A recent Norwegian study (Sigmundsson, 2020) of almost a thousand women and men between the ages of 14 and 77 found that shortly after the early 50s, participants tended to show a sharp decline in passion, perseverance, and positive mindset about the worthwhileness of pursuing new challenges.
“Igniting the spark is important, regardless of age. People 50 years and up can be very passionate but tend to have less grit or vice versa; [this means] that it’s more difficult to mobilize our grit and willpower, even if we have the passion. Or we may have the grit and willpower but aren’t quite as fired up about it. ‘Use it or lose it’ is the mantra, and this aligns with neuropsychology as well.”
Although Sigmundsson mentions that his findings ‘align with neuropsychology,’ his research doesn’t unearth specific brain-based reasons that may cause people’s motivation to fizzle with age. Coincidentally, a new study (Friedman et al., 2020) using specially engineered mice sheds light on how specific circuits in the basal ganglia tied to dopamine-driven, reward-seeking behaviors become less robust with age. These findings were published on October 27 in the journal Cell.
“As we age, it’s harder to have a get-up-and-go attitude toward things,” senior author Ann Graybiel of MIT’s McGovern Institute for Brain Research said in a news release. “This get-up-and-go, or engagement, is important for our social well-being and for learning—it’s tough to learn if you aren’t attending and engaged.”
Graybiel’s lab has been studying specific clusters of cells (striosomes) within the basal ganglia’s striatum for decades. In the late 1970s, Graybiel first identified how fiber connections within the basal ganglia’s striatum create an anatomical architecture consisting of striosomes and a surrounding matrix (Graybiel & Ragsdale, 1979). Although Graybiel discovered striosomes over 40 years ago, decoding their mysterious functions has taken decades of research.
A few years ago, Graybiel and her colleagues (Crittenden et al., 2016) identified a specialized “striosome-dendron bouquet” subsystem within the “dopamine-containing nigrostriatal system” of the basal ganglia that plays a crucial role in modulating dopamine-containing neurons that affect mood and movement.
For their latest study, Graybiel and colleagues used the same strain of mice to investigate how varying degrees of activity in the basal ganglia’s striosomes affect the cost-benefit analysis of the pros and cons associated with investing time and energy into a specific endeavor; this type of decision-making dilemma is called an approach-avoidance conflict.
Approach-avoidance conflicts arise when a goal or task has negative and positive characteristics that make pursuing these activities simultaneously unappealing and appealing. For example, vigorous HIIT workouts can feel like a sufferfest when you’re huffing and puffing, but breaking a sweat doing cardio is often followed by a euphoric cannabinoid-driven runner’s high, which makes the ‘blood, sweat, and tears’ of high-intensity interval training exercise worth the effort for many people.
When faced with an approach-avoidance conflict, the brain has to decide if “taking the good with the bad” is worth it because the positive and negative elements of an approach-avoidance conflict are inherently linked.
As Friedman et al. explain: “Learning valence-based responses to favorable and unfavorable options requires judgments of the relative value of the options, a process necessary for species survival.”
Notably, the researchers found that, much like humans, older mice (of an age equivalent to that of people in their 60s) tend to lose their get-up-and-go enthusiasm about learning new things that require hard work and sacrifice. The researchers also found that older mice have weaker striosomal signals when evaluating high-cost and high-reward options.
Although the researchers found that striosomal activity in the mouse brain declines with age, when they reactivated the striosomes’ circuitry, older mice became more motivated to engage in new learning. Conversely, suppressing this circuit decreased motivation regardless of age.
Until now, the exact basal ganglia circuitry that drives decision-making based on the evaluation of the cost and reward associated with the effort required to learn something new was unclear. The latest study suggests that striosomes in the basal ganglia’s striatum that are interconnected to dopamine-producing nerve cells in the substantia nigra play a critical role in assigning subjective value to a particular outcome associated with value-based learning.
In addition to typical age-related motivational declines, mental health factors such as clinical depression, PTSD, or generalized anxiety disorders can skew someone’s ability to assess the costs and rewards of approach-avoidance conflicts objectively.
For example, someone experiencing a major depressive episode (MDE) may undervalue the potential reward of taking small steps to achieve goals in day-to-day life. On the flip side, someone with a substance use disorder may overvalue the short-term rewards of using drugs or alcohol but undervalue the long-term expense of addiction in other aspects of their life.
The next phase of striosomes research by Graybiel and colleagues will explore possible pharmaceuticals or drug-free biofeedback interventions that hack into these brain circuits in ways that optimize value-based learning and improve cost-benefit evaluations across a lifespan.
Alexander Friedman, Emily Hueske, Sabrina M. Drammis, Sebastian E. Toro Arana, Erik D. Nelson, Cody W. Carter, Sebastien Delcasso, Raimundo X. Rodriguez, Hope Lutwak, Kaden S. DiMarco, Qingyang Zhang, Lara I. Rakocevic, Dan Hu, Joshua K. Xiong, Jiajia Zhao, Leif G. Gibb, Tomoko Yoshida, Cody A. Siciliano, Thomas J. Diefenbach, Charu Ramakrishnan. Karl Deisseroth, Ann M. Graybiel. “Striosomes Mediate Value-Based Learning Vulnerable in Age and a Huntington’s Disease Model.” Cell (First published: October 27, 2020) DOI: 10.1016/j.cell.2020.09.060