Extendable, miniaturized multi-modal optical imaging system: cortical hemodynamic observation in freely moving animals

Abstract

Observation of brain activities in freely moving animals has become an important approach for neuroscientists to understand the correlation between brain function and behavior. We describe an extendable fiber-optic-based multi-modal imaging system that can concurrently carry out laser speckle contrast imaging (LSCI) of blood flow and optical intrinsic signal (OIS) imaging in freely moving animals, and it could be extended to fluorescence imaging. Our imaging system consists of a multi-source illuminator, a fiber multi-channel optical imaging unit, and a head-mounted microscope. The imaging fiber bundle delivers optical images from the head-mounted microscope to the multi-channel optical imaging unit. Illuminating multi-mode fiber bundles transmit light to the head-mounted microscope which has a mass of less than 1.5 g and includes a gradient index lens, giving the animal maximum movement capability. The internal optical components are adjustable, allowing for a change in magnification and field of view. We test the system by observing hemodynamic changes during cortical spreading depression (CSD) in freely moving and anesthetized animals by simultaneous LSCI and dual-wavelength OIS imaging. Hemodynamic parameters were calculated. Significant differences in CSD propagation durations between the two states were observed. Furthermore, it is capable of performing fluorescence imaging to explore animal behavior and the underlying brain functional activity further.

Chronic wide-field imaging of brain hemodynamics in behaving animals

“…The methods and tools for measuring neurophysiological activity in awake, behaving animals including electrophysiological methods (such as EEG [4], LFP/Spike [5], whole-cell recording [6]) and imaging methods (such as two-photon [7][8][9], fluorescence imaging [10][11][12], laser speckle contrast imaging (LSCI) [13,14], and optical intrinsic signal imaging (OIS) [15,16]. While the electrophysiological methods provide an instantaneous recording of neural activities in the brain, optical imaging methods probe the brain's hemodynamics in a noncontact way and provide structural and functional information at high resolution.…”

“…For freely moving animals, miniaturized optical imaging systems have been developed but the usage of fibers (light delivery [13] or image transmission [14]) and cables (data transmission and power supply [17]) limits the mobility of the subjects. Furthermore, traditional imaging system cannot be applied to investigate the brain activities in social behavior and social motivations of groups.…”

Miniaturized optical neuroimaging in unrestrained animals

“…Most commonly, multispectral imaging, given its relative simplicity in implementation, is combined with another modality such as fluorescent or speckle imaging (Murari et al 2010, Liu et al 2013). Such systems provide scientists access to a multitude of biological variables enabling them to obtain a more holistic view of the neurobiology of awake and freely moving animals.…”

“…This spatial resolution was comparable to that of standard benchtop laser speckle imaging systems and suitable for studying the cerebral blood flow (CBF) of major vessels under different physiological conditions (Miao et al 2011). Liu et al (Liu et al 2013) designed a dual-modality LSCI/multispectral microscope, also extendable for fluorescence imaging (Fig. 4b).…”

“…wide-field fluorescence imaging (Ferezou et al 2006, Flusberg et al 2008), two-photon fluorescence imaging (Helmchen et al 2001, Sawinski et al 2009), as well as those that exploit intrinsic optical properties of biological tissues, e.g. multispectral imaging and blood flow based laser speckle imaging systems (Liu et al 2013). Finally, we discuss the relative advantages and disadvantages of each approach and the exciting prospects of this technology from the micro- (i.e.…”