Cholinergic systems mediate action from movement to higher consciousness

There is a fundamental link between cholinergic neurotransmitter function and overt and covert actions. Major cholinergic systems include peripheral motor neurons organizing skeletal muscle movements into overt behaviors and cholinergic neurons in the basal forebrain and mesopontine regions that mediate covert actions realized as states of consciousness, arousal, selective attention, perception, and memory. Cholinergic interneurons in the striatum appear to integrate conscious and unconscious actions. Neural network models involving cholinergic neurons, as well as neurons using other neurotransmitters, emphasize connective circuitry as being responsible for both motor programs and neural correlates of higher consciousness. This, however, is only a partial description. At a more fundamental level lie intracellular mechanisms involving the cytoskeleton, which are common to both muscle contraction and neuroplastic responses in targets of central cholinergic cells attendant with higher cognition. Acetylcholine, acting through nicotinic receptors, triggers interactions between cytoskeletal proteins in skeletal muscle cells, as has been long known. There is also evidence that acetylcholine released at central sites acts through muscarinic and nicotinic receptors to initiate responses in actin and microtubule proteins. These effects and their implications for cholinergic involvement in higher cognition are explored in this review.