RELATIONSHIP BETWEEN INTRINSIC CONNECTIONS AND FUNCTIONAL ARCHITECTURE REVEALED BY OPTICAL IMAGING AND IN-VIVO TARGETED BIOCYTIN INJECTIONSIN PRIMATE STRIATE CORTEX

In primate primary visual cortex, neurons sharing similar response pro perties are clustered together forming functional domains that appear as a mosaic of patches or bands, often traversing the entire corticaL depth from the pia to the white matter. Similarly, each cortical site connects laterally through an extensive network of intrinsic projectio ns that are organized in multiple clusters (patches) and reach distanc es of up to a few millimeters. The relationship between the functional domains and these lateraLly connected patches has remained a controve rsial issue despite intensive research efforts. To investigate this re lationship, we obtained high-resolution functional maps of the cortica l architecture by in vivo optical imaging. Subsequently, extracellular injections of the sensitive anterograde tracer biocytin were targeted into selected functional domains. Within the ocular dominance system, we found that long-range intrinsic connections tended to link the mon ocular regions of same-eye ocular dominance columns. Furthermore, we d iscovered that binocular domains formed a separate set of connections in area V1; binocular regions were selectively connected among themsel ves but were not connected to strictly monocular regions, suggesting t hat they constitute a distinct columnar system. In the other sub-syste m subserving orientation preference, patches of intrinsic connections tended to link domains sharing similar orientation preferences. Analys es of the precision of these connections indicated that in both functi onal subsystems, <15% of the connections were between domains having o rthogonal response properties. However, their selectivity was limited; almost-equal-to 30% +/- 10% of the interconnected patches contained n eurons exhibiting orientation tuning that differed from those found at the injection sites by at least 45-degrees. At short range (up to 400 mum from the injection site), this casual trend seemed markedly accen tuated; the local, synaptic-rich axonal and dendritic arbors crossed f reely through columns of diverse functional properties. These complex sets of connections can endow cortical neurons with a rich diversity o f response properties and broad tuning.