Drugs which increase the Functional Activity of the Brain

Nerve Stimulants

These are which increase the nervous activity of the cerebro-spinal system. They are subdivided into those which act on the cerebrum, or cerebral stimulants, and those which affect the spinal cord, or .Spinal stimulants have been already discussed (p. 181).

Cerebral Stimulants

In popular language, the name of stimulant is generally applied to drugs which have the power to increase the activity of the brain. From their producing a feeling of comfort and mirth they are also called exhilarants. The functional activity of the brain, like that of other organs, depends upon the tissue-change which goes on in the cells and fibres which compose it, and the amount of tissue-change is regulated to a great extent by the quantity and quality of supplied to the organ. A free supply of blood to the brain may be obtained by general excitement of the circulation, i.e. more powerful and rapid action of the of the vessels in other parts of the body driving blood into the brain, or by allowing blood more ready access to the brain, or by a combination of these factors.

Free circulation through the cerebral arteries may be induced to some extent by posture : thus, some men can think best when the head is low, and almost everyone naturally assumes the sitting posture with the head bowed down and held between the hands when suffering from the effects of mental depression. This posture is not, as is often supposed, merely consequent on the depressed condition of the nerve-centres, it is voluntarily assumed because it affords an actual sense of relief. In eager conversation also the body generally stoops forward and the head is held low so as to allow of a free supply of blood to the brain.1

The effect of local dilatation of the cerebral vessels is very greatly increased, if in addition to it the general circulation is increased and the raised by contraction of the arterioles in the body generally, or by more vigorous action of the heart.

General excitement of the circulation is induced by exercise short of and a brisk walk will sometimes remove a condition of low spirits. Sometimes the supply of blood to the brain is but slightly increased during continuous exercise, as a large portion of the blood is then diverted to the muscles, but after the exertion is over the excitement of the circulation continues for some time, and then the supply to the brain is increased. In some persons a cold wind acts as an exhilarant, causing contraction of the vessels, with consequent increase in the general blood-pressure and increased circulation in the brain. In persons who are debilitated and feeble, on the contrary, the cold may have an opposite effect, by depressing the action of the heart.

Some men can think best when walking about, on account of the excitement in the circulation which the exertion produces; but many such people, when they come to a very difficult point, will stand still or sit down, so as to allow the blood to flow more to the head and less to the muscles.

Where the circulation is feeble, so that the heart is not much stimulated by walking about, men often find that they can think better when lying down, or sitting with their head in their hands (Fig. 69), so as to gain the advantage of the greater flow of blood to the head in these positions.

The action of sipping is a powerful stimulant to the circulation, for, as Kronecker has shown, the inhibitory action of the vagus on the heart is abolished while the sipping continues, and the pulse-rate is very greatly increased. A glass of cold water slowly sipped will produce greater acceleration of the pulse for a time than a glass of wine or spirits taken at a draught. Sipping cold water has been recommended to allay the craving for alcohol in drunkards endeavouring to reform, and probably its use is Owing to this stimulant action on the heart. It is sometimes said that a single glass of ale sucked through a straw will intoxicate a man, although three times the quantity would not do so if taken in large draughts. If this he true, the more rapid intoxication caused by sucking is probably due to the conjoined effects of the and of temporary of the vagus caused by the suction, possibly aided by the effect of suction on the cerebral circulation .One of the most typical stimulants is alcohol. In small quantities it increases the arterial tension by locally stimulating, first the sensory nerves of the mouth, and afterwards those of the stomach, and thus causing reflex contraction of the vessels and reflex acceleration of the beats of the heart. This effect occurs before it, and is best marked when the alcohol is strong, and is but slightly marked when it is diluted. It is possible that by inducing local dilatation of the cerebral arteries while the heart still continues active, it may have a stimulant action on the cerebral functions, besides that which it induces by merely exciting the circulation generally.

Any stimulant action on the brain beyond what may be explained in this way is very slight, if indeed it exist at all. Its further actions are those of paralysis exerted on the nerve-centres in the order of their development, the higher centres being paralysed first (see p. 146).

At or about this point the stimulating action ceases and the action commences. The exhilarating effect of alcohol, however, may be most marked just at this point, because just here, while the circulation in the brain generally remains increased, the restraining or inhibitory parts of it begin to be paralysed. Thus, imagination and emotion are more readily excited and expression is free and unrestrained; external circumstances are less attended to, and a boyish or childish hilarity occurs.

Most of the substances belonging to those classes have a certain resemblance to one another in their action. Most of them stimulate the mental functions when given in very small doses. In larger doses they have also a stimulating action at first, i.e. while a small quantity only has been absorbed, but later on they diminish or abolish the mental faculties. The same drug - as, for example, or alcohol - in different doses may thus act as a stimulant, narcotic, soporific, and anaesthetic.

In a certain stage of their action opium and alcohol do not merely lessen the functional activity of the brain, but they disturb the normal relations of one part to another, so as to produce disorder of the mental functions. on the other hand, appears simply to lessen the functional activity of the brain without disturbing the relation of one part to another. We do not know what the causes of this difference in their action are, but with some degree of probability we may consider that such substances as bromide of or the normal products of tissue-waste, such as, simply diminish the functional activity of the nerve-cells without disturbing the nervous paths by which they communicate with one another, so that we have merely a general and even diminution of the mental faculties, as in natural sleep. Such substances as alcohol, on the other hand, may be supposed not only to diminish the functional activity of the cells, but also to disturb the rate at which the impulses pass from one cell to another, or to alter the direction in which these impulses are sent, so that instead of the mental activity being lessened in degree but natural in kind, as after the administration of bromide of potassium, we have a disturbance of the functions resembling that which we find in delirium or madness.