New Year’s Resolutions and the Neural Circuitry of Habitual Behavior

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As we leave 2013 behind and enter into a New Year, many of us make New Year’s resolutions.  Most everyone has bad habits that they would like to break or new habits that they would like to start.  Perhaps the resolutions center around diet, exercise, or work habits.  Whatever your New Year’s resolution may be, sticking to it is hard work!

Habits can become so ingrained in us that they can seem impossible to break.  In fact, a characterizing feature of a habit is its automaticity.  This year, one of the habits I am trying to break is the extent of my internet use.  Like many others in our web-obsessed society, particularly the internet-raised millennial generation, I check e-mail, news-sites, facebook, and other internet-based media more than I would like to.  ‘Surfing’ the internet—the continual brief reading, noticing an interesting link, and clicking behavior—can become habitual.  It can then be hard to break the reading, noticing, clicking… reading ,noticing, clicking… cyclical behavior.

During performance of a habit, the brain seems to be running on autopilot, executing an entire program of actions as if they were one action.  This notion of a habit as the brain on automatic is supported by several lines of evidence (see Yin et al. 2006 for review). Fortunately for those of us engaged in the fight against undesireable habits, a few intriguing studies from the Graybiel lab at M.I.T shed light on how to break out of such automatic brain states.  In this post, I’ll be summarizing one of the studies (Smith et al. 2012), and discussing how I think about it in the context of my own and general human habitual behavior, and what implications this study has for enacting long-term behavior change.

In this study, rats were trained to run through a T-shaped maze, and upon reaching the T, the decision point, had to run down either the left or the right arm to receive either a sucrose or chocolate milk reward. The rats were trained that an auditory instruction cue predicted whether they would find their food reward to the left or to the right (See Figure 1 from Smith et al 2012, below).

Rats underwent many, many training sessions, until they were considered ‘over-trained’ — beyond the point of any additional learning.  At this point the rats’ maze-running behavior became habitual – upon hearing the instructional cue, the rats would run to the side of the maze that contained the food reward.  The authors interpret this  as being habitual  behavior because the rats continued to run to the proper arm of the maze even after the reward had been “devalued” by pairing it with sickness-inducing Lithium Chloride. Have you ever eaten perfectly good food and then gotten sick after?  It totally ruins even the best of foods. Presumably that’s how the rat felt about the lithium chloride laced chocolate milk.

And yet, when these over-trained rats were placed back in the maze, they still followed the instruction cue and ran to the side of the maze that had contained the now unappealing reward, even when the maze was left empty. Even though the mean old researchers ruined the rats’ perfectly good chocolate milk, they still ran as fast as their wee little legs could carry them to get to the maze end where the devalued reward used to be.  Why?  Well, according to the researchers, it’s because the rats had developed a habit of running to this side of the maze upon hearing the cue, and continued to engage in the habit long after it was properly rewarded.

Now that they had rats exhibiting a silly but all too familiar habitual behavior, the researchers wanted to know if they could identify how habits can be broken. By using a technique called optogenetics, which allows direct control the neural activity in specific neurons using laser light, Graybiel’s team was able to shut down activity in an area of the medial prefrontal cortex (mPFC) called the Infralimbic (IL) cortex, which effectively broke the rats’ habitual response to the instruction cue.  It’s as if the IL were continually causing, or at least permitting, the rat to engage in the maze running habit.  Shutting off the IL produced a matching decrease in this habitual maze running. This was a striking finding because of how quickly shutting off the IL cortex changed the rats’ behavior.  On average, the rats’ behavior changed within only three trials, but some rats’ running habits were broken immediately, with the fastest responder taking only 3 seconds to change their behavior.

One of the reasons this research is so interesting is that scientists had long relegated automatic habitual behaviors to deep brain regions such as the striatum (Yin et al. 2006), while assuming that the more “advanced” cortex is responsible for intentional behaviors. The fact that Graybiel’s team was able to completely disrupt their rats’ habitual behavior by momentarily turning off cortical area IL suggests that it is actually cortex that produces the expression of this habit. Indeed, IL projects to a part of the striatum, where it may activate (or permit) a corresponding habit program that initiate the rats’ automatic running behavior.  If the striatum is where the habit motor program is stored, as earlier research suggests, then the moral of the story is that it may be under constant real-time control by cortex, even during the middle of the execution of the habitual behavior. Thus, even though habits do have a large degree of automaticity, their expression seems to be continually monitored by what we consider higher, executive regions of cortex.

Now, what lessons do rats running mazes over and over again have for us humans?  Well, one lesson is that though habits may seem hard to break, they may actually be under continual management by cortex.  The fact that IL stimulation stopped rats from automatically running to the maze end-arm is an important reminder, and inspiration, that it is indeed possible to completely stop a habit dead in its tracks.  Now, let’s ponder the analogy between this important study in rats, and my very modern-day human habit of having my fingers continually clicking on my computer mouse, in the endless time-wasting virtual maze known as the world wide web.  The ‘higher’, ‘executive’ centers of my brain are always functioning, throughout my habit, even if the habitual brain state I’m in when I’m engaged in habitual internet use makes it harder for these higher-order brain areas to flex their metaphorical muscles.  It is a reminder of the power of the mPFC to exert top-down control over our behavior.

But beyond just being a reminder of how important ‘higher’, executive control is in breaking habitual behaviors, I think this study may offer clues as to how best to break the habit: namely, outside interference.  Just as the rats’ habitual maze running was broken by a brief pulse of light that de-activated its IL cortex, I decided to try to think of more natural ways to suddenly interrupt my automatic, habitual motor patterns by using common environmental stimuli to quiet down my own IL cortex (or its human equivalent)?  I thought that maybe a strong stimulus, such as a timer or alarm going off within earshot would be enough to disrupt my cortical activity enough to get me to close out e-mail, either get up from my computer or sign in to a work-related computer application.  I now use this alarmed timer whenever I begin using the internet for personal e-mail, or non-work related internet use.  Even more, I have found that using a computer application called ‘Concentrate,’ which will automatically shut down any computer applications I may be using after a designated time-window, is really effective at stopping my computer-habit circuitry from running so readily on autopilot.

Now admittedly, it is a stretch to take one finding in a neuroscience paper studying animal models of complex traits like habit formation, immediately take it as incontrovertible truth about how humans work, and make crucial life decisions based on it. Even if this is just a placebo effect, and I simply feel more emboldened in thinking creatively about ways to design my own life by having read about habit learning in neuroscience literature, who cares?  The ultimate goal is for me to keep my New Year’s Resolution.  Why not arm myself in this experimental fight against my own bad habits with the intuition for how the mind works that comes from studying animal models of key, relevant brain functions? One of my greatest hopes for neuroscience is that knowledge we acquire about the human and animal brain will improve the human condition, not just through manipulation of our biology, but through intentional manipulation of our environment.  Modern psychology, I think, offers the same promise.  By familiarizing ourselves more intimately with the workings of the brain, I think we can gain intuition and inspiration about how to best design our lives to function optimally, and lead happier, healthier, and more productive lives.

Happy 2014 Everyone!

REFERENCES:

Smith, K. S., Virkud, A., Deisseroth, K. & Graybiel, A. M. Reversible online control of habitual behavior by optogenetic perturbation of medial prefrontal cortex. Proc. Natl. Acad. Sci. U.S.A.109, 18932–18937 (2012).

Yin, H. H. & Knowlton, B. J. The role of the basal ganglia in habit formation. Nat Rev Neurosci7, 464–476 (2006).