The Making & Breaking of Habits

The Making and Breaking of Habits

By Shana Ward

Recently, we had a talk by Ken Paller that discussed declarative memory, which falls under explicit memory, and that form of memory requires conscious recall or recognition of facts and events. Declarative memory is important when learning new things and trying to retain what has been learned. The hippocampus is an important brain region involved in declarative memory, but there is another type of memory called implicit memory that plays some different roles in our brains. Implicit memory is unconsciously recalled because the information is stored unconsciously. A specific kind of implicit memory is procedural memory which involves skills and habits, the focus of the following study. 

Habits can be useful for establishing set routines that make going through the day easier, but can also be a hindrance if unhealthy, obsessive habits form. Unhealthy habits such as addictions or Obsessive-Compulsive Disorder can be the result of the inability to switch between acting out of habit or acting in a purposeful, goal-oriented manner. A study working with mice has provided some insight into the neural networks and components that work when doing an action habitually versus deliberately. 

A study led by Christina Gremel that was published in Neuron suggested that the neural circuits in the brain for habitual action versus deliberate action actually compete for control within the brain. The main brain area that was looked at was the Orbitofrontal cortex (OFC) which is located in the prefrontal cortex, an area associated with higher level functioning in humans. The OFC is often involved in decision making, i.e. goal-oriented action, but competes with a neurochemical called an endocannabinoid which is what employs the use of habit. 

Endocannabinoids are a naturally produced class of chemicals with receptors in the brain and throughout the body as well. This system of receptors is involved in a variety of processes such as appetite, pain sensation, and memory. 

In a previous study, the Orbitofrontal cortex (OFC), through optogenetic techniques that increased signal output from OFC neurons, demonstrated that goal-oriented actions increased. Optogenetics works to precisely turn neurons on and off with flashes of light using light sensitive channels in cell membranes. So, decreasing activity of the same neurons with inhibitory light sensitive channels caused reliance of habit in the mice study, i.e. goal-directed actions decreased. 

The current study that is discussed in this article looks into endocannabinoids, which are known, general reducers of activity in neurons. It was hypothesized that endocannabinoids could be responsible for "quieting" the OFC, which reduces goal-directed action in favor of habit-based action.

Mice were trained to perform a task involved in lever-pressing to receive food, but to test their hypothesis, the researchers deleted cannabinoid type 1 (CB1) receptors in a specific OFC pathway, particularly the OFC-striatum pathway. Like the importance of the Hippocampus for declarative memory, the Striatum is key for procedural memory. The study showed that mice without the CB1 receptors did not form habits in the task, which shows exactly how critical neurochemicals, like endocannabinoids, can be in behavioral processes. 

The findings of the study may have significant implications on individuals who suffer from addictions or OCD where reliance on habit could be stopped in favor of a shift to more purposeful, goal-oriented action. 

This particular study demonstrates just how separate memory processing can be and how different the pathways are for different types of memory. Additionally, hearing Dr. Paller's talk and reading this article make it more obvious to me how the delicate intricacies of our brain make everything we do in life possible.

https://www.sciencedaily.com/releases/2016/05/160526185419.htm