol: (1) data collection, (2) pose tracking, (3) analysis of single trials, and (4) cross-condition comparisons.

Of mice and monkeys: Somatosensory processing in two prominent animal models.

Our understanding of the neural basis of somatosensation is based largely on studies of the whisker system of mice and rats and the hands of macaque monkeys. Results across these animal models are often interpreted as providing direct insight into human somatosensation. Work on these systems has proceeded in parallel, capitalizing on the strengths of each model, but has rarely been considered as a whole.

Available Sensory Input Determines Motor Performance and Strategy in Early Blind and Sighted Short-Tailed Opossums.

The early loss of vision results in a reorganized neocortex, affecting areas of the brain that process both the spared and lost senses, and leads to heightened abilities on discrimination tasks involving the spared senses. Here, we used performance measures and machine learning algorithms that quantify behavioral strategy to determine if and how early vision loss alters adaptive sensorimotor behavior. We tested opossums on a motor task involving somatosensation and found that early blind animals had increased limb placement accuracy compared with sighted controls, while showing similarities in crossing strategy.

Modelling the emergence of whisker barrels.

Brain development relies on an interplay between genetic specification and self-organization. Striking examples of this relationship can be found in the somatosensory brainstem, thalamus, and cortex of rats and mice, where the arrangement of the facial whiskers is preserved in the arrangement of cell aggregates to form precise somatotopic maps. We show in simulation how realistic whisker maps can self-organize, by assuming that information is exchanged between adjacent cells only, under the guidance of gene expression gradients.

Distributed Motor Control of Limb Movements in Rat Motor and Somatosensory Cortex: The Sensorimotor Amalgam Revisited.

Which areas of the neocortex are involved in the control of movement, and how is motor cortex organized across species? Recent studies using long-train intracortical microstimulation demonstrate that in addition to M1, movements can be elicited from somatosensory regions in multiple species. In the rat, M1 hindlimb and forelimb movement representations have long been thought to overlap with somatosensory representations of the hindlimb and forelimb in S1, forming a partial sensorimotor amalgam. Here we use long-train intracortical microstimulation to characterize the movements elicited across frontal and parietal cortex.

Early postnatal gene expression in the developing neocortex of prairie voles (Microtus ochrogaster) is related to parental rearing style.

The earliest and most prevalent sensory experience includes tactile, thermal, and olfactory stimulation delivered to the young via contact with the mother, and in some mammals, the father. Prairie voles (Microtus ochrogaster), like humans, are biparental and serve as a model for understanding the impact of parent/offspring interactions on the developing brain. Prairie voles also exhibit natural variation in the level of tactile stimulation delivered by the parents to the offspring, and this has been well documented and quantified.

Limit cycle dynamics can guide the evolution of gene regulatory networks towards point attractors.

Developmental dynamics in Boolean models of gene networks self-organize, either into point attractors (stable repeating patterns of gene expression) or limit cycles (stable repeating sequences of patterns), depending on the network interactions specified by a genome of evolvable bits. Genome specifications for dynamics that can map specific gene expression patterns in early development onto specific point attractor patterns in later development are essentially impossible to discover by chance mutation alone, even for small networks. We show that selection for approximate mappings, dynamically maintained in the states comprising limit cycles, can accelerate evolution by at least an order of magnitude.

A Modular Approach to Vocal Learning: Disentangling the Diversity of a Complex Behavioral Trait.

Vocal learning is a behavioral trait in which the social and acoustic environment shapes the vocal repertoire of individuals. Over the past century, the study of vocal learning has progressed at the intersection of ecology, physiology, neuroscience, molecular biology, genomics, and evolution. Yet, despite the complexity of this trait, vocal learning is frequently described as a binary trait, with species being classified as either vocal learners or vocal non-learners.

The Multiple Representations of Complex Digit Movements in Primary Motor Cortex Form the Building Blocks for Complex Grip Types in Capuchin Monkeys.

In the present study, we investigated motor cortex (M1) and a small portion of premotor and parietal cortex using intracortical microstimulation in anesthetized capuchin monkeys. Capuchins are the only New World monkeys that have evolved an opposable thumb and use tools in the wild. Like most Old World monkeys and humans, capuchin monkeys have highly dexterous hands.

Not all cortical expansions are the same: the coevolution of the neocortex and the dorsal thalamus in mammals.

