Let’s say you’re an army general and you want to move 1,000 troops from Point A to Point B. You’ll probably send out two types of orders. First, you’ll send direct orders to your officers, telling them how, when, and where to move.
Second, you’ll also send advisories to other units who need to be aware of your movements, including commissary, quartermaster, and transportation units. Though they don’t report directly to you, they need to know what your troops are doing. Otherwise, supplies, food, and ammunition will be in the wrong place at the wrong time. Chaos ensues.
According to Patricia Churchland in her brief-but-insightful book, Touching a Nerve, our brains essentially behave the same way. Let’s say your brain tells your eyes to move to the right. That’s pretty simple. But you also need to let the rest of your brain know what’s happening.
When your eyes move right, your brain could interpret it in at least two ways:
1) My eyes just moved to the right, or;
2) The whole world just moved to the left.
The second interpretation is scary. The world moves in an unpredictable manner. You didn’t cause the movement. So, what did? Is someone playing a trick on you? Are malevolent spirits up to no good?
You can get an inkling of how this feels just by sitting in a car. If the car next to you rolls forward, you may feel that you’re rolling backwards. It’s a startling and unsettling experience until you realize what’s actually happening. Now imagine that all of your actions feel the same way. Your arm moves but not because of you. If you didn’t cause it, who or what did? Is it really your arm or an impostor?
We normally solve this problem by sending a memo to ourselves known as the efference copy. In essence, it’s a copy of the direct order sent to the muscle(s) in question. It lets the relevant portions of your brain know that you’re causing the action. It explains what’s going on. The world is not acting on you. You’re acting on the world.
Churchland speculates that problems with the efferent copy could be at the root of many mental disorders. (Churchland is not arguing that this is proven, only that it’s a fertile ground for research). A simple example is that we (normally) can’t tickle ourselves. We know – via the efference copy – that we’re the one taking the action. We’re making something happen. When other people tickle us, there is no efference copy. Something is happening to us. On the other hand, people with efference copy problems can indeed tickle themselves. It’s as if something is happening to them.
Similarly, we all hear voices in our heads. But most of us realize that the voice is our own. What if you didn’t? Whose voice would it be? A dead relative? God?
Ultimately, this is a question of me versus not-me. Most of us have a pretty clear idea of what me consists of. Even very young infants have a pretty clear idea of what their boundaries are. We learn to send memos to ourselves very early on. For some people, however, the memo never arrives. Chaos ensues.