Salience, reward, and the brain
Kelly Dumais NU’10 and Jim Stellar
Kelly worked in my behavioral neuroscience laboratory in my last year at Northeastern and then she did a coop experience at McLean Hospital with my former graduate student Heather Brenhouse (see the next blog) in a neuroscience research drug addiction research laboratory. Like most students, she grew from her experience. But what was most important to this blog is that we begin to talk about how her experience working shaped her in some pretty basic ways that almost seem the same as how cocaine experience acts on the brain to reshape what animals and humans will do. So to begin, let me ask Kelly to talk about how cocaine acts on the brain, at least in terms of what she saw in the lab. Then we will try to work back to experiential education…if we can.
My time at McLean served not only as an opportunity to grow professionally in the field I want to pursue, but also as an amazing learning opportunity as I finish my undergraduate academic career. Filled with nerves and excitement, I dove into my first laboratory research project head first, to learn about the rewarding effects of cocaine, and how adolescents may neurobiologically have an increased vulnerability to drug-cue associations and addiction. How the brain develops, and how our specific neurobiology at different periods of our lives influences our decisions, has become of great interest to me.
To understand how adolescents may have this increased vulnerability to addiction, some background of the rewarding effects of cocaine may be helpful. Drugs of abuse act on particular neurological pathways in the brain to create the rewarding experience of pleasure. They increase the activity of the brain’s reward and motivational systems. These motivational and reward circuitries are located within the limbic system of the CNS, including areas such as the hippocampus and amygdala, providing memory and emotional salience, and the nucleus accumbens, creating a type of “pleasure center”. This reward circuitry consists of dopamanergic neurons originating in the ventral tegmental area (VTA) near the base of the brain, which send projections via the mesolimbic pathway to the nucleus accumbens (NAc), located in the striatum. Cocaine affects these brain systems by increasing the dopamanergic transmission, particularly in the NAc, by blocking dopamine transporter systems, therefore creating a rewarding experience.
A principal goal of the research I participated in at McLean was the study of cue learning and how cocaine creates cue associations when paired with environmental stimuli. Interestingly, adult and adolescent rats differ in their sensitivity to reward and drug-paired cues. Only adolescent rats were shown to form a strong preference for a drug-paired environment when using a comparatively low dose of cocaine. Also, adolescents maintained their drug-cue associations 75% longer than adults, and had a stronger drug-primed reinstatement (relapse model) of cocaine. This data suggests that adolescents assign greater salience attribution to cocaine-paired cues than adults. It was also found that the dopamine D1 receptor may play a role in this increased salience attribution. Adolescents have an elevated D1 expression on prefrontal cortex projections to the NAc relative to juveniles and adults, and it was found that by manipulating this receptor expression, adolescent cocaine-cue associations were altered. This suggests that the D1 receptor expression at different developmental stages may create a period of vulnerability to drug cue associations during adolescence, and therefore contribute to adolescents’ increased vulnerability to addiction. The role that salience attribution plays in addiction, and how emotion, memory, and cue-associations can alter our behavior. It is a fascinating area of research, and one which I believe can have applications to other arenas in life.
Thanks for the science lesson. Apparently you were a success because I want to tell the readers that as we were writing this piece you got into a variety of great Ph.D. and Master’s graduate programs, some with full financial support. We could talk about the value of serious undergraduate research (like you had) for making this happen, but instead let’s pick up on the last theme of salience. Here is a question for you. Did the work you did in the lab, increase the salience of your learning about the facts and theories of the field of psychobiology? As you are answering, go back and think about how increased salience in your experiential learning may have been positive emotionally and how that might have been accumbens dependent in you. I am not saying you are a rat, but let’s take the parallel seriously for a moment.
To simply say that my work in the lab increased the salience of my learning would be an understatement. My salience to the field of drug addiction, and to the field of neuroscience in general, has grown remarkably. Though it may be a combination of general maturity, or general increase of knowledge after four and a half years of college education, I have noticed a drastic increase in my understanding of, my participation in, and my interest toward all four of my classes this semester. Somehow I have managed to tie each and every topic I’m learning about to its application in animal models in the field of behavioral neuroscience. I feel that a huge part of my increased interest and participation in my courses is due to my experience in the lab, and the knowledge that the lab gave me about the field, and the confidence that it gave me in pursuing the field further. I find myself eagerly attending my courses, and I jump at the opportunity to discuss neuroscience with someone, whether it is a fellow psychology peer, or a friend where I get to teach new knowledge. As a drug-conditioned context becomes more salient to a conditioned rat, the realm of psychology and its associated contexts (Seminar classrooms, graduate open houses, school laboratories) become increasingly salient to me, and not only intellectually stimulating, but emotionally stimulating as well, because the love of psychology and neuroscience doesn’t become something of a hobby, but an emotional passion that finds its way into your everyday life.
We could go on, but to stop here, what we believe is that learning works on the limbic system as well as supplying data for what we can call the cognitive system that learns the facts and theories of the classroom and books. The limbic system is one of the components we refer to in this blog as “other lobe” with the others being sensory and motor systems (think about the effects of violin practice). Higher education does a great job of getting the facts and theories in to the cognitive part of the heads of students and experience helps those facts and theories impact the limbic system (cortical and subcortical) where we believe value judgments are made (see neuroeconomics research). In this world of interconnected learning, the mentor is very important. So, now we turn our attention in the next blog posted today about the mentoring of Kelly by Jim’s former graduate student, Heather, who was a Harvard Medical School Instructor in the laboratory at McLean Hospital in which Kelly worked on co-op.
Note from Jim: This is our first time connecting two blog posts.
