  The ability to acquire large-scale recordings of neuronal activity in awake
and unrestrained animals poses a major challenge for studying neural coding of
animal behavior. We present a new instrument capable of recording intracellular
calcium transients from every neuron in the head of a freely behaving C.
elegans with cellular resolution while simultaneously recording the animal's
position, posture and locomotion. We employ spinning-disk confocal microscopy
to capture 3D volumetric fluorescent images of neurons expressing the calcium
indicator GCaMP6s at 5 head-volumes per second. Two cameras simultaneously
monitor the animal's position and orientation. Custom software tracks the 3D
position of the animal's head in real-time and adjusts a motorized stage to
keep it within the field of view as the animal roams freely. We observe calcium
transients from 78 neurons and correlate this activity with the animal's
behavior. Across worms, multiple neurons show significant correlations with
modes of behavior corresponding to forward, backward, and turning locomotion.
By comparing the 3D positions of these neurons with a known atlas, our results
are consistent with previous single-neuron studies and demonstrate the
existence of new candidate neurons for behavioral circuits.

Neurons and Cognition;Biological Physics