Blood flow through the brain itself is automatically regulated so that it doesn't depend on changes in blood pressure for the body as a whole. If the systemic pressure falls, valves in the brain's vessels open up a bit to maintain flow. Another role for these valves is to protect the delicate brain capillaries from excessively high pressures. This control of blood flow and pressure breaks down during convulsions, a point to which we shall return.

Protecting the brain's chemical composition: the blood-brain barrier.

In most tissues the blood vessels are somewhat "leaky". Although red blood cells do not normally escape, some large molecules, such as proteins, and many smaller molecules do escape from vessels into the surrounding tissues. Were this to occur in the brain, it could be disastrous. First, the tiny channels between nerve cells could be plugged by larger molecules and barriers would be established to the normal flow of ions and nutrients. Second, if large molecules leaked from vessels into the brain, water would follow them (to maintain osmotic neutrality). The tissue would then swell. Although most tissues can swell and shrink without causing any difficulty, swelling is a serious matter for the brain because it is encased in bone. If it were to swell, pressure inside the skull would build up. Delicate structures would be squashed against bone, and the blood supply would be cut off by the rise in intracranial pressure. Third, the composition of the blood varies somewhat, even though it is regulated by kidney, liver and other organs. The blood sometimes contains toxic substances that some tissues, such as liver, can handle, but which may damage the brain. In general, the brain's chemical composition must be regulated far more perfectly than that of any other organ.

Accordingly, there are several lines of defense against changes in the brain's chemical composition that would result from leaky blood vessels. These defenses are referred to collectively as the "blood-brain barrier First, the vessels are sealed off from the brain by mechanical adhesions between the cells called "tight junctions". Second, a set of select substances that the brain needs are actively pumped into the brain from the blood. Third, undesirable substances, or those whose concentration must be actively controlled in the brain, are actively pumped out of the brain. You can get some feeling for these processes in slide 1. The brain on the left is from a cat with an intact blood-brain barrier. Blue dye which was injected into the blood was prevented from entering the brain by the blood-brain barrier. All the other tissues, however, are blue. On the right, the blood-brain barrier has been destroyed by irradiation (Klatzo and Seitleberger, 1967). Here, the vessels have become leaky and dye has penetrated the brain. This slide, therefore, has two purposes: to illustrate the existence of the blood-brain barrier and to indicate that it can break down under certain insults. This will be highly relevant when we consider the effects of electrical shock.

Protection of Neural Stability by Inhibition

One additional protective mechanism must be described before the effects of electrical shocks can be assessed. Nerve cells can either "excite" (turn on) or "inhibit" (turn off) each other. The inhibitory mechanisms are important here for one particular reason, inhibition serves to dampen the excitation, and without it the excitatory tendencies of nerve cells go out of control. All cells tend to be excited simultaneously and tend to re excite each other until massive neural activity swamps out any sensible, coordinated pattern. Such generalized excitation leads to massive, sustained contraction of the musculature, called a "fit", a convulsion, or a "seizure". Thus, a fit or seizure is a state in which, for one reason or another, the excitatory processes in the brain temporarily overwhelm the damping, inhibitory processes. A seizure, therefore, is evidence that one of the brain's protective mechanisms has temporarily been overwhelmed.

To summarize:

1. The brain is an organ of extraordinary complexity and is more complex in man than in lower animals.

2. Its complexity makes it extremely vulnerable to the slightest environmental insults which other tissues of the body could withstand. Neurons once lost as the result of insult are not replaced.

3. To prevent insult, many protective mechanisms, including mechanical, physiological, and behavioral mechanisms have evolved.

Relation Between Observations on Humans and Non-Human Mammals

I have showed a slide from the brain of a cat and will continue to refer to studies on other mammals. It is appropriate to ask, therefore, whether these studies are pertinent to the human brain since there are many differences between human and animal brains. The major difference between humans and animals that is relevant in the present context is that the human brain is a greater and more complex edifice. To return to the earlier analogy, it is more like a skyscraper than a hut. It needs even more protection, not less. All the protections I have discussed so far exist in humans and are, if anything, exaggerated in humans. In the remainder of my testimony, 1 shall refer to animal studies only where we can be reasonably sure that the human tissue would react in the same general way.

Effects of ECT on the Brain

We are now in a position to appreciate some of the effects of electrical shocks to the brain. Let us begin by describing the nature of the shock itself (reviewed by Grahn, et al., 1977). Typically, the electrodes of the ECT instrument are placed on the temples. Such ECT instruments usually contain nothing but a simple transformer that steps up the voltage from the wall outlet from 110V to about 150V. The machine may or may not have an automatic timing device to limit the duration of the shock. The current that passes through the head (between the electrodes) is limited mainly by the electrical resistance of the head. The total power drawn is about 60 watts -- enough to light a conventional light bulb. The result is not very different from what would be accomplished by plugging 2 pieces of metal into a wall outlet and placing their other ends on the temples -- except that the voltage from the wall outlet is a little lower. The duration of a typical ECT shock is 1/10-3/4 of a second.