[Reprinted from The Psychological Review, Vol. 27, No. 6, November, 1920.I 
 
 A BEHAVIORISTIC ACCOUNT OF SLEEP 
 
 BY CHARLES H. WOOLBERT 
 
 Division of Public Speaking, University of Illinois 
 
 The phenomenon of sleep does not lend itself conveniently 
 to explanation in terms of sensation, image, and feeling. 
 Accordingly structural psychology can offer little by way of a 
 description of the state of sleep. The behaviorist, on the 
 other hand, believing that his definition of consciousness 
 offers a statement not only of what consciousness is, but of 
 what it is not, is in a position to explain sleep. If, as be¬ 
 haviorism asserts, mind is a matter of reflex connections always 
 involving the movement, tension, or tonicity of muscles and 
 always correlated with the activity of glands, then conscious¬ 
 ness, in its varying degrees of clearness, is a matter of degrees 
 of complexity and ordination among systems of muscular 
 action. A high degree of consciousness thus becomes synony¬ 
 mous with an intricate and ordered complexity of tonicity in 
 muscular systems; while a low degree of consciousness is 
 equivalent to a complexity of low degree and an ordering of 
 simple texture. Consciousness thus may be, speaking in a 
 paradox, scattered, involving perchance abundant activity— 
 by way of muscular tonus in various muscle systems—but 
 activity of a low degree of intricacy in organization. 
 
 If consciousness, then, be a matter of the degree of com¬ 
 plexity of interacting muscle systems, non-consciousness is a 
 lack of activity or else a lack of this complexity. In either 
 case the factor of complexity is vital and needs describing. 
 Behaviorism’s explanation of this concept is based on the 
 continuative function of the sense endings within the muscles. 
 Always stimulated by any muscular event, they afford the 
 means for causing a single inaugurating stimulation to rever¬ 
 berate through a long series of tensions, or else to provide a 
 continued hardening of some one set of muscles. The type 
 of tensions running in a series is what is called the chain 
 
 420 
 
A BEHAVIORISTIC ACCOUNT OF SLEEP 
 
A BEHAVIORISTIC ACCOUNT OF SLEEP 421 
 
 reflex; the continued is that called circular. Chain reflexes 
 have much to do with that complexity of interacting muscle 
 systems that makes consciousness. Carried on by means of 
 proprioceptor organs of stimulation, they have a right of way 
 and a special kind of clearance. This insures them continuity 
 and lends a measurable degree of stability to the complexity 
 of structure that makes up consciousness. 
 
 This description recognizes, first, that the muscularity of 
 the body occurs in fairly well-defined systems: as those of 
 the back, the legs, the head, the face, and the throat; and, 
 secondly, that these muscle systems are set oflF one by the 
 other and in a certain order. This order is based on priority. 
 Priority of muscle systems is, in general, a matter of pre¬ 
 cedence in the development of working efficiency in reflex 
 arcs. Those systems that have an early development history 
 come to have a pronounced control over systems developed 
 later, in that the systems developed later get their initial 
 determinations from the workings of the habitual responses 
 of the earlier. Their most intense determinations are, both 
 earlier and later, then, conditioned by the determinations of 
 the systems already habituated. Their capacity for quick 
 and valuable response depends thus very largely upon their 
 close coordination and cooperation with habitual reactions 
 of systems determined at an earlier stage of development. 
 
 An understanding of sleep requires a description of this 
 development order, a description of gross muscle systems 
 and a statement of their superordination and subordination. 
 This is found in an account of the operation of Pawlow’s- 
 
 A 
 
 Law, as manifested in the conditioned, chain, and circular 
 reflexes. 
 
 By Pawlow’s Law a reflex arc may be a factor in new 
 activities by the stimulation of sense endings imbedded in the 
 muscles that are contracted by the operation of such an arc. 
 Every motor process stirs a muscle; this stirring starts new 
 impulses; and these impulses seek a new outlet. Two direc¬ 
 tions they can take: they can go around back by way of the 
 motor nerve that stimulates this muscle, and so stimulate it 
 again; or they can take some other motor nerve leading to a 
 
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 AT URHAMA-CHArr AIQM 
 
422 
 
 CHARLES H. WOOLBERT 
 
 quite different muscle. The former of these processes is the 
 circular reflex, the latter, when carried on through a series, 
 the chain reflex. By means of circular and chain reflexes in 
 various combinations the organism has within itself the 
 machinery for carrying on activity, for a while, at least, 
 without the intervention of peripheral stimulations. Only in 
 this way can the continued activity of involuntary organic 
 acts be accounted for, activities like heart-beat and breathing. 
 In this way also is given a satisfactory account of the mechan¬ 
 ism of such activities as catatonia, catalepsy, emotional com¬ 
 plexes, fixed ideation—in fact, repetitive and continuative 
 actions of all kinds. 
 
