Scientific Understanding of Consciousness
Mental Image, Neural Representation, etc.
I'll follow Damasio’s use of the term mental image to connote the mental pattern composed of inputs originating from sensory modalities -- visual, auditory, olfactory, gustatory, and somatosensory. The somatosensory modality includes varied forms of sense: touch, muscular, temperature, pain, visceral, and vestibular. The term mental image is not limited to visual images exclusively, and there is nothing static about them. The term also refers to sound images such as those produced by music. (Damasio; Feeling of What Happens, 317)
Mental images can arise from real-time inputs from the senses or can be produced by memory reenactment of prior experience.
In our subjective experience of consciousness, there is a continuous flow of mental images, many of which are sequentially and logically interrelated. The term thought is used to connote the flow of mental images.
The term mental image should be distinguished from the term neural pattern or map. Neural patterns can be accessed only in a third person perspective, perhaps with advanced imaging technologies such as and fMRI. In contrast, mental images are a part of consciousness that are experienced only in a first-person perspective.
· Neural representation is a momentary pattern of synaptically-connected neurons.
· Neurons have a range of firing rates between about 5 Hz at quiescence to several hundred Hz when maximally active.
· At any instant of time, many neurons will be quiescence at about 5 Hz; neurons forming the instantaneous pattern of thought will be active with a firing rate of perhaps 100 Hz.
· If you can imagine the neural network representing an instantaneous mental image, there will be many neurons that are continuously active within this brief time. There will also be neurons that are flickering on and off between quiescence and active state. Of course many neurons that appear physically a part of the network will be an active in a quiescence state.
· Neurons at the borderline of firing, may drift in and out between an active/quiescence state.
· Each neuron has an action potential while active and a refractory period before being capable of firing again.
· Each neuron has a dendritic tree of about 1000 synapses. Any neuron whose inputs signals exceed the firing threshold in a sliding 5 ms time window, will fire an action potential.
· In order to fire, a neuron must have an instantaneous quorum of excitation/inhibition signals in his dendritic tree summing to a fire command.
· Neural network pattern representing a memory is similar to, but not exactly the same, as the original. Many neurons will be different, but the pattern will be similar.