Three brain collections for comparative neuroanatomy and neuroimaging

A review of behavioral methods for the evaluation of cognitive performance in animal models: Current techniques and links to human cognition

INTRODUCTION

Memory is defined as the ability to store, maintain and retrieve information. Learning is the acquisition of information that changes behavior and memory. Stress, dementia, head trauma, amnesia, Alzheimer's, Huntington, Parkinson's, Wernicke-Korsakoff syndrome (WKS) may be mentioned among the diseases in which memory and learning are affected. The task of understanding deficits in memory and learning in humans is daunting due to the complexity of neural and cognitive mechanisms in the nervous system. This job is made more difficult for clinicians and researchers by the fact that many techniques used to research memory are not ethically acceptable or technically feasible for use in humans. Thus, animal models have been necessary alternative for studying normal and disordered learning and memory. This review attempts to bridge these domains to allow biomedical researchers to have a firm grasp of "memory" and "learning" as constructs in humans whereby they may then select the proper animal cognitive test.

RESULTS AND CONCLUSION

Various tests (open field habituation test, Y-maze test, passive avoidance test, step-down inhibitory avoidance test, active avoidance test, 8-arms radial maze test, Morris water maze test, radial arm water maze, novel object recognition test and gait function test) have been designed to evaluate different kinds of memory. Each of these tests has their strengths and limits. Abnormal results obtained using these tasks in non-human animals indicate malfunctions in memory which may be due to several physiological and psychological diseases of nervous system. Further studies by using the discussed tests can be very beneficial for achieving a therapeutic answer to these diseases.

Neural Correlates of Vocal Repertoire in Primates

Understanding the nature of the relationship between vocal complexity and brain architecture across non-human primates may help elucidate some of the key elements underlying the evolution of human speech. Here, we report a positive correlation between vocal repertoire size and the relative size of cortical association areas (governing voluntary control over behavioural output) in non-human primates. We further demonstrate that a hominid grade shift in the relative volume of cortical association areas coincides with a similar grade shift in the hypoglossal nucleus (which is associated with the cranial nerve that innervates the muscles of the tongue). Our results support a qualitative continuity in the neural correlates of vocal repertoire, but a quantitative discontinuity in the extent to which the neural system supporting speech is innervated by cortical association areas in great apes and humans.

Primate Brain Anatomy: New Volumetric MRI Measurements for Neuroanatomical Studies

Since the publication of the primate brain volumetric dataset of Stephan and colleagues in the early 1980s, no major new comparative datasets covering multiple brain regions and a large number of primate species have become available. However, technological and other advances in the last two decades, particularly magnetic resonance imaging (MRI) and the creation of institutions devoted to the collection and preservation of rare brain specimens, provide opportunities to rectify this situation. Here, we present a new dataset including brain region volumetric measurements of 39 species, including 20 species not previously available in the literature, with measurements of 16 brain areas. These volumes were extracted from MRI of 46 brains of 38 species from the Netherlands Institute of Neuroscience Primate Brain Bank, scanned at high resolution with a 9.4-T scanner, plus a further 7 donated MRI of 4 primate species. Partial measurements were made on an additional 8 brains of 5 species. We make the dataset and MRI scans available online in the hope that they will be of value to researchers conducting comparative studies of primate evolution.

A cerebellar substrate for cognition evolved multiple times independently in mammals

Given that complex behavior evolved multiple times independently in different lineages, a crucial question is whether these independent evolutionary events coincided with modifications to common neural systems. To test this question in mammals, we investigate the lateral cerebellum, a neurobiological system that is novel to mammals, and is associated with higher cognitive functions. We map the evolutionary diversification of the mammalian cerebellum and find that relative volumetric changes of the lateral cerebellar hemispheres (independent of cerebellar size) are correlated with measures of domain-general cognition in primates, and are characterized by a combination of parallel and convergent shifts towards similar levels of expansion in distantly related mammalian lineages. Results suggest that multiple independent evolutionary occurrences of increased behavioral complexity in mammals may at least partly be explained by selection on a common neural system, the cerebellum, which may have been subject to multiple independent neurodevelopmental remodeling events during mammalian evolution.

