Altered Feed-Forward Inhibition of Striosomes is Linked to Aberrant Value-Based Decision Making in Chronically Jessica Jenkins
Individuals suffering from disorders such as anxiety and depression often exhibit difficulty with rational decision making. Since these disorders are frequently a consequence of chronic stressors, Friedman et al. (2017) hypothesized that stress may also be responsible for maladaptive changes in the neural circuitry involved in evaluative thinking and decision making. Specifically, their region of interest was the prefrontal corticostriatal circuit since previous research identified this area to be important for evaluation. A T-maze task was used to identify differences in value-based decision-making behavior (decisions based on rewards and costs) between chronically stressed rats and control. Compared to control, stressed rats demonstrated flawed cost-benefit evaluation, since they chose absolute highrisk high-reward options more frequently than alternatives with a maximum benefit-cost difference (maximum value). This discrepancy in behavior correlated with a decrease in the spike activity in the prefrontal-prelimbic cortex neurons (PFC-PL), which in return caused a decrease in the firing of synapsing fast-spiking interneurons (FSI) and an increase in the activity of projecting neurons in the striosome (SPN). Optogenetic excitation of the PFC-PL neurons during the T-maze task successfully rescued decision making in chronically stressed mice, increasing confidence that the regulation of striosome activity plays an important role in healthy executive function. Freidman and colleagues (2017) referred to previous literature that identified striosomal projections that synapse directly with subsets of dopaminergic neurons in the substantia nigra. These neurons respond to rewarding and aversive stimuli, therefore it is possible that stress-induced overactivity in the striosome may be causing the erratic responses to costs and rewards in the T-maze task. Future studies are encouraged to implement some changes in the design of the T-maze task to overcome confounding effect, and to further explore the effect of chronic stress on the connection between the striosome and its downstream projections to the substantia nigra. Key words: chronic stress, cost-benefit evaluation, striosome, value-based decision making, prefrontalprelimbic cortex, striosomal projecting neurons, fast spiking interneurons, T-maze task, prefrontal corticostriatal circuit, feed-forward inhibition, foot shock, optogenetics
74
