"we found that apical and basal dendrites of layer 2/3 (L2/3) pyramidal neurons showed distinct activity-dependent synaptic plasticity rules. Strengthening of apical and of basal synapses is predicted by local coactivity with nearby synapses and activity coincident with postsynaptic action potentials, respectively. Blocking postsynaptic spiking diminished basal synaptic potentiation without affecting apical plasticity. "
This finding supports HTM theory. In specific: HTM theory predicts that all of a neuron’s proximal basal dendrites work together to form a single functional unit - the spatial pooler. In contrast distal dendrites (which includes apical dendrites) each operate independently as part of the temporal memory.
Here’s a clear, concise summary of chandelier cells and basket cells, both of which are GABAergic inhibitory interneurons involved in shaping the activity of pyramidal neurons in the cortex.
Cell Types
Chandelier Cells
Morphology: Named for their vertical axonal arbors that resemble a chandelier. These axons synapse exclusively on the axon initial segments (AIS) of pyramidal neurons.
Neurotransmitter: GABA (Îł-aminobutyric acid), like most cortical interneurons.
Markers: Often express parvalbumin and GAT-1; some subtypes are positive for calbindin or CR.
Distribution: Found primarily in the neocortex; relatively sparse but strategically placed.
Basket Cells
Morphology: Axons form dense, basket-like networks that surround the soma and proximal dendrites of pyramidal cells.
Neurotransmitter: Also GABA.
Markers: Usually parvalbumin-positive; fast-spiking.
Distribution: Common throughout cortex and hippocampus.
Function
Chandelier Cells (does numenta’s k means)
Precision Inhibition: Control whether a pyramidal neuron fires by targeting the AIS, the site of action potential initiation.
Temporal Gating: Influence spike timing and synchrony.
Mixed Signaling: Though inhibitory, some studies suggest chandelier inputs can depolarize under specific conditions (e.g. low intracellular chloride in the target cell), potentially making them paradoxically excitatory in some contexts.
High Control Leverage: Because they act right at the trigger point of the neuron, even a few chandelier cells can exert powerful control.
Basket Cells
Lateral Inhibition: Suppress neighboring pyramidal cells to sharpen tuning curves and prevent runaway excitation.
Network Oscillations: Key players in generating gamma rhythms (30–80 Hz) via tight perisomatic inhibition.
Population Control: Help regulate the excitability of entire cortical ensembles.
Fast-Spiking Synchronization: Contribute to temporal precision in neural firing through synchronous inhibition.
Summary
Chandelier and basket cells are both critical for inhibitory control of excitatory pyramidal neurons, but they do so with different tactics:
Chandelier cells lock down the ignition switch (AIS).
Basket cells suppress the firing engine (soma/dendrites) and coordinate network timing.
Yes, the spatial pooler has inhibitory interneurons.
Full diclosure: I only read the abstract. The paper’s primary finding is that basal dendrites form a single compartment, and apical dendrites each form their own compartment. Now I assume that the paper only investigates excitatory neurons, but I would expect that inhibitory neurons are affected by compartmentalization in the same way. The compartments are caused by the shape and electric properties of the dendrite, which should affect both inhibitory and excitatory synapses in the same way.
So in spatial pooler inhibition is used for WTA only?
I think lateral differences and gradients can be very meaningfull too, that will be alternative representations to K-means clusters.
I should have made it clearer: basket cells modulate lateral connections. This is distinctly different from chandelier cells that pick sparse local winners.