1. Layer V pyramidal neuron
Dendrites sample the entire cortical column.
Axons project locally, and distally to basal ganglia, brainstem, & spinal cord.
- Receives local inputs (from the same cortical column) and distal inputs (other cortical areas and thalamus).
From Lübke et al 1996

2. Excitatory connections between layer V pyramidal cells
Full connectivity predicted from morphology vs Sparse (10 %) functional connectivity
Kalisman et al 2005

3. The solution: All-to-All Potential Connectivity Unconnected Connected6 1 2 3 4 5
Unconnected
Connected
# axo-dendritic touches
Bouton
Touch
Whole-cell recordings &
Confocal connection analysis 1 2 3
# boutons

4. Connections between interneurons & pyramidal neurons

5. Summary
An inhibitory feedback loop is described for layer V pyramidal cells.
The loop is frequency dependent, and is more prevalent than monosynaptic excitation.
It is mediated by a facilitating excitatory connection onto GABAergic inhibitory neurons.
The inhibition is targeted to the dendrites of pyramidal neurons (low reversal & dendritic patch experiments).
Multi-patch recordings of PCs and Interneurons revealed that the loop was mediated by dendritic-targeting Martinotti cells.