Whole-brain calcium imaging with cellular resolution in freely behaving C. elegans (1501.03463v1)

Abstract: 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.

• The paper presents a novel spinning-disk confocal microscopy method enabling whole-brain cellular-resolution calcium imaging in freely behaving C. elegans.
• Using this method, researchers correlated neuronal activity with behavior, recording from 78 neurons and identifying specific neurons involved in locomotion.
• This method significantly advances understanding of the neural basis of behavior, providing a platform for future whole-brain circuit studies and technical improvements.

Whole-Brain Calcium Imaging in Freely Behaving C. elegans

This paper presents a novel approach to recording neuronal activity across the entire brain of the nematode C. elegans while the organism engages in free behavior. The method employs spinning-disk confocal microscopy to capture 3D volumetric fluorescent images at a rate of five volumes per second. This imaging is achieved using a calcium indicator, GCaMP6s, expressed in the nematode's neurons, enabling the capture of intracellular calcium transients as a proxy for neuronal activity. This is complemented by a dual-camera system for tracking the position and orientation of the worm, allowing for continuous observation and correlation of neuronal activity with behavior.

Key Results and Observations

The authors recorded calcium transients from 78 neurons in C. elegans, capturing the dynamics of multiple neurons that showed significant correlation with defined behaviors such as forward motion, backward motion, and turning. Using these observational results, they identified several neurons aligning with known behavioral circuits as reported in previous studies, and proposed new candidate neurons implicated in locomotory behavior. Their techniques facilitated the identification of neurons like AVBR and VB1 for forward motion and VA1, AVA, and AIB pairs for backward motion. This positions their approach as a comprehensive system to observe complex neural dynamics in an organism with a fully mapped connectome.

Implications and Future Directions

This research presents a substantial advance in the field of neuroscience, particularly for understanding the neural basis of behavior. By enabling whole-brain cellular resolution imaging in freely moving organisms, the paper provides a platform for exploring neural circuits at an unprecedented scale. The implications of this work extend to various domains, including understanding how neural networks encode behavior and potentially offering insights into the treatment of neurological disorders.

Looking forward, the work initiates possibilities for similar methodologies to be applied in other small transparent organisms, with potential advancements in light-field or two-photon microscopy further enhancing imaging capabilities. Development in genetically-encoded voltage indicators could also enrich the understanding of neural activity dynamics. Additionally, the challenge of matching 3D whole-brain images to known neuroanatomical atlases remains a critical area for future methodological improvements. Success in this endeavor would significantly bolster efforts to relate observed neural dynamics to specific neural circuits and behaviors.

In summary, this research integrates advanced imaging techniques with behavioral tracking to offer a detailed view of whole-brain activity in a model organism, contributing to the growing body of knowledge on neural encoding of behavior and laying the groundwork for future studies leveraging similar methodologies.