applied Neural PLasticity & dynamics

The brain has the amazing ability to change and rewire itself.

Lets use that as a tool and basis for treatment.

Two Memory systems

Two memory systems that complement each other and work together.

USUALLY!

When one becomes damaged or weakened, the other then dominates. Howe do we get the weakened back in to balance?

Two memory systems:

In this modern day we often forget that memory evolved as a system to guide behavior. A way to store past experiences, and to be able to adjust, adapt, or repeat actions and decisions based upon how successful or unsuccessful those actions and decisions were. 

In the simplest organisms, their limited neural system is only capable of processing very simple reflexive actions, such as the classic studies using the sea snail showing that it can learn and remember to withdraw its siphon on a cue instead of direct stimulation. This level of learning and memory (reflexive or habitual) is basic and fundamental to all animals with a nervous systems, including us.

As we get to more complex nervous systems in more advanced animals, we start get a more complete brain, and develop many different systems, including a new more flexible memory system. This doesn’t replace the old one—but works in addition to it. Both systems simultaneously acquiring information and learning which responses worked well, and which didn’t.

Generally they work well together. But we get plenty of evidence that that isn’t always the case in daily life:

You have a usual parking spot at work, but one day have to park in a much different spot. You finish work, start thinking about what you have to do later, and walk to usual spot—NOT to where you parked. You can now walk there, so you do obviously remember where you should have walked

Driving your common route home, but know you need to make a side trip to get something. Your mind gets occupied either in a conversation or in thinking about some issue that is bothering you, and you find yourself at home having forgotten to make that different turn at some point, or really remembering having driven those last few blocks.

When the flexible system was preoccupied, the habitual system took over you followed a habitual routine. These types of things happen all the time, but normally we catch our mistake, or something happens to bring the flexible system back into the current situation and correct our behavior.

UNLESS SOMETHING HAS ALTERED OR DAMAGED THE FLEXIBLE SYSTEM! Then we fail to update our learning, and just default back to what was habitual. Both stress and drugs of abuse cause significant physical (structural and physiological) alterations in the flexible memory system. But as these disorders are thought of as habitual issues, people have fixated on the habitual system. We need to start looking at the whole system, and how to get a person better able to over ride the habitual system.

Research has shown that the two systems are physically distinct in the brain. The habitual system is located in an area called the dorsal striatum (also known as the caudate and the putamen). The flexible system has been shown to be dependent on a structure called the hippocampus.  Somewhere in the brain there is a logical gate that compares what the two systems are telling the body to do, and decides which system’s instructions to follow. The current best estimate is the ventral striatum (also known as the nucleus accumbens).

This ‘gate’ is also the current focus of the majority of addiction research. But what if it isn’t the gate, but the gate controller? The hippocampus is poised perfectly to fulfill just such a role. It has direct projection to both the prefrontal cortex (one of the other primary target structures now getting attention, normally associated with ‘executive function’) and the nucleus accumbens as well as the amygdala (associated with emotion). Damage to the hippocampus prevents the formation of new declarative memories in humans, impairs the ability to apply contextual learning or rules, and causes failures to reverse behaviors. To me that is the issue in addiction: the person has problems learning new behaviors and actions, and so instead the brain defaults back into the old behavior pattern—relapse.

The habitual system is working, doing what it is supposed to do! The problem is that it isn’t getting an override from the flexible adaptive system. Current research focuses on ‘fixing’ the system that isn’t broken, instead of trying get the flexible, cognitive system BACK online. 

There is already highly successful strategies to counteract this phenomenon in aging, where it is called cognitive decline. If it works there, why not use similar strategies in other disorders where the key problem is loss of cognitive flexibility?

My research and hypotheses therefore focus on how information gets transmitted through these systems and then contributes to choice behaviors, and how drugs of abuse and  stress alter this information flow to prevent new adaptive behaviors and learning. How, therefore, drug associated behaviors do not get replaced, suppressed, or overridden by the conscious efforts and thoughts being expressed in the flexible memory system.  How do we strengthen this system?