The brain area for optimism...

Is called the rostral anterior cingulate cortex (rACC).

From physorg:

The more optimistic a person is, the brighter the [rACC] area showed up in brain scans, the scientists reported in a small study published online Thursday in the journal Nature. That same part of the brain, called the rostral anterior cingulate cortex (rACC), seems to malfunction in people suffering depression, said the study co-authors, Elizabeth Phelps of New York University and Tali Sharot of University College London.
Researchers gave 15 people functional magnetic resonance imaging scans while they thought about future possibilities. When the participants thought about good events both the rACC and amygdala, which is involved in emotional responses including fear, were activated. But the correlation with optimism was biggest with the cingulate cortex.

Makes me wonder what other personality characteristics may be hard wired, or are heavily based on brain chemistry. That, then also leads to deeper philosophical questions around the nature of free will, and how much of our hopes, fears, and choices are influenced by brain chemistry and various brain regions, and how much is due to conscious choice.