Working memory is an umbrella term for our ability to hold information in mind for a short period of time – of the order of minutes. Long term memory is about the past: information acquired in the past and information about past events. I like to think of working memory, in contrast, as being about the future. I consider working memory to be a bridge between stimuli and events from the immediate past and actions and plans for the immediate future.
A lot of research has focused on the role of the pre-frontal cortex in working memory. Researchers got very excited when they discovered that neural responses in some parts of the pre-frontal cortex lasted longer than presentations of sensory stimuli during memory tasks. In posterior cortex – traditionally considered sensory cortex – neural responses are transient and disappear shortly after the driving stimulus is removed.
If I show you a picture your whole visual cortex will light up. The moment I remove the picture from your view your visual cortex will bubble back to its baseline state. If you have to remember some aspects of the picture, however, parts of your pre-frontal cortex will activate and stay activated long after the original picture has been removed.
Researchers have focused on this persistent activity as part of the mechanism behind out ability to keep in mind plans and stimuli for short periods of time.
The pre-frontal cortex is densely connected with a collection of sub-cortical structures called the basal ganglia. These connections are sometimes called the frontal-striatal circuits. The basal ganglia are mostly implicated in motor responses (movements) and is notable for being severely affected in Parkinson’s disease. Recently people have begun to wonder if the basal ganglia play a prominent role in more cognitive functions because of their dense connections with the pre-frontal cortex.
In my current project I’m looking into what role the frontal-striatal circuits play (if any) in working memory function. I am having a lot of fun doing this because the neural responses from these brain regions can be very varied (different neurons can have very different kinds of responses to the same stimuli) and I am using that as an excuse to throw various pattern recognition algorithms at the data. This project is ongoing and I hope to have something fun to present shortly.
As a diversion, here’s a video made by some folks over in Japan of a chimpanzee doing a sequence memory task: