Author Archives: Min Ju Lee

Do neuronal ensembles of goal-directed behavior and habitual behavior change over the course of lever press training?

Min Ju Lee

Mentors: Victoria Hall, Nicole Calakos M.D.-Ph.D

Department of Neurbiology

Habitual behaviors are automatic reactions to a certain stimulus, which enables the brain to reduce cognitive load of performing repeated sequences. While habits can be beneficial, the process of transitioning between goal-directed and habitual behavior is necessary to act appropriately in variety of contexts. Neuropsychiatric disorders with impaired decision-making, such as Obsessive-Compulsive Disorder and addiction, are thought to involve an inability to shift between action control strategies. Still, little is known regarding the circuitry responsible for this transition. We hypothesize that there are neuronal ensembles specific to both goal-directed and habitual behavior. Targeted Recombination in Active Populations 2.0 (TRAP2) method was employed to selectively label neurons activated during goal-directed or habitual action strategy of lever press training. Images were taken with Zeiss 880 Confocal; analyzed using ImageJ to compare location and count of TRAPed cells across groups. Initial montages of the whole brain show different ensembles for habitual and goal-directed behavior in the sensorimotor cortices. Further research would involve capturing both ensembles in the same brain using immunohistochemistry. Our findings hope to elucidate the circuitry involved in action control to help us understand what happens when this adaptive process becomes maladaptive.

Neica’s talk on Recovering from Ischemic Stroke

As someone who had no prior exposure to biomedical engineering, this week’s chalk talks were especially enlightening. Out of the engineering related talks, Neica’s talk on developing drugs for ischemic strokes stood out to me because the methods used to test the drugs seemed to be similar to the methods used in the neurobiology labs that I knew of.

Ischemic strokes are strokes caused by blood clots forming in the capillaries of the brain, and leads to significant brain damage due to excitotoxic glutamate release. The brain’s natural defenses causes further damage; microglia leads to increased inflammation, meanwhile astrocytes causes scarring. An ideal treatment needs to stops these mechanisms in the affected area, and bring the neural progenitor cells close to the damaged site of the brain for regeneration. The Segura lab utilizes hydrogels to treat ischemic strokes, and thereby increasing the treatment efficacy from the current 5%. The concoction of hydrogels contain MAP gel and the CLUVENA. The Map gel recruits the neural progenitor cells. while the CLUVENA suspends the microglia and astrocytes in the damaged site. The design of the experiment, which aims to test the efficacy of the hydrogels, reminds me of the CRE-loxP system in neurobiology labs, where reactivating a gene in the knockout animal rescues the animal brain perturbation. Both methods need to damage the brain function in order to testify whether the treatment works or if the gene has a role in behavior, but they both ultimately links back to future clinical applications so that it could help people with abnormal neurological function.

Imaging, Imaging and Analysis

A typical day in the Calakos lab starts with reading through the literature on the topic of habitual behavior and goal-directed behavior. Sometimes I start by listening in on the lab meetings which are once every week in the morning. These days I have finally obtained permission to go work with Zeiss 880 inverted confocal microscope, so I have started to spend half of my day imaging mouse brain slices, and striatum in particular.

Obtaining the correct settings for each of the four lasers (I am trying to image with four fluorophores simultaneously) takes a surprising amount of time. It is critical for me to use the same settings for each experiment for a fair comparison. Furthermore, taking the images themselves takes hours. For example, one 20x tile scan with three fluorophores and 10 by 16 frames takes around 1 hour and 30 minutes. A whole brain constitutes of many individual slices, which will have to be imaged separately. I have a lot to do in the future.

In the last weeks of the program, I am planning to analyze these images in order to figure out the changes in ensembles of neurons activated for habitual behavior vs goal-directed behavior, and compare them with afferents into the different areas of dorsal striatum. I imagine this will be plenty (and more) work to keep me occupied in the coming weeks.

Unwavering Curiosity and Pursuit of the Answer

Today, I introduce my very awesome mentor, Tori, and how she came to be the inquisitive researcher she is now. As an undergraduate student, Tori majored in molecular, cellular and developmental biology with a concentration in neurobiology in Yale University. While she entered Yale thinking she may be pre-med, after spending a year working in neurobiology lab, she decided to pursue research. Her main reason for the change was this: she wanted to understand the science behind the treatments and extend the current knowledge by asking questions and answering those questions herself. Tori has always wanted to understand the maladaptations behind neuropsychiatric disorders and continue to do so now. Her current disorders of interest are dystonia(abnormal muscle tone as a resulting in spasms and abnormal posture) and Parkinson’s disease.

