The core function of all brains is to compute the current state of the world, compare it to a desired state of the world and select motor programs that drive behavior to minimize any mismatch. The neural circuits underlying these functions are unknown. Yet they are the key to understand brains in general, i.e. one of the major scientific challenges of our time. Beyond being one of the central enigmas of modern and ancient science, understanding how brains process information, on the level of individual neurons and circuits, could be the key for developing novel ways of computing, especially as traditional, transistor based technology has reached its limits. Several problems have hindered progress:
- Our brain is extremely complex, consisting of billions of neurons, interconnected by more synapses than there are stars in our galaxy.
- The circuits underlying complex behaviors in all vertebrates are widely distributed, containing millions of neurons.
- Generally, an animal’s desired state of the world is rarely known, making the identification of neural correlates challenging.
- Even in simpler model species, most studies have focused on sensory driven, reflex-like processes, ignoring self-initiated behavior, therefore missing the key processes.
With this project we have begun to overcome these problems using insects, whose tiny brains solve the same basic problems as our brains, but with 100,000 times fewer cells. Moreover, we focus on the central complex, a single conserved brain region consisting of only a few thousand neurons, which is crucial for sensory integration, motor control and state-dependent modulation, essentially a ‘brain in the brain’. To simplify the problem further we focus on navigation behavior. Here, the desired and actual states of the world are equal to the desired and current headings of the animal, with mismatches resulting in compensatory steering. It has recently become known how the central complex encodes the animal’s current heading. Using multiple methods including behavioral training, connectomics, electrophysiology, classic neuroanatomy and computational modeling, we pursue a highly comparative approach to unravel how head direction is combined with goal directions to drive behavior. To reveal which of the circuits involved comprise the conserved core circuitry that exists across insects we compare species with distinct lifestyles. This also aims at revealing how these circuits have evolved to match each species’ unique ecology. To directly link intentional behavior to neural activity we use behavioral training to generate animals with highly defined goal directions, and correlate neural activity with the animal’s ‘intentions’ and actions - at the level of individual neurons. Across species, my work on the central complex aims at uncovering central principles of sensory integration, premotor control, and state-dependent modulation of sensory motor transformations. Therefore, the overall aims of my work is to establish a coherent framework to study key concepts of these fundamental brain functions in unprecedented detail - using a single, conserved, but flexible neural circuit.