Scientific Understanding of Consciousness
Consciousness as an Emergent Property of Thalamocortical Activity

Memory Trace Pattern (Engram)

A memory trace pattern is a pattern of high synaptic efficacies  engraved in the neural network synapses as a result of prior network activity, which may be the result of sensory inputs, internally generated signals such as pain, or internal cognitive activity, i.e. thinking.

Neurons and synapses comprising a memory trace pattern become active when they are triggered by a cue. Via the associative property of memory, the triggering cue aligns with some subset or fragment of the memory trace pattern, activating it, causing it to spread (Baddeley, et.al.; Memory, 120) and recruit further neuronal assemblies by gestalt principles.

The memory trace pattern can arise from sensory input, internal cue from working memory, or internal visceral.

Activation state of memory -- a memory trace (subnetwork) is active or inactive. (Fuster; Memory in Cerebral Cortex, 12)

 

Research study — Overlapping Memory Trace Linking, but Not Recalling, Individual Memories

 

Memory Trace Pattern Is Sparse

A memory trace pattern is sparse.  During waketime, most of the neural network is active on a standby basis, not directly comprising the neural active circuits contributing to consciousness.  My conception is that the dynamic core of consciousness at any one instant is a subset of neuronal activity comprising perhaps 3-5% of the brain's neurons and perhaps 10% of the synapses associated with those momentarily active dynamic-core neurons.  In other words, my conception is that at any one instant, neurons comprising the dynamic core consist of a very small portion of the totality of the brain's neurons, involving an almost minuscule portion of the brain synapses.  Nonetheless, this minuscule portion of synapses could consist of hundreds of millions of synapses. This conception is closely aligned with Edelman's mandate that the dynamic core is highly differentiated.  A highly differentiated, sparse but widespread neural network implies that, combinatoriality, the brain can store vast quantities of information. Individual neurons are used and reused in myriad synaptic connection patterns.

Degeneracy, Redundancy, Fault-Tolerance

For an individual neuron the combination of synapses active will be different for each memory trace pattern.  Moreover, for each activation of a memory trace pattern, the combination of synapses active is likely to be slightly different.

Plasticity Functionality of Synapses

The plasticity of synapses provides memory functionality for the ~10⁴ synapses in each of ~10¹¹ neurons.

The neural network’s billions of synaptic efficacies, molded by biochemical plasticity in the short term and protein synthesis in the long term, mediate the brain’s synaptic efficacy distribution, which represents a person’s individuality and memory.

Memory trace pattern must persists for 100-500 ms

To become conscious as the dynamic core, the neural network activity comprising the memory trace pattern must persist for about 100-500 ms.

Gestalt Principles Apply

Network pattern of synaptically linked, neuronal assemblies  recruited via gestalt principles.

Frequency Spectrum of the EEG

Oscillation frequency spectrum of the EEG is a manifestation of nested hierarchies of local and widespread  recurrent connections with reentrant, recursive functionality.

Recursive Functionality and Associative Memory Operate over 100-500 ms

The forward and back projecting signal pathways follow the most efficacious synaptic connections.

Recursive functionality results in some neurons strongly active while others may be “twinkling on and off” near conduction.

An individual neuron has a firing state of ON or OFF.  The ON firing state is typically between about 10 and 100 spikes per second or 100 Hz.  The OFF or quiescent firing state is a few Hz sporadically.

Neurons Not Connected by a Prespecified Plan

Neurons are not connected according to a prespecified plan.  The gross layout of the brain's neural network is determined by genetics and by stochasticity in development.  Later, both prenatally, in infancy, in childhood, and continuing in adult life, the network is continually reconfigured via synaptic plasticity to reflect the vast assortment of experiences stored as memory mediated in synaptic efficacies.  Fundamentally, human DNA does not contain sufficient genetic information to wire the neural network precisely.  The neural network refinement details are engraved into the molecular configurations of synapses via the plasticity of neuronal synaptic efficacies engendered through experience.

 

A Memory Trace Pattern Is a Widespread, but Sparse, Conglomeration of Many Millions of Firing Synapses on Dendritic Trees

 

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