Characterizing the Spatiotemporal Dynamics of Dopamine and Noradrenaline During Flexible Associative Learning in Mouse Dorsal Cortex

In a Tortoiseshell

An abstract and brief introduction precede this excerpt. In these sections, I walk through some prior literature on the roles of dopamine and norepinephrine, two neurotransmitters, in the brain. I show that there is a notable absence of research looking into the functions of these molecules in the outermost layers of the brain called cortex. There are further conflicting theories about whether these molecules have global, unified functions across the whole brain, or if their effects are specific to local regions. I also cover the basics of a model of associative learning in which a certain sensory cue is paired with a rewarding or punishing event, referred to below as stimulus-outcome relationships. 

Excerpt / Tristan Szapary

Specific Aims

Neuromodulators regulate circuit dynamics across the entire brain, though their role in cortex during learning remains poorly understood. This proposed study will characterize the spatiotemporal dynamics of dopamine and noradrenaline during visual and auditory associative learning in the mouse dorsal cortex. We hypothesize that both learning and the reversal will depend on dopamine to learn reward associations while noradrenaline will enable the mouse to update the new stimulus-outcome relationships during reversals for both reward and punishment. Additionally, we predict targeted release of dopamine and noradrenaline in auditory or visual sensory processing regions respective to the stimulus modality, exhibiting spatial heterogeneity.

Aim 1: Assess Learning in a Two-Modality Associative Learning Paradigm with Reversals. Mice will conduct a task in which visual or auditory stimuli are paired with a reward of water or a punishment of an air puff to their eye. The outcome associated with the rewarded and punished stimuli will then be reversed. This aim seeks to develop metrics based on behavioral responses like anticipatory lick rate and eyelid closure to quantify learning.

Aim 2: Comparing Spatiotemporal Dynamics of Dopamine During Visual and Auditory Associative Learning. Mice will be virally induced to express sensors of dopamine and conduct the learning and reversal trials in Aim 1 with cortex-wide mesoscopic imaging. In this aim, we will observe changes in dopamine (DA) activity as they correlate with learning and localize them to specific regions in the dorsal cortex to determine whether DA is heterogeneously released across modality and confirm that DA encodes reward prediction error, as hypothesized by numerous theories.

Aim 3: Comparing Spatiotemporal Dynamics of Noradrenaline During Visual and Auditory Associative Learning. In this aim, we will conduct a similar experiment as Aim 2 but in mice with induced sensors for noradrenaline, again looking for heterogeneous release patterns and testing the hypothesis that NA is involved in encoding novelty and uncertainty.

Author Commentary / Tristan Szapary

This excerpt is the entirety of the “Specific Aims” section of my Spring Junior Paper (JP) in the Neuroscience Department. Our spring JP is expected to take the form of a prospectus, in which we propose a potential experiment that we may conduct in the future, commonly as our thesis. The motivation for this structure is to introduce us to the process of pitching scientific ideas to a critical audience and convince them that it is worthwhile, which is a common occurrence when working in STEM academia as seen with grant proposals. A prospectus contains various sections that I was already familiar with like an abstract, introduction, and methods. Yet I had never heard of Specific Aims before, and after some research learned that the section is meant to convey the problem your research aims to solve, the motive of why such a problem matters, and the concrete objectives your research plans to achieve, all in no more than a page!

At first, this felt like a daunting task. The expectations of Specific Aims seemed to match that of the entire paper, asking me to combine my abstract, introduction, and methods and distill them into a fraction of their length. I decided it was best to focus on writing the other sections first, so I could solidify my understanding of what I wanted to study, why I wanted to study it, and how I planned on doing so, before tackling its summation. Breaking down my methods into section headers based on each of my experimental goals seamlessly turned into the organization of my three listed aims. Further, when I began writing this excerpt, I forced myself to be as concise as possible with my language and then went back to cut down even more extraneous words when I proofread. This added constraint was the only way to reach the one-page limit, but it also pushed me to sharpen my language so that each word was both necessary and sufficient to get my point across. I tried to limit the technical jargon in this excerpt to broaden its scope, but there were occasional moments where I relied on concepts that were touched on in the introduction. Nevertheless, I wrote the last sentences of Aims 2 and 3 to give some theoretical background on dopamine and norepinephrine so that any reader could infer that the former is related to reward and the latter to novelty. I also included a broad overview of my proposed experimental protocol in Aim 1. This way, a reader unaware of the methodological details could read these Specific Aims and still grasp the larger framework of my experiments and the most important objectives they seek to accomplish.

The process of crafting my Specific Aims sections was in itself a writing exercise of efficient orientation. It asks you to boil down many pages of research into its bare bones and strike a careful balance between the specificity of your experimental objective with the broad scope of your problem in question. 

Editor Commentary / Molly Taylor

In independent work, Princeton undergraduates are asked to produce original research that contributes to scholarship in their discipline. Beyond generating a well-motivated research question, we must also determine how to answer it. In the “specific aims” section of his thesis research proposal, submitted as junior independent work for the neuroscience department, Tristan explicitly connects his motive to his methodology. 

The specific aims section begins with a succinct restatement of Tristan’s motive: to characterize the spatiotemporal dynamics of dopamine and noradrenaline during learning, which researchers do not understand well. This restatement is important in framing the study’s three specific aims, as it reminds the reader of what Tristan hopes to achieve before he explains how he will do it. Further, the hypothesis that follows the motivating question follows from the research presented in the preceding background section, allowing the reader to see how Tristan’s work builds on existing knowledge on dopamine and noradrenaline in the cortex—and how his proposed research will confirm or challenge it. 

Then, Tristan presents the three “specific aims” of his research with impressive concision. This section connects each element of his experimental design to its implication for the research question. While the full twenty-page proposal discusses the technical background and methodology in detail, this section succeeds in distilling the why and how of his research into fewer than 300 words. In a research proposal—with the goal of convincing an advisor of the merits of a project—this succinct overview is both persuasive and helpful, in the sense that it frames, at a high level, the more in-depth sections of the paper.  

Relatively few writing assignments at Princeton require a research proposal, and not all disciplines require a methodology as explicit as neuroscience. Still, Tristan’s work is a reminder that, regardless of the subject, it is important to be able to articulate the motivation behind the methodology, whether that methodology is a lab procedure or a close reading.

The author

Tristan Szapary

Tristan Szapary ’24 is a senior studying neuroscience with the hopes of pursuing medicine and research in the future. Outside of the classroom, he is a competitive fencer and enjoys reading and writing fiction.

Molly Taylor ’25 is a junior studying computer science and history from Chicago, Illinois. Outside of the Writing Center, she serves as head editor for the features section of the campus newspaper, The Daily Princetonian. In her free time, Molly enjoys going on long bike rides and making hot chocolate.