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Published on: September 18, 2015
Deep cortical layers are activated directly by thalamus
Christine M Constantinople1, Randy M Bruno
1Department of Neuroscience and Kavli Institute for Brain Science, Columbia University, New York, NY 10032, USA.
Science (New York, N.Y.)
|July 2, 2013
Summary
Sensory information reaches the cortex via direct thalamocortical (TC) synapses to deep layers (L5/6), not solely through layer 4 (L4). This reveals parallel processing streams in the brain.
Area of Science:
- Neuroscience
- Cortical circuits
- Sensory processing
Background:
- The thalamocortical (TC) projection is the primary pathway for sensory information to the cortex.
- It was widely believed that sensory information propagates from layer 4 (L4) to other cortical layers (L2/3, L5/6).
Purpose of the Study:
- To investigate the direct synaptic input from the thalamus to deep cortical layers (L5/6).
- To determine if layer 4 (L4) is an obligatory relay for sensory information to L5/6 neurons.
Main Methods:
- In vivo electrophysiological recordings in rats.
- Paired recordings from thalamic and L5/6 neurons.
- Pharmacological inactivation of layer 4 (L4).
Main Results:
- Many L5/6 neurons showed direct TC synaptic input with latencies similar to L4 responses.
- Substantial convergence of direct TC synapses onto various infragranular neurons, especially in L5B.
- Inactivation of L4 did not affect sensory-evoked synaptic input to L5/6 neurons.
Conclusions:
- Layer 4 (L4) is not an obligatory distribution hub for sensory cortical activity.
- The thalamus activates separate, parallel cortical processing streams, directly targeting both L4 and L5/6 neurons.
- This challenges the traditional view of hierarchical information flow within the cortex.
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