Origin of sharp waves during slow-wave sleepSWRs occured reliably in the DVR during slow-wave sleep, and slowwave sleep alternated regularly with REM sleep (Fig. 1a-c, Extended Data Fig. 1), as reported previously 3 . High-frequency ripples (around 70-150 Hz) rode on each sharp wave and contained action potentials. Local field potentials (LFPs) were highly correlated across DVR recording sites (peak correlation 0.74 over 18 h of slow-wave sleep, mean over two animals), but sharp waves that were recorded in the anterior medial pole of the DVR (amDVR) preceded their counterparts in more posterior or more lateral regions by up to 200 ms depending on the spacing between recording sites (Fig. 1d, e, Extended Data Fig. 1g, h), suggesting SWR propagation.We next recorded from thick anterior transverse, horizontal and parasagittal slices of DVR in artificial cerebrospinal fluid solution (ACSF) (Methods, Extended Data Fig. 2a-f). All configurations produced

Graphical Abstract Highlights d Presence or absence of food promotes the dwelling or dispersal behavior of C. elegans d Dopamine signals to peptidergic interneurons in response to food d Peptidergic interneurons antagonize each other to inhibit or excite motoneurons d Cholecystokinin and RFamide modulate motoneurons to generate food response behavior SUMMARY Finding food and remaining at a food source are crucial survival strategies. We show how neural circuits and signaling molecules regulate these foodrelated behaviors in Caenorhabditis elegans. In the absence of food, AVK interneurons release FLP-1 neuropeptides that inhibit motorneurons to regulate body posture and velocity, thereby promoting dispersal. Conversely, AVK photoinhibition promoted dwelling behavior. We identified FLP-1 receptors required for these effects in distinct motoneurons. The DVA interneuron antagonizes signaling from AVK by releasing cholecystokinin-like neuropeptides that potentiate cholinergic neurons, in response to dopaminergic neurons that sense food. Dopamine also acts directly on AVK via an inhibitory dopamine receptor. Both AVK and DVA couple to head motoneurons by electrical and chemical synapses to orchestrate either dispersal or dwelling behavior, thus integrating environmental and proprioceptive signals. Dopaminergic regulation of foodrelated behavior, via similar neuropeptides, may be conserved in mammals.

The existence of evolutionarily conserved regions in the vertebrate brain is well established. The rules and constraints underlying the evolution of neuron types, however, remain poorly understood. To compare neuron types across brain regions and species, we generated a cell type atlas of the brain of a bearded dragon and compared it with mouse datasets. Conserved classes of neurons could be identified from the expression of hundreds of genes, including homeodomain-type transcription factors and genes involved in connectivity. Within these classes, however, there are both conserved and divergent neuron types, precluding a simple categorization of the brain into ancestral and novel areas. In the thalamus, neuronal diversification correlates with the evolution of the cortex, suggesting that developmental origin and circuit allocation are drivers of neuronal identity and evolution.