“…if any one despises the contemplation of the lower animals, he must despise himself” -Aristotle, Parts of Animals (350 BCE)
"The will...is the common stuff of all beings...consequently we possess it...with the animals, and even further on down." -Arthur Schopenhauer, On Psychology (1851)
"Selection is the very keel on which our mental ship is built" -William James, Principles of Psychology (1890)
"Desire is the actual essence of man" -Spinoza, Ethics (1677)
"Where the vulgar laugh, the philosopher admires" -Voltaire, The Philosophical Dictionary (1764)
Motivational states are the brain’s way of matching our behaviors to our needs and capacities: we eat when we’re hungry and sleep when we’re sleepy—but we forgo food and sleep when other things seem more important. Our motivations are central to who we are, but too often they spiral out of control causing addictions and other behavior and mood disorders.
We study motivation in Drosophila melanogaster, an organism with remarkable behavioral flexibility despite its small brain. We focus on sexually dimorphic behaviors because they are controlled by neurons that we can identify and study using sex-specific markers. We have identified circuit elements that:
i) increase motivation with abstinence,
ii) reduce motivation with goal achievement,
iii) hold a motivational signal for days,
iv) receive a motivational signal and use it to bias behavioral initiation and persistence,
v) track time,
vi) integrate inputs from competing motivations,
vii) switch behaviors,
viii) induce fictive behaviors,
ix) store memories of previous behavioral outcomes,
x) generate motor patterns.
We put these elements together to form circuit diagrams and study the molecular- and circuit-level features that give each element its specific functions. Correlates to mammalian circuit features are often very clear. Our goal is to inspire researchers in other systems to adapt our hypotheses for behavioral control, as has previously been the case for molecular genetics, developmental biology, and circadian rhythms in the fly.