A Novel Layer 4 Corticofugal Cell Type/Projection Involved in Thalamo-Cortico-Striatal Sensory Processing
Alice Bertero1, Lucia Verrillo1, Alfonso Junior Apicella2
1Department of Biology, Neurosciences Institute, University of Texas at San Antonio, San Antonio, Texas 78249.
Summary
Researchers discovered a new type of neuron in the auditory cortex's layer 4 that sends long-range signals to the striatum. This finding challenges the traditional view of layer 4 neurons and reveals a new pathway for brain communication.
Area of Science:
- Neuroscience
- Auditory Cortex Research
- Cortical Circuitry
Background:
- Traditional models posit vertical information flow in sensory cortices, with layer 4 primarily relaying thalamic input locally to upper layers.
- Layer 4 neurons have been considered to form only local connections, with limited understanding of their subcortical projections.
Purpose of the Study:
- To investigate the existence and function of long-range projecting neurons within layer 4 of the auditory cortex.
- To elucidate the circuit mechanisms and connectivity of these novel layer 4 neurons with subcortical structures.
Main Methods:
- Utilized a combination of anatomical tracing, electrophysiology, and optogenetic techniques in mouse models.
- Characterized the input and output connections of identified layer 4 corticostriatal (CS-L4) neurons.
Main Results:
- Identified a novel class of pyramidal neurons in auditory cortex layer 4 (CS-L4 neurons) that receive direct thalamic inputs.
- Demonstrated that CS-L4 neurons project to the posterior striatum, forming a feedforward inhibitory circuit.
- Showed that these neurons differentially innervate striatal spiny projection neurons and parvalbumin-expressing interneurons.
Conclusions:
- Layer 4 neurons possess a previously unrecognized long-range projection capability to the striatum, expanding the known cortical circuitry.
- CS-L4 neurons establish a direct thalamo-cortico(L4)-striatal pathway, potentially modulating striatal output and bypassing extensive intracortical processing.
- Introduced CS-L4 neurons as a new functional element for understanding cortical processing and top-down control of subcortical structures.
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