Podcast with Kathy Rockland on neocortex and cortical anatomy

Is the neocortex really uniform , and do feedforward and feedback connections mean what we think they mean? Kathy Rockland challenges foundational assumptions about cortical organization with evidence that structure and function are more discrepant than textbooks suggest. Subscribe for more from the Convergent Science Network podcast series. Kathy Rockland is a neuroanatomist who has spent her career examining cortical connectivity at a level of detail that most theorists and imagers never encounter. In this interview, she delivers a series of provocative challenges to standard assumptions about how the neocortex is organized. Her first point is counterintuitive: the most striking property of cortical axons is not their specificity but their divergence. When you trace individual axons and examine their collateralization, the word that comes to mind is distributed , connections fan out broadly before any question of specificity arises. Rockland then dismantles the textbook story of ocular dominance columns. The functional columns are unambiguously about 500 microns in diameter, but the anatomical inputs that supposedly create them, thalamocortical axons from the LGN, come in at wildly different scales: parvocellular arbors at 250 microns, magnocellular clusters larger with multiple foci, layer 4A inputs at 100 microns, and layer 1 projections that are highly divergent. Some operation within intrinsic cortical circuitry must be converging these mismatched inputs into the 500-micron functional unit. This means that thalamocortical connections are not the basis of ocular dominance columns in any simple sense , the cortex itself is doing something essential to create the functional organization we observe. The conversation turns to feedforward and feedback pathways, which Rockland argues carry misleading temporal assumptions. She proposes reframing these as layer-4-biased connections and layer-1-biased connections, respectively , a description that captures the anatomical reality without implying a sequential relay. In rodents, the laminar scheme breaks down substantially, and even in primates there are abundant exceptions. Rockland also notes that the supposed unimodality of primary sensory areas is threshold-dependent: lower your detection threshold and cross-modal inputs appear even in monkey V1 and V2. Her overarching message is that structure-function correlation, long treated as a guiding principle, is more often the exception than the rule. The brain works, but not in the way our simplified models suggest.