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Scientific Understanding of Consciousness |
Spreading Activation
Spreading activation typically involves sensory input such as the auditory input during conversation in which multiple parallel paths emanate from the two cochlear and then through subcortical circuits to primary auditory circuits in the temporal lobes. From there multiple parallel paths emanate into the association cortices. These multiple parallel pathways must operate extremely rapidly, on the order of a few tens of milliseconds. Signal along the pathways proceed and if the following manner in which a few neurons a few activated neurons along the pathway centers as a cue to activate the next group of neurons along the pathway. In this way, a multidimensional input signal finds its way in the neural network buyer at activating the most efficacious synapses along the pathway. This rapid feet forward propagation by the most efficacious synapses forms the basis for spreading activation. Memories automatically spread activation to other memories to which they are associated. Spreading activation is like "energy" flowing through connections linking traces. (Baddeley, et.al.; Memory, 166)
Spreading activation applies to sensory input signals where response times must be on the order of a few tens of milliseconds. Damasio’s Convergence Divergence Zones circuitry applies to association cortex where response times are perhaps 50 to a few hundred milliseconds. In the frontal, temporal and parietal cortex where the attention circuitry of the dynamic core constricts activity to a sparse, widespread network with neuron spike rates of perhaps 50 – 100 Hz, while the remainder of the neural network maintains unconscious activity at a few hertz. Sensory input spreads in the neural network via the most efficacious synapses to activate a sparse, widespread network corresponding to the sensory input pattern. The association nature of memory activates closely similar network patterns. The network activations occur within a few tens of milliseconds.
To use a crude metaphor of ‘hand in glove,’ the sensory input pattern (hand) of an input activates a (glove) pattern of many millions of the most efficacious synaptic connections that most closely fits the (hand) pattern of the sensory input. The fringes of the active pattern excited by sensory input serve as cues to activate ancillary memories. Retrieval is a progression from one or more cues to a target memory, via associative connections. (Baddeley, et.al.; Memory, 165)
fMRI and PET scans are not adequate to record the short time short response times of these neural patterns.
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