Associative retuning in the thalamic source of input to the amygdala and auditory cortex: Receptive field plasticity in the medial division of the medial geniculate body.

Abstract

The medial division of the medial geniculate body (MGm) projects to the lateral amygdala and the upper layer of auditory cortex and develops physiological plasticity rapidly during classical conditioning. The effects of learning on frequency receptive fields (RFs) in the MGm of the guinea pig have been determined. Classical conditioning (tone-footshock), as indexed by rapid development of conditioned bradycardia, produced conditioned stimulus (CS)-frequency specific RF plasticity: increased response at the CS frequency with decreased responses at other frequencies, both immediately and after a 1-hr retention period. Sensitization training produced only general changes in RFs. These findings are considered with reference to both the elicitation of amygdala-mediated, fear-conditioned responses and the mechanism of retrieval of information stored in the auditory cortex during acquisition.

Specific long-term memory traces in primary auditory cortex

“…NIH-PA Author Manuscript NIH-PA Author Manuscript because MGm RFs are much more complex, multipeaked and broadly tuned than those of auditory cortical cells [55][56][57] . Therefore, long-term, specific plasticity in A1 is not merely a reflection of plasticity in the subcortical auditory system but probably reflects processes in the cortex.…”

“…The Suga model ignores the MGm, its intrinsic associative plasticity and its influences on both A1 and the lateral amygdala (LA), but the following findings directly implicate the MGm: acoustic and nociceptive information converge directly in the MGm 58,59 ; associative learning is accompanied by the development of plasticity in the MGm [60][61][62][63][64][65][66] , which is longlasting 63 and is evident as CS-specific RF plasticity after conditioning 56,67 ; the MGm holds an associative memory trace after CS offset during conditioning 68 ; analogues of learning show that stimulation of the MGm induces long-term potentiation in A1 (REF. 69) and tone paired with stimulation of the MGm induces heterosynaptic long-term potentiation in A1 (REF.…”

Medial Geniculate Lesions Block Amygdalar and Cingulothalamic Learning-Related Neuronal Activity

“…An involvement of the medial geniculate (MG) nucleus in aversively motivated learning is indicated by the observation of TIA in the medial division of the MG nucleus (MGm) (Olds et al., 1972;Gabriel et al, 1975;Gabriel et al, 1976;Ryugo and Weinberger, 1978;Birt and Olds, 1981;Weinberger, 1982;Edeline, 1990;Edeline and Weinberger, 1992;McEchron et al, 1995), and by impaired conditioning in animals with MG lesions (Iwata et al, 1986;Jarrell et al, 1986; LeDoux et al, 1986a,b;McCabe et al, 1993). Amygdalar and MG neurons are involved in aversively motivated instrumental conditioning processes, as well as in classical aversive conditioning.…”

“…A central role of amygdalar neurons is indicated by findings that amygdala lesions impair the acquisition of conditioned immobility (LeDoux et al, 1988; Fanselow and K im, 1994;LeDoux, 1995), autonomic responding (Blanchard and Blanchard, 1972;Spevack et al, 1975;Kapp et al, 1979;Gentile et al, 1986;Iwata et al, 1986;Helmstetter, 1992) and fear-potentiated startle behavior (Davis, 1986(Davis, , 1992Hitchcock and Davis, 1987;Sananes and Davis, 1992). Also, amygdalar neurons exhibit associative, training-induced activity (TIA) during Pavlovian conditioning (Umemoto and Olds, 1975;Applegate et al, 1982;Pascoe and Kapp, 1985;Nishijo et al, 1988; Muramoto et al, 1993;McEchron et al, 1995;Quirk et al, 1995).An involvement of the medial geniculate (MG) nucleus in aversively motivated learning is indicated by the observation of TIA in the medial division of the MG nucleus (MGm) (Olds et al., 1972;Gabriel et al, 1975;Gabriel et al, 1976;Ryugo and Weinberger, 1978;Birt and Olds, 1981;Weinberger, 1982;Edeline, 1990;Edeline and Weinberger, 1992;McEchron et al, 1995), and by impaired conditioning in animals with MG lesions (Iwata et al, 1986;Jarrell et al, 1986; LeDoux et al, 1986a,b;McCabe et al, 1993). Amygdalar and MG neurons are involved in aversively motivated instrumental conditioning processes, as well as in classical aversive conditioning.…”

Neuroscience of Pavlovian Conditioning: A Brief Review

“…Some studies have indicated the existence of a double sub-cortical pathway for auditory processing, only one of them showing neuronal plasticity. Specifically, the ventral division of the medial geniculate body (MGBv) does not show plasticity, while changes similar to those observed at the cortical level have been detected in the medial division of the MGB, which might thus be considered functionally as part of the neuronal system for learning (Edeline & Weinberger, 1992).…”