A central question in comparative neurobiology concerns how evolution has produced brains with expanded neocortices, composed of more areas with unique connectivity and functional properties. Some mammalian lineages, such as primates, exhibit exceptionally large cortices relative to the amount of sensory inputs from the dorsal thalamus, and this expansion is associated with a larger number of distinct cortical areas, composing a larger proportion of the cortical sheet. We propose a link between the organization of the neocortex and its expansion relative to the size of the dorsal thalamus, based on a combination of work in comparative neuroanatomy and experimental research.

Alterations in cortical and thalamic connections of somatosensory cortex following early loss of vision.

Early loss of vision produces dramatic changes in the functional organization and connectivity of the neocortex in cortical areas that normally process visual inputs, such as the primary and second visual area. This loss also results in alterations in the size, functional organization, and neural response properties of the primary somatosensory area, S1. However, the anatomical substrate for these functional changes in S1 has never been described.

The Combinatorial Creature: Cortical Phenotypes within and across Lifetimes.

The neocortex is one of the most distinctive structures of the mammalian brain, yet also one of the most varied in terms of both size and organization. Multiple processes have contributed to this variability, including evolutionary mechanisms (i.e.

The rod signaling pathway in marsupial retinae.

The retinal rod pathway, featuring dedicated rod bipolar cells (RBCs) and AII amacrine cells, has been intensely studied in placental mammals. Here, we analyzed the rod pathway in a nocturnal marsupial, the South American opossum Monodelphis domestica to elucidate whether marsupials have a similar rod pathway. The retina was dominated by rods with densities of 338,000-413,000/mm².

Neural Coding of Whisker-Mediated Touch in Primary Somatosensory Cortex Is Altered Following Early Blindness.

Sensory systems do not develop and function independently of one another, yet they are typically studied in isolation. Effects of multisensory interactions on the developing neocortex can be revealed by altering the ratios of incoming sensory inputs associated with different modalities. We investigated neural responses in primary somatosensory cortex (S1) of short-tailed opossums (; either sex) after the elimination of visual input through bilateral enucleation very early in development.

Cortical connections of area 2 and posterior parietal area 5 in macaque monkeys.

The overarching goal of the current investigation was to examine the connections of anterior parietal area 2 and the medial portion of posterior parietal area 5 in macaque monkeys; two areas that are part of a network involved reaching and grasping in primates. We injected neuroanatomical tracers into specified locations in each field and directly related labeled cells to histologically identified cortical field boundaries. Labeled cells were counted so that the relative density of projections to areas 2 and 5 from other cortical fields could be determined.

Architectonic characteristics of the visual thalamus and superior colliculus in titi monkeys.

Titi monkeys are arboreal, diurnal New World monkeys whose ancestors were the first surviving branch of the New World radiation. In the current study, we use cytoarchitectonic and immunohistochemical characteristics to compare titi monkey subcortical structures associated with visual processing with those of other well-studied primates. Our goal was to appreciate features that are similar across all New World monkeys, and primates in general, versus those features that are unique to titi monkeys and other primate taxa.

Representations of Fine Digit Movements in Posterior and Anterior Parietal Cortex Revealed Using Long-Train Intracortical Microstimulation in Macaque Monkeys.

The current investigation in macaque monkeys utilized long-train intracortical microstimulation to determine the extent of cortex from which movements could be evoked. Not only were movements evoked from motor areas (PMC and M1), but they were also evoked from posterior parietal (5, 7a, 7b) and anterior parietal areas (3b, 1, 2). Large representations of digit movements involving only the index finger (D2) and thumb (D1), were elicited from areas 1, 2, 7b, and M1.

Cortical plasticity following stripe rearing in the marsupial Monodelphis domestica: neural response properties of V1.

Unlabelled: The functional organization of the primary visual area (V1) and the importance of sensory experience in its normal development have been well documented in eutherian mammals. However, very few studies have investigated the response properties of V1 neurons in another large class of mammals, or whether sensory experience plays a role in shaping their response properties. Thus we reared opossums (Monodelphis domestica) in normal and vertically striped cages until they reached adulthood.

The evolution of whisker-mediated somatosensation in mammals: Sensory processing in barrelless S1 cortex of a marsupial, Monodelphis domestica.

Movable tactile sensors in the form of whiskers are present in most mammals, but sensory coding in the cortical whisker representation has been studied almost exclusively in mice and rats. Many species that possess whiskers lack the modular "barrel" organization found in the primary somatosensory cortex (S1) of mice and rats, but it is unclear how whisker-related input is represented in these species. We used single-unit extracellular recording techniques to characterize receptive fields and response properties in S1 of Monodelphis domestica (short-tailed opossum), a nocturnal, terrestrial marsupial that shared its last common ancestor with placental mammals over 160 million years ago.