Negative thinking arises as a barely conscious emotional decision to flip our primordial switch toward anger and fear. And we have done this so often it has become an inherited characteristic, a sort of "original sin" buried in the brain, an inherent disposition toward negativity.
But we can brush the amygdula with a breath of attention, and flip this deep switch back to the positive.
We do it not by intellectual self-analysis, or by thought tripping, but by an effortless intuition, feeling our way down into the old brain and bathing the amygdala in a breath of intent. This is accomplished in a moment, an exhalation.
Become aware of your mid-brain, any sensation there at all, even numbness. Now let a silent stream of attention flow with your breath through this ancient region at the base of the brain. With the softest intent, just brush the amygdala: flip the switch. Don't complicate this process with thought. Just do it.
Now allow a glow of positivity to stream up through the ancient brain into the cerebral cortex, like nectar through a green stem, into a blossoming flower.
Neither an affirmation, a concentration, nor a visualization, this is an actual felt experience, at the finest level of sensation. Yet this fraction of a moment can change one's whole day. Best to do it for only a breath, and not as a sustained "meditation." That would only ruin the innocence of direct experience. Brush the amygdala switch with a gentle breath often throughout the day, re-attuning your whole physiology to the stream of positive energy that our Mother, the Earth Shakti, always sends up into our bodies.