Intrinsic collaterals of layer 6 Meynert cells and functional columns in primate V1

Meynert cells are a distinct type of large neuron which project to area MT/V5 and to subcortical targets, including the superior colliculus. They have recently been shown to have extensive intrinsic collaterals spreading up to 8.0 mm within layer 6 of area V1 [J Comp Neurol 441 (2001) 134]. Using intrinsic signal imaging combined with tracer injections, this study investigates how Meynert cell collaterals are mapped in relation to the functional architecture of area V1 in macaque monkeys. In particular, we examined whether terminations of individual axon segments are selective for same-eye or opposite-eye domains. Analysis of 39 anterogradely labeled axon segments (from six injection sites in four hemispheres) showed that terminal segments cross over several pairs of ocular dominance columns (ODCs) and contact both left- and right-eye ODCs, with a slight bias for the contralateral eye. This contrasts with the same-eye bias previously reported for intrinsic collaterals of pyramidal neurons in layer 3. The suggestion is that the system of Meynert intrinsic collaterals is involved with binocular interactions over wide sectors of the visual field. This might be related to processes such as optic flow or, especially given the wide-field spread, even contour completion or interpolation.