Dynamic routing of task-relevant signals for decision making in dorsolateral prefrontal cortex

Abstract

Neurons in the dorsolateral prefrontal cortex (DLPFC) encode a diverse array of sensory and mnemonic signals, but little is known about how this information is dynamically routed during decision making. We analyzed the neuronal activity in the DLPFC of monkeys performing a probabilistic reversal task where information about the probability and magnitude of reward was provided by the target color and numerical cues, respectively. The location of the target of a given color was randomized across trials, and therefore was not relevant for subsequent choices. DLPFC neurons encoded signals related to both task-relevant and irrelevant features, and task-relevant mnemonic signals were encoded congruently with choice signals. Furthermore, only the task-relevant signals related to previous events were more robustly encoded following rewarded outcomes. Thus, multiple types of neural signals are flexibly routed in the DLPFC so as to favor actions that maximize reward.

Prefrontal Neurons Encode a Solution to the Credit-Assignment Problem

“…The observation that neuronal activity represented the cues at the time of feedback is distinct from the "chosen-value" representations previously observed throughout the PFC (Padoa-Schioppa, 2009Sul et al, 2010;Kennerley et al, 2011;Donahue and Lee, 2015). Specifically, all the cues in our experiment were associated with identical reward, so neural activity could differentiate the cues solely by their visual features.…”

“…Note that information about the correct cue picture could be present before the appearance of the cue array because a single cue was designated correct for an entire block. Note also that significant information about outcome can be present before the feedback epoch because the prior trial's outcome was reflected in the outcome categories used here (Asaad and Eskandar, 2011; Donahue and Lee, 2015).…”

Lateral orbitofrontal cortex anticipates choices and integrates prior with current information

“…Our results are in line with a theoretical proposal11 recently supported by human functional magnetic resonance imaging (fMRI) and rat inactivation studies4650 that OFC represents the state-space, and hence add electrophysiological single-cell and neuronal population evidence for such theoretical scenario. In contrast, previous work has shown that in other brain areas, like the dorsolateral prefrontal cortex in monkeys, both task-relevant and task-irrelevant information is encoded in value-based decision-making4751. In addition, we also embedded animals in an environment in which they had to ignore prior information.…”

“…4; Supplementary Figs 4 and 8) was the number of neurons that had the firing rate significantly modulated by each task-variable over the total number of neurons used in the analysis. We preferred employing a permutation to test for significance in the regressors against more traditional methods that assume that the residuals are Gaussian204751, because the residuals that we observed in our data were strongly non-Gaussian. Furthermore, permutation tests are in general more conservative (lower probability of type I errors).…”

“…For each regressor a binomial test was used to assess if the fraction of neurons that had their firing rates modulated by that particular regressor was significantly greater than chance2051 (5%; one-tailed). Statistical significance for the difference in fractions between two conditions was tested by a non-parametric difference binomial test that sampled the null hypothesis as follows.…”