Although considerable progress has been made towards understanding the neural systems mediating conditioned fear, little is known about the neural mechanisms underlying conditioned inhibitors of fear (or safety signals). The present series of experiments examined the involvement of the nucleus accumbens (NAC) in mediating the effects of safety signals on behavior using a conditioned inhibition of fear-potentiated startle paradigm. Neither increasing dopaminergic nor decreasing glutamatergic function in the NAC altered the magnitude of conditioned fear or conditioned inhibition of fear in rats. Furthermore, large pre- or post-training electrolytic lesions of the NAC did not affect acquisition or expression of fear-potentiated startle or conditioned inhibition of fear-potentiated startle. Taken together, these data suggest that the NAC is not critically involved in the acquisition or expression of fear-potentiated startle or conditioned inhibition of fear-potentiated startle. Previous research has implicated the NAC in 'reward-attenuated startle' in which presentation of a stimulus paired with food decreased startle responding. The present results, therefore, indicate important neural dissociations between the processing of appetitive and safety signals, even though behavioral studies and learning theories have suggested that these two forms of learning share some commonalities.
Bibliographical noteFunding Information:
This work was supported by a National Institute of Mental Health Grants MH-57250 and MH-47840, Research Scientist Development Award MH-0004, a grant from the Air Force Office of Scientific Research, and the State of Connecticut to MD and a National Alliance for Research on Schizophrenia and Depression (NARSAD) Young Investigator Award to SAJ. We thank Bernard Balleine and Paul W Frankland for helpful discussions and comments on an earlier version of this paper.
- Conditioned inhibition
- Nucleus accumbens
- Pavlovian conditioning