Abstract
The rodent prelimbic cortex has been shown to play an important role in cognitive processing, and has been implicated in encoding many different parameters relevant to solving decision-making tasks. However, it is not known how the prelimbic cortex represents all these disparate variables, and if they are simultaneously represented when the task requires it. In order to investigate this question, we trained rats to run the Multiple-T Left Right Alternate (MT-LRA) task and recorded multi-unit ensembles from their prelimbic regions. Significant populations of cells in the prelimbic cortex represented the strategy controlling reward receipt on a given lap, whether the animal chose to go right or left on a given lap, and whether the animal made a correct decision or an error on a given lap. These populations overlapped in the cells recorded, with several cells demonstrating differential firing to all three variables. The spatial and strategic firing patterns of individual prelimbic cells were highly conserved across several days of running this task, indicating that each cell encoded the same information across days.
Highlights
Do they co-occur on a single task? Are the different firing correlates particular to the task, or could several of them be observed on the same task if required? And do these different firing correlates arise from different populations of cells, or do the populations somehow overlap? We tested these questions by recording from the prelimbic cortex (PL) of rodents as they attempted to solve a spatial decisionmaking task
We attempted to assess whether the cells we discovered on this region of the track that encoded strategy laps before vs. after the switch, left-going vs. right-going laps, or correct vs. error laps could be explained by spatial differences
BEHAVIOR Performance on MT indicates recognition of the change in reward contingency In order to verify that the rodents did learn the Multiple-T Left Right Alternate task (MT-LRA) task and respond to its changes in reward contingency, we considered their composite percentage of correct laps for each lap from the start of the session and for 10 laps before and after the switch lap
Summary
The rodent prelimbic cortex (PL) plays an important role in cognitive processing and the solving of decision-making tasks (Kolb, 1990; Dalley et al, 2004; Kesner and Churchwell, 2011) including working memory (Yoon et al, 2008; Horst and Laubach, 2009), interval timing (Kim et al, 2009; Narayanan and Laubach, 2009), the encoding of uncertainty (Karlsson et al, 2012), reward receipt (Pratt and Mizumori, 2001), and behavioral strategy (Jung et al, 1998; Peyrache et al, 2009; Rich and Shapiro, 2009; Benchenane et al, 2010; Durstewitz et al, 2010). The Multiple-T Left Right Alternate task (MT-LRA ) is a multiple-choice, sequential decision task which allows us to spatially differentiate low cost choices, high cost choices, and the reward location (Gupta et al, 2010; Blumenthal et al, 2011; Steiner and Redish, 2012, see Figure 1) This task has a number of features which will allow us to study these different components: It is a spatial task, in which different strategic components need to be active on different parts of the maze, allowing us to identify intra-lap strategies (akin to that of Jung et al, 1998), and compare them to spatial firing patterns (akin to that of Hok et al, 2005; de Saint Blanquat et al, 2010). It forces animals to run through the central track on every lap which should produce similar behavior, allowing us to control for subtle differences in posture that have been previously identified as potential confounds in identifying prefrontal neural correlates (Euston and McNaughton, 2006; Cowen and McNaughton, 2007)
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