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

Abstract

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 conditioned stimulus 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.

About Sleep's Role in Memory

“…Cue-induced firing patterns during SWS were not investigated in these studies. Increased neural responses were also observed after cue reexposure during REM sleep in the medial geniculate body of the auditory thalamus and, for aversive cues, in the lateral amygdala (542,543,755). Taken together, these studies by Hennevin's group indicate that learning-induced plasticity can be reexpressed by cueing during REM sleep, whereas expression of conditioned responses was not consistently observed during SWS (541).…”

Learned material content and acquisition level modulate cerebral reactivation during posttraining rapid-eye-movements sleep

“…At the behavioral level, increase in REM sleep duration is observed in rats after aversive conditioning in which a tone is paired with a footshock, but not after pseudo-conditioning in which the tone and the footshock are given unpaired (Bramham et al, 1994). Using a similar procedure at the systems level, tone-evoked responses are obtained in the medial geniculate nucleus (Hennevin et al, 1993) and in the hippocampus (Maho et al, 1991) during REM sleep after a conditioning procedure initiated at wake, but not after pseudo-conditioning. Likewise in humans, REM sleep percentage increases after learning textbook passages, but only when they are meaningful (Verschoor and Holdstock, 1984).…”

Retrieval and Reconsolidation: Toward a Neurobiology of Remembering

“…A physiological substrate for the interpretation of this reactivation experiment has been provided by more recent experiments showing that brain structures comprising a circuit involved in the initial learning maintain and express plasticity during REM sleep. Conditioned responses to tone paired with shock during the awake state can be expressed in both the hippocampus and the medial geniculate nucleus during sleep (Hennevin et al 1993). Conditioned neuronal responses in the amygdala, which probably mediates the affective component of the memory, are likewise elicited by the CS during REM sleep (Hennevin et al 1998).…”