I think I have now a better understanding of the L2/3 dynamics.
I will rephrase and expand the idea with my words.
A map is a continuous subregion of the cortex which can form stable hex-grid patterns on its L2/3 layer.
Each stable hex-grid pattern corresponds to the representation of an object/concept at the map level.
The human neocortex is composed of thousands (ten of thousands ?) of those maps, so an object/concept is represented in parallel in numerous maps at the same time (see TBT)
In a given map, 3 “external” forces are at play to form a stable hex-grid pattern in L2/3:
- Inputs from other maps (from L2/3 pyramidal neurons of maps either higher or lower in the hierarchy)
- Sensory inputs (from L4 stellate cells)
- Temporal predictions inside the given map (from L5 ?)
Those “external” forces apply strongly to the L2/3 layer every 4 cycles (alpha rate processing).
In between, the internal L2/3 dynamics has 3 more cycles to converge towards a stable hex-grid via a competition at each cycle (gamma rate processing).
It is as if the “external” forces put the L2/3 map in its initial position before the relaxation of the system.
At the cellular level, the strong map-2-map input corresponds to a bursting mode happening at each downside of alpha oscillation.
This would be in line with experimental results which show that “gamma amplitude and burst duration are inversely related to alpha amplitude”
Ref:
Layer-Specific Entrainment of Gamma-Band Neural Activity by the Alpha Rhythm in Monkey Visual Cortex
Eelke Spaak, Mathilde Bonnefond, Alexander Maier, David A. Leopold, and Ole Jensen, 2012
Layer-specific entrainment of γ-band neural activity by the α rhythm in monkey visual cortex - PubMed
Concerning the sensory inputs, they could theoretically arrive in L2/3 at any time but they will have a stronger impact if they are phase-locked to alpha oscillations, because they will have more time to influence the hex-grid formation before it is broadcasted to the other maps. That’s why the brain has optimized this timing to do active sensing (for example: by synchronizing the saccades with alpha cycle).
Ref:
Saccades are phase-locked to alpha oscillations in the occipital and medial temporal lobe during successful memory encoding
Tobias Staudigl ,Elisabeth Hartl,Soheyl Noachtar,Christian F. Doeller,Ole Jensen (2017)
Saccades are phase-locked to alpha oscillations in the occipital and medial temporal lobe during successful memory encoding
I haven’t thought much about the link with temporal predictions yet. I understand that this is the next piece of the puzzle to get closer to a coherent theory with SP/TP/TM (and that the thalamus will be involved).
Did I get it well ?