 To get the full significance of these circular and chain 
 reflex systems in the coordination and superordination of 
 actions, it is necessary to envisage them in connection with 
 the development order of muscular systems. Systems de¬ 
 veloped early in the life of the organism are obviously deter¬ 
 mined strongly; in the case of the very earliest, heart-beat 
 and breathing, no stimulus short of that adequate to stop 
 life can divert them. Moreover, their continued activity is 
 but little dependent upon other stimulation than that pro¬ 
 vided by the circular reflexes that keep them regular; at 
 least so long as the muscles concerned receive nourishment 
 from the blood. Systems developed one stage later, like 
 those involving walking, reaching, turning the head, have 
 within themselves much of the same continuative mechanism. 
 Their ability to function, however, they have gained largely 
 as an adjustment from the successful functioning of systems 
 developed earlier. At the start of their functioning they do 
 not possess a full measure of self-determination; they are of 
 necessity dependencies, subject to the caprice of superiors 
 holding power by a rule of seniority. Certain things they 
 can do so long as the older systems go about their business 
 in an orderly fashion; certain other things, under the same 
 conditions, they are not privileged to attempt. Thus the 
 use of the eyes, the hands, the legs, is conditioned very 
 materially by the regularity of the beating of the heart and 
 of breathing. Let, once, something go wrong with either of 
 
A BEHAVIORISTIC ACCOUNT OF SLEEP 
 
 423 
 
 these older activities, and the organism loses complete control, 
 eventually, of hands, legs, eyes, and of all other muscle 
 systems. Under similar circumstances any determinations 
 that are ordinarily well established give way to a recrudes¬ 
 cence of the wildest of random movement. 
 
 Thus the muscle systems operate in a kind of hierarchy, 
 with jurisdictions fairly distinct, though not exclusive. Most 
 firmly enthroned of all are the primary reflex systems con¬ 
 trolling heart-beat, flow of blood, operation of vital organs, 
 and breathing. Next come those developed in the organism’s 
 earlier days, use of arms and legs, back, torso, and neck 
 muscles; later, and probably overlapping the earlier systems, 
 muscles of the eyes, ears, face, and head; lastly—coincident 
 with the development of speech—the muscles of.jaws, lips, 
 tongue, and throat. Thus consciousness as complexity of 
 muscle systems is a pyramid with the organic systems at the 
 base and the muscles of thinking, reasoning, and speech at the 
 top. Or, changing the figure, it is a hierarchy with the 
 organic systems as autocrats and the other systems holding 
 office on a descending scale of self-government, dependent 
 always upon the commands of the autocrats ruling by virtue 
 of prior possession of power. 
 
 This hierarchy operates to provide the difference between 
 sleep and waking consciousness. Without the tension of head 
 and face systems there is not complexity enough for conscious¬ 
 ness. So vital are they to clear cognition that they are 
 easily confused with the totality of consciousness; remove 
 them altogether from the systems active at any one time, and 
 unconsciousness occurs. Yet they are not autonomous; when 
 fatigued and free from intense peripheral stimulation they 
 normally yield easily to the relaxing of the lower systems and 
 go out of function along with them. Any condition in which 
 they refuse to stop functioning when free from peripheral 
 stimulation or when fatigued, and when the lower systems 
 have relaxed, is looked upon as abnormal. In fact psycho¬ 
 pathic conditions can be described either in terms of an 
 actual lack of the upper systems, or in terms of their failure to 
 cooperate with the activities of the lower. Sleep is accounted 
 
424 
 
 CHARLES H. WOOLBERT 
 
 for in the formula: Remove the higher systems from activity, 
 and consciousness departs altogether; weaken the lower, and 
 consciousness is in a precarious condition, especially if the 
 higher systems are affected by fatigue. When the lower 
 systems are thrown out of function, the higher circular reflexes 
 either stop at once or, in abnormal cases, ultimately wear 
 themselves out; in either case consciousness breaks up. 
 Remove the lower entirely, and death is instantaneous. 
 