Is the prefrontal cortex especially enlarged in the human brain allometric relations and remapping factors

There has been no agreement as to whether the prefrontal cortex is especially enlarged in the human brain. To answer this question, we analyzed the only two datasets that provide information on total prefrontal cortex volume based on cytoarchitectonic criteria. One delineated the prefrontal cortex proper on the basis of cytoarchitectonic criteria; the other used a proxy of the prefrontal cortex based on a cytoarchitectonic delineation of the frontal lobe. To investigate whether all cortical association areas, including the prefrontal cortex, are enlarged in the human brain, we scaled the different areas to a common reference, the primary visual cortex. To investigate whether the prefrontal cortex is more enlarged than other association areas, we scaled it relative to its inputs from and outputs to other nonprimary areas. We carried out separate regression analyses using different data samples as a predictive baseline group: data for monkeys alone informs us on whether great apes are different from monkeys; data for all non-human anthropoids, including great apes, informs us on whether humans are different from all other primates. The analyses show that the value for the human prefrontal cortex is greater than expected, and that this is true even when data for the great apes are included in the analysis. They also show that the chimpanzee prefrontal cortex is greater than expected for a monkey with a similar sized cortex. We discuss possible functional consequences.

Laterality and the evolution of the prefronto-cerebellar system in anthropoids

There is extensive evidence for an early vertebrate origin of lateralized motor behavior and of related asymmetries in underlying brain systems. We investigate human lateralized motor functioning in a broad comparative context of evolutionary neural reorganization. We quantify evolutionary trends in the fronto-cerebellar system (involved in motor learning) across 46 million years of divergent primate evolution by comparing rates of evolution of prefrontal cortex, frontal motor cortex, and posterior cerebellar hemispheres along individual branches of the primate tree of life. We provide a detailed evolutionary model of the neuroanatomical changes leading to modern human lateralized motor functioning, demonstrating an increased role for the fronto-cerebellar system in the apes dating to their evolutionary divergence from the monkeys (∼30 million years ago (Mya)), and a subsequent shift toward an increased role for prefrontal cortex over frontal motor cortex in the fronto-cerebellar system in the Homo-Pan ancestral lineage (∼10 Mya) and in the human ancestral lineage (∼6 Mya). We discuss these results in the context of cortico-cerebellar functions and their likely role in the evolution of human tool use and speech.

Sexual dimorphism and laterality in the evolution of the primate prefrontal cortex

Social selective pressures are commonly considered as the main driving force of primate brain evolution. Primate social behaviour is, however, known to be sexually dimorphic, and no previous study has made a direct comparison between male and female brain structures across species. We quantify sex-specific evolutionary trends in the prefrontal cortex of anthropoid primates (including humans) to investigate how sexual selection has shaped brain evolution in primates. The prefrontal cortex is of particular importance to the investigation of sexual dimorphism in primate brain evolution because of its association to those cognitive capacities central to primate (and human) evolution: sociality and higher-order cognitive processing. Our results demonstrate sex-by-hemisphere differences in the evolution of the prefrontal cortex in humans and non-human anthropoid primates congruent with the principal selective pressures considered to underlie anthropoid behavioural evolution. Our findings further show how sexual selection can shape brain adaptation in primates and provide an evolutionary framework for interpreting sex and sex-by-hemisphere differences in cortical organization in humans and non-human primates.

Modeling the evolution of cortico-cerebellar systems in primates

Although it is commonly accepted that brains work as functionally distributed systems in which interconnected structures work together in processing particular types of information, few studies have investigated the evolution of functionally specialized neural systems across many different lineages. MR-related research has provided in-depth information on connectivity patterns, but because of its focus on particular species, it has given only indicative clues about evolutionary patterns shaping brain organization across primates. Here, we combine depth with breadth of analysis by investigating patterns of covarying size evolution in substructures of the cortico-cerebellar system across 19 anthropoid species spanning 35 million years of divergent evolution. Results demonstrate two distinct patterns of size covariation in substructures of the cortico-cerebellar system, suggesting neural systems involving profuse cortico-cerebellar connections are a major factor in explaining the evolution of anthropoid brain organization. We set out an evolutionary model of relative cortico-cerebellar expansion and provide a detailed picture of its branch-specific evolutionary history suggesting the ape radiation is the clade with the strongest and most consistent evolutionary history in relative (frontal) cortico-cerebellar expansion.