Whole brain dynamics during optogenetic self-stimulation of the medial prefrontal cortex in mice

Abstract

Intracranial self-stimulation, in which an animal performs an operant response to receive regional brain electrical stimulation, is a widely used procedure to study motivated behavior. While local neuronal activity has long been measured immediately before or after the operant, imaging the whole brain in real-time remains a challenge. Herein we report a method that permits functional MRI (fMRI) of brain dynamics while mice are cued to perform an operant task: licking a spout to receive optogenetic stimulation to the medial prefrontal cortex (MPFC) during a cue ON, but not cue OFF. Licking during cue ON results in activation of a widely distributed network consistent with underlying MPFC projections, while licking during cue OFF (without optogenetic stimulation) leads to negative fMRI signal in brain regions involved in acute extinction. Noninvasive whole brain readout combined with circuit-specific neuromodulation opens an avenue for investigating adaptive behavior in both healthy and disease models.

Fig. 1. Illustration of the fMRI experimental setup and behavioral training procedures.

a–c Illustration of the experimental setup to record fMRI during optogenetic MPFC self-stimulation in an awake mouse. A Laser pulse train is delivered when (i) the light cue is ON, and (ii) the mouse performs a spout lick, breaking a light beam that senses tongue movement. No Laser pulse is delivered when the cue light is OFF. d Experimental timeline illustrating the behavioral conditioning procedures.

Fig. 2. Group behavior (spout licking) and raw time courses of behavioral and corresponding BOLD responses from two mice.

a Counts of optogenetic stimulation self-administered by 10 mice averaged across the last 2 scan sessions. There was a significant increase in beam breaks during the cue ON versus OFF period (p = 0.008, Wilcox Rank Sum test), suggesting that animals had learned the association between the cue and reward availability. b, c Raster plots of beam breaks from 2 mice during a 640 sec scan session with corresponding BOLD time courses in the infralimbic cortex (the stimulus loci) and the nucleus accumbens (NAc), indicated by the two red blocks in d. The blue and red lines in b and c indicate spout lick during cue ON and OFF respectively. Opto-ICSS was delivered only during cue ON.

Fig. 3. BOLD activation during Cue ON and Cue OFF.

a Group activation maps following optogenetic self-stimulation during the Cue ON period (N = 10, corrected p < 0.01). Activated areas include: anterior olfactory nucleus, cingulate cortex (CG1/CG2), prelimbic and infralimbic cortex (IL), nucleus accumbens core (NAc), septum, reuniens thalamic nucleus (RE), medial dorsal (MD) thalamic nucleus and habenula. b Group activation maps during Cue OFF period when mice licked the spout in the absence of Opto-ICSS (N = 10, corrected p < 0.01). Negative BOLD responses were detected in anterior olfactory nucleus (AO), anterior nucleus accumbens (NAc), dorsal and fimbria (fi) hippocampus and lateral septum (LS). Numbers below images are coordinates relative to bregma.