Abstract
The anterior thalamic nuclei (ATN), a central node in a complex memory system, process spatial and temporal memory. Here, we show that ATN lesions do not affect acquisition of a simple odour discrimination or a simple object discrimination in a runway apparatus. The same procedures were used to test learning of an arbitrary association between non-spatial object-odour pairings (A+X or B+Y were rewarded; but not A+Y or B+X). If ATN lesions recapitulate hippocampal function, specifically CA1 function, then they should disrupt acquisition only when an explicit delay (i.e., a 10-second trace) is inserted between the odour and object. Acquisition was completely abolished by ATN lesions, irrespective of the presence of the temporal trace, and despite extensive training (50x12-trial sessions). Faster acquisition with the 10-second trace was found in the sham-lesion rats. During recall, 5 days after criterion, sham rats but not ATN-lesion rats showed elevated Zif268 expression in hippocampal CA1 for the trace compared to no-trace condition; both sham and lesion rats tested in the trace condition showed increased IEG expression in the superficial layers of the prefrontal cortex and retrosplenial cortex. ATN lesions markedly reduced Zif268 expression in the prefrontal cortex and retrosplenial cortex. This is the first evidence that ATN lesions impair non-spatial paired-associate tasks. The findings suggest that the ATN influence memory beyond time and space, and constitute a critical neural structure for learning arbitrary associations even in the task version that is not disrupted by hippocampal lesions.
Competing Interest Statement
The authors have declared no competing interest.
- Abbreviations
- A29a
- area 29a of the granular retrosplenial cortex
- A29b
- area 29b of the granular retrosplenial cortex
- A29c
- area 29c of the granular retrosplenial cortex
- A30
- area 30 of the dysgranular retrosplenial cortex
- A32D
- area 32D of the anterior cingulate cortex
- A32V
- area 32V of the medial prefrontal cortex
- A24a
- area 24a of the anterior cingulate cortex
- A24b
- area 24b of the anterior cingulate cortex
- ATN
- anterior thalamic nuclei
- AD
- anterodorsal thalamic nuclei
- AM
- anteromedial thalamic nuclei
- AV
- anteroventral thalamic nuclei
- CA1
- cornu ammonis 1
- CA3
- cornu ammonis 3
- Cc
- corpus callosum
- Cg1/Cg2
- cingulate area 1 / 2
- DG
- dentate gyrus
- DG Hilus
- hilus of the dentate gyrus
- dSub
- dorsal subiculum
- IEG
- immediate early gene
- lEC
- lateral entorhinal cortex
- MD
- mediodorsal thalamic nuclei
- mEC
- medial entorhinal cortex
- MTT
- mammillothalamic tract
- NAc
- nucleus accumbens
- PRh
- perirhinal cortex
- Re/Rh
- reuniens/rhomboid nuclei
- Rga
- dysgranular a retrosplenial cortex
- Rgb
- dysgranular b retrosplenial cortex
- Rdg
- granular retrosplenial cortex
- vCA1
- dorsal cornu ammonis area 1
- vCA3
- dorsal cornu ammonis area 3
- vSub
- ventral subiculum.