The mouse midbrain periaqueductal gray is organized into target-specific output populations

Mouse periaqueductal gray (PAG) output is organized into target-specific projection populations, with dorsal and ventral outputs and segregated PAG populations linked to four motor-related targets.

• Why it matters: The classical columnar framework cannot explain how PAG drives many, often mutually exclusive, instinctive behaviours from one region.
• What they did: The team built a whole-brain, column- and cell-type-specific synaptic projection atlas of mouse PAG, then used retrograde tracing from four motor-related target regions and Channelrhodopsin-2-assisted circuit mapping.
• The result: A PAG population projecting to the cuneiform nucleus sends substantial local collaterals that are positioned to shape ongoing PAG activity, revealing a modular output architecture beyond columns.

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