A morphological basis for orientation tuning in primary visual cortex.
Feedforward connections are thought to be important in the generation of orientation-selective responses in visual cortex by establishing a bias in the sampling of information from regions of visual space that lie along a neuron's axis of preferred orientation. It remains unclear, however, which structural elements-dendrites or axons-are ultimately responsible for conveying this sampling bias. To explore this question, we have examined the spatial arrangement of feedforward axonal connections that link non-oriented neurons in layer 4 and orientation-selective neurons in layer 2/3 of visual cortex in the tree shrew. Target sites of labeled boutons in layer 2/3 resulting from focal injections of biocytin in layer 4 show an orientation-specific axial bias that is sufficient to confer orientation tuning to layer 2/3 neurons. We conclude that the anisotropic arrangement of axon terminals is the principal source of the orientation bias contributed by feedforward connections.
Mooser
François
F
Department of Neurobiology, Box 3209 Duke University Medical Center, Durham, North Carolina 27710, USA.
Bosking
William H
WH
Fitzpatrick
David
D
D000818:Animals; D001369:Axons / Q000502:physiology*; D005260:Female; D007091:Image Processing, Computer-Assisted; D008297:Male; D008959:Models, Neurological; D009949:Orientation / Q000502:physiology; D014418:Tupaiidae / Q000033:anatomy & histology* / Q000502:physiology; D014793:Visual Cortex / Q000033:anatomy & histology* / Q000502:physiology; D014795:Visual Pathways / Q000033:anatomy & histology* / Q000502:physiology; D014796:Visual Perception / Q000502:physiology*