 A prime requisite of easy and deep sleep is freedom from 
 stimulation for the eye, ear, nose, tongue, and parts of the 
 skin not constantly pressed by clothes; forms of stimulation 
 that have little to do with the organic systems. Yet sleep is 
 possible even in the face of such stimulations; but only in 
 cases where great fatigue throws lower systems, like those of 
 leg muscles, back, and neck, out of commission. The chief 
 power of estopping other systems, especially under conditions 
 when fatigue is present, is authoritatively appointed to the 
 organic systems; because they get their determination at a 
 time when the organism is in its most plastic state—in its 
 early stages. 
 
 Thus sleep becomes behavioristically a matter of the 
 efficient domination of the upper systems by the lower, 
 operating through the relaxing power of fatigue; while wake¬ 
 fulness and insomnia always imply that the higher and later 
 systems are assuming dominance over their precursors. 
 Wakefulness, so, is characteristically the dominance of the 
 lower systems by the upper when fatigue is not present. 
 Accordingly when wakefulness exists at the same time that 
 fatigue is present, the condition is abnormal. 
 
 This means that when the muscles of the back, legs, and 
 neck are relaxed, a powerful stimulator is lost to the muscles 
 of the arms, hands, feet, and head. When arms, hands, feet, 
 and head muscles in turn are relaxed, there is lost a powerful 
 source of stimulation to the muscles of the face, jaw, tongue, 
 and throat. While systems are undoubtedly more finely 
 differentiated than this, still their hierarchical interdependence 
 is on just such an order—and sleep can be explained by gross 
 characterizations as well as by those more minute. In the 
 
A BEHAVIORISTIC ACCOUNT OF SLEEP 
 
 425 
 
 inducing of sleep much significance must be attached to the 
 order in which muscle systems go out of function. When the 
 organism follows the development sequence, sleep is easy; 
 when the order of relaxation is in any way reversed, restless¬ 
 ness and wakefulness follow. In cases of complete reversal 
 of the order, we get such states as hypnosis, temporary high 
 degress of attention, manic conditions, and forms of insanity. 
 
 The beginning of sleep then normally is the relaxation of 
 the muscles that hold the body erect. As soon as these 
 muscles are relaxed, the prime determiner of higher systems 
 is taken away, the proprio-ceptor foundation, and the higher 
 systems then are kept in function by only a veritable bom¬ 
 bardment from the outside world or from very strongly deter- . 
 mined circular or chain reflex arcs within their own system, j 
 Among these latter are emotional states, fixed ideas, tunes , ** 
 running through the head, repeated attempts to solve a|y 
 problem, rhythmical verbalizing, and thinking in circles. 
 
 The next step in normal sleep is the sequential relaxation 
 of each of the systems hierarchically dependent upon the 
 erect-holding systems. Finally through the sufficient dissolu¬ 
 tion of the complexity that makes consciousness, sleep comes. 
 Consequently once a person lies down, relaxing the muscles 
 of legs, back, and neck, the beginning is made of sleep. 
 Providing there is no interference from outside stimulations— 
 chiefly those acting upon the sense endings in the head—and 
 also so long as there is no intense circular reflex process 
 going on in the muscles of the jaw, lips, tongue, or throat,— 
 ‘thoughts that will not go out of one’s head’— such a be¬ 
 ginning once made leads to complete sleep and loss of con¬ 
 sciousness. 
 
 Certain easily-made empirical observations as to sleep 
 confirm this account, (i) Sleep is characteristically accom¬ 
 panied by relaxation of muscles. (2) Characteristically also 
 it takes place with the body in a horizontal position, a position 
 that induces first of all a relaxation of the muscles of the legs, 
 back, and neck, all of which must maintain a high degree of 
 tonicity to maintain erect posture. (3) When the muscles 
 of the back, legs, and neck are relaxed, the muscles of the 
 
426 
 
 CHARLES H. WOOLSERT 
 
 head, face, jaw, and throat all tend to relax in a short time 
 ensuing. (4) These muscles also are most easily relaxed 
 when freed from stimulation of the head sense endings, in the 
 dark and in silence and free from intense taste or smell. (5) 
 All these relaxations occur parallel with a scattering of con¬ 
 sciousness, a defocalizing of attention; and the greater the 
 degree of relaxation, the less the ability to perform any act 
 implying a high degree of concentration. (6) Organic activi¬ 
 ties, though, are kept up despite any relaxation of the volun¬ 
 tary muscle systems. (7) Again, deep sleep implies complete 
 relaxation; also it connotes rest and recuperation from 
 fatigue, a retoning of muscles for future work. (8) The 
 degree of sleep involved conditions the number and vividness 
 of dreams had; deep sleep implying few dreams and light; 
 light sleep implying many dreams or dreams that are vivid. 
 (9) Deep sleep also leaves little recollection of dreams, except 
 for the moment when one is coming out of sleep to conscious¬ 
 ness. (10) Great numbers of dreams, or dreams that are 
 vivid, it is generally assumed, are equivalent to defective rest, 
 and restlessness is always accompanied by the inability to 
 stop thinking or by numerous and intense dreams, (ii) 
 During widespread muscular activity there is no such thing 
 as sleep; as during walking, eating, reading, talking, giving 
 active attention in any way. 
 
