Chapter XI: The Nervous System (4)

If we were to admire the perfection of any special aspect of the brain’s functioning, the rarity of hallucinations might give us cause for wonder. That impulses so seldom leave their own paths is more astonishing than that occasionally, when the brain is excited and its nutritive conditions deranged, the impulses which the ego can direct into channels where they revive an image should sometimes, and with far greater force, make their own way down well-worn paths, lighting up a picture which deceives the ego. Dreams, by contrast, throw up in a strong light the part played by attention in intelligent life. The capacity for alertness is due to the favouring of one set of impulses by suppressing others. The favoured impulses hold the road. Concentration of attention is keeping thought to one line by resisting all temptation to wander into by-paths. The waking condition is the state in which all nerve-ways are closed, with the exception of those which consciousness is using. The more severe the closure, the more vivid is consciousness. In sleep all paths are open. In none is the potential acquired by impulses in the process of overcoming resistance high enough to evoke consciousness. A burst of impulses ascends from the stomach, set a-flowing by undigested fragments of salmon and cucumber, or mounts from the arm on which the sleeper has been lying until its circulation has been arrested. They reverberate through the open corridors of the brain. If they are sufficiently noisy to awaken the sleeper, he, detecting them in this path and in that, supposes them to be on the same errands as the impulses which commonly pass thus. If dreams are analysed, it will be found that, although the combinations of impressions may be uncommon and extremely bizarre, the impressions are selected from the most familiar. The images of which the dream is compounded, which may have lost all normal relations and may have assumed impossible proportions, are those which the mind most frequently conjures up. In the large majority of instances some happening of the day preceding can be recognized as the prompting cause. A remembered dream is the photograph taken by consciousness of the sensations which have bombarded it into activity. Especially if due to impulses originated by visceral discomfort, the dream may have an unpleasant tone. This may take various forms, but the emotion most commonly aroused is fear. The objects visualized may have preposterous dimensions, or they may be not sufficiently distinct for recognition—elusive imps; but most commonly distress is caused by the want of harmony of sensations, due to the absence of kinæsthetic elements. A man is lying on the railway-line; a train is approaching with increasing speed; he cannot get up. He is in the pulpit, but cannot speak. Dreams thus confirm the view set forth above as to the cause of volitional action. Ability to perform an act depends upon the flow through the kinæsthetic centres of the brain of impulses generated in the muscles by which the act is to be, or is being, performed. Kinæsthetic sensations do not under any circumstances play the same part in mental life as sensations from the skin, the eye, or the ear; when the body is passive in bed they are not flowing into the cortex. The dream-photograph shows elements demanding movement, but affords no evidence that movement is in progress.