Monitoring brain activities in awake and freely moving status is very important in physiological and pathological studies
of brain functions. In this study, we developed a new standalone micro-device combining electrophysiology and optical
imaging for monitoring the cerebral blood flow and neural activities with more feasibility for freely moving animals.
Optical intrinsic signals (OIS) and laser speckle contrast imaging (LSCI) have been used for years in
the study of the cerebral blood flow (CBF) and hemodynamic responses to the neural activity under
functional stimulation. So far, most in vivo rodent experiments are based on the anesthesia model when
the animals are in unconscious and restrained conditions. The influences of anesthesia on the neural
activity have been documented in literature. In this study, we designed a miniature head-mounted
dual-modal imager in freely moving animals that could monitor in real time the coupling of local
oxygen consumption and blood perfusion of CBF by integrating different imaging modalities of OIS
and LSCI. The system facilitates the study the cortical hemodynamics and neural-hemodynamic
coupling in real time in freely moving animals.
We designed a miniature laser speckle imager that weighs ∼20 g and is 3.1-cm high for full-field high-resolution imaging of cerebral blood flow (CBF) in freely moving animals. Coherent laser light illuminates the cortex through a multimode optical fiber bundle fixed onto the supporting frame of the imager. The reflected lights are then collected by a miniature macrolens system and imaged by a high-resolution CMOS camera at a high frame rate (50 fps). Using this miniature imager, we achieve high spatiotemporal resolution laser speckle contrast imaging of CBF in freely moving animals in real time.
Hypothermia can unintentionally occur in daily life, e.g., in cardiovascular surgery or applied as therapeutics in the neurosciences critical care unit. So far, the temperature-induced spatiotemporal responses of the neural function have not been fully understood. In this study, we investigated the functional change in cerebral blood flow (CBF), accompanied with neuronal activation, by laser speckle imaging (LSI) during hypothermia. Laser speckle images from Sprague-Dawley rats (n = 8, male) were acquired under normothermia (37°C) and moderate hypothermia (32°C). For each animal, 10 trials of electrical hindpaw stimulation were delivered under both temperatures. Using registered laser speckle contrast analysis and temporal clustering analysis (TCA), we found a delayed response peak and a prolonged response window under hypothermia. Hypothermia also decreased the activation area and the amplitude of the peak CBF. The combination of LSI and TCA is a high-resolution functional imaging method to investigate the spatiotemporal neurovascular coupling in both normal and pathological brain functions.