Mark Barad

Biography

Fear responses confer important protections from environmental threats, but are not always adaptive. Extinction is the gradual reduction of conditioned responding by persistent presentation of the conditional stimulus (i.e., tone; CS) without a paired unconditional stimulus (i.e., footshock; US), and it is the explicit basis for behavior therapy of anxiety disorders, and for cognitive behavioral therapy of depression, two psychotherapies of proven efficacy. Extinction is a form of learning, not erasure or passive forgetting, and is also one of the most elemental forms of learned inhibition. Even after complete extinction the original conditional response can return spontaneously with the passage of time, or be renewed by a change of context, demonstrating that the original memory remains, and that extinction only inhibits its expression. Despite its importance as a paradigm of inhibitory learning and its enormous relevance to human psychotherapy, little is known of the molecular or cellular mechanisms underlying the extinction of fear conditioning. Only a handful of papers have demontrated effects of drugs on extinction. Anatomically, only the amygdala has been unambiguously implicated in extinction. My laboratory is now focused on elucidating the neurotransmitters and second messenger systems involved in the extinction of fear conditioning, with the ultimate goal of developing adjunctive treatments to accelerate and facilitate the behavioral psychotherapy of anxiety disorders, psychotherapy in general, and inhibitory learning, the type of learning most dependent on intact frontal function. The underlying hypothesis governing the design of these experiments is that extinction should share mechanisms and molecules with other, well-studied forms of learning and of synaptic plasticity, such as long-term potentiation (LTP), and that differences from other forms of learning will be particularly interesting and relevant to inhibitory learning and to psychotherapy. Based on this hypothesis, we began with experiments to design an efficient extinction protocol, and immediately discovered an important difference between extinction and other forms of learning. We found that, unlike other forms of learning, extinciton is more efficient with temporally massed rather than spaced training. In exploring the basis of this finding, we discovered that the response to the CS is a compound of two opposing behavioral processes.

Research Interest

My general interest is in the cellular basis of learning and memory,and my lab focuses on understanding the cellular and molecular mechanisms underlying one particular type of learning, the extinction of Pavlovian fear conditioning. Classical, Pavlovian, fear conditioning is an important model both of learning and memory, and, of the pathogenesis of human anxiety disorders.