Neurons and networks organizing and sequencing memories

Abstract

Hippocampal CA1 and CA3 neurons sampled randomly in large numbers in primate brain show conclusive examples of hierarchical encoding of task specific information. Hierarchical encoding allows multi-task utilization of the same hippocampal neural networks via distributed firing between neurons that respond to subsets, attributes or “categories” of stimulus features which can be applied in events in different contexts. In addition, such networks are uniquely adaptable to neural systems unrestricted by rigid synaptic architecture (i.e. columns, layers or “patches”) which physically limits the number of possible task-specific interactions between neurons. Also hierarchical encoding is not random; it requires multiple exposures to the same types of relevant events to elevate synaptic connectivity between neurons for different stimulus features that occur in different task-dependent contexts. The large number of cells within associated hierarchical circuits in structures such as hippocampus provides efficient processing of information relevant to common memory-dependent behavioral decisions within different contextual circumstances.

Barlow versus Hebb: When is it time to abandon the notion of feature detectors and adopt the cell assembly as the unit of cognition?

“…Hierarchical organization of knowledge in different brain areas: A. for visual object catagories in the inferotemporal cortex of monkeys (23), B. for reward outcomes, objects, their positions, and even versus odd numbered trials in orbitofrontal cortex in rats (43), and C. for contexts, positions, reward outcomes, and object identities in the dorsal hippocampus (56). …”

Random neuronal ensembles can inherently do context dependent coarse conjunctive encoding of input stimulus without any specific training

“…Such a conjunction of activity patterns has been considered important for meaningful information processing, efficient storage, retrieval from partial cues, pattern completion and generalization behaviors in the brain 2 . Conjunctive neurons allow for hierarchical encoding of information by spatio-temporal convergence of inputs which show up as “Trial Type Cells” 3 . Conjunctive binding is a key operation in mechanistic models for hippocampus 2 , brain inspired computational models 4 and VLSI architectures 5 , 6 .…”