As well, talk-therapy represents a massive effect on the brain. The brain is not only plastic, but rather sensitive. While we think of drugs as more powerful than therapy (and they are), the effects of therapy are not minor. Merely with words, we can activate many regions of the brain, and these then respond to the stimulus. There's a reason why I can teach myself about quantum mechanics by listening to a lecturer - the brain responds. Teaching yourself to not be depressed or scared anymore is tougher, but only because our methods are imprecise; it's still the same neuronal activation and rewiring.