Evolution of the amniote basal ganglia

Recent findings indicate that the basal ganglia of amniotes, i.e. modern birds, reptiles and mammals, contain similar neuronal subpopulations, as defined by the transmitters these neurons use and their connections. These data suggest that the evolution of the basal ganglia has been much more conservative than once believed and that this region of the forebrain performs a similar motor role in birds, reptiles and mammals. The basal ganglia of birds and reptiles, however, differ from those of mammals in that they appear to have their major influence over motor functions by an output to the tectum via the pretectum. In contrast, the mammalian basal ganglia are thought to have their major influence over motor functions by an output to the motor cortex via the thalamus.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/24712/1/0000133.pd

A proposal for a coordinated effort for the determination of brainwide neuroanatomical connectivity in model organisms at a mesoscopic scale

In this era of complete genomes, our knowledge of neuroanatomical circuitry remains surprisingly sparse. Such knowledge is however critical both for basic and clinical research into brain function. Here we advocate for a concerted effort to fill this gap, through systematic, experimental mapping of neural circuits at a mesoscopic scale of resolution suitable for comprehensive, brain-wide coverage, using injections of tracers or viral vectors. We detail the scientific and medical rationale and briefly review existing knowledge and experimental techniques. We define a set of desiderata, including brain-wide coverage; validated and extensible experimental techniques suitable for standardization and automation; centralized, open access data repository; compatibility with existing resources, and tractability with current informatics technology. We discuss a hypothetical but tractable plan for mouse, additional efforts for the macaque, and technique development for human. We estimate that the mouse connectivity project could be completed within five years with a comparatively modest budget.Comment: 41 page

Vertebrate brains and evolutionary connectomics: on the origins of the mammalian ‘neocortex’

The organization of the non-mammalian forebrain had long puzzled neurobiologists. Unlike typical mammalian brains, the telencephalon is not organized in a laminated 'cortical' manner, with distinct cortical areas dedicated to individual sensory modalities or motor functions. The two major regions of the telencephalon, the basal ventricular ridge (BVR) and the dorsal ventricular ridge (DVR), were loosely referred to as being akin to the mammalian basal ganglia. The telencephalon of non-mammalian vertebrates appears to consist of multiple 'subcortical' groups of cells. Analysis of the nuclear organization of the avian brain, its connections, molecular properties and physiology, and organization of its pattern of circuitry and function relative to that of mammals, collectively referred to as 'evolutionary connectomics', revealed that only a restricted portion of the BVR is homologous to the basal ganglia of mammals. The remaining dorsal regions of the DVR, wulst and arcopallium of the avian brain contain telencephalic inputs and outputs remarkably similar to those of the individual layers of the mammalian 'neocortex', hippocampus and amygdala, with instances of internuclear connections strikingly similar to those found between cortical layers and within radial 'columns' in the mammalian sensory and motor cortices. The molecular properties of these 'nuclei' in birds and reptiles are similar to those of the corresponding layers of the mammalian neocortex. The fundamental pathways and cell groups of the auditory, visual and somatosensory systems of the thalamus and telencephalon are homologous at the cellular, circuit, network and gene levels, and are of great antiquity. A proposed altered migration of these homologous neurons and circuits during development is offered as a mechanism that may account for the altered configuration of mammalian telencephalae

Are Visual Hierarchies in the Brains of the Beholders?: Constancy and Variability in the Visual System of Birds and Mammals

Contemporary concepts of the organization of the visual system began to emerge in the mid to late 19th century. It had long been appreciated that penetrating wounds of the occipital region of the brain resulted in blindness. Lesions of more lateral portions of the hemisphere often resulted in varying degrees of visual agnosias, though it was not until the middle third of the twentieth century that the contribution of such cortical areas to visual performance became an object of interest