Artificial Consciousness/Neural Correlates/Neural Groups/Laberge's Apical Dendrite Function
LaBerge - Kasevich Theory of the Apical Dendrite
editSo far we have encountered theoretical functions for the first 4 layers of the cortex, and the 6th layer, so to round out the model we need a theoretical function for the 5th layer. While there might be other models out there, the only one I know of, is The LaBerge - Kasevich theory of the Apical Dendrite, which links the 5th layer of the cerebral cortex to the thalamus, via the Apical Dendrites of the 5th layer pyramidal neurons.
LaBerge and Kasevich's work is on the Attention System, and so their theory is based on the idea that the 5th layer is the target of the bottom-up attention system. while I disagree with some of the assumptions they have made, mostly about the nature of Awareness and Consciousness, I think their work is important, if only because it stresses the importance of the length of the Apical Dendrites of the 5th layer pyramidal neurons, to the timing of attention, and links the bottom-up attention system to the Mini-column architecture of the Cerebral Cortex.
The idea is that 80 to a hundred of pyramidal neurons from layer 2/3 form mini-columns, and the 5th layer Pyramidal Neurons act as the axis of those mini-columns. Then about a hundred of the Mini-Columns form a column as described in the center surround function page.
Thalamic connections cause the Axis Pyramidal Neuron to fire, and this in turn causes the layer 2/3 pyramids to pre-activate which encourages them to respond to any patterns found in the stimuli coming from the mossy dendrite layer. This might in fact be necessary for the stimulation of the phenomenally implicit memory using a place-code addressing scheme.
Now this might seem confusing, since it suggests an activation role for the 5th layer, that connects at a level below the Column Architecture, and so causes us to ask, at what level does the brain react?
However we can clearly see that at one level of organization the output is likely to be at the mini-column level, and at another level of organization the output is likely to be at the column level. Some experiments have shown that the center surround effect is less prevalent on the Right Hemisphere which would make the output at the minicolumn level dominate, while the left hemisphere has a stronger center surround function and so the column level is more likely to dominate.