Lessons from drug addiction in rats and from PTSD for college students choosing their major/career in college
By Maeve Lampman UM’28 and Jim Stellar
I (ML) am a sophomore Honors neuroscience student at UMass Amherst, who is considering attending medical school in the future. Here, JS and I are writing about how I, and millions of other college students, make decisions like this using our frontal cortex when the plans are also evaluated by our limbic systems. We think this limbic process is like what happens in homeostasis when an imbalance of water and salt, for example, leads to a motivation called thirst, and then the cognitive apparatus in the frontal cortex makes a plan to drink some water. But how does this happen with purely cognitive decisions, like deciding (or not) to go to medical school? From where does that motivation that can drive planning originate?
During the college application process, high school seniors are expected to have their future careers and majors decided as soon as possible. Going into my senior year of high school, although I (ML) constructed the plan of studying neuroscience and becoming a physician, many of my peers were struggling to decide on their future career path. This led me to wonder: How are we making these complex life decisions?
One of the contributions to the cognitive decision-making about plans, comes from the limbic system where emotional reactions are generated. FYI, that is something about which we have written much in the past in this blog series. Here what we want to emphasize is that the two emotions of pleasure/anticipation and pain/fear are organized in the brain even at the level of the hypothalamus. Lateral hypothalamic stimulation elicits pleasure as evidenced by the fact that even rats will work to get it turned on; whereas medial hypothalamic stimulation produces the opposite effect, and even rats will work to get it turned off. Each of these hypothalamic areas sits in the middle of pathways that run up to forebrain structures and down to the brainstem and reflexes. For example, the lateral hypothalamus pathway goes to the nucleus accumbens, delivering the neurotransmitter dopamine and famously interacting with cocaine use. The medial hypothalamus sits in the middle of a pathway that goes to the amygdala and is famously involved with fear learning, such as in PTSD. While oversimplified, these two pathways and their limbic system structures are positioned to tell the cognitive system that its plan (or execution) is working out or not.
To me (ML), once the limbic system establishes the sensations of pleasure and pain through the guardrails, the frontal cortex is responsible for interpreting them and making a decision on whether to act physically. As we have written, the frontal cortex acts as an integrator, receiving limbic input and placing it into context, like weighing past outcomes and predicting future consequences. The frontal cortex and the guardrails work together as a team. Limbic signals provide urgency and value, whereas the frontal cortex evaluates meaning. For instance, a strong “avoid” signal does not automatically require withdrawal, and a strong “approach” signal does not automatically mean action. The frontal cortex is responsible for framing inputs and outputs and either delaying or prioritizing responses.
This relationship is very important in understanding how the limbic system shapes brain cortical learning. Certain neural pathways to the frontal cortex are strengthened by constant, repeated limbic signaling, whether it is reward or stress. Over time, this has a great influence on how the frontal cortex can evaluate options and regulate behavior. Emotional experience does not disappear at high levels of neural cognition, but is rather embedded within them. This interaction is especially relevant in college students making academic and career decisions for their futures. Recognizing the process of short-term signals and long-term outcomes allows students to pause, reflect, and engage their frontal cortex. They do this using emotional information as guidance when choosing their own path going forward into adulthood.
One lesson in how powerful these limbic influences can be comes from the cravings that drug addicts report that keeps them approaching and taking a drug like cocaine. As shown in a recent study, researchers found that after repeated cocaine exposure, neural cues that had been paired with cocaine start to trigger dopamine release and motivational responses on their own, almost as if the cue becomes as powerful as the drug itself. Neural stimuli begin to increase dopamine in brain areas such as the dorsal striatum and nucleus accumbens, which are both parts of the mesolimbic reward circuitry and are strongly tied to motivation and reinforcement. This reinforcement activation is one of the mechanisms that makes it so you crave the drug, because the brain starts responding to the cue as if the reward were immediately available, making avoidance or withdrawal from the drug extremely difficult.
This has a clear parallel for students who are thinking about where their lives will go in terms of majors and careers. Just as drug-paired cues can come to command attention and action in rats, certain academic experiences and signals like grades, praise, and social approval can become strong emotional motivators. These emotional signals can make some options feel particularly attractive, while others feel distant and even threatening.
This summer, ML and JS will come back with a long blog on how these mechanisms in the brain (neocortex and limbic system) work together.
