Bioinspired Devices Quotes

“How is regeneration of the spinal cord in the salamander related to its initial development ? There is now evidence that in the salamander, the steps of progenitor cell-patterning and controlled neurogenesis that naturally regenerate a severed tail largely recapitulate the steps followed during early embryonic development to initially build the central nervous system. For example, ependymal cells are descendants of radial glial cells retained from the earliest developmental stages in regenerating vertebrates. The ependymal tube that gives rise to regenerated spinal cord following salamander tail amputation is very similar in appearance to the early structure of the neural tube of developing amniotes. But how does that recapitulation occur ? By using a transgenic axolotl that expresses green fluorescent proteins (GFPs), they further examined the regenerated spinal cord by replacing a segment of the spinal cord from a typical animal with a piece of the spinal cord from a GFP-expressing animal - that is, one with green fluorescent cells. They found that the implanted cells in the experimental animals regenerated a green spinal cord ! Thus, regeneration may be a more neural stem-cell like, or pluripotent, state as a response to injury.”
― Eugene C. Goldfield, Bioinspired Devices: Emulating Nature’s Assembly and Repair Process

“At the heart of the decoding problem is how to understand the vast information contained in neural signals, the challenge of what is being called "big data". For neuroscientists, big data is a means for exploring populations of neurons to discover the macroscopic signatures of dynamical systems, rather than attempting to make sense of the activity of individual neurons. Two surprising results from numerous experiments recording from neurons in different brain regions have revealed a wonderful secret of nature about the relation between the number of neurons recorded and and their dimensionality (the number of principal components required to explain a fixed percentage of variance). First, the dimensionality of the neural data is much smaller than the number of recorded neurons. Second, when dimensionality procedures are used to extract neuronal state dynamics, the resulting low-dimensional neural trajectories reveal portraits of the behavior of a dynamical system. This means that it may not be necessary to record from many more neurons within a brain region in order to accurately recover its internal state-space dynamics.”
― Eugene C. Goldfield, Bioinspired Devices: Emulating Nature’s Assembly and Repair Process

“Diffusion tensor imaging (DTI), or tractography, is an in vivo MRI technology that uses water diffusion in brain tissue to visualize in stunning detail the brain's three-dimensional white matter anatomy. DTI is made possible by characterizing water diffusion in tissues by means of a mathematical tool called a tensor, based on matrix algebra: (1) a 3 x 3 matrix, called a diffusion tensor, is used to characterize the three-dimensional properties of water molecule diffusion; (2) from each diffusion tensor, the three pairs of eigenvalues and eigenvectors are calculated using matrix diagonalization; and (3) the eigenvector that corresponds to the largest eigenvalue is selected as the primary eigenvector. A 'streamline' algorithm then creates "tracts" by connecting adjacent voxels if their directional bias is above some treshold level. Does the orientation of the primary eigenvector coincide with that of the actual axon fibers in most white matter tracts ? Takahashi et al. (2011), for example, have demonstrated that radial organization of the subplate revealed via tractography directly correlates with its radial cellular organization, and G. Xu et al. (2014) were able to determine that transient radial coherence of white matter in the developing fetus reflected a composite of radial glial fibers, penetrating blood vessels, and radial axons.”
― Eugene C. Goldfield, Bioinspired Devices: Emulating Nature’s Assembly and Repair Process