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

Neural Network Plasticity


 Synaptic connections are modified by activity and experience

In the prenatal embryo, neurons begin firing and signals begin circulating as the neural network is developing. As growth cones on axons chemotaxially seek out dendrites on other neurons, a surplus of synapse connections is formed. The circulating signals in the neural network use some synapses frequently, while other synapses are used rarely. Synapses on the frequently used pathways are strengthened, while synapses on the rarely used pathways wither.

Hebbian Cell Assembly and Plasticity

Human brain networks are in a state of constant change. (Andreasen, Creating Brain, 59)

Long-term potentiation (LTP), the mechanism by which memories are formed in synapses. (Andreasen, Creating Brain, 60)

A cell assembly in the nervous system can have as many as 10,000 neurons distributed over a large part of the brain, with as many as 10,000 synapses per neuron. (Waldrop; Complexity, 160)

Donald O. Hebb    (Llinás; I of the Vortex, 188)

Donald Hebb, 'assemblies' of neurons. (Zeman; Consciousness, 72)

Hebb's cell assemblies were supposed to be the fundamental units of thought. (Waldrop; Complexity, 164)

Donald O. Hebb — Organization of Behavior

Any two cells or systems of cells that are repeatedly active at the same time will tend to become "associated," so that activity in one facilitates activity in the other. (Hebb; Organization of Behavior, 70)

Donald Hebb, 1949, 'Cells that fire together wire together' (LeDoux; Synaptic Self, 79)

Hebb's rule - connections between neurons that are active together are strengthened. (Zeman; Consciousness, 203)

The idea that neural assemblies underlie percepts goes back at least as far as Donald O. Hebb (1949). (Koch; Quest for Consciousness, 24)

Hebbian cell assembly - spatiotemporal pattern of neuron activity (Calvin; Neil's Brain, 282)

Hebbian plasticity (LeDoux; Synaptic Self, 136)

The efficiency of neurotransmitter pulses in a synapse depends on the past history of pulses crossing the synapse. An unrelated metaphor - exercise can improve muscle efficiency; disuse can decrease it. Can think of synapses as weighted according to past experience. (Holland; Emergence, 85)



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