Does paralizing the muscles used to frown actually effect the brain?

Here's some completely antecdotal findings that preventing people from physically frowning might actually have effects that make them happier. (Not scientifically validated of course.)

The facial feedback hypothesis states that facial movement can influence emotional experience. Charles Darwin was among the first to suggest that physiological changes caused by an emotion had a direct impact on, rather than being just the consequence of that emotion. Recently, strong experimental support for a facial feedback mechanism is provided through the use of Botox to temporarily paralyze facial muscles.

In a functional neuroimaging study, Andreas Hennenlotter and colleagues, Botox decreased activation of brain regions implicated in emotional processing and emotional experience (namely, the amygdala and the brainstem). These studies suggest that botox can dampen the ability to understand another's emotions, and they lend considerable support to Darwin's original notion.