Distinct relationships of parietal and prefrontal cortices to evidence accumulation

Abstract

Gradual accumulation of evidence is thought to be fundamental for decision-making, and its neural correlates have been found in multiple brain regions1–8. Here we develop a generalizable method to measure tuning curves that specify the relationship between neural responses and mentally-accumulated evidence, and apply it to distinguish the encoding of decision variables in posterior parietal cortex (PPC) and prefrontal cortex (frontal orienting fields, FOF). We recorded the firing rates of neurons in PPC and FOF from rats performing a perceptual decision-making task. Classical analyses uncovered correlates of accumulating evidence, similar to previous observations in primates and also similar across the two regions. However, tuning curve assays revealed that while the PPC encodes a graded value of the accumulating evidence, the FOF has a more categorical encoding that indicates, throughout the trial, the decision provisionally favored by the evidence accumulated so far. Contrary to current views3,5,7–9, this suggests that premotor activity in frontal cortex does not play a role in the accumulation process, but instead has a more categorical function, such as transforming accumulated evidence into a discrete choice. To causally probe the role of FOF activity, we optogenetically silenced it during different timepoints of the trial. Consistent with a role in committing to a categorical choice at the end of the evidence accumulation process, but not consistent with a role during the accumulation itself, a behavioral effect was observed only when FOF silencing occurred at the end of the perceptual stimulus. Our results place important constraints on the circuit logic of brain regions involved in decision-making.

Robust neuronal dynamics in premotor cortex during motor planning

“…2). Previous optogenetic inactivation studies focusing on related brain areas have interpreted a lack of effect of transient inactivation as a lack of role in behavior 13,42 . Our results imply that redundancy across a distributed network could mask possible causal roles in optogenetics experiments.…”

“…Neurons in frontal and parietal cortex show slow dynamics, including persistent and ramping activity, related to motor planning [1][2][3][4] , action timing 5,6 , working memory [7][8][9][10] and decision making [11][12][13] . Neurons have intrinsic time constants on the order often milliseconds 14 .…”

Segregated fronto‐cortical and midbrain connections in the mouse and their relation to approach and avoidance orienting behaviors

“…Behaviorally, M2 has been implicated in top–down modulation of somatosensory based orienting and appetitive approach behaviors (Erlich et al, 2011; Guo et al, 2014). Additionally, M2 projects to parietal regions (MPtA, LPtA), which are involved in evidence accumulation and decision formation (Hanks et al, 2015). M2 neurons encode a categorical classification of evidence in decision making, while parietal neurons encode a more continuous representation of accumulated evidence (Hanks et al, 2015).…”

P300 amplitude variations, prior probabilities, and likelihoods: A Bayesian ERP study

“…Studies of perceptual decisions in primates (Kira, Yang, & Shadlen, 2015;Yang & Shadlen, 2007) and in rodents (Hanks et al, 2015) showed that the firing rates of neurons in the parietal cortex reflected the gradual accumulation of logLR when different logLRs were assigned to various sensory cues. Although the underlying neural mechanisms are less understood, a similar framework explains a variety of P3b-like phenomena that are related to perceptual decisions in humans (Kelly & O'Connell, 2013;O'Connell, Dockree, & Kelly, 2012).…”