Figure 3. Memory contributions to value-based decisions are related to BOLD activity in the hippocampus, striatum, and vmPFC.

Three tasks in humans use fMRI to assess brain regions involved in value-based decisions involving memory. A. Decisions based on transfer of reward value across related memories (following (Wimmer and Shohamy, 2012). In this “Sensory Preconditioning” task, participants first learn to associate pairs of stimuli with each other (e.g. squares with circles of different colors), without any rewards (Association phase). Next, they learn that one stimulus (e.g., the grey circle) leads to monetary reward, while another (e.g., the white circle) leads to no reward (Reward phase). Finally, participants are asked to make a decision between two neutral stimuli, neither of which has been rewarded before (e.g. blue vs. yellow squares; Choice phase). Participants often prefer the blue square to the yellow square or other neutral and equally familiar stimuli, suggesting they have integrated the reward value with the blue square because of the memory associating the blue square with the rewarded grey circle. The tendency to show this choice behavior is correlated with BOLD activity in the hippocampus and functional connectivity between the hippocampus and the striatum. These sorts of tasks allow experimenters to measure spontaneous memory-based decisions, without soliciting an explicit memory or rewarding it. In actual experiments, all stimuli are controlled for familiarity, likability, value, etc. B. Decisions about new food combinations involve retrieval of memories (following (Barron et al., 2013). In this task, foods are first evaluated separately (e.g. raspberries, avocado, tea, jelly, etc.). Then, participants learn to associate each food with random shapes (e.g. Asian characters; not shown here). Finally, participants are presented with a series of choices between two configurations of abstract shapes, which represent a new configuration of foods (e.g. raspberry-avocado shake vs. tea-jelly). These new choices, which involve retrieval and integration of two previously experienced stimuli, are correlated with activity in the hippocampus and in the vmPFC. C. Decisions about preferred snacks elicit retrieval of spatial memories (following (Gluth et al., 2015). After providing participants’ subjective preference for a series of snack items (not shown), participants learn a series of associations between snacks and a spatial location on the screen. Some associations are trained twice as often as others, creating memories that are relatively strong or weak. Participants are then probed to make choices between two locations, choices that require retrieval of the memory for the location-snack association. Choice accuracy and reaction times conform to bounded evidence accumulation and are impacted by the strength of the memory. Choice value on this task is correlated with BOLD activity in the hippocampus and in vmPFC. D. Overlay of regions in the hippocampus, striatum and vmPFC where memory and value signals were reported for the studies illustrated in A (red) B (green) and C (blue). Across studies, activation in the hippocampus, striatum and vmPFC is related to the use of memories to guide decisions. These common patterns raise questions about the neural mechanisms and pathways by which memories are used to influence value representations and decisions.