Differential processing of decision information in subregions of rodent medial prefrontal cortex
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In this study, Diehl and Redish present a novel account of functional variability in the rodent medial prefrontal cortex. The authors report that, in general, the dorsal regions encode decision-related variables, whereas the ventral regions encode variables more linked to motivation, such as trial number in the session and amount of lingering time. Overall, the study is interesting, the experimental design is excellent, and the uniquely large neural data set is a strength. The suggestion of functional subdivisions in the prelimbic area is particularly provocative, and this conclusion, along with the data supporting it, will be of broad interest to those who study the anatomy and function of the rodent medial prefrontal cortex.
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Abstract
Decision-making involves multiple cognitive processes requiring different aspects of information about the situation at hand. The rodent medial prefrontal cortex (mPFC) has been hypothesized to be central to these abilities. Functional studies have sought to link specific processes to specific anatomical subregions, but past studies of mPFC have yielded controversial results, leaving the precise nature of mPFC function unclear. To settle this debate, we recorded from the full dorso-ventral extent of mPFC in each of 8 rats, as they performed a complex economic decision task. These data revealed four distinct functional domains within mPFC that closely mirrored anatomically identified subregions, including novel evidence to divide prelimbic cortex into dorsal and ventral components. We found that dorsal aspects of mPFC (ACC, dPL) were more involved in processing information about active decisions, while ventral aspects (vPL, IL) were more engaged in motivational factors.
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eLife assessment
In this study, Diehl and Redish present a novel account of functional variability in the rodent medial prefrontal cortex. The authors report that, in general, the dorsal regions encode decision-related variables, whereas the ventral regions encode variables more linked to motivation, such as trial number in the session and amount of lingering time. Overall, the study is interesting, the experimental design is excellent, and the uniquely large neural data set is a strength. The suggestion of functional subdivisions in the prelimbic area is particularly provocative, and this conclusion, along with the data supporting it, will be of broad interest to those who study the anatomy and function of the rodent medial prefrontal cortex.
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Reviewer #1 (Public Review):
Diehl & Redish set out to capture how cognitive and behavioral linked activity varies along the medial wall of the rodent prefrontal cortex during a complex decision-making task. They found four clusters of cells along the dorsal-ventral axis that were firing more similarly to other cells in the same cluster than cells in other clusters, suggesting there are 4 distinct subdivisions in rodent mPFC. Their detailed analysis of decision-making, reward, and evaluation showed that though some cells in each area responded to these different cognitive aspects, there was a difference in how widespread these signals were in the different subdivisions. They found more decision-related activity in the ACC, more post-decision evaluative activity in the dorsal parts of the prelimbic, and more ventral areas involved with …
Reviewer #1 (Public Review):
Diehl & Redish set out to capture how cognitive and behavioral linked activity varies along the medial wall of the rodent prefrontal cortex during a complex decision-making task. They found four clusters of cells along the dorsal-ventral axis that were firing more similarly to other cells in the same cluster than cells in other clusters, suggesting there are 4 distinct subdivisions in rodent mPFC. Their detailed analysis of decision-making, reward, and evaluation showed that though some cells in each area responded to these different cognitive aspects, there was a difference in how widespread these signals were in the different subdivisions. They found more decision-related activity in the ACC, more post-decision evaluative activity in the dorsal parts of the prelimbic, and more ventral areas involved with motivational factors. They argue that the prelimbic area is actually 2 distinct areas that should be considered separately. This paper is very well analyzed and the methodological aspects regarding histological confirmation and neuronal spiking are exceptionally thorough. The task is well-studied and conclusively provides insights into multiple facets of high-level cognition. The main weakness is the unequal distribution of cells recorded in each area. Mainly, this is a problem for the ACC where substantially fewer units were recorded. This takes away some from the interpretation of ACC activity, however, most of the findings about ACC are consistent with previous reports from this lab and others. This does not take away from the success the authors achieved in characterizing the differences and similarities in functional correlates along the medial wall. The identification of two distinct subdivisions in the prelimbic area is novel and is likely to have a substantial impact on the field. At the least, the specific location within prelimbic that future studies purport to either record from, sample from, or manipulate will need to be reported so that these future findings can be correctly interpreted. This is a major shift in the field's conceptualization of this oft-studied part of the brain.
