In my dissertation research under Douglas A. Nitz at UC San Diego, I am investigating the spatial correlates of multiple regions hypothesized to be crucial in spatial navigation. To do this, I utilize in vivo electrophysiology of behaving rats navigating a complex environment with many paths and potential reward locations. In this project, I have recorded from medial precentral cortex (a subregion of mPFC), dorsal subiculum, CA1, posterior parietal cortex, and superior colliculus. Our results are pointing towards a potential pathway for information flow during spatial navigation. Read more about particular projects below.
Generalization in the Dorsal Subiculum
The subiculum is one of the primary outputs of CA1 to cortex, especially associative cortex such as parietal and retrosplenial cortex. Despite this, few experiments have been conducted in subiculum, especially compared to its extremely popular neighbor, CA1. Previous research has described subicular neurons in open field foraging as very similar to CA1, but with broader firing fields (Sharp 1994). Furthermore, they generalized to the same relative locations of similar environments (Sharp, 1997). When placed on a U-shaped track results were consistant with this account (Kim et al., 2012). In our work, utilizing a multi-path and multi-turn with 4 possible reward sites, a much more diverse activity pattern has emerged. Overall, neural representations do seem to fit with this idea of generalization, but the manner in which they do so is quite different, with neurons that generalize across spaces that are spatially and behaviorally distinct, but similar in their function (i.e. halfway back on a path to a reward). We also see a subset of subiculum neurons that fire when the animals run in either of two opposite directions. That is they seem to mark the axis of travel of the animal! See our preprint at bioarchive for more information. I am excited to learn more about this region and how these representations interface with two regions subiculum is highly interconnected with: CA1 and entorhinal cortex.
Medial Precentral Cortex and the Planning and Execution of Action
Medial precentral cortex (MPC) is a brain region in medial prefrontal cortexi (mPFC) of the rat and is a region hypothesized to be highly involved with decision making and action planning. Unlike the other subregions of mPFC; however, MPC has garnered less attention, largely due to a lack of correlates to decision making. We are examining MPC neural activity patterns in the context of our multi-turn navigational task. The task structure allows for the teasing apart of spatial and action correlates as well as assessing when action activity is maximal with respect to the action (such as before or during). We can also inspect the sequence of actions to see if MPC encodes turns in a sequence of actions differantly, a known property of premotor cortex in non-human primates.