Content area
Full Text
A R T I C L E S
Thalamus provides layer 4 of primary visual cortex with orientation- and direction-tuned inputs
Wenzhi Sun, Zhongchao Tan, Brett D Mensh & Na Ji
Understanding the functions of a brain region requires knowing the neural representations of its myriad inputs, local neuronsand outputs. Primary visual cortex (V1) has long been thought to compute visual orientation from untuned thalamic inputs, but very few thalamic inputs have been measured in any mammal. We determined the response properties of ~28,000 thalamic boutons and ~4,000 cortical neurons in layers 15 of awake mouse V1. Using adaptive optics that allows accurate measurement of bouton activity deep in cortex, we found that around half of the boutons in the main thalamorecipient L4 carried orientation-tuned information and that their orientation and direction biases were also dominant in the L4 neuron population, suggesting that these neurons may inherit their selectivity from tuned thalamic inputs. Cortical neurons in all layers exhibited sharper tuning than thalamic boutons and a greater diversity of preferred orientations. Our results provide data-rich constraints for refining mechanistic models of cortical computation.
npg 201 6 Nature America, Inc. All rights reserved.
In the conventional pathway of mammalian early vision, information from the retina is conveyed by the dorsal lateral geniculate nucleus (dLGN) of the thalamus to L4 of V1 and, after computations in the cortical circuit, is communicated to the rest of the brain1 (that is, mainly dLGN L4 L2/3L5). Since the discovery of orientation selectivity in V1 neurons2, how the mammalian nervous system computes the orientation of visual stimuli has been a flagship question in neuroscience.
Providing the principal thalamic inputs to V1 (Supplementary Fig. 1)3, dLGN has long been thought to convey only untuned inputs to cortex. Orientation selectivity is therefore considered to be a feature computed in cortex, beginning at the first stage of thalamocortical interaction46. In the classical feedforward model of Hubel and Wiesel7, cortical orientation selectivity is generated by the convergence of untuned dLGN inputs with offset receptive fields onto a L4 simple cell. Although such an arrangement has not been directly observed, existing experimental evidence is consistent with its basic premise that thalamic inputs to the main thalamorecipient L4 lack orientation tuning8.
In mouse, some dLGN neurons encode...