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Reviewer #2 (Public Review):
In this paper, Diehl and Redish recorded simultaneously from multiple medial frontal cortical regions while rats are performing a restaurant-row task. Their results provide insights into how neurons in the different regions may represent different aspects of the decision-making process.
The strength of the study is the experimental design. The restaurant-row task is an excellent and rich paradigm for evaluating decision-making, with specific unique components that may be relatable to economic subjective choices. The other strength is the electrophysiological approach, which enables the author to simultaneously record from multiple medial frontal cortical regions. This leads to a large data set of >3,000 single units recorded during behavior. A weakness of this study is the insistence to dissect the results …
Reviewer #2 (Public Review):
In this paper, Diehl and Redish recorded simultaneously from multiple medial frontal cortical regions while rats are performing a restaurant-row task. Their results provide insights into how neurons in the different regions may represent different aspects of the decision-making process.
The strength of the study is the experimental design. The restaurant-row task is an excellent and rich paradigm for evaluating decision-making, with specific unique components that may be relatable to economic subjective choices. The other strength is the electrophysiological approach, which enables the author to simultaneously record from multiple medial frontal cortical regions. This leads to a large data set of >3,000 single units recorded during behavior. A weakness of this study is the insistence to dissect the results and assign each region to specific behaviors, while the data seem to suggest that similar signals can be observed across multiple regions, albeit to different degrees. The framework of distributed vs. gradient vs. subregions seems like a strawman idea that does not help with the interpretation of the results, whereas the actual data are already quite rich and interesting.
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Reviewer #3 (Public Review):
This is an interesting study in which the authors record simultaneously from neurons along the medial bank of the rodent PFC as rats perform the restaurant row task, an economic decision-making task in which subjects are offered different reward types with a specified delay, and they need to decide whether to accept or reject the offer. The authors find functional correlates of anatomical subdivisions of the mPFC; interestingly, they find that PL perhaps should be subdivided into dorsal and ventral subregions, a finding that is consistent with some known anatomical features. They characterize the task-related responses of neurons in these different subdivisions and find that in general, the dorsal regions (ACC, dPL) encode decision-related variables, whereas the ventral regions (vPL, IL) encode more …
Reviewer #3 (Public Review):
This is an interesting study in which the authors record simultaneously from neurons along the medial bank of the rodent PFC as rats perform the restaurant row task, an economic decision-making task in which subjects are offered different reward types with a specified delay, and they need to decide whether to accept or reject the offer. The authors find functional correlates of anatomical subdivisions of the mPFC; interestingly, they find that PL perhaps should be subdivided into dorsal and ventral subregions, a finding that is consistent with some known anatomical features. They characterize the task-related responses of neurons in these different subdivisions and find that in general, the dorsal regions (ACC, dPL) encode decision-related variables, whereas the ventral regions (vPL, IL) encode more motivational variables, such as the trial number in the session and the amount of lingering time.
Strengths:
- The observed dichotomy between decisional and motivational factors mapping onto dorsal and ventral aspects of mPFC is interesting and, as far as I am aware, novel.
- There are a number of rich, interesting observations, such as a lack of encoding of the reward delay in the offer zone, but then encoding of that variable in the wait zone (in all areas except ACC). This is intriguing given that their previous work has suggested that the decisions made in the offer and wait zones are in some ways dissociable, implying that they might rely on distinct neural circuits.
- Overall, the data and analyses are of high quality, and the results are interesting.
- The finding that PL should be subdivided into two distinct subregions will be of broad interest to researchers studying the mPFC. The approach and finding will also be of interest to the growing number of groups using linear silicon (including Neuropixels) probes to record from multiple brain areas simultaneously.Weaknesses:
- The authors find that dorsal regions of mPFC, particularly ACC, encode the upcoming decision of the animal. However, the upcoming choice will be correlated with animal movements (as is often the case). Given that ACC is adjacent to the motor cortex, and more posterior parts of the cingulate have been documented to reflect particular types of movements, it would be helpful to know if these signals would be observed for movements outside of the task, or if they really reflect the upcoming decision in this behavioral context.
- I think some of the statistical analyses can be strengthened. For instance, the authors correlate neural activity against a large number of behavioral variables, some of which are correlated with each other. I would encourage a regression-based approach, which takes into account the correlations between variables for error bars/significance tests for each regressor.In general, I think the authors' claims about their data are justified.
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