Matthew Adusei, MS - PhD Candidate, Neuroscience Graduate Program
Visual signals follow a feedforward progression: the dorsal lateral geniculate nucleus (LGN) receives and relays signals from the retina to primary visual cortex (V1). V1, in turn, provides reciprocal feedback to the LGN. Because the vast majority of LGN inputs target V1 (and secondary visual cortex or V2), their complementary corticogeniculate neurons are assumed to be similarly restricted to V1 and V2. However, there are direct inputs mainly from koniocellular LGN neurons to mid-level, extrastriate visual areas. Whether there are corticogeniculate neurons in mid-level extrastriate cortex that project to the LGN remains unknown. Additionally, since corticogeniculate neurons in V1 modulate the timing and precision of LGN responses, it would be important to investigate whether extrastriate corticogeniculate neurons serve analogous or different functions. In this thesis work, I investigate these unknown questions using virus-mediated gene delivery to 1) retrogradely trace corticogeniculate circuits and 2) optogenetically activate corticogeniculate feedback in primates and ferrets, carnivores with visual pathways similar to those in primates.
First, we identified and characterized the morphology of multiple distinct corticogeniculate neurons in mid-level extrastriate visual cortical areas of ferrets: posteromedial lateral suprasylvian (PMLS), posterolateral lateral suprasylvian (PLLS), and area 21a, and macaque monkeys: middle temporal (MT), medial superior temporal (MST), and area V4. Importantly, all three areas in both species were dominated by corticogeniculate neurons with spiny stellate morphology, suggesting possible preferential targeting of W/koniocellular LGN layers. We also observed corticogeniculate neurons in other extrastriate visual cortical areas, although we did not systematically characterize them.
Toward the second aim, we found that activating corticogeniculate feedback from PMLS in ferrets shifted the preferences of LGN neurons to low spatial and high temporal frequency stimuli, which aligns with the preference of PMLS neurons for fast-moving stimuli.
Together, our results suggest that: (1) extrastriate corticogeniculate feedback from PMLS may enhance LGN responses to fast-moving (high temporal frequency) stimuli, (2) evolutionary preservation of corticogeniculate neurons throughout visual cortex supports their critical role in visual function, (3) extrastriate geniculo-cortico-geniculate loops, that bypass V1, could provide a substrate for residual vision following V1 damage, (4) other sensory systems may contain corticothalamic neurons beyond primary and secondary sensory cortex that also target first order thalamus, (5) broader characterizations of these circuits could provide additional clues about the overall functional roles of corticothalamic feedback in sensory perception, and (6) the presence of corticogeniculate neurons across visual cortex necessitates a reevaluation of the LGN as a hub for visual information rather than a simple relay.
Nov 22, 2024 @ 9:00 a.m.
Medical Center | K207 (2-6408)
Host: Advisor: Farran Briggs