The Negative-Image Model for Habituation: A Proposal.

Modern biology explains natural phenomena in terms of molecules and the context within which they function.  However, this has been difficult to achieve for psychological phenomena, which are innately complex and many levels removed from participating molecules.  For these, our current understanding remains relatively superficial.  And therefore, relationships between different psychological concepts, e.g. latent inhibition, association, habituation and extinction, remain poorly studied.

About 7 years, ago Veronica Rodrigues' group and mine began experiments to understand mechanisms of behavioral habituation, a fundamental form of implicit learning that allows organisms to ignore the familiar and, probably as a consequence, focus increased cognitive resources on novel or more salient stimuli. 

Defining features of habituation include: (a) attenuation of behavioral responses to frequently encountered stimuli that are not associated with positive or negative reinforcement; (b) instant "dis-habituation" in response to arousing stimuli; and (c) a negative correlation between stimulus intensity and "habituation learning."

In this talk, I will first provide a mechanistic framework for learning and memory storage in nervous systems.  I will then attempt to clarify and communicate a general mechanistic model for habituation that is crystallizing from our observations of olfactory habituation in the fruit fly, Drosophila melanogaster.   A keystone of this construct, tentatively named "the negative image model," is a conserved cellular and circuit mechanism that allows a stimulus to create a "negative image" of itself in the brain.  This negative image acts to reduce the amplitude of neural responses to familiar stimuli.    

I will end by suggesting how habituation mechanisms that we have uncovered may function in other forms of learning, in allowing selective attention, and how these processes may be altered in psychiatric disease.