CiNet Seminar: Toru Takahata “Possible parallel projections from the pulvinar to V2 in macaques”

CiNet  Seminar

August 22, 2019
(We may stop the seminar at 13:00, but continue the discussion until 13:15.)
CiNet 1F Conference Room

Toru Takahata
Interdisciplinary Institute of Neuroscience and Technology
Zhejiang University

Host: Hiromasa Takemura (Kida Group)

Besides the conventional visual stream through the lateral geniculate nucleus (LGN) and V1 (geniculate stream), primates apparently utilize another visual stream through the superior colliculus (SC), the pulvinar nuclei (pulvinar stream) and extrastriate visual cortices. Pulvinar nuclei greatly evolved in primate species, and the counter part is tiny in rodents. The observations of “blindsight” patients illustrate significant contribution of the pulvinar to visual perception. However, the development and functional importance of this stream is poorly understood. Here, we studied precise connectivity patterns and existence of sub-compartments within the pulvinar to provide anatomical and molecular basis for future physiological and molecular studies. It has been known that primate V2 is subdivided into at least three sub-compartments: thick stripes, thin stripes, and pale stripes. These histochemical sub-compartments are associated with functional reactivity to distinct types of visual stimuli, such that thick stripes are more responsive to directional movement and depth coding, thin stripes are more responsive to color stimuli, and pale stripes are more responsive to form and orientation of the visual stimuli. They are recognized as “parallel visual pathways”: The “P” pathway that goes through geniculate parvocellular layers/V1 cytochrome oxidase (CO) blobs/V2 thin stripes and the “M” pathway that goes through geniculate magnocellular layers/V1 interblobs/V2 thick stripes. On the other hand, it was previously revealed that thick and thin stripes receive direct projections from the pulvinar, but pale stripes do not. Furthermore, previous electrophysiological studies also revealed that there are two distinct visuotopic maps within the lateral pulvinar. Thus, we hypothesized that there is another set of parallel pathways between the pulvinar and V2. To address this possibility, we injected different kinds tracers, BDA, CTB-Alexa-488 and CTBAlexa-555, into three consecutive thick/thin stripes in V2 and examined retrograde labeling in the pulvinar of macaques. As a result, we found that there are a few patchy clusters of retrograde labeling for each tracer, and that thick stripe-projecting compartments and thin stripe-projecting compartments are segregated, although they are located next to each other within all clusters. Our study indicates a possibility that there are several parallel pathways within the pulvinar-V2 projection, similar to the manner of geniculo-striate projections.