This is a long article and I think it would greatly benefit if it were more focused on a single or few aspects of the brain, instead of proposing a grand theory.
I think it is a mistake to focus on delayed input tasks. These tasks are challenging and performing them involves many brain regions and many different mechanisms. This means they are not great for studying an individual phenomena in isolation.
This article proposes a hypothesis for how the neocortex learns viewpoint invariant representations (“unique sequence codes”). A projection from the hippocampus to cortical layer 5 will hold a set of layer 5 cells active throughout the duration of a sequence, and Hebbian plasticity will cause those active cells to associate with all of the elements in the sequence. There are several issues with this hypothesis:
- This does not actually solve the problem of viewpoint invariance, rather it moves the challenge from the cortex to the hippocampus. How does the hippocampus know when to hold the cortical activity constant versus allowing it to change?
- Sequence learning (viewpoint invariance) is a critical function of the cortex, and you’re proposing that it happens far away in a smaller brain region. This seems like an information bottleneck. There are many cortical regions, all operating independently and in parallel, but there is only one hippocampus.
I have a competing hypothesis for how the neocortex learns viewpoint invariant representations. I have described it in this video: Video Lecture of Kropff & Treves, 2008