TWO papers with starkly contradictory conclusions, published three weeks apart, have reignited debate about whether adult human brains can grow new neurons. For over a century, neuroscientists believed brains have acquired all the neurons they will ever have shortly after birth. But research over the past two decades has questioned this, producing evidence that new neurons are indeed generated in the adults of several species, people included. The matter is of more than just theoretical concern.
Brain size and cortical structure in the adult human brain
Study: Does Adult Neurogenesis Exist in Humans? - The Atlantic
We investigated the scale relationship between size and cortical structure of human brains in a large sample of magnetic resonance imaging data. We found significantly larger scaling exponents than geometrically predicted for cortical surface area, absolute mean curvature in sulcal regions and in sulcal walls, and smaller ones for cortical volume and thickness. As brain size increases, the cortex thickens only slightly, but the degree of sulcal convolution increases dramatically, indicating that human cortices are not simply scaled versions of one another. Our results are consistent with previous hypotheses that greater local clustering of interneuronal connections would be required in a larger brain, and fiber tension between local cortical areas would induce cortical folds. We suggest that sex effects are explained by brain size effects in cortical structure at a macroscopic and lobar regional level, and that it is necessary to consider true relationships between cortical measures and brain size due to the limitations of linear stereotaxic normalization. Abstract We investigated the scale relationship between size and cortical structure of human brains in a large sample of magnetic resonance imaging data.
Abundant Neurogenesis Found in Adult Humans’ Hippocampi
Sex differences in the human brain are of interest for many reasons: for example, there are sex differences in the observed prevalence of psychiatric disorders and in some psychological traits that brain differences might help to explain. We report the largest single-sample study of structural and functional sex differences in the human brain female, male participants; mean age Males had higher raw volumes, raw surface areas, and white matter fractional anisotropy; females had higher raw cortical thickness and higher white matter tract complexity. There was considerable distributional overlap between the sexes. Subregional differences were not fully attributable to differences in total volume, total surface area, mean cortical thickness, or height.
Most of our knowledge on human CNS circuitry and related disorders originates from model organisms. How well such data translate to the human CNS remains largely to be determined. Human brain slice cultures derived from neurosurgical resections may offer novel avenues to approach this translational gap.