All visual information is conveyed to the cortex via geniculocortical (GC) synapses, yet how GC inputs drive intracortical interactions is only poorly understood. The common view is that visual activation, initiated in the retina, is relayed through the lateral geniculate nucleus (LGN) to layer 4 (L4) neurons. Activity then flows through the cortex from L4 to layer 2/3 (L2/3), then layer 5 (L5) followed by layer 6 (L6). However, several lines of evidence suggest that this description is grossly simplified. First, while anatomical studies show that GC axons primarily innervate L4 and lower L3, additional GC terminals target L6 and L1. Although the innervation of L6 and L1 is relatively modest anatomically, the functional impact of these synaptic inputs may be significant. Thalamic input will drive these different layers in parallel, and its impact will depend on intracortical interactions among the thalamorecipient cells. Second, the synaptic strength and dynamics of GC synapses may play an important role in shaping the transmission of visual information to the cortex. Whether geniculocortical synapses are exceptionally efficacious and reliable is controversial. Different classes of geniculate relay neurons may exhibit distinct synaptic properties, but this has not been explored. Furthermore, GC inputs target different classes of excitatory and inhibitory neurons, and the identity of the cortical postsynaptic targets may also influence the functional properties of GC synapses. Diversity in the synaptic properties of GC synapses could change the balance of excitation and inhibition during ongoing GC activity, profoundly affecting cortical processing of visual information. To address these issues, we will selectively express a light-gated cation channel, channelrhodopsin-2 (ChR2), in GC neurons to optically stimulate GC fibers in isolation. Combined with our extensive experience in targeted recording from different classes of inhibitory and excitatory neurons in visual cortex, this novel approach will allow us to develop a comprehensive view of how different GC inputs drive cortical circuits during ongoing visual stimulation.

Public Health Relevance

The proposed experiments will uncover mechanisms that underlie the flow of visual information through the brain. Understanding these mechanisms will further our understanding of normal brain function and facilitate the diagnosis and treatment of neurological and psychiatric disorders.

Agency
National Institute of Health (NIH)
Institute
National Eye Institute (NEI)
Type
Research Project (R01)
Project #
5R01EY012114-15
Application #
8531937
Study Section
Central Visual Processing Study Section (CVP)
Program Officer
Steinmetz, Michael A
Project Start
1998-04-01
Project End
2014-08-31
Budget Start
2013-09-01
Budget End
2014-08-31
Support Year
15
Fiscal Year
2013
Total Cost
$364,099
Indirect Cost
$138,380
Name
Stanford University
Department
Veterinary Sciences
Type
Schools of Medicine
DUNS #
009214214
City
Stanford
State
CA
Country
United States
Zip Code
94305
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