Appetitive conditioning-induced plasticity is expressed during paradoxical sleep in the medial geniculate, but not in the lateral amygdala.

This study examined whether neurons in the medial division of the medial geniculate (MGm) and the dorsal part of the lateral amygdala (LAd) express learning-induced plasticity in paradoxical sleep (PS) after appetitive conditioning, as they do in PS after fear conditioning. Rats received tone-food pairings in 3 sessions. After each session, the tone was presented at a nonawakening intensity during PS. Multiunit activity was simultaneously recorded in MGm and LAd. During waking, increases in tone-evoked discharges developed in MGm and LAd; however, as training continued, they lessened in LAd, but not in MGm. During PS, conditioned tone responses were expressed in MGm, but not in LAd. Thus, these results demonstrate dissociation of MGm and LAd plasticity. Moreover, compared with fear conditioning results, they suggest that expression of amygdalar plasticity in PS depends on the emotional salience of the stimulus. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Learning-induced plasticity in the medial geniculate nucleus is expressed during paradoxical sleep.

Fear conditioning to an acoustic stimulus produces increases in tone-evoked discharges of neurons in the medial division of the medial geniculate nucleus (MG). This study examined the responses of MG neurons to a conditioned tone presented in paradoxical sleep (PS). After 1 session of habituation to a tone, awake rats underwent conditioning in 3 sessions during which the tone was used as the CS preceding a footshock. Control rats received unpaired presentations of tone and shock. The same tone, which never awakened the animal, was presented during PS following each daily session. Responses of MG neurons to the tone in PS were increased after conditioning. This enhancement was as large as that in waking and was manifested earlier after tone onset than in waking. No change appeared after pseudoconditioning. These results demonstrate that associatively induced plasticity in the MG can be expressed during PS. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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 (     

Fear conditioning-induced plasticity in auditory thalamus and cortex: To what extent is it expressed during slow-wave sleep?

After fear conditioning to a tone, rats received nonawakening presentations of the tone alone during slow-wave sleep (SWS) episodes. Multiunit activity was recorded in the medial part of the medial geniculate (MGm) and in the primary auditory cortex (ACx). Although tone-evoked responses were increased in MGm and ACx during the 3 conditioning sessions, group data failed to show any significant changes during SWS. Nonetheless, the few recordings (5/29) that exhibited the strongest conditioned responses during wakefulness expressed enhanced responding during SWS. Compared with previous data obtained in MGm during paradoxical sleep, associative plastic changes were less easily expressed during SWS. These results are discussed with regard to functional changes that occur in the thalamocortical system across vigilance states. (PsycINFO Database Record (c) 2010 APA, all rights reserved)