MINIMAL/MAXIMAL BRAIN HOMOLOGY
The formal inversion theory suggests that the Minimal Model Brain activity of the last figure (here repeated in the lower diagram) is an entirely credible stripped-down-to-the-essentials version of what is going on in our own minds at this very moment -- and that organic evolution has seen to it that our own Maximal Model Brains are massively multiplied versions of the minimal model case.
The upper diagram of the six basic layers of our human left and right cerebral cortices shows just one of the very many ways in which the principle of left-right bicyclic inversion might be realised in our own brains. We do not yet know which of the many possibilities is the correct one but at least the theory provides one highly credible pattern for which we should be looking.
In broad outline, in mammalian (including human) cerebral cortices, intrinsic cells of layers 3 and 4 are the main receivers of subcortical and cortical input and are here represented by cells in layer 4. Layers 2 and 3 provide the main outputs to cortical destinations and are here represented by cells in layer 3. Layers 5 and 6 provide the main outputs to subcortical destinations and are here represented by cells in layer 5. The connections shown between cells are standard and profuse in life.
In keeping with the 'broad brush' nature of this introduction, we shall next look at one brief 'snapshot' of how simple bilateral brains become complex bilateral brains -- by considering the chordates.
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