Reward magnitude tracking by neural populations in ventral striatum

Abstract

Evaluation of the magnitudes of intrinsically rewarding stimuli is essential for assigning value and guiding behavior. By combining parametric manipulation of a primary reward, medial forebrain bundle (MFB) microstimulation, with functional magnetic imaging (fMRI) in rodents, we delineated a broad network of structures activated by behaviorally characterized levels of rewarding stimulation. Correlation of psychometric behavioral measurements with fMRI response magnitudes revealed regions whose activity corresponded closely to the subjective magnitude of rewards. The largest and most reliable focus of reward magnitude tracking was observed in the shell region of the nucleus accumbens (NAc). Although the nonlinear nature of neurovascular coupling complicates interpretation of fMRI findings in precise neurophysiological terms, reward magnitude tracking was not observed in vascular compartments and could not be explained by saturation of region-specific hemodynamic responses. In addition, local pharmacological inactivation of NAc changed the profile of animals’ responses to rewards of different magnitudes without altering mean reward response rates, further supporting a hypothesis that neural population activity in this region contributes to assessment of reward magnitudes.

Calcium-dependent molecular fMRI using a magnetic nanosensor

“…Stimulation parameters chosen for the experiments were within range of previous studies 24,25 , and suitable for evoking robust self-stimulation behavior in a standard operant paradigm (Supplementary Figure S7), demonstrating their relevance to naturalistic behavior and its underlying neurophysiology. To measure calcium responses to the stimulation, MaCaReNas were infused into dorsal striatum and then imaged using a block design paradigm 26 in conjunction with T 2 -weighted spin echo echo planar imaging performed with a frame rate of 0.25 Hz, which is characteristic also of conventional hemodynamic fMRI.…”

Local and global consequences of reward-evoked striatal dopamine release

“…A corresponding striatal map of BOLD fMRI responses to LH stimulation was also obtained ( Fig. 2b ) 9 , 10 ; a separate group of five uninjected animals was used for this, in order to avoid the attenuating effects of contrast agent on hemodynamic signals in the areas of infusion ( Fig. 1 and Extended Data Fig.…”

Adaptation effects of medial forebrain bundle micro-electrical stimulation

“…We continue training until the number of pressures reaches a certain level, and after that, no stimulation is sent to the rats for two days. According to a recent study [29], MFB stimulation was applied every day 30 minutes to an hour for 2-10 days. Regarding the multiplicity of stimulation parameters and the wide range of each one and to prevent the fatigue and also the saturation of the stimulation parameters, MFB stimulation was planned as such.…”