Morphological Substrates for Parallel Streams of Corticogeniculate Feedback Originating in Both V1 and V2 of the Macaque Monkey

Abstract

Corticothalamic circuits are essential for reciprocal information exchange between the thalamus and cerebral cortex. Nevertheless, the role of corticothalamic circuits in sensory processing remains a mystery. In the visual system, afferents from retina to the lateral geniculate nucleus (LGN) and from LGN to primary visual cortex (V1) are organized into functionally distinct parallel processing streams. Physiological evidence suggests corticogeniculate feedback may be organized into parallel streams; however, little is known about the diversity of corticogeniculate neurons, their local computations, or the structure-function relationship among corticogeniculate neurons. We used a virus-mediated approach to label and reconstruct the complete dendritic and local axonal arbors of identified corticogeniculate neurons in the macaque monkey. Our results reveal morphological substrates for parallel streams of corticogeniculate feedback based on distinct classes of neurons in V1 and V2. These results support the hypothesis that distinct populations of feedback neurons provide independent and unique information to the LGN.

Corticogeniculate feedback sharpens the temporal precision and spatial resolution of visual signals in the ferret

“…S1 C and D). Consistent with prior studies of retrograde-labeled CG neurons (26,(29)(30)(31), virus-infected CG neurons were entirely restricted to layer 6 of areas 17 and 18 in the visual cortex ( Fig. 1C and SI Appendix, Fig.…”

“…G-deleted rabies virus is taken up by axon terminals and moves exclusively in the retrograde direction to infect cell bodies but is prohibited from crossing synapses (22)(23)(24)(25). We took advantage of the fact that CG neurons are the only visual cortical neurons that project axons to the LGN (26)(27)(28), combined with the exclusively retrograde action of G-deleted rabies virus, to selectively infect CG neurons following injection of virus into the LGN (29) (Fig. 1A).…”

Large-scale Reconstructions and Independent, Unbiased Clustering Based on Morphological Metrics to Classify Neurons in Selective Populations

“…Note: The tissue examined in this study was prepared as a part of a separate study 5 . Therefore, all of the experimental methods involving the use of animals have been described in detail in the Experimental Methods section of Briggs et al (2016).…”

“…Therefore, all of the experimental methods involving the use of animals have been described in detail in the Experimental Methods section of Briggs et al (2016). All procedures involving animals conducted as a part of the prior study were approved by the Institutional Animal Care and Use Committees.…”

“…Methods for labeling and reconstructing neurons have greatly improved with recent innovations, including genetic and virus-mediated circuit tracing approaches 3,4 , enabling more comprehensive morphological surveys of neuronal populations 5 . In addition to improvements in labeling individual neurons, quantitative data analysis techniques have also emerged that enable independent and unbiased classification of neurons into distinct subpopulations based on morphological data 5,6 . These unbiased techniques are an improvement upon more traditional qualitative classification methods that have been the standard in the field for over a century.…”