Neuronal plasticity induced by fear conditioning is expressed during paradoxical sleep: evidence from simultaneous recordings in the lateral amygdala and the medial geniculate in rats.

The lateral amygdala (LA) and its afferent connections from the medial geniculate (MG) play a pivotal role in auditory fear conditioning. The authors evaluated whether those neurons could express in paradoxical sleep (PS) physiological plasticity acquired in waking. After a habituation session, rats received tone-footshock pairings in 3 sessions. After each session, the tone alone was presented during PS episodes. Multiunit activity was simultaneously recorded in the LA and the medial part of the MG. Both in LA and MG, conditioned responses emerged rapidly (within 5 trials), were expressed with short latency (<20 ms), and were maintained in PS after training. Such changes were not observed in pseudoconditioned rats. These results are discussed regarding the question of the primary sites of plasticity in auditory fear conditioning and regarding the functional significance of preserved expression in PS of learning-induced neuronal plasticity.