 These general observations, and many others of similar 
 nature, point clearly to the close relation existing between 
 sleep and the movement or tonicity of muscles. 
 
 In the subjective terms of ideation, sensation, and feeling 
 it is difficult to explain what happens to conceptual thought 
 during sleep. The behaviorist, by assuming that thought 
 of all kinds and in all degrees is a matter of muscular tonus, 
 precisely as in walking or standing erect or moving the hands 
 or talking, can give an account of sleep that fits in with his 
 whole program. Sleep to him is nothing but a disorganiza¬ 
 tion of muscle systems which in waking consciousness are 
 closely interrelated hierarchically, the action of each deter¬ 
 mined in part by the continued action of the others. When 
 conditions are set for the relaxation of sundry systems of 
 
A BEHAVIORISTIC ACCOUNT OF SLEEP 
 
 427 
 
 muscles, consciousness begins to be more scattered, system 
 after system drops out of function, and ultimately, in the 
 soundest sleep, nothing is left by way of muscular activity 
 but the functioning of the organic systems. 
 
 Dreams are clearly the result of systems involving throat, 
 face, tongue, and lip muscles which remain in function when 
 other systems have been thrown out of gear, systems which, if 
 combined, would make consciousness. The Freudian dream 
 psychology presents agreement with obvious facts in that it 
 recognizes the existence during sleep of mental processes 
 which seem very like others that go on in waking conscious¬ 
 ness, yet which at the same time are partly unlike them. 
 The behavioristic explanation of this is that in so far as a 
 dream is a matter of the activity of muscle systems involving 
 a high degree of complexity and coordination, in so far it is 
 similar to waking consciousness; and so has a way of seeming 
 logically coherent. The illogical dream, on the other hand, 
 the freakish dream, the dream that seems to forbid explana¬ 
 tion and interpretation, can be explained broadly as a type 
 of organization and coordination not met with in that form 
 in waking life; so that, speaking generally, the more unusual 
 the combination left operative during sleep, the more fan¬ 
 tastic the dream. From these suppositions can also be found 
 the reason why dream analysis cannot be a matter of accurate 
 interpretation and why the Freudians who assume to inter¬ 
 pret all dreams give promises in reality beyond powers of 
 observation to fulfill. So entirely beyond inspection and 
 prediction can be the permutations and combinations of the 
 hierarchy of muscle systems, that they can defy all powers 
 of analysis. 
 
 From these observations follow certain therapeutic in¬ 
 ferences worthy of note, most of them current already through 
 the experience of the race. If you would sleep soundly, exer¬ 
 cise much, in particular the muscle systems of the body below 
 the head; for if the ‘body’ is tired, the ‘mind’ will rest also. 
 If restless in sleep, study how to relax, first of all the muscles 
 of the legs, back, and neck. Then reduce the breathing rate: 
 high tension almost invariably is accompanied by rapid breath- 
 
428 
 
 CHARLES H. WOOLBERT 
 
 ing; low tension by slow-breathing. Also hands and feet, 
 fingers and toes, must be inert. If thoughts crowd thick 
 and fast and will not leave, let the jaw drop, make the 
 muscles of the cheeks and lips flabby, avoid screwing up 
 the muscles around the forehead and the eyes, see that the 
 tongue lies limp in the mouth, and make certain that the 
 muscles of the throat are not in any way tensed. These 
 last-named muscles, together with those of the jaw, tongue, 
 and lips, are more likely than any other to get in the way of 
 sound sleep. Make sure to observe the right order of relaxa¬ 
 tion of systems; gross lower systems first, then the finer sys¬ 
 tems below the head, and finally the fine systems of the head. 
 Sleep is synonymous with carrying out the following order 
 in relaxation: Reduce the breathing rate; then relax legs, 
 back, abdomen, and neck; then arms, hands, fingers, and 
 toes; next the muscles around the eyes, forehead, scalp, and 
 ears; and finally those around the mouth, jaws, tongue, and 
 throat—the muscles of speech and conceptual thought.