# Functional characterization of distinct cortical inputs to higher-order visual thalamus

> **NIH NIH F31** · SALK INSTITUTE FOR BIOLOGICAL STUDIES · 2020 · $43,064

## Abstract

Abstract
The lateral posterior nucleus of the thalamus (LP), which is the mouse analog of the primate pulvinar, is a
higher-order visual thalamic nucleus that is thought to play an important role in visual attention. A key
difference between LP/pulvinar and the first-order visual thalamic nucleus LGN is that LP/pulvinar receives two
distinct cortical inputs: one from layer 6 that it shares with LGN, and one from layer 5 that avoids LGN. Prior
studies of the morphological and physiological characteristics of these inputs have suggested that the two
corticothalamic (CT) populations may have very different effects on activity in LP/pulvinar. In particular, it has
been hypothesized that the layer 5 CT group, which has large synaptic terminals in LP/pulvinar that resemble
retinal ganglion cell terminals in LGN, provide the primary “driving” input to LP/pulvinar and shape its visual
response properties. Meanwhile, the layer 6 CT population, which has more numerous but smaller terminals in
LP/pulvinar, may contribute “modulatory” input. While this “driver/modulator” framework has been very
influential in generating hypotheses about LP/pulvinar's interactions with cortex, whether layer 5 and layer 6
CT cells are functional drivers and modulators, respectively, of LP/pulvinar has never been directly tested. This
is due to the lack of tools for selectively targeting each of these CT populations in primates, in which the
pulvinar has been much more extensively studied than LP in rodents. However, transgenic and viral tools
enabling cell-type specificity as well as a recently improved understanding of the mouse visual system now
make this a tractable question in mice. To test this longstanding hypothesis, the layer 5 CT population will be
selectively targeted for optogenetic manipulations by injecting a retrograde viral vector carrying Cre
recombinase to superior colliculus (which is another projection target of layer 5 CT neurons in addition to LP),
and layer 6 CT neurons will be specifically targeted with the Ntsr1-Cre transgenic mouse line. Multi-shank
neural probes with high-density microelectrode arrays will be used to record extracellular single-unit activity in
LP of awake mice while optogenetically manipulating CT neurons. This will make it possible to measure each
CT subpopulation's effect on visual and spontaneous activity in LP and determine if they are functional
“drivers” or “modulators”. Layer 5 and layer 6 CT neurons originating from primary versus higher visual cortex
will also be separately targeted in order to more precisely evaluate how different visual cortical areas
communicate with LP. This will also address the question of whether either of the CT subpopulations relay the
visual preferences of their source cortical area to LP as would be hypothesized of a functional “driver” but not a
“modulator”. Together, the proposed set of experiments will have significant implications for understanding
LP/pulvinar's role in visual processing throu...

## Key facts

- **NIH application ID:** 9841937
- **Project number:** 5F31EY028853-03
- **Recipient organization:** SALK INSTITUTE FOR BIOLOGICAL STUDIES
- **Principal Investigator:** Megan Anne Kirchgessner
- **Activity code:** F31 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $43,064
- **Award type:** 5
- **Project period:** 2018-01-16 → 2021-01-15

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/9841937

## Citation

> US National Institutes of Health, RePORTER application 9841937, Functional characterization of distinct cortical inputs to higher-order visual thalamus (5F31EY028853-03). Retrieved via AI Analytics 2026-05-23 from https://api.ai-analytics.org/grant/nih/9841937. Licensed CC0.

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