A photoacoustic fiberscope was developed for high-spatiotemporal-resolution cerebral imaging in freely behaving mice. The 4.5-gram imaging probe has a 9-μm lateral resolution and 0.2-Hz frame rate over a 1.2-mm wide area. The probe can continuously monitor cerebral oxygenation and hemodynamic responses at single-vessel resolution, showing significantly different cerebrovascular responses to external stimuli under anesthesia and in the freely moving state. For example, when subjected to high-concentration CO₂ respiration, enhanced oxygenation to compensate for hypercapnia can be visualized due to cerebral regulation in the freely moving state. Comparative studies exhibit significantly weakened compensation capabilities in obese rodents. This new imaging modality can be used for investigating both normal and pathological cerebrovascular functions and shows great promise for studying cerebral activity, disorders and their treatments. The photoacoustic fiberscope uses two optical fibers for photoacoustic excitation and detection. The probe weight is only 4.5 grams. The scanner driving and sensor interrogation modules can freely rotate in compliance with the animal motion, allowing continuous cerebral imaging over the whole waking process from anesthesia to the freely moving state. The fiberscope can be used to quantify the oxygen saturation (sO₂), relative hemoglobin concentration (Hb), and vessel diameter associated with blood perfusion to assess cerebral oxygenation conditions. It has a 9-μm lateral resolution and 0.2-Hz frame rate, enabling the recording of cerebrovascular responses to external stimuli at single-vessel resolution. The photoacoustic fiberscope facilitates the monitoring of both normal and pathological cerebrovascular functions in freely moving animals, enabling advanced studies on diagnosis and treatment of cerebral disorders. In the hypercapnia experiment under anesthesia, the results showed a significant reduction in both the overall oxygen saturation (sO₂) and the relative hemoglobin concentration (Hb). After the hypercapnia experiment, the sO₂ and Hb levels recovered to normal levels. The oxygen extraction fraction (OEF) increased from 5% to 15% in the hypercapnia experiment due to insufficient oxygen delivery. In the hypercapnia experiment with freely moving mice, the results showed that the overall sO₂ level increased slightly. The mouse could move freely in the chamber during the hypercapnia experiment. The results suggest that the cerebral vessels tend to deliver more oxygen to compensate for hypercapnia. This oxygenation enhancement induced by CO₂ respiration was not observed in the anesthetized mice. The results also showed that the oxygen compensation capability is notably weaker in obese mice compared to that in control mice. The photoacoustic fiberscope can measure sO₂/Hb changes with an error of <5% in the anesthetized state and 10% in the freely moving state for multiple mice monitoring. This precision enables us to visualize cerebrovascular responses induced by hypoxiaA photoacoustic fiberscope was developed for high-spatiotemporal-resolution cerebral imaging in freely behaving mice. The 4.5-gram imaging probe has a 9-μm lateral resolution and 0.2-Hz frame rate over a 1.2-mm wide area. The probe can continuously monitor cerebral oxygenation and hemodynamic responses at single-vessel resolution, showing significantly different cerebrovascular responses to external stimuli under anesthesia and in the freely moving state. For example, when subjected to high-concentration CO₂ respiration, enhanced oxygenation to compensate for hypercapnia can be visualized due to cerebral regulation in the freely moving state. Comparative studies exhibit significantly weakened compensation capabilities in obese rodents. This new imaging modality can be used for investigating both normal and pathological cerebrovascular functions and shows great promise for studying cerebral activity, disorders and their treatments. The photoacoustic fiberscope uses two optical fibers for photoacoustic excitation and detection. The probe weight is only 4.5 grams. The scanner driving and sensor interrogation modules can freely rotate in compliance with the animal motion, allowing continuous cerebral imaging over the whole waking process from anesthesia to the freely moving state. The fiberscope can be used to quantify the oxygen saturation (sO₂), relative hemoglobin concentration (Hb), and vessel diameter associated with blood perfusion to assess cerebral oxygenation conditions. It has a 9-μm lateral resolution and 0.2-Hz frame rate, enabling the recording of cerebrovascular responses to external stimuli at single-vessel resolution. The photoacoustic fiberscope facilitates the monitoring of both normal and pathological cerebrovascular functions in freely moving animals, enabling advanced studies on diagnosis and treatment of cerebral disorders. In the hypercapnia experiment under anesthesia, the results showed a significant reduction in both the overall oxygen saturation (sO₂) and the relative hemoglobin concentration (Hb). After the hypercapnia experiment, the sO₂ and Hb levels recovered to normal levels. The oxygen extraction fraction (OEF) increased from 5% to 15% in the hypercapnia experiment due to insufficient oxygen delivery. In the hypercapnia experiment with freely moving mice, the results showed that the overall sO₂ level increased slightly. The mouse could move freely in the chamber during the hypercapnia experiment. The results suggest that the cerebral vessels tend to deliver more oxygen to compensate for hypercapnia. This oxygenation enhancement induced by CO₂ respiration was not observed in the anesthetized mice. The results also showed that the oxygen compensation capability is notably weaker in obese mice compared to that in control mice. The photoacoustic fiberscope can measure sO₂/Hb changes with an error of <5% in the anesthetized state and 10% in the freely moving state for multiple mice monitoring. This precision enables us to visualize cerebrovascular responses induced by hypoxia