Input-output gating

Both the natural and artificial conditions that alter consciousness affect one or more of three crucial brain functions that correspond to the three major attributes of consciousness that are altered as its states change. The first function is activation, corresponding to the raised or lowered level of consciousness. The second is input-output gating, corresponding to... 

Because we can measure—or reliably estimate—all three of these brain functions, we can construct a three-dimensional model representing (1) the energy level of the brain and its component parts (Factor A, for Activation) (2) the input-output gating status of the brain, including its internal signaling systems (Factor I, for Information Source) and (3) the modulatory status of the brain, which is determined by those chemical systems that determine the mode of processing to which the information is subjected (Factor M, for Modulation). 

To accommodate the effects on the activated brain of pulling it off-line with respect to its external inputs and outputs, and to recognize the fact that this gating does not parallel the electrical activation of the brain in REM, I have assigned the second dimension of the three dimensional AIM model, the dimension I, to input-output gating. In the case of factor I, we have an elaborately detailed picture of the cellular and molecular mechanisms that are called into play during REM sleep. 

We can readily appreciate that because the neuromodulatory systems diverge in such radical ways between waking and sleep, they do not obey the simple activation rule any more than input-output gating functions do. They must therefore be accorded a special functional place in models of conscious state alteration. 

Conventional models only implied input-output gating. The models indicated eye movement as if it were constant in REM and didn t occur in waking. Muscle tone was sometimes used in scoring sleep records and its absence in diagnosing REM, but it was at least as often ignored, and exclusive reliance placed on EEG and eye movement criteria. 

With respect to the input-output gating issue, we know from recording... 

I hope it is clear from this discussion that the muscles can be both targets (of increased postural tone motor output) and sources (of increased sensorimotor input). They thus contribute doubly to move the input-output gating function (I) further back in the state space at the same time that the activation level (A) moves to the extreme right. The participation of the limbic system, especially the amygdala, creates a positive feedback loop that raises the level of aminergic modulation (M) toward the ceiling of the state space. 

The reason for this is twofold first the input-output gates are closed by active inhibition second, the central representations of sensation and movement in the cortical and subcortical brain are self-activated. 

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