Jon C Horvitz PhD
7-217 NAC building; 138 St and Convent Ave
NY , NY 10031
NY , NY 10031
Email: jhorvitz [ AT ] ccny [ DOT ] cuny [ DOT ] eduOffice Phone: (212) 650-5744
- Postdoctoral Fellowship: Princeton University
- PhD: University of California at Santa Barbara
- BA: Haverford College
We are interested in the role of brain dopamine in learning and motivation. Dopamine activity is implicated in the reinforcing effects of cocaine, amphetamine and natural rewards. However, dopamine abnormalities are also believed to underlie some of the core attentional abnormalities seen in acute schizophrenics. Our laboratory examines the neurochemical bases of learning and motivation, particularly with respect to dopamine activity within its major brain target sites.
Current Research Team:
Post-doctoral Associate Rosa Isabel Caamano Tubio
Graduate Students Cecile Morvan and Veronica Dobrovitsky
Cecile Morvan and her research associates are observing the performance of simple behaviors in rats - e.g., entering a food compartment in response to a tone (an auditory CS). Disruption of brain dopamine activity strongly disrupts the animal's ability to perform these tasks (just as it disrupts behavior in humans). However, when the animal repeats that behavior hundreds of times (i.e., the response becomes a habit), disruption of brain dopamine activity no longer disrupts the behavior. In some way, the "habit" has become invulnerable to dopamine disruption. We are pursuing the following questions: What are the neurobiological changes that permit well-learned behaviors to occur when dopamine transmission is compromised? It is possible that the neural representation of the behavior may shift from dopamine target regions of the brain to regions that are not DA-innervated. Alternatively, the behavioral representation may remain in the same DA-innervated anatomical site, but (glutamatergic) input signals to the region may become stronger over the course of training, and therefore less dependent upon dopamine facilitation.
Veronica Dobrovitsky and her team are testing the hypothesis that dopamine transmission at D1 receptors within the nucleus accumbens sets the threshold for reward expectation (generated by conditioned stimuli associated with varying probabilities of reward delivery) to generate behavioral approach responses. In collaborative studies conducted at Rutgers University, Mark West and his colleagues are testing the complementary hypothesis that the firing rate of individual nucleus accumbens neurons codes for reward expectation magnitude. Together, we predict that a) accumbens neurons code for the magnitude of expected reward (e.g., they respond more strongly to a conditioned stimulus associated with a high likelihood of reward delivery compared to conditioned stimuli associated with lower probability of reward delivery), and b) accumbens D1 transmission sets the threshold for these reward expectations to generate reward-directed approach responses.
Rosa Isabel Caamano Tubio is examining the molecular events occurring within dopamine target regions (striatum) that we believe underlie stimulus-response (habit) and goal-directed learning. These critical molecular events begin at the time dopamine binds to the D1 receptor and gluatamate binds to the NMDA receptor and result in changes in the strength of striatal glutamate synapses.
Ashby, F. G., Turner, B. O., & Horvitz, J. C. Cortical and basal ganglia contributions to habit learning and automaticity, Trends Cogn Sci, 14, 208-15, 2010.
Choi, W., Morvan, C., Balsam, P.D., Horvitz, J.C. Dopamine D1 and D2 antagonist effects on Response Likelihood and Duration. Behavioral Neuroscience , 123, 1279-87, 2009.
Horvitz, J.C. Stimulus-Response and Response-Outcome Learning Mechanisms in the Striatum. Behavioral Brain Research , 199, 129-40, 2009.
Wickens, J., Horvitz, J.C., Costa, R., Killcross, S. Dopaminergic Mechanisms in Actions and Habits, Journal of Neuroscience, 27, 8181-3, 2007.
Horvitz, J.C., Choi, W., Morvan, C., Eyny, Y. Balsam, P.D. A “Good Parent” function of dopamine: transient modulation of learning and performance during early stages of training. Annals of the New York Academy of Sciences, 1104, 270-288, 2007.
Choi, W., Balsam, P.D., Horvitz, J.C. Extended Habit Training Reduces Dopamine Mediation of Appetitive Response Expression, Journal of Neuroscience, 25, 6729-33, 2005.
Eyny, Y.S. and Horvitz, J.C. Opposing roles of D1 and D2 receptors in appetitive conditioning. Journal of Neuroscience, 23, 1584-87, 2003.
Horvitz, J.C. Dopamine gating of glutamatergic sensorimotor and incentive motivational inputs to the striatum. Behavioral Brain Research, 137, 65-74, 2002.