What Tori particularly like about Science is the process of pursuing an answer to her question.  What got her into research are the “spark moments” when she finds an answer, or a major revelation to her question. However, part of the difficulty of pursing research is that these “spark moments” seem to come very slowly. Many types of failures deter scientists from conducting successful experiments; there could be technical mistakes, or non-significant results that reveal there could be a fundamental problem with the theory. Troubleshooting will always be a part of a scientist’s life. Furthermore, research in academia has a very slow return rate, and could take anywhere between several months to several years.

There could be four qualities that constitute a successful scientist: unwavering curiosity, independence, self-efficacy and attention to detail. Curiosity may originate from personal motivation, or just simply from the love of a question like Tori. While collaboration in Science is very important, the expectation is that you will be the expert in your field, and conduct your own experiment. Scientists need to be independent. Self-efficacy is necessary to persevere in between the “spark moments”. Attention to detail is needed to do troubleshooting. Ultimately, the life of a scientist is a hard one, but could be one of the most rewarding in the long run.


Brain Circuits of Habit and Goal Directed Behavior

What do you think creates a habit? Habitual behaviors are defined by learning  an automatic response to a certain stimulus. For example, you could have breakfast in the morning, even if you are not feeling particularly hungry at the time. Here, the action(having breakfast) is executed regardless of the goal(consume calories to feel full), but instead follows a learnt stimulus(time). Thus, habitual behaviors are not conducted for the aim of fulfilling a goal, but is dependent on the stimulus.

Calakos lab investigates the cellular and circuit changes in the brain(with a focus on striatum) as a behavior changes from goal-directed to habitual. This can be done by overtraining, where an initial goal directed response to press a lever to obtain food pellets becomes habitual/automatic over repeated trials. In this case, the point when the researcher knows the behavior is no longer goal-directed is when the mouse still presses the lever with same frequency, regardless of whether it was full or hungry before the behavioral test. This is called the devaluation test as you devalue the utility of the outcome.

Striatum is a brain area known to be involved in not only initiating or inhibiting movement, but also changing from goal-directed to habitual behavior. My research project is to image the afferent connections into the DMS and DLS-dorsomedial striatum and dorsolateral striatum- using retrograde tracer AAV. Active brain circuits during goal-directed and habitual behavior will be selectively labeled, which would be used to compare how the inputs into the DMS and DLS changes as lever press behavior turns from goal to habit.

Papers, Papers and the Gap in knowledge

The first time when I was exposed to what neuroscience research really was, I was only in tenth grade and yet to learn University level Biology. I did not know what a PCR is, nor how each neuron was connected to each other in various different types ways(via neurotransmitters like glutamate-excitatory- and GABA-inhibitory) and in such a temporally sensitive manner. From start to finish, I was at lost of what was going on, and my kind, super-smart bench mentor had to teach me everything from the basics. That was my tenth grade summer.

Fast forward four years and I have dedicated much time into learning Biology and Neuroscience. At this point in time, I considered myself to be much more prepared for lab (“I got this!”). However, although I was able to understand some basic procedures and general knowledge related to the brain, I quickly noticed a lot of the knowledge that was specific about lab’s research topic pouring in, and was ready to read to get started. Two days in, I observed one of the postdoc members of the lab giving a presentation for his seminar next week. He talked about how some GABAergic neurons could actually function as excitatory in the striatum, depending on the type of stimulation. Already on the first week, new research was shown that challenged my previous notion of how neurons were connected.

What I expect this summer is not to understand every single detail of what we are doing in the lab, but to contribute to Calakos lab’s efforts to reveal circuit level changes as striatum adjusts from goal-direct to habitual behavior. I will be learning how to analyze and use confocal microscopes to help me get going, and probably have a ton of learning before me. Does this intimidate me? Yes, probably. A little bit. But I also know that this is the start of a long journey ahead. My goals for the summer is to understand the group dynamics in lab, and perhaps identify a gap in knowledge about this topic that I can fill in during my independent study in the future. Most importantly, I want to learn a really crucial skill in the Sciences: how to ask the right questions. I think I can have plenty of practice doing that this summer.