Well, I have no intention of leading your thread in a direction you didn't intend, so I just wanted to make sure I understood your intended definition.
Even if a definition is provided, it may not provide the whole picture. I've seen people, for instance, assert that only matter exists, but what they really meant was that only the basic physical things exist because they were not all that familiar with physics. Materialism itself is a very old philosophy, and the concepts of matter being interchangeable with energy (convertible from one to the other), spacetime being a dynamic component to the system, and all sorts of quantum fields and such are only 100 years old or so.
So sometimes it can be hard to know what people mean. Many early materialists defined the two things that existed as matter and void. If materalism, in light of recent scientific understanding replaces "matter" with "matter/energy" and "void" with "spacetime and fields", then I think their original intent remains intact. I think that's why the terms can be used interchangeably sometimes. I wager that finding current people that believe that literally only matter exists is a pretty big hurdle.
Information shared between intelligent social animals.
Well, I'm not a biologist or psychologist, so I can't go into all the tiny details. But the placebo effect seems basically to be the mind affecting the body, much like it always does.
The brain/body system is enormously complex. The brain can coordinate the release of various hormones and chemicals that have dramatic effects on the body including the brain itself. Certain chemicals make us happier, more energetic, have a stronger immune system, faster healing, and so forth. The placebo effect is basically the brain putting itself in the optimal position for healing by having the body do as much of the work it can. When the opposite is the case, and people have various mental hang-ups about living, healing, and so forth, the brain body system is not operating at is optimal level.
Depending on the order that it's in, software can affect hardware. I mean, a few weeks ago at work, one of our machines damaged part of itself by causing a short circuit. It was set up so that it can change the flow of electricity, and includes some states that can potentially short circuit itself, but it's not programmed to go to those states. But a bug caused it to, and damage occurred. The software was just the hardware controlling aspects of itself, and it led to damage.
The brain is interesting in that it has a huge control loop unlike most of our computers. The brain can affect itself. There's no reason why our computers can't do the same if they are designed that way, but the complexity and technology requirements are high. For instance, many things are made by machines (computers), including computers themselves. so hardware can and does lead to software that then makes more hardware.